Search

• Modal analysis is conducted on the prototype blade at its first-order frequency. • Blades machined at different current densities were subjected to detailed surface-integrity evaluation. • Fatigue testing and fracture surface analysis is conducted on the blades. • The failure mechanism of blades machined by ECM was characterized. Blades made from Inconel 718 (IN718) are generally machined using electrochemical machining (ECM), and the high-cycle fatigue (HCF) of such blades significantly impacts the service life of aeroengines. In this study, modal analysis was performed to obtain the blade modal shape and stress distribution at first-order frequency, after which blades were machined at different current densities (9.5 A/cm2, 18.2 A/cm2, 34 A/cm2, 46.7 A/cm2, 61.2 A/cm2, 70.1 A/cm2) and then subjected to detailed surface-integrity analysis and fatigue tests. No surface defects (e.g., intergranular corrosion, recast layers) were observed, the microhardness was unchanged, and new residual stress was not found to be introduced to the machined surfaces. The machined surfaces were uneven and contained micro-pits, and high current density contributed to better surface quality. At a constant load of 520 MPa, the blade machined at 70.1 A/cm2 had the best fatigue life of 1.4×106. The blades fractured because of micro-pits, and as the surface quality of the blades improved, so did their fatigue performance. Therefore, the fatigue failure mechanism characterized in this work provides a reference for the HCF behavior of blades machined by ECM. [ABSTRACT FROM AUTHOR]

• A refined track dynamic model considering the bending properties of iron pad is proposed and validated. • An improved three-element Kelvin-Voigt model accurately simulates the nonlinear behavior of iron pads under dynamic loads. • A strain correction method using different element types in FE model for iron pads is developed. • A simplified simulation method based on distributed coupling theory is introduced. • Dynamic response indicators of iron pads effectively detect failure conditions of track structures. • The dynamic response data of iron pads provide potential for real-time monitoring and warning of track structure failures. Iron pads are crucial components in rail fastening systems, characterized by their load-bearing and force-transmitting capabilities. This study presents and validates a track dynamic model considering the bending properties of iron pad, offering a comprehensive analysis of their dynamic performance under train loads. The primary aim is to employ iron pads as key elements for monitoring and detecting potential defects throughout the track's service life. Initially, the construction of the track dynamic model is outlined, followed by an in-depth explanation of how the iron pads integrate with the track model. This involves introducing an enhanced Kelvin-Voigt three-element model and elaborating on the parameter selection for the spring element using a nonlinear spring model that accounts for voids and their relevant conditions. Subsequently, a systematic comparative analysis is performed to evaluate the accuracy of simulating iron pads using solid, shell, and beam elements, along with a proposed strain correction method. Finally, the established model and methods are employed to simulate and analyze the dynamic response of iron pads under typical defect conditions. These results indicate that iron pads can effectively reflect the failure conditions of the railway track system, making them ideal sensing elements for the dynamic monitoring of track structures. The enhanced model developed in this study holds significant theoretical and practical value, contributing to the safety monitoring and defect analysis of railway operations. [ABSTRACT FROM AUTHOR]

• The fatigue strength of notched specimens is much lower than that of smooth ones. • Fatigue reduction is high even for small notch depths. • Stress concentration is the main cause of fatigue reduction. A correct assessment of the fatigue strength of Ti6Al4V titanium alloy is paramount for ensuring component integrity and durability during service life in many industries, such as aerospace, naval, and biomedical. This study investigates the failure of smooth and notched specimens under axial fatigue loading, at a stress ratio R=0. The stress concentrations at the notches are evaluated with the finite element method. Experimental results obtained with a step loading procedure reveal significant differences in fatigue strength between smooth and notched specimens. The fatigue strength of notched specimens is found to be much lower than that of smooth ones mainly due to stress concentration effects. The role of stress concentrators in premature cracking is confirmed by the observation of the fracture surfaces of the tested specimens. The Goodman failure criterion is used to describe the observed fatigue behavior. The discrepancies found between the experimental results and those obtained using the Goodman criterion can be considered acceptable. This work contributes to a better understanding of the failure behavior of Ti6Al4V under fatigue, which is essential for the design of reliable components subjected to dynamic loading. [ABSTRACT FROM AUTHOR]

• Types and causes of fatigue failure in main bearings of Tunnel Boring Machines (TBMs) are reviewed. • It is described based on the authors' practical experiences during inspecting and maintenance of over 100 sets of TBM main bearings made by various manufacturers. • The properties of different structural designs of the main bearing and their effect on the fatigue life of the main bearing are presented. A large-scale tunnel boring machine (TBM) is currently the most advanced equipment for underground tunnel excavation. The main bearing, carrying all the load and moment from the cutterhead, is hailed as the heart of TBMs, which connects the cutterhead and main drive system. Due to the harsh underground working conditions, the main bearing is prone to fatigue failures, which decreases its service life and could lead to extremely high replacement cost. To enhance the service life, different types of main bearings are used in TBMs depending on the geological structures. To develop a reasonable asset management and maintenance solution, it is crucial to understand the types of fatigue failures of the main bearings. This paper reviews the types and causes of fatigue failures in TBM main bearings based on practical experiences during the inspection and maintenance of over 100 sets of TBM main bearings made by different manufacturers. Fatigue failures in the TBM main bearings, including fatigue wear of components, etching cracks, peelings, rustiness, crushing damages, and bolt fractures, are mainly caused by overload, poor lubrication, foreign objects entering the main bearing interior, and non-standard operation and maintenance. The properties of different structural designs and their effects on the fatigue life of the main bearings are also presented. Furthermore, the selection of main bearings under different working conditions is discussed in order to reduce the occurrence of bearing failures. Finally, future research directions for TBM main bearings are elaborated. [ABSTRACT FROM AUTHOR]

• The gradual transition of the plowshare from the initial wear stage to the stable wear stage. • Changes in wear size are concentrated at the edge of the plowshare. • Dp value is less than 0.2, the wear mechanism is micro-plowing. • The coupling of abrasive wear, impact wear and corrosive wear exacerbates the wear of the plowshare. The ploughshare represents a pivotal component of high-speed plough. The condition of the ploughshare's wear and tear directly affects a soil tilling operation. This paper carries out experimental field wear studies on the ploughshare of a high-speed plough to investigate the changes in mass, thickness, cutting edge parameters, wear profile, 3D wear morphology, microscopic wear morphology, and tissue composition of the 65Mn ploughshare in 35 ha, 70 ha, 105 ha, and 140 ha cultivation areas, and calculates the degree of penetration (D p value) of the wear surface to analyze the wear mechanism, with a view to prolonging the service life of the ploughshare from the perspective of its design and materials. The results showed that the ploughshare showed adaptive wear changes in response to cultivation, most pronounced in the first 35 ha. The wear rate of the ploughshare shows a decreasing trend with the increase of the cultivated area, indicating a gradual transition from the initial wear stage to the stable wear stage. During cultivation, the stresses are concentrated in the ploughshare cutting edge area, and the wear size of the cutting edge varies significantly. Wear of the ploughshare in parts other than the cutting edge is dominated by a reduction in thickness. The roughness of the wear surface stabilized at about 0.4 μm throughout the wear period. With the change of Y-axis position, the wear mechanism changes from impact wear to micro-ploughing, and finally the form of micro-ploughing action decreases gradually. The D p values of the calculated wear surface grooves are all less than 0.2, and the wear mechanism is micro-plowing. Observation of the microscopic wear morphology reveals traces of corrosive wear in addition to abrasive wear, where the soil reacts chemically with the metal and cracks the surface and subsurface layers of the metal. The coupling of abrasive wear, impact wear and corrosive wear exacerbates the wear of the ploughshare. [ABSTRACT FROM AUTHOR]

From the data, structural defects and cracks evolution patterns are identified to determine a statistically significant service life of approximately 5500 h. In this paper, a statistical analysis of failure form and work time of MHJ is conducted. Microscopic test of cracks reveals four main forms of type of cracks. Improper weld technology causes defects in the metallographic structure of weld seam. Improper design causes fatigue cracks of weld seam. Improper machining of parts causes stress concentration and cracks. Improper structural design causes uneven load-bearing capacity of the overall weld structure. According to the above problems, weld structure are optimized. Detailed research is conducted on weld technology of key weld bead. The differences in microstructure and weld efficiency of three different weld technologies are determined by microscopic tests on three key weld seam structures. Therefore, it is concluded that weld bead of MHJ can use full fusion of 9–12 passes multi-pass weld form. This method can achieve a balance between weld efficiency and weld quality. According to simulation analysis and comparison, lifespan after optimization of MHJ increases from 5863 h to 10,374.8 h. Structural performance of MHJ is greatly improved after optimization. Effectiveness of optimal design is verified by zero feedback within 5 years. • Optimizing the structure to increase load-bearing capacity and weldability. • 9–12 passes multi-pass weld is a reasonable weld technology parameter. • Lifespan after optimization of MHJ increases from 5863 h to 10374.8 h. [ABSTRACT FROM AUTHOR]

• Root causes analysis of the coining tool failure served as a tool for revealing the causes of damage and early decommissioning of the punch. • The cause of crack initiation was plastic deformation during pressing, hardening during martensitic transformation, and improper chroming process. • The cracks appeared outside the relief of the coining die, and also in the core of its working part. • Changes in production allowed for a 148-fold increase in the number of minted coins produced by a single minting tool. The article deals with a root cause analysis of coining tool failure after its untimely discarding and the design to extend its service life by innovating the manufacturing process. The analysis was performed on the coining die which had to be put out of service due to the insufficient quality of minted stainless coins. The purity of steel and the microstructure of the material of the semi-finished goods were evaluated. Furthermore, an analysis of the coining die failure under the surface and in the core was performed as well as the state of the chromium layer failure on the coining die relief. Based on the results of the analysis, a new experimental coining die was designed and produced according to an innovative manufacturing process. The pressing of the relief was carried out in a vacuum furnace and relief was coated with a TiAlN by the PVD method. New processes introduced in the production of coining die prevented the failure of die punches, extended the time of operation, thereby increasing quality of the coin production. [ABSTRACT FROM AUTHOR]

• Deriving/estimating plain strain fracture toughness for ASTM A322 material. • Developing flaw tolerance limit plots for ASTM A322 and ASTM A722 material. • Estimating remaining service life of existing post-tension grouted anchors. Brittle failure of grouted post-tensioned anchors used in trunnion girders at dams has given rise to concerns and questions surrounding their continued use and remaining service life. This paper reviews the brittle failure of five grouted post-tensioned anchor rods due to stress corrosion cracking at dams in California. To provide an early warning system to dam owners and expand on available resources for practicing engineers, this study derives plain strain fracture toughness from the failed grouted post-tension anchors using cross sectional photos. Using derived and available fracture toughness values, flaw tolerance limit plots, which can quickly illuminate the severity of a defect for various anchor diameters, were developed for semicircular and straight fronted flaw types using linear elastic fracture mechanics and stress intensity factors for both ASTM A322 and ASTM A722 materials. To help demonstrate the use of flaw tolerance limit plots and estimate the remaining service life of an in-situ anchor, an example problem was developed. [ABSTRACT FROM AUTHOR]

• The fatigue life of welded joints considering initial defects is investigated, for theoretical prediction and optimal design. • The influence line range of the welded joints and the most unfavorable loading conditions are determined. • Compared with the segmental model, the local model can effectively represent the true stress state of the fatigue detail. • The POWER criterion parameters for calculating the crack propagation are obtained by the fatigue test. • The crack propagation of the welded joints and influence of equivalent initial crack size parameters are studied. Orthotropic steel bridge decks (OSBDs) have been widely used in the field of bridges. However, their service life is significantly limited by fatigue issues. This study presents an analysis of the fatigue performance at the structural details of the rib-to-diaphragm joint, taking into account the impact of initial defects. A numerical segment model employing shell-solid coupling is established to determine the influence surface range and the most unfavorable working condition of the fatigue details, using fatigue standard vehicle loading. The accuracy of the local full-scale model is validated. A local model test of the rib-to-deck welded joint is carried out to deduce the parameter selection for the numerical simulation, based on the test results. Additionally, the crack propagation process in rib-to-diaphragm joints is simulated using XFEM. The simulation results of crack propagation demonstrate good agreement with the actual bridge crack path and shape. The crack propagation model can effectively evaluate the fatigue life, crack development stage, and shape of fatigue details. The study determines the effects of crack depth, crack length, and crack angle on fatigue performance. This study provides a basis for studying the residual fatigue life and crack propagation behavior of rib-to-diaphragm welded joints with initial defects. It is of great significance for understanding the crack propagation mechanism, formulating repair measures, and determining repair time. [ABSTRACT FROM AUTHOR]

• Elucidating the various factors that impact the longevity of concrete structures. • Revealing that the construction of a hydrophobic barrier to safeguard concrete materials against environmental factors is crucial for ensuring their protection and durability. • Suggesting that silane-based protective materials have emerged as a promising solution that reduces the surface energy of substrates, limits the penetration of harmful substances, and provides multidimensional protection for concrete substrates. Concrete is the most commonly used construction material in infrastructure worldwide. However, due to its porous nature, it is highly susceptible to the surrounding environment which can lead to corrosion and deterioration, thereby reducing its service life and increasing maintenance costs. Inspired by the "lotus leaf effect" effective waterproofing measures can improve the durability of concrete structures. Silane-based protective materials have emerged as a promising solution that reduces the surface energy of substrates, limits the penetration of harmful substances, and provides multidimensional protection for concrete substrates. The versatility of silanes makes them valuable materials for improving the durability of concrete structures under harsh environmental conditions. This paper initiates with an exploration into the formidable challenges confronting concrete infrastructure. Subsequently, it provides an exhaustive analysis of the utilization of silane-based protective materials in augmenting the longevity of concrete structures, accompanied by a thorough assessment of their applicability in diverse aspects of concrete infrastructure. Furthermore, this study introduces pioneering strategies designed to elevate the protective efficacy of these materials, particularly within forthcoming corrosive environments. As we look ahead, safeguarding infrastructure through the implementation of silane-based materials presents a novel perspective on resource efficiency, assuming escalating significance within the realm of concrete construction. [ABSTRACT FROM AUTHOR]

• A method to evaluate the reliability of air spring is proposed. • The assess of reliability take the road spectrum into consideration. • Failure analyses were performed based on reliability analyses. • The failure result of air spring unit is compared with actual failure condition. The air spring bears complex multi-dimensional random load in the running of the vehicle, and its excellent performance plays a very important role in ensuring the safety and stability of the running of the rail vehicle and improving the comfort of the ride. Taking a certain type of air spring system capsule of Shanghai Metro as the research object, a composite rubber material failure and reliability analysis method based on the virtual joint simulation experimental platform of dynamics software, finite element simulation software and fatigue calculation software is proposed, considering the influence of the train load on track irregularity. The fatigue life assessment and internal damage mechanism analysis of the air spring system are realized by this virtual simulation technology, and reduce the dependence on the actual material test. The effectiveness of the proposed method is verified by comparing it with the actual failure of air springs. This method has an important reference value for the fatigue characteristics study of complex rubber parts with multi-physical field coupling characteristics. It can help urban rail vehicle maintenance units to more accurately understand the remaining service life of air springs, thus reducing safety hazards economic waste and other issues. [ABSTRACT FROM AUTHOR]

• The impact test results of the scaled model corresponding to the finite element model were used to verify the accuracy of the adopted material models and contact relationships. • Based on the spatial complexity of urban overpasses, the dynamic responses and failure mode of the full-bridge model under non-bottom impact were numerically simulated. • Four comparative models were established to study the effect of the bridge model parameters on impact responses. Urban viaducts are likely to be subjected to non-ground-level vehicle collisions during their service life period. However, current research primarily focus on vehicle impacts on the bottom of bridge piers. In this research, a full-bridge scale model impact test was conducted to validate the accuracy of the finite element (FE) model. Then, LS-DYNA is used to establish refined vehicle-bridge collision FE models. The dynamic responses and failure mode of the pier impacted by the non-bottom vehicle are investigated. Besides, the effects of bridge structure spatial stiffness, superstructure mass, and double-column structure on the impact responses of bridges are analyzed. The results show that vehicle collisions are characterized by a continuous impact action involving multiple components. The damage to the full bridge model is concentrated in the directly impacted double-column pier, where the head-on column sustains three-point bending damage, the indirectly impacted column sustains bending damage at the top and bottom, and the cover beam sustains tensile shear damage. The non-bottom impact significantly increases displacements and bending moments of the pier while causing a substantial decrease in bottom shear. The impact responses of the pier are greatly influenced by the superstructure mass and double-column structure, while the spatial stiffness of the bridge has minimal affection. [ABSTRACT FROM AUTHOR]

• The four sets of bearings have different degrees of wear, including fatigue shedding (FS), wear (W), corrosion (C), peristalsis (P), burn (B) and defect (D). • In the extreme speed service, taking the bearing No.2 with the highest temperature as the research object, the tangential residual stresses of the outer and inner ring raceways are tensile stresses, which are 31.3 MPa and 110.8 MPa, respectively. The retained austenite in the outer and inner ring raceways of bearings increased abnormally, reaching 36.7 % and 34.7 %, respectively. • In addition to the highest Fe element, the outer and inner ring raceways of bearings also contain higher Pr elements, reaching 35.5% and 14.5%, respectively. • The maximum thickness of the "white layer" of the outer and inner ring raceways of the bearing is 15 μm and 17 μm, respectively. The surface layer of bearing outer and inner ring raceways contain nanocrystals of 200 nm and 100 nm, respectively. Certain nanocrystalline layer will prolong the service life of bearings. Nanocrystals mainly contain P and Cu elements. • The retained austenite in the outer and inner ring raceways of bearing decreased gradually from the surface layer to the inner layer, and the grain size increased. The crystal plane spacing on the surface layer of outer ring raceway was larger than that of surface layer of inner ring raceway. The grain size in the inner layer of outer ring raceway was smaller than that of inner layer of the inner ring raceway. Four sets of high precision spindle bearings (HPSB) had been in extreme service for 6040 h and 85,000 r/min. The service temperature, wear fatigue form, hardness, residual stress, retained austenite, metamorphic layer and element content of the bearing raceway were analyzed. The surface layer and inner layer of bearing raceway were analyzed by Electron Backscatter Diffraction (EBSD), Focused Ion Beam (FIB) and Transmission Electron Microscopy (TEM). The results show that the service temperature range of the four sets of bearings is from 17.5℃ to 74.7℃. With the increase of rotating speed, the bearing temperature can reach 65℃ at 85,000 r/min. The four sets of bearings have different degrees of wear, including fatigue shedding (FS), wear (W), corrosion (C), peristalsis (P), burn (B) and defect (D). In the extreme speed service, taking the bearing No.2 with the highest temperature as the research object, the maximum and minimum hardness differences of outer ring raceway, inner ring raceway and ball are 423.1 HV, 368.7 HV and 405 HV, respectively. The tangential residual stresses of the outer and inner ring raceways are found to be tensile stresses, which are 31.3 MPa and 110.8 MPa, respectively. The retained austenite in the outer and inner ring raceways of bearings are found to increase abnormally, reaching 36.7 % and 34.7 %, respectively. In addition to the highest Ion (Fe) element, the outer and inner ring raceways of bearings also contain higher Praseodymium (Pr) elements, reaching 35.5 % and 14.5 %, respectively. The maximum thickness of the "white layer" of the outer and inner ring raceways of the bearing is 15 μm and 17 μm, respectively. The surface layer of bearing outer and inner ring raceways contain nanocrystals of 200 nm and 100 nm, respectively. Certain nanocrystalline layer will prolong the service life of bearings. Nanocrystals mainly contain Phosphorus (P) and Copper (Cu) elements. The research findings of this study can provide theoretical and data support for enterprises and scholars in the engineering field. [ABSTRACT FROM AUTHOR]

• The fatigue fracture life of the same batch of flexible shaft is not the same. • By analyzing the fracture flexible shaft, it is found that there is a corrosion pit at the fracture location. • After the specimen is corroded, the fatigue life is shortened by 30%. • The fatigue life of the flexible shaft is prolonged after anti-corrosion treatment. In order to solve the problem of non-expectancy life fracture of the flexible shaft of oil drilling, the force of the flexible shaft is analyzed and calculated, and the static load strength of the flexible shaft and the fatigue strength of torque and bending moment all meet the safety factor requirements, and the fracture flexible shaft is further analyzed for the fracture shaft of metal materials, and it is found that it is fatigue fracture, and there is corrosion at the fracture, in order to determine the effect of corrosion on fatigue fracture, fatigue tests were carried out on corroded specimens and uncorroded specimens, and it is found that the life of the corroded specimens is reduced by 30% compared with the non-corroded specimens. According to the fatigue test conclusion, the deformation zone of the flexible shaft was anti-corrosion treatment, and the service life was found to be improved after on-site trial, which effectively solved the problem of non-expected life fracture of the flexible shaft. [ABSTRACT FROM AUTHOR]

• A failure pressure prediction model of gas pipelines was established using a combination of ANN and FEM. • Global bending and thermal loadings were considered. • Parametric sensitivity was analyzed using the RF algorithm. • Reliability analysis of corroded gas pipelines was conducted. • Five different corrosion rate models were considered for the first time. The long-distance gas pipelines inevitably experience global bending deformation due to the ground movements. Meanwhile, a harsh environment where both the temperature may change drastically and the high chloride ion soil condition possibly causes more severe corrosion on the pipelines, could pose a significant challenge to pipeline safety. It is very crucial to ensure gas pipeline safety and durability in the energy transportation industry. Therefore, this study aims to systematically investigate the failure pressure of corroded gas pipelines under the combined effects of global bending and temperature difference. Considering gas pipelines potentially exposed to soil conditions with different contents of sodium chloride (NaCl), five corrosion rate models were for the first time employed to carry out reliability-based lifetime prediction analysis. The results show that compared to the case without global bending and temperature difference, the service life of gas pipelines can be reduced by 14 % in the case of global bending strain of 0.25 % and temperature difference of −40 °C. As for the corrosion rate model, the Model 4 plays a strongly adverse role in the service life of gas pipelines. Furthermore, parametric sensitivity analysis indicates that apart from the working pressure, initial corrosion depth and the radial corrosion rate are the two more influential factors in affecting the service life of gas pipelines. [ABSTRACT FROM AUTHOR]

• Extreme load and welding defects lead to fatigue failure of wire bracket. • The stress of the optimized wire bracket is reduced and the service life is increased. • Different forms of the same acceleration load have different effects on structural damage. • Vibration fatigue analysis based on safety factors can predict the fatigue life well. Fracture analysis and structure optimization of faulty wire bracket to improve service life. Bench tests and simulation analysis are carried out to evaluate the vibration fatigue damage of optimized structures. The failure reason for wire bracket is the synergistic effect of extreme load and welding defect and the optimized configuration demonstrates reduced stress and a protracted service lifespan. Multi-mode bench tests indicate that only the damage under on-track multiaxial load in time domain is greater than that of the on-track test, and there is a safety margin of at least 10 %. The damage of standard, frequency domain and uniaxial cumulative load are about 0.07, 0.46 and 0.45 times of the on-track test, respectively. The vibration fatigue analysis results show that the variance between the beach tests and simulation outcomes is below 20 %. The life of the wire bracket can be evaluated by vibration fatigue simulation with appropriate safety factor adjustments. [ABSTRACT FROM AUTHOR]

• Loose failure of the slipper ball-socket pair in a water hydraulic axial piston pump is investigated. • The finite element simulation model of the crimping and closing processes and the dynamic model during operation of the slipper ball-socket pair are established. • The residual internal stress may be the main cause of slipper loosening and failure, while wear is a secondary factor. • The direct injection molding method of the slipper ball-socket pair is proposed, which is validated through the durability test. The slipper ball-socket pair in the piston-slipper assembly is one of the key friction pairs in a Water Hydraulic Axial Piston Pump (WHAPP). The slipper ball-socket pair usually manufactured using a closing process to ensure its flexible swing and approximate zero axial clearance. Once the closure of the slipper becomes loose during use, resulting in excessive axial clearance, it will lead to pump failure. Similar problems occur on the WHAPP of the steel plate production line. In order to find out the root cause of the loose closure failure of the slipper ball-socket pair, the stress and strain during the closing process of the slipper ball-socket pair, the load during use, the size of the failed parts, and the macroscopic and microscopic morphologies were systematically characterized and analyzed. Through comprehensive failure analysis, the residual stress generated by the crimping and closing processes of the slipper ball-socket pair may be the main cause of its loosening and failure, while wear probable a secondary factor. Based on the conclusions, the direct injection molding method of the slipper ball-socket pair is proposed to solve this problem. The durability test results of the improved slipper ball-socket pair indicate that the countermeasures are effective. The obtained achievements would be helpful to improve the quality of the slipper closure and increase the service life of the WHAPP. [ABSTRACT FROM AUTHOR]

Cast iron pipes have been extensively utilised in water supply networks worldwide. Many of these pipes are either at the onset or within their wear-out phase, during which failure rates rapidly increase, and the pipes should be repaired or replaced. However, the replacement and rehabilitation of these pipes might require extensive resources and time. Therefore, it is essential to investigate the effects of operational practices that might reduce failure rates for ageing cast iron pipes. In this paper, we investigate the conditions under which water pressure fluctuations may impact and accelerate fatigue failures in cast iron pipes. We carried out a systematic review of the mechanical properties of cast iron pipes and conducted sensitivity analyses to estimate fatigue crack propagation using fracture mechanics. Our investigation suggests that cast iron pipes which are affected by reduced wall thickness due to corrosion may experience a significant decrease in their operational life when subjected to water pressure fluctuations. Moreover, this negative influence of pressure fluctuations is exacerbated with an increase in the mean operating pressure. As an example, a 150 mm pipe featuring a corrosion patch of about 7 mm depth could extend its remaining fatigue life by over fourfold through a minor reduction of both mean pressure and pressure fluctuations of approximately 10 m H 2 O each. The manuscript further explores various pressure reduction combinations and trends, demonstrating the beneficial effects of reducing both mean pressure and pressure fluctuations. Consequently, the presented analysis suggests that water operators should proactively manage (reduce) the magnitude of both pressure components to extend the operating life of ageing cast iron pipes. • Investigate the relevance of pressure-induced fatigue failures in cast iron pipes. • Review and present published literature on the material properties of cast iron pipes. • Study fracture mechanics phenomena for pit and spun cast iron pipes. • Determine conditions for pressure-induced fatigue failures in cast iron pipes. • Define methods to reduce fatigue in aged cast iron pipes through pressure management. [ABSTRACT FROM AUTHOR]

The main functions of the sleepers in ballasted tracks include transferring loads, securing rail gauge and maintaining railway track geometry. Sleepers can be manufactured using timber, concrete, steel or other engineered materials, but concrete is most commonly used around the world. There are a number of researches on the impact load characteristics and the ultimate load carrying capacity of prestressed concrete sleepers, but research on the fatigue life of prestressed concrete sleepers is very limited. A prestressed concrete sleeper's fatigue damage is mainly due to the repeated loads derived from dynamic wheel-rail interactions, especially when either wheel or rail irregularity is present. Fatigue failure is thus a time-dependent limited state where a concrete sleeper accumulates damage to a failure point over its service life. Concrete sleepers could usually suffer from the dynamic fatigue loading spectra throughout their whole lives, and simultaneously, both static and dynamic load-carrying capacities of concrete sleepers degrades over time. Therefore, a fatigue life assessment is an important and complicated research frontier. Field loading conditions, material time-dependent and dynamic properties, and the dynamic bending moments of prestressed concrete sleepers are quantitatively analysed in this study. This paper also presents an updated fatigue life assessment method for concrete sleepers, and provides a case study based on actual field loading conditions and the time-dependent behaviour of materials. The new insights obtained from this study will improve concrete sleeper maintenance and inspection criteria, and provide a new reference for a rational dynamic design principle of railway concrete sleepers and bearers. • Life cycle modelling of railway sleepers is firstly presented. • Track loading annals are analysed from the fields. • Fatigue life assessment model of railway concrete sleepers has been validated with experimental data. • It is the first time that the endurance of railway sleepers is identified using the actual annual loading conditions. • Time-dependent effects play a significant role on the remaining fatigue life of concrete sleepers. [ABSTRACT FROM AUTHOR]

Impact (or blast) and fire always take place concomitantly and threaten the service life of engineering structures. Combined effect of high temperature and strain rate on the mechanical behaviors of reinforced concrete (RC) structures has attracted much attention of researchers. In this work, a three-dimensional meso-scale simulation method was established to study the combined effects of high temperature and strain rate on the failures of RC beams. In the method, the nonlinear interaction between concrete and longitudinal rebar was taken into account by using a bond-slip relationship. A two-step analysis method (thermal transfer analysis followed by impact analysis) was adopted. Mechanical analysis was carried out to understand the failures of RC beams under impact loading after fire exposure. In addition, impact responses of RC beams under fire exposure and after cooling down were compared and analyzed under different fire durations. The effects of impact mass and velocity on the impact performances of RC beams after fire exposure were discussed. It is found that the proposed meso-scale numerical model can effectively simulate the failures of RC beams subjected to impact loadings. Under impact loadings, RC beams after fire exposure show more serious damage while have better deformation capacity compared to the RC beams at room temperature. Fire duration has a significant influence for the impact behaviors of RC beams no matter whether they are cooled down or not. Compared to RC beams which are under fire exposure for >60 min, specimens after cooling down are subjected to less damage at all the involved temperatures. The difference is widening along with the increase of fire duration. Besides, the response of the RC beam after fire exposure is affected remarkably by both impact mass and velocity. • The proposed FE model can effectively simulate RC beams under impact loadings. • Considering the nonlinear steel-concrete bond-slip makes results more accurate. • The beam at fire for long time is damaged more serious than the cooled down one. • The maximum impact force of beam after fire is mainly affected by impact velocity. [ABSTRACT FROM AUTHOR]

Material failure of runway centerline lights was observed in Beijing Capital International Airport after a period of service. In the present paper, visual inspection indicated that cracks initiated from the threaded surface of the lamp, and propagated until fracture. The mechanical properties of three typical lamps were evaluated by tensile, fatigue and impact tests. Microstructural features were also observed. The effects of microstructure and chemical composition on the mechanical properties were identified. It is indicated that improving the material properties of runway centerline lights is beneficial for extending service life and avoiding similar failures. • Reasons for failure of runway centerline light were obtained by visual inspection. • Mechanical properties and microstructure of three typical lamps were compared. • The effects of microstructure and composition on mechanical properties were studied. • Lamps performance is improved by optimizing composition, processing, and shape. [ABSTRACT FROM AUTHOR]

In this paper are presented results of tests and analyses of complex dynamic loads carried out on the bucket-wheel excavator SchRs 650/5 × 24 Krupp, as well as assessment of service life of vital welded structures of a bucket-wheel excavator boom subjected to cyclic loading with a variable amplitude through the use of experimental tests carried out in order to determine operational strength and growth of a fatigue crack for one structural part. Bucket-wheel excavator was built by "Thyssen Krupp" company, Germany. Outer loads, or in other words digging forces for the overburden and coal have been calculated on the basis of measured values of actual current intensity of the bucket-wheel drive and recorded output values of changeable loads. Correlations between the power of the bucket-wheel drive system and adequate hourly production, depending on the overall digging resistance which affects the stress condition of the bucket-wheel, were also determined. Results of the theoretical and experimental analysis of natural and forced oscillations of the support structure for various exploitation conditions are presented in first part of the paper. Deformations ε i determined by tensometric measurements on the rotating shaft of the bucket-wheel were converted into tangential stresses through the introduction of the modulus of elasticity and Poisson's ratio, which, along with the polar moment of inertia of the cross-section, define the moment of rotation on the bucket-wheel shaft. Through the use of the load - strength comparison method (maximization of the ratio of load and strength indicators) the application factor of the gear with the largest number of turns K A has been determined. In the second part of the paper methodological approach for the assessment of service life of vital welded structures of a bucket-wheel excavator boom was presented. Assessment was done in order to determine operational strength and growth of a fatigue crack, through the use of experimental tests. Realized researches and results presented in this paper offer great possibilities for the analyses of behaviour of vital welded structures of the bucket-wheel boom. By the application of the measurement device with 8 channels for registration and processing of electric signals HBM Spider 8 and measurement tapes HBM 6/350 × XY31 deformations were measured at vital welded structures of the boom in the area of the bucket-wheel. The objective of the test is to determine if there is a possibility of occurrence of plastic deformations or initial cracks due to fatigue at vital welded structures and to obtain data which define crack growth. • Specific digging resistances per knife at highest loads are 20% higher than the average value for overall measurements. • Hourly production N(Q e) show that the bucket-wheel excavator during operation cannot reach the designed capacity of Q t =4212 [m3/h]. • Determined application factor K A =1.6 is smaller than the one prescribed in standards for the gearbox of the excavator drive (K A =1.75-2.0). • In exploitation there is a possibility of the occurence of resonance due to their matching, and therefore of the occurence of damaging of critical cross-sections. • Fracture mechanics parameters have shown that the service life of the welded structure if a new edge crack occuris 4.55 years. [ABSTRACT FROM AUTHOR]

An assembly of movable and fixed hood tubes provide safe passage to LD gas produced during primary steel making process. These water-cooled tubes, made up of ASTM A106 : Grade B steel are exposed to most extreme environment involving severe thermal cycling, corrosion from hot LD gas as well as cooling water, wear and erosion from lime and slag splashing, etc. Current work analyzed the failure of movable tubes that led to generation of multiple cracks on the outer surface of the tube facing the LD gas. Analysis revealed cracks parallel to each other in circumferential direction of the tubes. Most of the cracks originated from outer wall of the tube and propagated inwards, however, some of the cracks emanated from inner wall which was in contact with cooling water as well. Elemental analysis revealed the presence of calcium, potassium and sulphur in the oxide scale along the cracks. The nature of scale was confirmed using Energy Dispersive Spectroscopy and Raman Spectroscopy. Presence of these elements are known to reduce the thermal conductivity of the scale and thus can make the cooling inefficient and promote greater thermal stresses. A number of circumferential and longitudinal cracks were observed in tube-to-tube weld zone as well and these were related to microstructural abnormality therein. Overall failure analysis suggested that "thermo-mechanical corrosion fatigue" resulted in premature failure of the hood tubes. Based on detailed laboratory study and field trial, Inconel 625 coating using twin wire thermal spray method has been proposed as a viable techno-economic solution for improved reliability of these tubes. • Failure of water cooled movable hood tubes of LD Convertor is analyzed. • Metallography, energy dispersive spectroscopy, Raman Spectroscopy etc. confirmed "thermo-mechanical corrosion fatigue" as the mode of failure. • A techno-economic coating solution for improved reliability and service life has been proposed and its effectiveness is validated. • Field trial of the coating has no practical difficulty in application and showed encouraging results. [ABSTRACT FROM AUTHOR]

Tie rod is a part of lifting and lowering mechanism of skirt of steel making vessel. The design stress on tie rod was1000 MPa and working temperature is 650–700 °C. Tie rods were approximately 1.9 m (1900 mm) long and 65 mm in diameter. The presently used EN24 material has average life of 6 months. The tie rod thinned as the diameter reduced to 45 mm and length increased upto 2055 mm. The unaffected microstructure showed martensite with bainite and the thinned region shows grain boundary chromium carbide precipitates which indicated microstructural degradation due to high temperature exposure over long period. The grain boundary precipitates is indication of creep which led to precipitate-induced void formation, and their growth and propagation. The steady state creep rate was calculated for 6 months with a change in length of 0.175 m and it is found to be 1.12 × 10−8 m/s which is 3 order magnitude lower than the creep resistant steel. The yield strength and UTS deteriorated due to creep and found to be much lower than the designed stress. At 650 °C which is working temperature of tie rod with a time of 105 h and the rupture strength was compared for different materials. Recommended martensitic steel AISI 431 rupture strength at the same condition is around 100 MPa. The comparison of two materials at 650 °C showed better service life for recommended material. • Tie rod failed in high temperature creep. • Creep occurred due to improper selection of material for application. • Steady state creep rate was calculated for material and found it was lower than creep resistant material. [ABSTRACT FROM AUTHOR]

In this work the failure analysis of a coupled shaft from a shredder is presented. The failure analysis was performed using both experimental methods (visual and microscopic inspection, tensile and hardness tests) and theoretical calculations (stress analysis) aiming to determine the root causes of failure of the coupled shaft. The failure of the shaft occurred due to fatigue, on a perpendicular plane to the rotation axis, in the region of the coupling transverse hole. The shaft fracture surface presents characteristics of fatigue due to torsion combined with bending high loads, with an associated strong plastic deformation. The contribution of bending solicitations related with radial misalignment between the shaft and the shredder module was evaluated. The radial misalignment plays an important role on the failure of the shaft. For the reported life service of the shaft under maximum torsional moments, and considered working conditions, the design guidelines of radial misalignments compromise the structural integrity of the shaft in the shredder system. Recommendation regarding the design and assembly of the shaft are also presented. • The root causes of failure of the coupled shaft are determined. • The shaft fractured surface was investigated by visual and microscopic examination. • The fracture presents features of fatigue associated with high plastic deformation. • The radial misalignment is quantified and plays an important role on the failure. [ABSTRACT FROM AUTHOR]

Periodic deviation of the diameter of wheel across its circumference is referred to as the out-of-round (OOR) defect that can cause significant damages to wheel – rail interface, affect the service life of various components of the vehicle/track system and the safety of trains. Under braking, OOR defect may exacerbate these damages; to uncover such exacerbation, a multi-body dynamic simulation model in a fixed coordinate system for wagons containing new/ defect free or OOR wheels subject to braking torques has been formulated and validated using a dataset in the literature. Using the validated model, the effects of the repetition order (single or multiple deviations of diameter) of OOR defect and the severity of application of braking torques to wheel wear has been examined. It has been found that under constant speed, the normal contact force increased with the repetition order. The OOR defect dominated the normal contact force with a dynamic impact force factor of 1.48, whilst the new/ defect free wheels exhibited negligible impact force. It is shown that the effect of OOR defect is significant for wear of wheels under normal braking whist under wheel skid, braking torque dominates wear. Wheel unloading ratio is shown to be a better indicator for the determination of risk to derailment, than the commonly used Nadal's derailment quotient where the wheel contains OOR defect. • Out-of-round wheels under normal, severe and emergency braking investigated. • A fixed coordinate model was formulated to investigate wheel skid under braking. • Wheel-rail contact frictional power was used to determine wear depths. • Wear under skid was significantly large irrespective of presence or absence of OOR. • Unloading of OOR wheels better predict wagon derailment than Nadal's Criterion. [ABSTRACT FROM AUTHOR]

Failure analyses of five centrifugal casting ethylene cracking furnace tubes within one year and eight months during 2014 to 2017 were investigated through the electro-hydraulic servo universal testing machine, the high temperature endurance testing machine and the scanning electron microscope method, etc. The results showed that the cracking failure parts of five ethylene cracking furnace tubes had microporosity cavities (circa 10–50 μm size). The distribution of the microporosity cavities had a local characteristic (usually within the range of 300 mm). The microporosity cavities connected into microcracks in a relatively short time. The furnace tube is accelerated into the third stage of creep, and eventually failed during service in short term. So the microporosity affects the life of the furnace tube, but does not need to become macroporosity during service. The microporosity is harmful, and it is hard to detect by the existing nondestructive testing method. Prevention measures are put forward from solidification rate, pouring temperature and cylinder rotating speed to prevent microporosity from the manufacturing process of furnace tubes. • The dense microporous cavity accelerated the tube into the third stage of creep, resulting in cracking failure in short-term. • The microporosity was not needed to develop into macroporosity and would have impact on the life of furnace tube. • Reducing solidification rate and increasing pouring temperature could reduce the possibility of microporosity formation. [ABSTRACT FROM AUTHOR]

Abstract The aim of the current investigation is to understand the reason of failure of a deaerating feed-water heater in Bisotun power plant located in Kermanshah, Iran. The vertical deaerator failed after a service life of around 25 years. Optical Microscopy (OM), Scanning Electron Microscopy (SEM) equipped with the accessory Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) methods were used to characterize microstructural changes during in-service process. In addition, to understand integrity of microstructure, mechanical testing including universal tensile and hardness tests were conducted. The appearance of deaerator wall surface was both smooth and pitted, but a distinctive wave-like pattern with smooth scallops was generally prevalent in the areas of more severe damage, especially at the bottom position of the deaerator as a result of Flow Accelerated Corrosion (FAC). FAC resulted in thickness thinning of the deaerator, as in some location caused through-thickness loss (a leaky hole). Microstructural observation showed that leaky hole was formed at the locations in which the microstructure underwent recrystallization, during deaerator manufacturing process. This in turn led to low strength (hardness) of the deaerator steel against FAC. Highlights • Failure analysis of a deaerating feed-water heater in a power plant • SEM analysis, microstructure study and mechanical testing to show damage mechanism • Distinctive wave-like appearance with smooth scallops at the areas of severe damage • Flow accelerated corrosion as main damage mechanism caused through-thickness loss • Recrystallization as large diameter ferrites at leaky holes due to forming process [ABSTRACT FROM AUTHOR]

Abstract With the abundance application of rock and soil anchors in high slope and underground projects, more concerns have been paid to the working condition and durability of the anchorage system. To effectively evaluate the corrosion of anchors in service and the influence factors, field exhumations were performed in four typical application sites and tests of samples were conducted in laboratory. Chemical composition, metallurgical structure and mechanical performance of anchors are tested. Microstructure and component of corrosion byproducts and grout were analyzed. The environmental influence factors are also assessed. The results demonstrate that the anchor head is most liable to corrode in comparing to other section of the anchor. Presence of damaging ions can accelerate the initiation and development of corrosion. Chemical and mechanical properties of anchors remain basically unchanged after 1.5 to 20 years' service. Groundwater and stray currents in the underground do not induce noticeable influence on the corrosion of anchors. This research accomplished a set of evaluation methods of influencing factors and the general law of anchors' corrosion in field environments, which may provide a reference framework for evaluating the environmental effects, durability and service life of rock anchors. Highlights • Field exhumations of rock anchors in four typical sites • Investigation of in-service anchors' corrosion in field • Evaluation of the environmental factors' contribution to corrosion [ABSTRACT FROM AUTHOR]

Abstract Exposure to an aggressive marine atmosphere can seriously harm reinforced concrete (RC) structures and affects a building's service life. In particular, buildings close to the sea are at high risk of suffering damage, mainly due to the effects of chloride. The scientific and technical communities are interested in studying new parameters related to building degradation, including "exposure to aggressive environments" in order to predict a building's service life and schedule maintenance and monitoring systems. This paper proposes a marine exposure index aimed at quantifying potential risks and damage to RC building structures. The definition of the index includes three synergistically related techniques: i) the Analytic Hierarchy Processes to analyze the complexity of the problem and the parameters involved in marine exposure; ii) a state-of-the-art technique to evaluate the degree of building degradation; iii) an optimization calibration procedure by setting a Mathematical Programming problem. The resulting index can be extensively and fruitfully applied by researchers and practitioners in order to assess the building's exposure to an aggressive marine atmosphere. Architects and engineers could apply the proposed index in any phase of the building process, from the project to the maintenance and management phases. The effectiveness of the proposal was tested in a survey of 1816 buildings on the Valencia coast (Spain). Graphical abstract Unlabelled Image Highlights • Marine atmosphere can seriously harm reinforced concrete structures. • This paper proposes a new marine exposure index. • The definition of the index includes three synergistically related techniques. • The index can be used to assess a building's exposure to a marine atmosphere. • The index has been calibrated by surveying close to two thousand buildings. [ABSTRACT FROM AUTHOR]

Abstract This study is an attempt to predict the evolution of damage in a central core constituting a steel wire rope of 19 × 7 non-rotating type, using the energy of rupture determined by the method of a numerical trapezoidal rule of a discreet function. The numerical integral used here is based on the experimental results of simple tensile tests carried out on virgin and artificially damaged specimens, breaking the wire constituting specimens at different percentages. The results obtained made it possible to evaluate the energy behavior of the central core subjected to static loads and subsequently to predict the evolution of the damage. Indeed we were able to determine three stages of damage that allowed us to predict its earlier stages then the moment of its acceleration where a predictive maintenance is required as well as the critical life fraction which can lead to the failure of strand. The present study also includes a comparison between two approaches of calculating damage: The static damage consists in tracking the evolution of the energy at different percentages of the life of the test specimen. The second approach of damage is based on the reduction of the energy, and the energy corresponds to endurance limit of damage strand according to the unified theory. These techniques can help the industrials to have anticipatory maintenance strategy and an awareness the safety requirements. Highlights I present in the following, all the main contributions of this article. • Monitoring the loss of the central core strand's energy of rupture, at different percentage of its degradation. • Damage modeling through four new models based on static tests. • Determination of the critical life fraction of the central core strand. • Determination of the strand's failure stages for maintenance purpose. [ABSTRACT FROM AUTHOR]

• Developing a new probabilistic model for service life prediction and revealing the probability distribution. • Newly constructing the probabilistic model of chloride diffusion coefficient based on mesoscopic concrete. • Comprehensively and quantitatively identifying the sensitivity of reliability index to multiple factors. • Proposing some anti-corrosion countermeasures in conjunction with the engineering practice based on the research results. Chloride attack is the primary cause of performance deterioration and life attenuation of reinforced concrete (RC) structures in marine environments. In an attempt to accurately predict the reliability and service life of RC structures under the co-effects of multiple factors, a comprehensively modified chloride-transport-based model is proposed in this paper. Based on Fick's second law, a multifactor integrated deterministic chloride transport model is developed considering the time dependence, concrete mix proportion, chloride binding capacity, freeze–thaw cycles, sustained load, temperature, humidity and concrete deterioration. Based on extensive literature review combined with the results of multitudinous long-term field exposure tests used in the durability design of Hong Kong-Zhuhai-Macao Bridge and Shenzhen-Zhongshan Bridge, the probability distribution types and parameter values of the governing variables are determined. Taking Qingdao Bay Bridge as an example, the time-variant reliability index, failure probability and reliability-index-based corrosion initiation are determined by using the equivalent normalization method (JC method) and Monte Carlo simulation technique for different environmental zones including atmospheric/splash/tidal/submerged zones. The sensitivity of the reliability index to the control variables and the effects of age index, chloride binding capacity, numbers of freeze–thaw cycles, stress level and concrete deterioration on the reliability index are quantitatively investigated. The results show that the time-variant reliability of different environmental zones is sequenced as: atmospheric zone > submerged zone > tidal zone > splash zone; the sensitivity of reliability to the governing variables sequenced as: concrete cover thickness > surface chloride concentration > chloride diffusion coefficient > critical chloride concentration; the time dependence of the diffusion coefficient has a significant effect on the time to corrosion initiation and cannot be ignored in the predictive model for both the high-performance or ordinary concrete; the number of freeze–thaw cycles and the tensile stress level are relatively insensitive but substantially detrimental to the reliability of corrosion initiation. [ABSTRACT FROM AUTHOR]

• Failure of a LPTR cover plate of an aero-engine was investigated. • Fracture in the cover plate had occurred at incipient fatigue cracks emanating from assembly pin-holes. • Joint preparation, pin hardness and design related issues promoted premature fatigue crack initiation. A twin-engine fighter aircraft met with an accident immediately after take-off and had fallen into sea. Investigation showed that the primary cause of the accident was the fracture in the low-pressure turbine rotor (LPTR) cover plate of right hand (RH) engine. Fractography study confirmed that fractures in the cover plate have originated from incipient fatigue cracks that were developed at the pin-holes meant for assembly with the turbine disc. Investigation revealed that there was deficiency in joint preparation during refitment of the cover plate onto the disc after a fault repair servicing. As a result, there was fatigue crack initiation in multiple pin-holes and the fracture in the cover plate had occurred at these pre-existing fatigue crack locations. The situation was further aggravated because of use of pins possessing hardness substantially higher than that of the cover plate. Further, study of pin-holes on the cover plate of left hand (LH) engine showed that in general, the LPTR cover plate was susceptible to fatigue failure within the prescribed service life itself. In this article, a detailed analysis of the failure that led to the aircraft accident is presented. [ABSTRACT FROM AUTHOR]

• Developing an innovative model, addressing existing limitations, by incorporating critical plane and phase difference angle in multiaxial fatigue life prediction. • Increased accuracy and reliability in predicting the fatigue life of engineering materials under complex multiaxial loading conditions. • Comprehensive investigations ensure the validity and applicability of the proposed model for multiaxial fatigue prediction. • Rigorous statistical analyses and comparisons demonstrate superior performance of the proposed model over existing models. Multiaxial loads are the main cause of fatigue failure in engineering applications, where this failure affects the components and structure of these applications directly. The probability of failures can be decreased by using multiaxial fatigue analysis to assess the service life of components. This study proposes a simple and effective approach for measuring fatigue life in the presence of multiaxial loading. The proposed damage parameter includes terms such as the critical plane and phase difference angles. Calculating fatigue life using this model under proportional and nonproportional loading conditions is possible. The accuracy and validity of the model were tested by comparing the experimental results of four experimental datasets with the life estimation results. The analysis results of four metal materials show that the predicted life correlated well with the experimental observations. In addition to the proposed model, five famous fatigue prediction models were used, and the results of the proposed model were compared with these models. The suggested damage parameter is better for predicting fatigue life under different loads. This was shown through model comparison and prediction error analysis. The findings show good agreement between the suggested model's life estimation results and the experimental findings. Predicting fatigue life becomes more realistic with the suggested approach for any angle between 0 and 90°. The proposed model showed the highest accuracy among the tested models. Afterwards, the Fatemi and Socie FS, Kandil Brown and Miller (KBM), Smith Watson and Topper (SWT), maximum share stress (MSS), and ES models demonstrated lower levels of prediction error, respectively. [ABSTRACT FROM AUTHOR]

• Establishment the coupling model for CRTS Ⅲ slab ballastless track. • Shear stress is the main cause of separation of ballastless track. • The ballastless track interlayer shear bond strength should be ≥2.5 MPa. • Polymers can reduce the probability of ballastless track interlayer separation. Inadequate bonding can bring detrimental interlayer separation problems in high-speed slab ballastless tracks. Thus, it is imperative to elucidate the stress characteristics of the interlayer in high-speed railway ballastless track when subjected to the combined influence of train and environmental factors. The present study employs finite elements to elucidate the change pattern, with the CRTS III slab ballastless track serving as an illustrative case. The findings indicated that interlayer separation of ballastless track under coupling effect of temperature gradient and train load was primarily attributed to shear stress. An evaluation index of "shear bond strength ≥2.50 MPa" was proposed and used to assess interlayer bonding performance of ballastless track in high-speed railway. Additionally, based on polymer modification technology, a method of using phenylpropylene and styrene-butadiene emulsions has been developed to improve the interlayer bonding behaviour of high-speed railway ballastless track. This work is expected to provide theoretical and technical support for a prolonged service life of high-speed railway ballastless track. [ABSTRACT FROM AUTHOR]

• Determines, experimentally, equivalent initial damage size (EIDS) values applicable to fatigue failure analysis of Type 1C anodised AA7085-T7452 aircraft materials. • Notes a significant increase in the average EIDS value whenever material or loading condition changes led to a increased number of crack nucleation sites. • Observes an increased number of nucleation sites and significantly increased average EIDS as the cyclic stress spectrum's severity is increased. Aluminium alloy (AA) 7085-T7452 is a high strength, low weight alloy used in large forgings in primary airframe applications. For corrosion protection, airframe components are anodised and this study looks at the influence of type 1C anodising on the fatigue crack growth behaviour in AA 7085-T7452 specimens that were fatigue tested with fighter wing spectrum loading. Surface etch pits formed during essential anodising preparatory processes were the primary cause of fatigue crack nucleation. The severity of the early crack growth caused by those etch pits that nucleated the worst crack in each specimen was evaluated using quantitative fractography-based fatigue crack growth measurements and the equivalent initial damage size (EIDS) of those etch pits was determined. Characterising the EIDS distribution of aircraft alloys with representative surface treatments is a fundamental input into Linear Elastic Fracture Mechanics (LEFM) based fleet failure analysis of aircraft structures. In this study, a notable increase in the average EIDS value for the worst crack present was observed whenever material or loading condition changes led to a significantly increased number of crack nucleation sites. In particular, an increase in the cyclic stress spectrum's severity increased the number of nucleation sites in a specimen and significantly increased the average EIDS. It appears that due to variable nucleating discontinuity properties (e.g. size, shape and orientation) and material property variations, an increased number of nucleation sites increases the probability that the worst crack present will nucleate at a location that is conducive for relatively fast early crack growth. This will potentially cause shorter overall airframe component fatigue lives and so both the mechanisms and conditions of etch pit fatigue nucleation in this material and material finish shall be discussed for the benefit of failure analysts evaluating unexpected fleet fatigue cracking. [ABSTRACT FROM AUTHOR]

• Boundary condition has distinct impact on the deformation of slewing bearing. • The propagation rate was expressed by extend length per revolution of bearing instead of extend length each rolling cycle. • Crack fronts near points cf = 0, 0.5,1 propagate faster than other points. • Compared with growth rate, kink angle is less sensitive to external loads and bearing design parameters. • Decreasing external load and channel curvature coefficient is beneficial to retard crack propagation. Although increasing ball number leads to a lower equivalent SIF amplitude, it results in a larger propagation rate. As slewing bearings in wind turbines are exposed to complex operational environments, they are prone to crack initiation, propagation and evolution that can lead to contact fatigue problems. Reliable crack extension prediction is a critical requirement. With the goal of obtaining more accurate crack characteristics, this study proposes a crack initiated contact finite element model (CI-CFEM) targeted at the raceway of slewing bearings by introducing a modified sub-model. In the application of the global finite element model (G-FEM) to the slewing bearing system, the rolling displacements of the ball and the boundary displacements are employed in CI-CFEM to take account of external ring deformations and the support conditions. The crack is embedded using FRANC3D, and the stress intensity factor distribution and propagation characteristics of the crack front are investigated. Furthermore, the effect of external load and the design parameters of the slewing bearing on crack propagation are explored, providing insight for optimizing the design of slewing bearings to extend service life. The results reveal that changing external loads and bearing parameters are an effective means of retarding crack propagation rate, while have relatively minor influence on crack growth angle. [ABSTRACT FROM AUTHOR]

• Fatigue failure mechanism was elucidated for multi-stage centrifugal pump shaft. • Specific technical measures to prevent pump shaft failure were proposed. • Fatigue resistance design is performed for pump shaft structure and coupling. • Feasibility of the new pump shaft system has been verified by experiment. In the operation of multistage centrifugal pump, the pump shaft of 304 stainless steel is subjected to a variety of alternating loads. It is one of the parts prone to failure. The fracture microscopic observation, chemical composition analysis and mechanical property measurement of the fractured pump shaft are carried out. Through the fracture analysis, it is found that the pump shaft failure is caused by fatigue mechanism with characteristic of multi-source crack initiation, and there are many cavities and inclusions at the fracture. From the numerical analysis, it is found that there is significant stress concentration at the fracture, which exceeds the fatigue limit of the material and eventually leads to the fatigue fracture. Besides, the appropriate fillet radius and elastic coupling are designed for the pump shaft, which can effectively reduce the stress concentration and improve the service life of the pump shaft. Finally, the fatigue life of the improved pump shaft was experimentally verified. [ABSTRACT FROM AUTHOR]

• Bearing capacity of soil and allowable eccentricity limit control the wall dimensions. • Shear strength parameters of soil are more dominant than seismic parameters of soil, which are influenced by the local soil class. • The critical water height is one-fifth of the wall height in regions with PGA < 0.2. • Regression equations are proposed to estimate the minimum foundation width and critical water height. • To protect the wall from the influence of water, the design of inclined perforated pipes has been proposed. The present study has two objectives for the design of cantilever walls based on the local site conditions: i) estimating the minimum foundation width in the seismic loading condition and ii) determining the critical water level, which causes wall failure, for the design of an effective drainage system. Therefore, cantilever retaining walls are designed according to different design considerations such as stem height (H = 2.5, 4, 6 m), local soil class (ZC, ZD, ZE), and seismic characteristics of ground (PGA = 0.095–0.687 and k h = 0.057–0.403). Stability analyses (bearing capacity, allowable eccentricity, sliding, overturn, overall stability, and settlement) were performed using the limit equilibrium method. Static and dynamic earth thrusts were determined using the Coulomb and Mononobe-Okabe methods, respectively. Analysis results show that local soil class is a more effective parameter than PGA in the seismic design of cantilever walls. Regression equations (R2 > 0.97) are proposed to estimate minimum foundation width (B) easily. Moreover, the critical water height decreases to one-fifth of the wall height, especially in regions with low earthquake risk (PGA < 0.2). Regression equations (R2 > 0.98) are proposed to find critical water height. In the design of the drainage system, inclined perforated pipes should be connected to horizontal ones and continued up to the critical water height on the interface layer between the backfill and natural ground. [ABSTRACT FROM AUTHOR]

Fatigue is among the most decisive degradation phenomena that can potentially occur in steel bridges. However, accurate assessments of the fatigue damage and optimal decision-making based on these assessments are still challenging. This paper aims to present a study on decision-making for existing fatigue-sensitive bridges. It includes a discussion about different assessment methods and acceptance criteria; this discussion concerns whether similar decisions can be made using reliability-based analysis and risk-based analysis, respectively. Different system setups have also been studied to determine their impact on decision-making. Probabilistic fatigue assessment is used as the basis of the study, and a utility-based decision analysis is used to evaluate possible action alternatives to extend the service life of an existing bridge. The decision scenarios are established by considering the associated consequences and potential costs. A general application and a selected critical railway bridge are utilised to demonstrate the framework. The study shows that system setups directly impact the system reliability and further lead to different optimal decisions. Additionally, when the probability of failure due to fatigue is low to a certain extent, local fatigue will not greatly influence the failure of the whole bridge or the optimal decision. • Reliability-based and risk-based analyses can sometimes lead to different decisions. • Several system setups are studied to determine their impact on decision-making. • Conditional probability shows negligible impact when the system has high redundency. • A decision contour is suggested, facilitating decision-making for similar cases. • Comprehensive case studies have been evaluated and presented. [ABSTRACT FROM AUTHOR]

• A sophisticated vehicle dynamics model considers both wheel out-of-roundness and P2 resonance. • Quantitative analysis of effect of wheel out-of-roundness on dynamic stress of coil spring. • Relationship between wheel OOR amplitude and stress amplitude. • Fatigue life of coil spring in suspension system of metro vehicle with wheel OOR. • Calculation of mileage and time interval for wheel reprofiling in metro system. Many Chinese metros experienced numerous fatigue failures of the coil springs in the suspension of vehicles. The field test results presented in our previous work showed that wheel out-of-roundness (OOR) was responsible for the failure of the coil springs. It is believed that the most effective countermeasure to eliminate wheel OOR is to reprofile wheel. The fatigue life of coil springs is an important reference for determining the reprofiling parameters. A sophisticated vibration model for train and track with flexible coil springs and flexible track was established and validated with field test results. The effects of wheel OOR and P2 resonance on the coil spring can be evaluated with this model. The relationship between wheel OOR and coil spring dynamic stresses was determined using multibody simulation (MBS). The fatigue life of the coil springs was evaluated using the parameters of the amplitude of the wheel OOR and the mileage. Under the premise of finding a balance between improving the service life of the coil springs and reducing the cost of reprofiling the wheel, viable proposals were made to solve the problem of coil spring fracture. [ABSTRACT FROM AUTHOR]

• Failure analysis of bearings over the past 20 years are summarized and reviewed. • Different failure modes and mechanisms of bearings are classified and introduced. • It is described in details based on the corresponding characteristics of the failure mechanisms. • Wear and fatigue are the most common failure modes of bearings. • The main causes of failure are summarized. This work reviews the failure modes, mechanisms and causes of bearings in mechanical equipment. Bearings are among the most important basic mechanical components. Their operating conditions directly affect the safety and stability of mechanical equipment. In industries, users have very high requirements for the quality, accuracy, and service life of bearings and pay much attention to the selection, installation, use, and maintenance of bearings. However, bearing failures during operation has not been eliminated. Possible failure modes of bearings include fracture, corrosion, deformation and wear have been reviewed. Failure analysis is crucial for the safe operation of bearings. By identifying the modes and causes of failure, effective measures can be proposed to improve the service life of the bearings and eliminate potential accidents. Herein, the contributions of various researchers to bearing failure analysis over the past 20 years are reviewed. The failure modes and mechanisms of the bearings are classified and discussed. Typical bearing failure cases are discussed. According to statistical results, wear and fatigue are the most common failure modes of bearings, as bearings are affected by cyclic loads, friction, and lubrication during operation. Incorrect assembly, use, and maintenance is the main causes of bearing failure. The aim of this review is to provide information on systematic failure analysis of bearings, identify the failure mechanisms under different conditions, and propose an effective plan to improve the bearing reliability, reducing the occurrence of similar bearing failures. [ABSTRACT FROM AUTHOR]

• Local stress peaks in shape-complex forging die usually exceed yield point for hundredths of a second. • Calculated stress and temperature distributions in the hot forging die. • Fatigue resistance reduction influenced by numbers of re-profiling of die cavity. • Pragmatic knowledge for forging industry about fatigue dies failure. Re-profiling of hot forging dies is the most common method of die repairing in industry. Due to the surface to core hardness gradient caused by the limited hardenability of the die material, the surface layer after re-profiling possesses lower hardness than the first one, causing decrease of the tool lifetime in means of wear, but also can lead into total failure of the die due to other damaging mechanisms. Performed failure analysis of a hot forging die manufactured from 56NiCrMoV7 which included microstructure analysis, hardness profile, tensile and fatigue tests showed a 31 % decrease of fatigue properties when surface and core material is compared. Based on the experimental results it was calculated, that an optimal preventive action to increase the service life is to perform the re-heat treatment after every 10th re-profiling. The 16th re-profiling is critical; beyond this point, there is a significant risk of total die failure. [ABSTRACT FROM AUTHOR]

Due to the superior properties of polyethylene (PE) pipes, their applications covered a broad range of urban and engineering demands. Currently, one of the crucial issues in highly developed pipe line systems is the life and failure prediction in distribution network. Since PE pipes have been employed in gas transmission systems, the safety issue has been considered precisely. This aspect is directly related to the service life and occurrence of failures on the PE pipes. In this research, we comprehensively reviewed previous studies and investigations which have been carried out to predict the life time or mechanical failures in different PE pipes. The existing works are analyzed and discussed in details concerning the mechanical tests, artificial intelligence approaches, failure rates and time to failure in PE pipes. The aim of the present study is to classify and analyze the obtained results from previous researches to describe details of the employed techniques, tests, and models in this field. Analysis and discussion presented in this review, indicates advantages, limitations and research gaps in this area. Finally, perspectives and future research directions are presented. • A brief overview of failure in PE pipes has been presented. • Different types of chemical and mechanical failures have been explained. • Effects of environmental parameters on the failure in PE pipes are discussed. • A comprehensive review on prediction of lifetime and failure of PE pipes is presented. • Developments, advantages, limitations, and future research directions have been outlined. [ABSTRACT FROM AUTHOR]

• The failure mechanism of elastic strip fracture is studied by resonance response and fatigue failure. • A wheelset-rail-cologne-egg fastener system in corrugated section is built. • Elastic strip failure can be controlled by grinding and changing fastener damping. • The elastic strip model, installation state and constraint conditions are verified. Rail corrugation is a typical problem on rail surface, and its high-prevalence section is often accompanied by the fracture of fastener elastic strip. The present paper focuses on the fracture mechanism and control method of the Cologne-egg fastener elastic strip in the high-prevalence section of rail corrugation. Firstly, the numerical simulation model of wheel-rail-fastener system considering the key components of Cologne-egg fastener is completely constructed. Then, the fracture mechanism of Cologne-egg fastener is explored by comprehensively considering the resonance response and fatigue failure of the fastener elastic strip. Finally, the corresponding control methods are proposed by the passive control of rail grinding and active adjustment of fastener structure. Analysis results show that the intensified wheel-rail friction coupling vibration in the corrugation zone leads to the resonance response of the Cologne-egg fastener elastic strip, which intensifies the vibration response of elastic strip. Then, the aggravation of vibration response of the Cologne-egg fastener elastic strip leads the fatigue of the elastic strip, and the outer elastic strip is easier to fracture than the inner elastic strip on the low rail of small-radius curve. Controlling the corrugation depth before 0.16 mm or adjusting the elastic modulus of the damping rubber to be 2.20 MPa and 9.40 MPa can increase the service life of Cologne-egg fastener elastic strip. [ABSTRACT FROM AUTHOR]

• The chemical composition in the length of the concrete sleepers was similar. • All samples presented the boggsite phase, indicating the formation of (N,C)ASH gels. • Formation of brucite was detected in S2C which may be associated with ACR. • Two morphologies of ettringite crystals (ball-like and massive) were identified. • Degradation of the concrete occurred through coexisting mechanisms: ASR, DEF, ACR. Some concrete ties have failed prematurely around the world, influencing the structural integrity, service life, and safety of users. Therefore, this study aims to identify the mechanisms of deterioration in concrete ties made with two types of coarse aggregates after ten years of use in Brazilian railroads. The findings will play a crucial role in informing the decision-making process concerning the ongoing presence these elements on the railway track. The study involved a detailed investigation, including petrographic analysis, X-ray diffraction, FTIR/ATR and SEM/EDS on specimens taken from concrete ties. Petrographic analysis confirmed the presence of different types of coarse aggregates in the two concrete groups: one comprising carbonate coarse aggregates and the other featuring granitic aggregates. The presence of ASR gel (boggsite) filling the voids and cracks extending from these aggregates into to the paste was also confirmed. The S1G concrete sample exhibited two types of morphologies of ettringite: ball and massive crystals. The S2C specimens showed incipient carbonation and the presence of brucite, suggesting the occurrence of ACR. Microstructural analysis of both concrete samples showed that concrete degradation occurred through coexisting mechanisms: ASR, DEF, and ACR. [ABSTRACT FROM AUTHOR]

• A full-bore rupture in the form of a fast-running ductile fracture has occurred at an 18-inch offshore pipeline in the subsea portion. • The visual inspection and ROV survey both revealed a conspicuous dent on the outer surface of the pipeline. • The visual examination revealed that the crack originated at a sharp weld toe angle (149°) at the outer surface. • The rupture origin was a fatigue pre-crack of 0.078-inch depth and 6.7-inch length that propagated at a sharp weld toe angle during the pipeline service life. • The stress analysis revealed that the burst was not due to the operation pressure, but rather due to stresses introduced by a sharp tool dragging over the bare pipeline surface. In the current work, a full-bore rupture in the form of a fast-running ductile fracture has occurred at an 18-inch offshore pipeline in the subsea portion. The pipeline was constructed from longitudinal seam welded pipe conforming to API 5L Grade X42. A subsea survey using the remote operation vehicle showed a pipeline rupture at a depth of 2756 in. from the sea surface. Shiny scratch marks on the outer surface of the pipeline at the rupture location were observed as well. The visual examination revealed that the crack originated at a sharp weld toe angle (149°) at the outer surface. The crack originated in the HAZ region and propagated along the longitudinal seam weld. The rupture origin was a fatigue pre-crack of 0.078-inch depth and 6.7-inch length that propagated at a sharp weld toe angle during the pipeline service life. The stress analysis revealed that the burst was not due to the operation pressure, but rather due to stresses introduced by a sharp tool dragging over the bare pipeline surface. The tool introduced huge external stresses to the pipeline. Both of the internal pressure and the external stresses contributed to the crack propagation during the rupture. [ABSTRACT FROM AUTHOR]

The degradation of material microstructure was frequently encountered in radiant tubes during high temperature service, resulting in their premature failure. Effect of service time on the phase transformation and oxidation behavior of the Cr35Ni45 radiant tubes was analyzed using scanning electron microscopy (SEM), electronic probe coupled with wavelength dispersive spectrometer, X-Ray diffraction (XRD) and transmission electron microscopy (TEM). The orthorhombic M 7 C 3 and the face-centered cubic NbC primary carbides in the as-cast tube transformed into the face-centered cubic M 23 C 6 and the face-centered cubic G phase, respectively, during service at 1000 °C. Metallographic observation showed that a continuous Cr 2 O 3 layer and a discontinuous SiO 2 layer formed on the inner surface of the radiant tubes due to the oxidizing environments, and a precipitate free region was found beneath the oxide layers. Mechanical properties of the tubes decreased with the increasing degree of microstructure degradation as service time prolongs. Residual life assessment of the serviced tubes was conducted by nonlinear fitting Larson–Miller parameter versus rupture testing stress. In spite of lower mechanical properties for the serviced tubes compared to as-cast tube, residual life assessment indicates that they have considerable residual life at the service temperature. [ABSTRACT FROM AUTHOR]

Introduction Despite knowledge and expertise nowadays, minimizing capital costs may continue to be the remote cause of failure of many engineering structures. Failure analysis of a telecommunication tower, which collapsed during a thunderstorm recently in a public institution, was carried out in this work. Method The service history was obtained, and the design, fabrication and the material selection were scrutinized along with standard specification for such structure and microstructural examinations were done. Results and discussion The material choice, joint design and weld fabrication allowed differential aeration cells and heat affected zone stress induced corrosion at the welded endplate joints on the structural members. External painting was of no use because while the structure was intact outside, the pipe had the option of corroding from inside due to differential aeration cells. Galvanizing also is sacrificial and consumed interior coating cannot be replaced in-situ. As materials degraded, stresses concentrated. Under wind current, the structure gave up where stress concentrated most. The tower came down after nine years of service, crushing nearby roof and walls. Comparison shows costs factor weighted heavily in the material selection and design, trading off service life. Conclusion Remote cause of failure - cost minimization. This reality features in many designs in today's world of ever tighter capital budgets. It appears an index of service life trade-offs for costs is now needed in designs. [ABSTRACT FROM AUTHOR]

Buildings' façades play an important role in the protection of buildings and, therefore, their envelope system must comply with its function, fulfilling the performance requirements and withstanding the external environmental agents during the buildings' life cycle. Although the degradation of buildings is a natural process, there are various factors that influence their durability. The assessment of the buildings' durability and service life is a research field that brings together several knowledge areas, e.g. construction technology, building physics and meteorology. This paper intends to identify the main factors that influence the durability of adhesive ceramic external wall claddings, developing models to predict their service life that involve these variables. The service life prediction models proposed in this study are defined based on simple and multiple regression analysis, both linear and nonlinear. The proposed models are defined based on the in situ evaluation of the degradation condition of 96 ceramic claddings of residential buildings in Brasília. The methodology led to coherent results and its applicability and adequacy to predict the service life of ceramic claddings in Brasília is demonstrated. The knowledge regarding the influence of the façades' characteristics on their durability is extremely useful to designers, in order to improve the selection of a given cladding for a specific situation, and to managers and stakeholders, allowing the optimization of maintenance policies and thus increasing the sustainability of the solutions adopted during the buildings' life cycle. [ABSTRACT FROM AUTHOR]