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Structural components with different scales normally show different fatigue behaviors, which are virtually dominated by defects originated from multiple sources, including manufacturing processes. This paper reviews three types of size effects (statistical, geometrical, technological) as well as their recent advances in metal fatigue, aiming to provide a guide for fatigue strength assessment of engineering components containing defects, inclusions and material inhomogeneity. Firstly, the background of inherent defects and defect-based failure mechanism are briefly outlined, and fatigue failure analysis based on fracture mechanics as well as statistics theory are emphasized. Then, two approaches commonly applied in statistical size effect modeling, i.e. critical defect method and weakest link method, are elaborated. In addition, the highly stressed volume method is introduced for considering the geometrical size effects, and the technological (production and surface) size effect is briefly overviewed. Finally, further directions on size effect in metal fatigue under defects are explored.

PurposeThe purpose of this scientific work is to simulate the fatigue damage under random loading, taking into account the mean stress effect on fatigue lifetime and using the Rainflow counting technique to assess the fatigue damage by the Ansys software. The used material is aluminum alloy 6082-T6. A comparison with literature results has confirmed this investigation in this paper.Design/methodology/approachThe study of fatigue under random loading is based on the same concepts as constant loading with the addition of damage summation. The proportion of damage caused by a stress cycle depends not only on the alternating stress but also on the mean stress.FindingsAnalysis of the fatigue damage shows that the number of relative damage due to each cycle.Originality/valueThis paper aims to simulate the fatigue damage under random loading for aluminum alloys.

The mechanical performance of fused filament fabrication printed parts is considered the weak point of the technology due to its high anisotropic structure and irregular behaviour. This research focuses on the application of the Arcan-based method to fused filament fabrication printed parts, to better understand their mechanical behaviour. In order to characterise and quantify the anisotropic behaviour, a butterfly type specimen was developed, taking into account the flaws presented by the process (e.g. need for support material for tilted surfaces, low resolution, etc.). Together with the Arcan type grip, a combination of vertical–transversal (VT), vertical-longitudinal (VL) and horizontal (H) printed samples were tested under three distinct loading conditions, 90° – tensile, 45° – combined loading and 0° – pure shear. For each set of samples, digital image correlation was used to analyse the deformation fields imposed by the distinct building orientations and loading conditions. Regarding the material, two different types of Nylon® (PA 12) were used, namely FX256 and CF15, being the second a short carbon fibre reinforced version of the first, allowing a comparison of the mechanical behaviour. The results show that the building orientation prevails, originating distinct fracture types and overall behaviour difference. It was shown that fibre presence does not create a stronger material, yet an increase in stiffness is observed for all building orientations, except VT, where both materials presented similar values, indicating that the fibre orientation is critical when taking into account the loading conditions. It was also observed that of all sample types, FX256 H specimens showed the closest to isotropic behaviour.

Modeling of the notch and size effects on fatigue behavior of materials is vital for ensuring structural integrity and reliability of engineering components. This study presents a methodology considering both effects of notch and size to analyze the fatigue life distribution of specimens with different geometries using the highly stressed volume approach. Specifically, a dynamic model coefficient considering the influence of different maximum local stresses is developed by modeling the size effect of highly stressed volumes with Weibull distribution. Experimental data of three aluminum and titanium alloys are utilized for model validation and comparison. Fatigue lives of three materials with different geometries are evaluated respectively, and predicted P-S-N curves indicate that proposed model predictions agree well with the probabilistic scatter band of experimental results.

Purpose The purpose of this paper is to evaluate the fatigue process through the dynamic analysis of the global structural model and local static sub-modelling in a critical detail using the hot-spot stress approach. The detail was studied in three different positions at the “Alcácer do Sal” access viaduct, and the methodologies from the IIW and Eurocode EN 1993-1-9 were compared. Design/methodology/approach In this study, the fatigue life process based on the hot-spot stress approach was evaluated using a global dynamic analysis and a local sub-modelling based on a static analysis of welded connections in the “Alcácer do Sal” railway structure, Portugal, taking into consideration the recommendations from IIW and Eurocode EN 1993-1-9. The hot-spot stresses were calculated through the static analysis of the sub-model of the welded connection for each vibration mode with the aim to obtain the temporal stresses using the modal coordinates and modal stresses of the extrapolation points. The Ansys® and Matlab® softwares were used for the numerical analysis and the hot-spot stress calculations, respectively. Findings The proposed methodology/approach to obtain fatigue assessment is based on the modal analysis of the global structural model and local static sub-modelling. The modal analysis was used to extract the boundary conditions to be used in the local model to determine the temporal stresses of the extrapolation points. Based on the modal superposition method, the stresses as function of time were obtained for fatigue life evaluation of a critical detail by the hot-spot stress approach. The detail was studied in three different positions. Originality/value In the present study, a global-local fatigue methodology based on dynamic analysis of the global structural model and local static sub-modelling of the critical detail using the hot-spot stress approach is proposed. Herein, the modal analysis of the global structural model supported by the modal superposition method was used to obtain the matrix of modal coordinates. The static analysis of the local sub-model for each mode from the modal analysis of global structural model was done to estimate the hot-spot stresses. The fatigue damage calculation was based on S-N curve of the critical detail and rainflow method. The IIW recommendation proved to be more conservative compared to the proposed rules in the Eurocode EN 1993-1-9. The global-local modelling based on dynamic analysis is an important and effective tool for fatigue evaluation in welded joints.

Fatigue failures are a concern for old riveted steel bridges since most of them were not originally designed taking into account fatigue. The usual fatigue assessment approach for riveted joints consists of using the fatigue class 71 S-N curve proposed in Eurocode 3, part 1–9. However, this approach may lead to excessive conservative predictions since it is applied indistinctly for different riveted connection geometries and materials. Riveted joints fatigue classification according to the proposal of Taras and Greiner produce more consistent description of the experimental data rather than the Class 71 S-N curve as proposed in the EC3. Local approaches are an alternative methodology to perform fatigue characterization of any type of joints, made of any material, providing that material fatigue properties are available as well as accurate numerical models of the joints. This paper presents an experimental campaign and a numerical analysis concerning down-scale riveted specimens. The fatigue behaviour of these riveted joints was also modelled using standard and extended finite element methods. The different models produced diverse predictions, depending on the failure modes considered.

This paper presents a fatigue analysis of a type of fillet welded joint representative of one main joint of the steel box girder of the Alcacer do Sal railway bridge. From previous studies, it was found that the welded joint between the box girder diagonal and the central hanger gusset is one of the most stressed details of the bridge. This welded joint was not fully manufactured according to current construction procedures, as regards the fillet weld end configuration. In order to assess the fatigue behaviour of such welded joint, the present study combines an experimental campaign and numerical analysis. A total of four welded joint series were produced in order to allow the comparison of the fatigue performance of similar type of welded joint of the Alcacer do Sal bridge with welded joints produced according to existing recommendations, such as EC3. Since scale-down specimens were considered, two different thicknesses were included in this study for each joint configuration, to allow the verification of any thickness effect. Concerning the numerical analyses, two main numerical tools were used: the standard Finite Element Method (FEM) with ANSYS and the eXtended Finite Element Method (XFEM) with ABAQUS. Fatigue life predictions were performed including both fatigue crack initiation and fatigue crack propagation phases. The number of cycles to initiate a fatigue crack was computed using local notch strain-life approaches, and the number of cycles for fatigue crack propagation was computed by integrating the Paris fatigue crack growth law with stress intensity factors computed with ANSYS (virtual crack closure technique) and ABAQUS (contour integral method, 3D XFEM model). Experimental tests demonstrated little influence of fillet weld end geometry on fatigue behaviour of welded joints and plate thickness effects were also reduced as also confirmed by the similar fatigue crack propagation rates. Both numerical simulations provided very accurate predictions of the experimental S-N curves, however the XFEM modelling opens new possibilities for mix-mode fatigue crack propagation simulations.

In this work, the yielding response of high-density polyethylene (HDPE) under different stress states and strain rates was experimentally examined and the ability of classical yield criteria to capture their deformation response assessed. A series of biaxial loading tests (pure shear, combined shear and tension/compression, pure tension/compression) using a designed Arcan testing apparatus were performed. In order to investigate a wider range of stress states, flat and cylindrical notched specimens with different curvature radii were also tested. The predictive ability of the Von Mises and the Drucker-Prager yield criteria are compared against the acquired experimental data. The Drucker-Prager yield model allowed an improved description of the available experimental results, demonstrating the need to account for pressure dependency in the yield model's formulation for semi crystalline polymers. Some differences observed may be attributed to the third invariant stress tensor effects. The evolution of stress triaxiality and Lode angle parameters with equivalent plastic strain were extracted from simulations with Drucker-Prager yield criterion. The results show sensitive stress state dependency of the plastic yielding behaviour, which can be attributed to different combinations of stress triaxiality and Lode angle parameters. Also numerical simulations show that there is variation of the stress triaxiality and equivalent plastic strain along the cross section and the location of the maximum plastic strain and maximum stress triaxiality in the specimens are located at the centre of the specimens.

In this paper, the failure probability of corroded pipelines made by X60 steel grade is evaluated. For this complex real engineering failure problem, the burst corroded performance function is developed using an M5Tree model based on calibration with real burst test database. In addition statistical analysis of ILI-report data is conducted for best modeling of corrosion defects geometries (i.e. defects length and depth) based on Anderson-Darling statistic where different PDFs (i.e. Normal, Lognormal, Frechet, Gumbel, Weibull) were tested. Moreover, the effect of defects geometries on the failure probability of the case-studies were investigated for various operating regimes. Then the influence of distributions on the reliability analysis were also illustrated. Results indicated that increases in defects depth are strongly reduced the safety levels of this problem, where miss-selection of defects distributions could lead to conservatives results.

Engineering structures, such as bridges, pressure vessels, machines, etc., are subject to variable load cycles during their lifetime that can cause fatigue damage. Fatigue design of steel structures is based on double S-N curves and the estimation of fatigue damage caused by load cycles. This estimation is calculated by cycle counting methods combined with the Palmgren-Miner rule. The presented software, Fatigue Damage Tool (FDT), is based on the design assumptions of the Eurocode 3 EN1993-1-9 standard. The cycle counting method implemented in FDT is the rainflow counting algorithm according to the ASTM E1049-85 standard, and it uses the Palmgren-Miner rule to calculate de fatigue damage for a critical detail. In this paper, the software is applied to estimate the fatigue damage accumulation for a critical detail at the mid-span of the Varzeas railway bridge. Additionally, FDT can also be applied to several other types of engineering structures.

The First International Symposium on Risk Analysis and Safety of Complex Structures and Components (IRAS 2019) was organised in-teamed with the ESIS/TC12 Technical Committee on Risk Analysis and Safety of Large Structures and Components, which took place between 1-2 July 2019 at the Faculty of Engineering of the University of Porto (FEUP), in the City of Porto, located at seaside in the northwest region of Portugal. The guest editors of the IRAS 2019 deeply acknowledges all members of the International Scientific Committee, Thematic Sessions Organizers, Keynote Speakers and authors that contributed to the success of this event, that gathered more than 126 participants presenting more than 168 papers and posters. Sponsors are also fully acknowledged for their important contributions. The ESIS/TC12 2019 winners of the Robert Moskovic Award, Award of Merit TC12, and ESIS/TC12 Young Scientist Award were announced during the conference. Additionally, the guest editors (conference chairs) sincerely thank the tireless efforts of the Organizing Committee members as well as students and other FEUP and Construction Institute staff involved in the organization. Finally, the guest editors are pleased to inform that the second edition of the IRAS event will be organised by Prof. Aleksandar Sedmak (University of Belgrade, Serbia) which will take place in Belgrade in Serbia in the year 2021.

In the context of fatigue evaluation of riveted railway bridges, cross-girder to main beam connections are frequently critical details. Secondary effects, such as out-of-plane bending and dynamic amplifications due to the proximity to loading paths which in the case of old bridges were not taken into account in the original design, may lead to severe increase of fatigue damage. The fatigue assessment of old riveted railway bridges has been addressed in the last years by developing local models of critical riveted joints that are linked to global models. This local-global modelling approach aims at evaluating local secondary stresses. Former fatigue probabilistic analyses of riveted joints have been focused on resistance variability rather than on loading/stresses (actions) variability. In this paper a probabilistic procedure to include the variability of loading in the fatigue analysis of complex riveted joints of railway bridges is proposed assuming loading as a random variable. Local finite element models were developed and later coupled with the global model in order to obtain the real stresses associated to real trains crossing the bridge. To reduce computational time, the results obtained from these local models were inputted in a Linear Fracture Mechanics model, supported by Paris fatigue crack propagation law. Monte Carlo simulation technique was applied to calculate the fatigue reliability of an old riveted railway bridge, considering traffic records from previous studies on the bridge.

Wire arc additive manufacturing (WAAM) has increasingly attracted attention in the construction sector because of its ability to produce large metallic structural parts in short times. In this paper, Coffin-Manson and Morrow (CMM) equation is employed to compare the fatigue life of WAAM stainless steel with the structural steels S355 and S690. The results showed that the fatigue performance of structural steel is better than the WAAM stainless steel, the fatigue performance vertical to printing direction (WAAM-900) is better than it along the printing direction (WAAM-00). In addition, the fatigue cycle of the transition reversals of structural steel is much less than it of WAAM stainless. With the increasing the fatigue cycle, the maximum density of the strain amplitude ratio is gradually increased to 1.0. The probabilistic parameters of CMM equation were obtained by a stochastic analysis using Latin hypercube sampling strategies. The probabilistic strain-fatigue life behaviour obtained from the constant exponent sampling strategy is higher when compared with the varied exponent sampling strategy for both WAAM stainless and structural steels.

The paper deals with the subject of diagnostics and the quick repairs of long-term operated metallic materials. Special attention was paid to historical materials, where the structure (e.g., puddle iron) is different from modern structural steels. In such materials, the processes of microstructural degradation occur as a result of several decades of exposure, which could overpass 100 years. In some cases, their intensity can be potentially catastrophic. For this reason, the search for minimally invasive diagnostic methods is ongoing. In this paper, corrosion and fracture toughness tests were conducted, and the results of these studies were presented for two material states: post-operated and normalized (as a state &ldquo, restoring&rdquo, virgin state). Moreover, through the use of modern numerical methods, composite crack-resistant patches have been designed to reduce the stress intensity factors under cyclic loads. As a result, fatigue lifetime was extended (propagation phase) by more than 300%.

Racking systems applied in logistics warehouses are built with thin steel sections that are joined by bolted connections. In fully automatic systems, these structures are loaded 7/7 days and 24/24 hours raising fatigue issues due to the cyclic nature of the resulting stresses. According to the current industrial practice, those bolted joints are tight with no torque control, leading to the concept of snug tight bolts, which behaves similarly to non-preloaded bolted joints. Eurocode 3 has no reference about fatigue rules of bolted connections between thin-walled cold formed steels. This paper aims at analyzing the fatigue behaviour of bolted (snug tight vs. preloaded) joints in order to provide fatigue design rules for possible update of Eurocode 3 existing rules. A significant fatigue testing program was performed to investigate the influence of different bolts arrangements, stress R-Ratios and bolt preloads, including snug tight, on fatigue life. The obtained results were analyzed under ASTM E739 procedure in order to obtain S-N curves. This work revealed an average fatigue strength of 114 MPa at 2E6 cycles for the snug tight bolted joints. Preloaded bolt joints presented an average fatigue strength of 108 MPa at 2E6 cycles. Discrepancies between S-N curves suggested by Eurocode 3 and fatigue data obtained experimentally were verified.&nbsp

Aero engine components like compressor discs normally operate under harsh conditions like complex multiaxial stress states. Notch effect is often critical for structural integrity assessment in virtue of complex structure and discontinuities. According to the notch effect under cyclic loadings, a computational framework for multiaxial fatigue analysis of compressor discs is established by coupling finite element (FE) simulation of stress gradient with Fatemi-Socie (FS) criterion. Specifically, a notch support extension method accounting for stress gradient effect is elaborated through elasto-plastic FE analysis, which can be determined for fatigue life prediction of arbitrary shaped components. Experimental fatigue data for smooth and notched specimens of TC4 and GH4169 alloys demonstrated the appropriateness of the proposed computational approach. The applicability and performance of the prediction model to a compressor blade-disc attachment subjected to field spectra is presented. Results show that testing effect can be significantly reduced by using this framework with acceptable prediction accuracy.

This paper presents the results of an experimental investigation about fatigue crack paths and fatigue crack growth on S355J0 steel subjected to I + II and I + III mixed mode conditions both under load ratios R = 0 and 0.1 and different mode mixities. In particular, compact specimens with distinct notch inclinations were exposed to mixed mode I + II (tension and shear) whereas prismatic specimens provided with an external one-sided sharp notch were subjected to mixed mode I + III under distinct bending to torsion ratios. The influences of distinct load mixities on fatigue crack growth rates and fatigue crack growth directions are analysed and discussed in relation to existing theories. Also the influence of each loading mode for the resulting mixed mode fatigue crack propagation is also discussed.

The fatigue damage assessment of large bridges is highly conditioned by the required computational high demands. Generally, in order to overcome the multi-scale problem, global and local models are needed to properly account for both global structural behaviour and the local nature of the fatigue damage. The analysis of such structural problems using direct time-integration algorithms is impracticable in most of the cases, which leads to the necessity of developing alternative methodologies in order to increase the computational efficiency and the accuracy of fatigue cracking assessments. In this respect, effective computational algorithms based on the modal superposition technique have been proposed and implemented in previous works. Overall, such workflow considers the interaction between the global and local models combined with the application of the modal stress intensity factor concept. Aiming at performing an efficient and accurate assessment of the fatigue damage, firstly, combining the Fracture Mechanics principles and crack propagation laws, the crack propagation phase in a complex bridge detail is analysed. In this regard, the present paper aims at proposing relevant improvements to the above-mentioned methodology, namely: i) the refinement of the implemented submodelling techniques in order to increase the accuracy of stress and strain fields computation and allow to account for smaller initial crack lengths; ii) the analysis and limitation of the considered number of vibration modes to the relevant ones for the local dynamic response; and iii) the implementation of a parallel computing approach for the calculation of the modal stress intensity factors related to the vibration modes defined in ii). The fatigue assessment procedures were applied to an assumed cracked welded detail of a recent railway composite bowstring bridge located in Portugal. Also, since the assumption of a pre-existing crack may lead to very conservative predictions, the modal superposition technique is further extended to evaluate the fatigue crack initiation phase, demonstrating the safety of the analysed case study in the absence of existing defects.

Steel and composite steel-concrete bridges are subjected to random traffic loads along their life cycle which generate significant dynamic impacts. The road-roughness of asphalt pavements is one of the most important aspects that contributes to the significant increase of the stress amplitudes and hence to serious load-induced fatigue concerns. In this context, welded joints are well known as the weakest points in bridges, since they are prone to stress concentrations leading to initiation of fatigue cracks being in current design codes evaluated using primarily the nominal stress method (NSM). However, a more accurate stress definition, which considers the complexity of the stress field at the welds, becomes necessary mainly in old roadway steel bridges that are often subjected to out-of-plane stresses. In this paper, the hot-spot stress method (HSM) is used to evaluate the fatigue life of a welded joint subjected to distortion induced-fatigue, considering the vehicle speeds and a progressive deterioration model for the road pavement. The welded joint was modelled by solid elements and was integrated with a 3D dynamic bridge model using the sub modelling technique. Besides the importance of considering the bridge-vehicle dynamic interactions with the pavement road-roughness, the dynamic amplification effects on local stresses and the relatively high scatter found in the fatigue lives considering global and local approaches show that a detailed local stress definition is fundamental to evaluate the fatigue performance of existing roadway bridges. The effects of the annual traffic increase rate on the fatigue life are also discussed.

Purpose The case-study building of this work is the Medieval Inn of Gralheira (“Pousada Medieval da Gralheira”) located in Vila Pouca de Aguiar, Portugal. This building is an example of the structures of that time, located in Trás-os-Montes, Portugal. A large amount of the built heritage suffers from advanced degradation, making the recovery, increasing the complexity of the rehabilitation and restoration intervention and implying a highly specialized interdisciplinary component. Therefore, the purpose of this paper is to carry out a study of the building in order to perform an analysis of its wood floor and assess its structural behaviour and conservation status. This work also presents some examples of intervention methods and rehabilitation techniques used to solve problems in the masonry structure and wood structures. Design/methodology/approach In this work, a numerical model of a wood pavement of a medieval building is presented, which was developed and calibrated with values obtained in an experimental campaign of wood specimens extracted from the floor structure and the deformation measured in situ. This model aims to analyse and predict the behaviour of the structure in terms of serviceability limit states. Rehabilitation and reinforcing techniques are described, for specific damages, complemented with a critical comparative analysis to define the most appropriate rehabilitation measures for each situation. Findings In this work, for the numerical model of the medieval building under consideration, the support of the beams in the walls between 50 per cent embedded and simply supported (hinge supports) was used. Since the beams have some restriction imposed by the wall, they have a delivery about 20 cm in the wall. The consideration of the delivery between beam and columns as simply supported (hinge supports) is a reasonable approximation. There is a difference between the values of deformation obtained in the numerical model and in situ due to the support conditions and also due to the consideration of the pavement loads as a distributed load, which does not correspond entirely to reality, since the pavement confers rigidity to the floor, behaving like a diaphragm. The presented intervention techniques are not applicable in all structures because each building has different characteristics, in terms of materials and construction. The pathologies occur due to many sources and each case is unique, and must be carefully studied before taking decisions about the rehabilitation methods to use. Originality/value This work presents a numerical model of wood pavement of a medieval building developed according to some experimental values obtained in an experimental campaign using wood specimens extracted from original beams and based on in situ measurements. This study is part of master thesis of Michael Andrade, an original research work.

PurposeThe purpose of this paper is to investigate the fatigue performance of a welded detail from a composite steel-concrete railway twin girder bridge caused by a passenger train circulating at varying speeds, by identifying the dynamic amplification scenarios induced by resonance. For this purpose, the hotspot stress method is used, instead of the traditional nominal stress methods.Design/methodology/approachThis paper assesses the fatigue behavior of a welded connection considering critical stress concentration locations (hotspot). Finite element analysis (FEA) is applied, utilizing both a global and a local submodel, made compatible by displacements field interpolation. The dynamic response is obtained through the modal superposition method. Stress cycles are extracted with the rainflow counting method and the fatigue damage is calculated with Palmgren-Miner’s rule. The feasibility of five submodels with different mesh densities, i.e. 1, 2, 4, 8 and 20 mm is verified.FindingsAn increase in the fatigue damage due to the resonance effect was found for the train traveling at a speed of 225 km/h. A good agreement between the computed fatigue damage for the submodels is achieved. However, a non-monotonic hotspot stress/fatigue damage vs mesh density convergence was observed with a peak observed for the 4 mm model, which endorses the mesh sensitivity that could occur when using the surface stress extrapolation detailed rules specified in the standards for the hotspot stress method.Originality/valueAdvanced dynamic analyses are proposed to obtain local stresses in order to apply a local method for the fatigue assessment of a bridge’s structure subjected to high-speed railway traffic on the basis of the mode superposition technique resulting in much less computing times.

Purpose Recent studies have proposed the application of local fatigue approaches based on fracture mechanics or on strain-life material relations for the fatigue analysis of metallic structures. However, only few studies in the literature apply local approaches in the riveted bridges analysis; although these approaches can be applied to any type of connections, requiring a detailed stress analysis of joints and, consequently, considerable computational resources costs. The approach based on S-N curves, formulated in nominal or net stresses, is more usual in the fatigue analysis of riveted bridges. Due to economic factors, riveted bridges have had their operating life extended, while changes in the transport system over the years have subjected such structures to overloads different from those originally planned. These bridges, most of them centenary, were not originally designed accounting for fatigue damage; they represent an important group of structures that are very likely subjected to significant fatigue damage indexes. These factors make necessary detailed residual fatigue life studies to substantiate the decisions of extend (or not) the operational period of these bridges. The paper aims to discuss these issues. Design/methodology/approach The present paper presents a methodology aiming at applying the local approaches in the fatigue analysis of riveted joints of metallic bridges, through the use of sub-modeling techniques and procedures automation. The use of such techniques made such an application viable by keeping the computational costs involved at a moderate level. The proposed procedures were demonstrated using the Trezói Railway Bridge, located on the Beira Alta line, Portugal, built shortly after the Second World War. The proposed set of procedures allowed, through finite elements analysis, to obtain the relevant stresses to perform local fatigue damage analysis. A global structural model was constructed, using beam elements, and local models of a critical node were built with solid finite elements. The structure is analyzed under the passage of regulatory trains. The details of the modeling performed and the computation of the principal stresses in the vicinity of a node and the tangential/circumferential stresses at the holes of two critical riveted connections of that node are analyzed and a fatigue damage analysis is carried out. Findings In the proposed submodelling approach, disassembling the complex riveted nodes into riveted subassemblies allowed the evaluation of the local stresses at riveted holes at an affordable computational cost. Originality/value A methodology is proposed to allow the application of local fatigue analysis in real complex riveted joints, mitigating the computational costs that would result from a full model of the node with all rivets.

Purpose For nowadays construction purposes, it is necessary to define the life cycle of elements with defects. As steels 42CrMo4 and 41Cr4 are typical materials used for elements working under fatigue loading conditions, it is worth to know how they will behave after different heat treatment. Additionally, typical mechanical properties of material (hardness, tensile strength, etc.) are not defining material’s fatigue resistance. Therefore, it is worth to compare, except mechanical properties, microstructure of the samples after heat treatment as well. The paper aims to discuss these issues. Design/methodology/approach Samples of normalized 42CrMo4 (and 41Cr4) steel were heat treated under three different conditions. All heat treatments were designed in order to change microstructural properties of the material. Fatigue tests were carried out according to ASTM E647-15 standard using compact tension specimens. Later on, based on obtained results, coefficients C and m of Paris’ Law for all specimens were estimated. Similar procedure was performed for 41Cr4 steel after quenching and tempering in different temperatures. Findings The influence of heat treatment on the fatigue crack growth rates (42CrMo4, 41Cr4 steel) has been confirmed. The higher fatigue crack growth rates were observed for lower tempering temperatures. Originality/value This study is associated with influence of microstructural properties of the material on its’ fatigue fracture. The kinetic fatigue fracture diagrams have been constructed. For each type of material (and its heat treatment), the Paris law constants were determined.

Purpose The purpose of this paper is twofold: first, to observe an influence of different Composite Fibre-Reinforced Polymer (CFRP) patches, whose application to metals is very easy, in suppling and significantly elongating the service time; and second, the numerical calculation of the reduced stress intensity factor (SIF) range for strengthened cracked steel specimens. Design/methodology/approach One of the successful strengthening methods is the CFRP patching along the fatigue crack paths. The presented approach has been studied and discussed in this paper on the background of the numerical and experimental data. As it was expected, the proposed strengthening method is efficient and promising in case of the “immediate” repairs of critical members with cracks. The manufacturing process of specimens and test methodology as well as numerical approach to calculate SIFs for various reinforcements of steel specimens are presented. For this purpose, the Extended Finite Element Method was involved and described. Findings The main mechanism of fatigue crack growth retardation is associated with local ΔK reduction due to CFRP patches; any type of reinforcement results in an increase in af and a significant decrease in SIF values. The beach-marking method is described as a good, reliable and comprehensive method to capture the crack propagation in structures consisting of various materials and could be applied successfully for mixed mode testing. Originality/value A detailed experimental-numerical approach for fatigue crack growth in long-term operated structures made of steel is presented. The strengthening methodology is presented with consideration of the various CFRP patches configurations.

Surface damages caused by the impact of flying objects are important factors responsible for fatigue performance degradation of high-speed railway axles, both qualitative and quantitative assessment of these damages are necessary for the maintenance of these axles. In this paper, cubical projectiles were used to reproduce actual damages on S38C axle specimens by a compressed-gas gun at varying velocities. Morphologies of simulated impact damages were characterized, and fatigue strengths of specimens under different impact damages were determined by the step-loading method. Results show that fatigue strength of impacted specimens reduces with the increase of damage depth; besides, other factors, including damage orientation, damage shape, and microstructural damage also exert their contributions. Finally, evaluation on fatigue strength reduction has been performed based on the damage tolerance philosophy.

Local fatigue approaches, such as, the stress-life, strain-life or energetic approaches defines a framework to estimate the fatigue crack initiation from notches of structural details. Various engineering structures, such as, bridges, wind towers, among others, are subjected to cyclic dynamic loadings which may substantially reduce the strength of these structures. Nowadays, the structural systems tend to be more complex being necessary to find computationally efficient solutions to perform their fatigue analysis, accounting for dynamic actions corresponding to long complex loading events (e.g. diversity of trains crossing a bridge), mainly if local approaches are envisaged. Thus, this paper aims at presenting and validating a generalization of a methodology based on modal superposition technique, for fatigue damage parameters evaluation, which can be applied in fatigue analysis using local approaches. This technique was applied recently in the context of fatigue crack propagation based on fracture mechanics, although it can be extended to compute the history of local notch stresses and strains at notches. A very important conclusion is that the technique can be explored for the case of local confined plasticity at notches whenever the global elastic behaviour of the component prevails. Local submodelling can be explored with this technique to avoid the necessity of large computational models. Local models are only needed to be run under linear elastic conditions for the selected modal shapes of the structure, being the local time history of fatigue damage variable computed by modal superposition for each loading event. That time history may be further post-processed for elastoplastic conditions using Neuber or Glinka’s analyses. Comparisons with direct integration elastoplastic dynamic analysis confirmed the feasibility of the proposed approach.

The full-scale static testing of wind turbine blades is an effective means to verify the accuracy and rationality of the blade design, and it is an indispensable part in the blade certification process. In the full-scale static experiments, the strain of the wind turbine blade is related to the applied loads, loading positions, stiffness, deflection, and other factors. At present, researches focus on the analysis of blade failure causes, blade load-bearing capacity, and parameter measurement methods in addition to the correlation analysis between the strain and the applied loads primarily. However, they neglect the loading positions and blade displacements. The correlation among the strain and applied loads, loading positions, displacements, etc. is nonlinear, besides that, the number of design variables is numerous, and thus the calculation and prediction of the blade strain are quite complicated and difficult using traditional numerical methods. Moreover, in full-scale static testing, the number of measuring points and strain gauges are limited, so the test data have insufficient significance to the calibration of the blade design. This paper has performed a study on the new strain prediction method by introducing intelligent algorithms. Back propagation neural network (BPNN) improved by Particle Swarm Optimization (PSO) has significant advantages in dealing with non-linear fitting and multi-input parameters. Models based on BPNN improved by PSO (PSO-BPNN) have better robustness and accuracy. Based on the advantages of the neural network in dealing with complex problems, a strain-predictive PSO-BPNN model for full-scale static experiment of a certain wind turbine blade was established. In addition, the strain values for the unmeasured points were predicted. The accuracy of the PSO-BPNN prediction model was verified by comparing with the BPNN model and the simulation test. Both the applicability and usability of strain-predictive neural network models were verified by comparing the prediction results with simulation outcomes. The comparison results show that PSO-BPNN can be utilized to predict the strain of unmeasured points of wind turbine blades during static testing, and this provides more data for characteristic structural parameters calculation.

This paper proposes a strain prediction method for wind turbine blades using genetic algorithm back propagation neural networks (GA-BPNNs) with applied loads, loading positions, and displacement as inputs, and the study can be used to provide more data for the wind turbine blades’ health assessment and life prediction. Among all parameters to be tested in full-scale static testing of wind turbine blades, strain is very important. The correlation between the blade strain and the applied loads, loading position, displacement, etc., is non-linear, and the number of input variables is too much, thus the calculation and prediction of the blade strain are very complex and difficult. Moreover, the number of measuring points on the blade is limited, so the full-scale blade static test cannot usually provide enough data and information for the improvement of the blade design. As a result of these concerns, this paper studies strain prediction methods for full-scale blade static testing by introducing GA-BPNN. The accuracy and usability of the GA-BPNN prediction model was verified by the comparison with BPNN model and the FEA results. The results show that BPNN can be effectively used to predict the strain of unmeasured points of wind turbine blades.

The maintenance and safety of ancient bridges is a major concern of governmental authorities. In particular, the safety of old riveted bridges fabricated and placed into service at the end of the 19th century deserves particular attention. These structures are susceptible to exhibit high fatigue damage levels due to their long operational period with increasing traffic intensity associated to an original design not covering the fatigue phenomenon. This paper reviews recent fatigue behaviour investigations on single and double shear riveted joints performed by Universities of Porto (Portugal), Tras-os-Montes e Alto Douro (Portugal), and Wroclaw (Poland), in particular concerning the fatigue characterization of riveted joints extracted from representative Portuguese riveted bridges, namely the Eiffel, Luiz I, Fao, Pinhao and Trezoi bridges. In order to overcome the influence of scatter and establish a reliable assessment for the obtained experimental data, two statistical approaches were used: implement linearized boundaries following the recommendation in ASTM E739 standard and defining probabilistic S N fields using the Castillo & Fernandez-Canteli model. This statistical analysis allows to propose design S N curves for single and double riveted joints and evaluate the applicability (safety) of using the design curves suggested in Eurocode 3 as well as design curves proposed by Taras and Greiner.

The paper summarises an experimental study on the fatigue crack propagation and cracks paths in ancient steel&mdash, 19th-century puddle iron from the Eiffel bridge. The tests were performed with the load R-ratio equal to 0.05 and 0.5. All tests were performed under different notch inclinations (mode I + II). The fatigue crack growth rate in the tested material is significantly higher than its &ldquo, modern&rdquo, equivalent&mdash, low carbon mild steel. The crack closure phenomenon occurs in specimens during the process of crack growth. Understanding this aspect is crucial for the examination of a stress R-ratio influence on kinetic fatigue fracture diagram (KFFD) description. Both the experimental and numerical approach, using the HP VEE environment, has been applied to the crack closure as well as the crack opening forces&rsquo, estimation. These analyses are based on the deformation of the hysteresis loop. The algorithm that was implemented in the numerical environment is promising when it comes to describing the kinetics of fatigue crack growth (taking into consideration the crack closure effect) in old metallic materials.

Foreign object damage (FOD) introduced in service, indentations, and nicks encountered during maintenance are typical defects leading to pre-scrap of high-speed railway axles. A comprehensive assessment of the influence of these defects on the structural integrity of axles is critical for ensuring their operation safety with low maintenance costs. Three types of defects were produced artificially on specimens extracted from EA4T axles, electronic discharge machine (EDM) crater, indentation via compressing balls, and FOD by tungsten steel balls and cubes. Rotating bending fatigue tests were performed for fatigue strength evaluation of smooth and defected specimens. Morphologies of defects and fracture surfaces were studied. EDM defect surface is rough and the secondary notches are the fatigue crack initiation sites, while fatigue crack of indented and impacted specimens initiates from the sharp point of defect rims. Fatigue strength of specimens with indentation or tungsten ball impact damage is superior to that of EDM specimens and cubical projectile impacted specimens under the same depth. A large dispersion was found in the shape of impact damages by cubic projectiles and scattered fatigue strength as a consequence. Except for the defect depth, other parameters including produce modes and shape of the defect, should be considered to give a reliable evaluation on the fatigue strength of defected specimens.

There are many old riveted bridges constructed 100–150 years ago around the world. In Portugal, it is counted that about 100 riveted bridges, which were built based on traffic intensity and vehicle weight, are no longer suitable nowadays. However, mainly due to economic reasons, those riveted bridges are still in service. Thus, the remaining performance is suggested to be accurately evaluated to determine possible repairs. However, the fatigue performance investigation of such riveted joints in old bridges is relatively limited. Then, fatigue assessment concerning the riveted joint is not contemplated in the current standard as EC3. This paper presents an experimental campaign of riveted joints. Three types of riveted connections are conducted to obtain the fatigue behaviour. Then experimental results, and its design curves obtained based on the ASTM E739 standard, are compared to S-N design curves, suggested for riveted connection. The fatigue strength predicted from class 71 in EC3 is lower than it obtained from test results.

In this paper, the normalized variable V=(log N-B)(log Ao-C), as derived from the probabilistic S-N field of Castillo and Canteli, is taken as a reference for calculation of damage accumulation and probability of failure using the Miner number in scenarios of variable amplitude loading. Alternative damage measures, such as the classical Miner and logarithmic Miner, are also considered for comparison between theoretical lifetime prediction and experimental data. The suitability of this approach is confirmed for it provides safe lifetime prediction when applied to fatigue data obtained for riveted joints made of a puddle iron original from the Fao bridge, as well as for data from experimental programs published elsewhere carried out for different materials (aluminium and concrete specimens) under distinct variable loading histories.

This paper presents a study aiming at characterizing the fatigue crack growth behaviour of the 6082-T6 aluminium alloy using standard CT specimens. The fatigue crack growth threshold is also characterized according to the ASTM E 647 standard. Besides the standard CT specimens with sharp notches, specimens with initial circular notches were also fatigue tested. The threshold stress intensity factor ranges, ΔK th , are compared for the distinct notches under study. The fatigue crack propagation rate in the regime II are obtained using the Paris law. A comparison is made between the CT specimens geometries with distinct notches under consideration. The ΔK th values for the geometry of standard CT specimens present lower values when compared with the geometry of the CT specimens with blunted notches.

Non-conventional machining processes, such as the Electrical Discharging Machining (EDM) offers the possibility to machine very hard materials with great potential to generate complex geometries. However, the EDM process involves significant microstructural changes in the as machined surfaces, which are known to have a significant impact on fatigue behaviour of mechanical parts. This study aims at investigating the fatigue behaviour of the AISI D2 tool steel subjected to EDM machining. Both smooth and notched specimens are tested aiming at assessing the fatigue notch sensitivity of this material and results compared with conventional grinding techniques in terms of fatigue resistance and residuals stresses. The AISI D2 steel shows a microstructure composed of large dendritic primary carbides detrimental to the fatigue resistance. Also, the EDM process is responsible for the generation of detrimental tensile residual stresses that justifies the lower fatigue resistance when compared with the ground material that exhibits beneficial compressive residual stresses. The fatigue test data of the notched specimens machined by EDM process show a high fatigue notch sensitivity of the AISI D2 tool steel. The heterogeneous structure of the material, showing large undissolved carbides, leads to a notch fatigue reduction factor that is higher to the apparent theoretical elastic stress concentration factor.

The mean stress effect plays an important role in the fatigue life predictions, its influence significantly changes high-cycle fatigue behaviour, directly decreasing the fatigue limit with the increase of the mean stress. Fatigue design of structural details and mechanical components must account for mean stress effects in order to guarantee the performance and safety criteria during their foreseen operational life. The purpose of this research work is to develop a new methodology to generate a constant life diagram (CLD) for metallic materials, based on assumptions of Haigh diagram and artificial neural networks, using the probabilistic Stussi fatigue S-N fields. This proposed methodology can estimate the safety region for high-cycle fatigue regimes as a function of the mean stress and stress amplitude in regions where tensile loading is predominance, using fatigue S-N curves only for two stress R-ratios. In this approach, the experimental fatigue data of the P355NL1 pressure vessel steel available for three stress R-ratios (−1, −0.5, 0), are used. A multilayer perceptron network has been trained with the back-propagation algorithm; its architecture consists of two input neurons ( σ m , N ) and one output neuron ( σ a ). The suggested CLD based on trained artificial neural network algorithm and probabilistic Stussi fatigue fields applied to dog-bone shaped specimens made of P355NL1 steel showed a good agreement with the high-cycle fatigue experimental data, only using the stress R-ratios equal to 0 and −0.5. Furthermore, a procedure for estimating the fatigue resistance reduction factor, K f , for the fatigue life prediction of structural details (stress R-ratios equal to 0, 0.15 and 0.3) in extrapolation regions is suggested and used to generate the K f results for stress R-ratios from −1 to 0.3, based on machine learning artificial neural network algorithm.

FBG sensors are often packaged within composites before they are pasted on the blade surface, and many studies have shown that the materials, fatigue properties, geometric parameters, etc. of intermediate layer have influences on the measuring accuracy of the FBG sensors. Thus, this paper established an reliability calculation model based on strain transfer efficiency for the measuring accuracy of FBG sensors packaged by composites, analyzed the influences of material properties and geometric parameters of the adhesive layer on the performance of FBG sensors based on finite element analysis (FEA) method, and then compared the differences of strain transfer efficiency and reliability of the FBG sensors under different load conditions. The results show that the bond length and the bond thickness of the adhesive layer have greater influences on the performance of the FBG sensors compared with other parameters, both the strain transfer efficiency and the reliability of the FBG sensors will reduce over time under suddenly applied load and increase with increasing frequency of the alternating load.

Bridge cables are subjected to small relative sliding and high contact stresses among wires under fluctuating loads and repeated bending, eventually leading to fretting-fatigue failure. This paper presents a series of fretting fatigue tests with different fretting and fatigue parameters to investigate the tribological properties, fretting fatigue characteristics and fracture failure mechanism. Results show that the fretting-fatigue failure evolved from surface micro cracks at the trailing edges generated from a mixed slip regime. Larger fretting amplitude induced larger tangential force and coefficient of friction, and decreased life. Fretting scar depth increased as fretting-fatigue proceeded while the growth rate was declining.

The maintenance of old riveted bridges has become a major concern for railroad managers across Europe. These metallic structures, built on their majority on the second half of the 19th century, are indeed submitted to ever increasing traffic loads (augmentation in weight and speed of rolling stock). To assess the remaining life of these metallic bridges, some critical structural details have been identified and associated to S-N curves to be used in damage estimation (using Palmgren-Miner's rule for cumulative damage, for example). These constructional details are often described in construction standards, such as the EN 1993-1-9, the BS 5400 and the AASHTO standards. The particularity of older hot-riveted bridges is that their numerous geometric configurations are often under-represented, thus, limiting the accuracy of damage estimation. To compensate the absence of hot riveted assemblies in the standards, numerous research groups have performed extensive experimental campaigns. However, the heterogeneity and rarity of the material (no longer produced nowadays), as well as the very diverse geometrical configurations used at the time of the construction of the bridges (given the novelty proposed by the introduction of metal as a new material in monumental construction), makes difficult the comparison of experimental data. In order to facilitate interpretation and differentiation of fatigue data of a particular type of constructional detail, experimental data from double shear assemblies manufactured from three different metallic ancient bridges is considered (French and Portuguese puddled iron bridges). Then, through statistical analysis (linearized boundaries and the Fernandez-Canteli model), the S-N curves corresponding to their structural configuration are identified. Comparisons to the EN 1993-1-9, the BS 5400 and the AASHTO standards are also proposed. The combination of the S-N curves and Fracture Mechanics approaches can be used to evaluate the residual life of the old riveted metallic bridges. Thus, a statistical analysis and discussion of experimental fatigue crack propagation data available for materials from the ancient riveted metallic bridges are made. This analysis is important for the application of the Fracture Mechanics approaches to predict the residual life of structural details.

Different strategies can be used to perform reparations and reinforcements of ancient bolted and riveted metallic bridges. As the riveting process is not currently a common practice, it requires proper equipment and skilled workers. Another solution is the use of welding. However, the weldability of old steels is poor. Bolts are very attractive alternative solutions, and are most commonly used to repair old metallic bridges. Fitted bolts are expensive solutions; the alternative is the use of resin-injected bolts. The behavior of bolted joints with preloaded resin-injected bolts has been studied using quasi-static and creep tests; however, few studies on the slip and fatigue behavior of these joints can be found in the literature. This paper presents an overview of a few experimental programs that were carried out by several authors aiming at evaluating the fatigue behavior of single and double shear resin-injected bolted connections. A comparison between the experimental data of joints with preloaded standard bolts and preloaded resin-injected bolts shows a fatigue strength reduction in the latter. Since Eurocode 3 (EC3) suggests the same fatigue strength curve for joints made of resin-injected bolts and standard bolts, this may raise some concerns. Furthermore, research on the feasibility of using both bonded and bolted connections is shown. This last study was performed with high-strength low-alloy structural steel plates and an acrylic structural adhesive for metal bonding. For both case studies, a statistical analysis is performed on fatigue experimental data using linearized boundaries and the Castillo and Fernández-Canteli model. Fatigue design curves are proposed and compared with the design suggestions of several European and North American standards. Keywords: Fatigue, Connections, Structural reinforcements, Structural adhesives, S-N curves, Resin-injected bolts

Cumulative fatigue damage analysis and life prediction of engineering structures/components is vital for ensuring their structural integrity and operational reliability under variable amplitude loadings. In this regard, a new nonlinear fatigue damage accumulation model is proposed by introducing a damage function related to the isodamage curves and remaining life aspects. Specifically, its damage exponent is refined by considering effects of loading history. Experimental data from tests available in literature are utilized for model validation and comparison. Compared with four existing models, the proposed model shows higher precision for cumulative damage modelling and fatigue life prediction than others. Moreover, it improves the deficiencies inherent in other rules under the promise of maintaining its simplicity in practice.

This paper presents the results of several mechanical tests aiming at characterizing the constitutive behaviour of the AlSi9Cu3 cast alloy, covering different temperatures and stress fields, including tensile and compressive tests of smooth and notched specimens as well as combined shear/tension and shear/compression with special designed specimens. The Johnson-Cook model was able to correlate the flow stress under quasi-static uniaxial compression, including thermal effects. However, under tension the yield stress does not reduces monotonically and gradually with temperature, which impedes the application of Johnson-Cook model for positive triaxialities. At room temperature, the AlSi9Cu3 alloy shows significant asymmetrical tensile and compressive behaviours requiring a plasticity model sensitive to the stress triaxiality such as the Drucker-Prager. As regards the ductility limits of the material, different data was analysed to generate fracture loci for the material where equivalent fracture strains were plotted against the stress triaxialities. The calibrated Drucker-Prager constitutive model together with a damage approach based on the fracture loci generated was successfully verified using test data from specimens loaded under combined shear/tension or shear/compression. The AlSi9Cu3 cast alloy exhibits a sharp reduction in ductility between the negative stress triaxiality cut-off and −0.1, keeping at low levels above this triaxiality value.

Structural design taking into account fatigue damage requires a thorough knowledge of the behaviour of materials. In addition to the monotonic behaviour of the materials, it is also important to assess their cyclic response and fatigue crack propagation behaviour under constant and variable amplitude loading. Materials whenever subjected to fatigue cracking may exhibit mean stress effects as well as crack closure effects. In this paper, a theoretical model based on the same initial assumptions of the analytical models proposed by Hudak and Davidson and Ellyin is proposed to estimate the influence of the crack closure effects. This proposal based further on Walker’s propagation law was applied to the P355NL1 steel using an inverse analysis (back-extrapolation) of experimental fatigue crack propagation results. Based on this proposed model it is possible to estimate the crack opening stress intensity factor,Kop, the relationship betweenU=ΔKeff/ΔKquantity and the stress intensity factor, the crack length, and the stress ratio. This allows the evaluation of the influence of the crack closure effects for different stress ratio levels, in the fatigue crack propagation rates. Finally, a good agreement is found between the proposed theoretical model and the analytical models presented in the literature.

Fatigue crack growth models based on elastic-plastic stress-strain histories, at the crack tip vicinity, and strain-life damage models have been proposed. The UniGrow model is a particular case of fatigue crack propagation models. The residual stresses developed at the crack tip play a central role in these models, since they are used to assess the actual fatigue crack driving force, taking into account mean stress and loading sequential effects. The performance of the UniGrow model is assessed based on available experimental constant amplitude crack propagation data, derived for the 6061-T651 aluminium alloy. Key issues in fatigue crack growth prediction, using the UniGrow model, in particular the residual stresses evolution, are discussed. Using available strain-life data, it was possible to model the fatigue crack propagation behaviour for the AA6061-T651, taking into account the stress R-ratio effects. A satisfactory agreement was found, between the predictions and the experimental crack propagation data.

The ESIS Executive Committee decided to nominate a new team for the leadership and management of the TC12/ESIS technical committee (TC), as well as update the TC name as “Risk Analysis and Safety of Large Structures and Components”. In this paper, the new organization of the TC12/ESIS as well as the objectives and tasks, and forthcoming events are presented. In addition, this document has editorial purposes regarding the selected and published papers from the International Symposium on Risk Analysis and Safety of Large Structures and Components (ISRAS-TC12) organized within of the “2nd International Conference of Structural Integrity (ICSI)”, which took place at Madeira Island, Portugal, on 4–7 September 2017. As guest editors and TC12/ESIS members, we hope the ISRAS-TC12 Special Issue provides a remarkable impact in the research related to fatigue, fracture, structural integrity, risk analysis and safety of complex structures and components. We also would like to express our gratitude to all authors for their contributions and to all reviewers for their generous work to guarantee the excellence of the papers. Finally, the guest editors would like to express a special thanks to Professor Richard Clegg, Editor-in-Chief of Engineering Failure Analysis journal, and to Elsevier staff for their support during the preparation of this issue.