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This study evaluates the potential use of discarded plasterboard paper as fibers from buildings to reinforce concrete. Various concentrations of wastepaper fibers (0.5%, 1%, 1.5%, 2%, and 2.5% by weight of the binder) were investigated in this research. To mitigate the water absorption effect of the paper fibers, metakaolin was employed as a partial cement replacement. The results demonstrate that the inclusion of the wastepaper fiber enhances the mechanical and durability performance of the concrete. The optimal fiber proportion was identified as 1%, leading to a 29% increase in the compressive strength, a 38% increase in the splitting tensile strength, a 12% decrease in the water absorption, and a 23% decrease in the drying shrinkage with respect to the concrete containing 20% metakaolin. However, exceeding this optimal fiber content results in decreased mechanical and durability properties due to the fiber agglomeration and non-uniform fiber distribution within the concrete matrix. Based on the microstructural analysis, the improved performance of the concrete is ascribed to decreased porosity, more refined pore structure, and reduced propagation of microcracks within the concrete matrix in the presence of wastepaper fiber. According to the results, concrete containing 20% metakaolin and 1% wastepaper fiber exhibits durability and mechanical properties comparable to those of the traditional concrete. This finding highlights the significant promise of reducing dependency on conventional cement and incorporating suitable recycled materials, such as discarded plasterboard, and secondary by-products like metakaolin. Such a strategy encourages the preservation of resources, reduction in carbon dioxide emissions, and a decrease in the ecological footprint resulting from concrete production. [ABSTRACT FROM AUTHOR]

In supporting the stable operation of high-penetration renewable energy grids, flywheel energy storage systems undergo frequent charge–discharge cycles, resulting in significant stress fluctuations in the rotor core. This paper investigates the fatigue life of flywheel energy storage rotors fabricated from 30Cr2Ni4MoV alloy steel, attempting to elucidate the material's mechanical properties, crack propagation behavior, and impact of internal defects on fatigue life. Tensile tests reveal that the material exhibited high yield (992 MPa) and tensile strengths (1130 MPa). The Paris formula is used to model crack growth rates, ending in good agreement with the experimental data. Fatigue tests at various stress conditions highlight the material's significant variability in fatigue life and emphasize the need for reliable design approaches. This paper also demonstrates that internal defect size and location critically affect fatigue life, calling for improvements in forging inspection standards. Overall, the present study provides a comprehensive analysis of 30Cr2Ni4MoV steel's suitability for flywheel rotors, balancing safety, and operational efficiency. [ABSTRACT FROM AUTHOR]

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It is necessary to study the propagation path of cracks in concrete materials and its influence on the loading capacity of specimens. The phase-field method for fracture offers a distinct benefit in simulating the crack propagation behavior of brittle materials, which is achieved by implementing a phase field that continuously fluctuates to approximate the crack configuration, abolishing the need for mesh reconstruction and tracking the cracks. In this paper, we have implemented a phase field model using ABAQUS, whose reliability is verified through a tensile test. Then, the splitting test of Brazilian disc is simulated and the results are similar to those of the laboratory experiment. Furthermore, the crack configuration of the prefabricated cracked discs with different tilt angles and different initial lengths is explored. The two important parameters of the phase field method, Gc and l0, are discussed in the Discussion section. A larger Gc value means a larger material toughness and a larger failure load, and a larger l0 value means a larger crack smear range as well as a smaller failure load. [ABSTRACT FROM AUTHOR]

The high-cycle bending fatigue experiment is one of the most important necessary steps in guiding the crankshaft manufacturing process, especially for high-power engines. In this paper, an accelerated method was proposed to shorten the time period of this experiment. First, the loading period was quickened through the prediction of the residual fatigue life based on the unscented Kalman filtering algorithm approach and the crack growth speed. Then, the accuracy of the predictions was improved obviously based on the modified training section based on the theory of fracture mechanics. Finally, the fatigue limit load analysis result was proposed based on the predicted fatigue life and the modified SAFL (statistical analysis for the fatigue limit) method. The main conclusion proposed from this paper is that compared with the conventional training sections, the modified training sections based on the theory of fracture mechanics can obviously improve the accuracy of the remaining fatigue life prediction results, which makes this approach more suitable for the application. In addition, compared with the system's inherent natural frequency, the fatigue crack can save the experiment time more effectively and thus is superior to the former factor as the failure criterion parameter. [ABSTRACT FROM AUTHOR]

The mechanical properties of fractured rock have always been a focal point in the rock mechanics field. Based on previous research, this paper proposes improvements to the SPH method and applies it to the study of crack propagation in fractured rocks. By conducting uniaxial compression tests and simulating crack propagation on various specimens with different crack shapes, the characteristics of crack propagation were obtained. The comparison between the simulated results in this study and existing experimental and numerical simulation results confirms the validity of the SPH method employed in this paper. The present study utilizes the proposed methodology to analyze the influence of the crack angle, width, and orientation on crack propagation. The SPH method employed in this study effectively demonstrates the expansion process of fractured rock under uniaxial compression, providing valuable insights for the engineering applications of SPH. [ABSTRACT FROM AUTHOR]

The joints and fissures in a natural rock mass can affect the mechanical properties of the rock mass, the propagation of a blasting stress wave, and the blasting effect of the smooth surface of roadways. In the process of roadway drilling and blasting, there will inevitably be some joints between the two blast holes. Taking the joint angle as the starting point, this paper studies the rule of rock explosion crack propagation and stress variation when there are joints with different angles between two blast holes and analyzes the influence of joints on rock mechanical properties and blasting effects. The numerical simulation method and the software ANSYS/LS-DYNA are used to establish 7 rock mass models with various joint angles. When there is no joint between two holes and joints of 15°, 30°, 45°, 60°, 75°, and 90°, the propagation of explosive cracks and stress variations in the rock mass are discussed. The results show that the joints at different angles have obvious guiding and blocking effects on the propagation of explosive cracks, and as joint angles increase, the guiding effect becomes more apparent and the blocking effect becomes weaker. The effective stress of the rock mass will vary depending on the angles of the joints between the hole and the joint. As the joint angle increases, the joint's influence on the reflection and superposition of stress waves gradually weakens, and the peak value of the effective stress of the rock mass gradually decreases. The peak effective stress of the rock mass on the blasting side of the joint is similarly impacted by the superposition of stress waves, and the extreme value may be seen at the critical node of each change curve. The explosive crack will break through at the critical location because the maximal effective stress of the rock mass is distributed in a "W" form on the blasting side of the joint. [ABSTRACT FROM AUTHOR]

This paper shows a new low-cost technology for the measurement of crack propagation in quasi-fragile materials based on a stereo pair of cameras and LED light spots. The two cameras record the displacement experienced by a series of LED white lights. For each frame, the X, Y and Z 3D coordinates of all the centroids of the LED points are obtained. From this information, it is possible to determine the variation of the distance between any two of them. In this case, 2 strips of 12 LED lights each were arranged in such a way that the points of both strips coincided in pairs in height. The algorithm made it possible to monitor the increase in distance that occurred between each pair of lights at the same height. The paper shows the mathematical basis of this technological solution. A test has been carried out by installing this system in a concrete cube 150 mm side and subjected to a wedge-splitting test. The results show that it is possible to monitor the crack propagation (position of the crack front) during the test and to know the crack width too. At present, the accuracy of this technique is only limited by the camera resolution and the computer processing capability. [ABSTRACT FROM AUTHOR]

The primary focus of this paper is to investigate the application of ANSYS Workbench 19.2 software's advanced feature, known as Separating Morphing and Adaptive Remeshing Technology (SMART), in simulating the growth of cracks within structures that incorporate holes. Holes are strategically utilized as crack arrestors in engineering structures to prevent catastrophic failures. This technique redistributes stress concentrations and alters crack propagation paths, enhancing structural integrity and preventing crack propagation. This paper explores the concept of using holes as crack arrestors, highlighting their significance in increasing structural resilience and mitigating the risks associated with crack propagation. The crack growth path is estimated by applying the maximum circumferential stress criterion, while the calculation of the associated stress intensity factors is performed by applying the interaction integral technique. To analyze the impact of holes on the crack growth path and evaluate their effectiveness as crack arrestors, additional specimens with identical external dimensions but without any internal holes were tested. This comparison was conducted to provide a basis for assessing the role of holes in altering crack propagation behavior and their potential as effective crack arrestors. The results of this study demonstrated that the presence of a hole had a significant influence on the crack growth behavior. The crack was observed to be attracted towards the hole, leading to a deviation in its trajectory either towards the hole or deflecting around it. Conversely, in the absence of a hole, the crack propagated without any alteration in its path. To validate these findings, the computed crack growth paths and associated stress intensity factors were compared with experimental and numerical data available in the open literature. The remarkable consistency between the computational study results for crack growth path, stress intensity factors, and von Mises stress distribution, and the corresponding experimental and numerical data, is a testament to the accuracy and reliability of the computational simulations. [ABSTRACT FROM AUTHOR]

The structural health monitoring (SHM) of buildings provides relevant data for the evaluation of the structural behavior over time, the efficiency of maintenance, strengthening, and post-earthquake conditions. This paper presents the design and implementation of a continuous SHM system based on dynamic properties, base accelerations, crack widths, out-of-plane rotations, and environmental data for the retrofitted church of Kuñotambo, a 17th century adobe structure, located in the Peruvian Andes. The system produces continuous hourly records. The organization, data collection, and processing of the SHM system follows different approaches and stages, concluding with the assessment of the structural and environmental conditions over time compared to predefined thresholds. The SHM system was implemented in May 2022 and is part of the Seismic Retrofitting Project of the Getty Conservation Institute. The initial results from the first twelve months of monitoring revealed seasonal fluctuations in crack widths, out-of-plane rotations, and natural frequencies, influenced by hygrothermal cycles, and an apparent positive trend, but more data are needed to justify the nature of these actions. This study emphasizes the necessity for extended data collection to establish robust correlations and refine monitoring strategies, aiming to enhance the longevity and safety of historic adobe structures under seismic risk. [ABSTRACT FROM AUTHOR]

Textured coating technology is an effective method to improve the friction and wear performance of mold surfaces. The adhesion strength at the interface between the texture and the coating is crucial for its long-term serviceability. This paper studies the adhesion strength of micro-dimple's topography textured coatings, aiming to reveal the influence mechanism of micro-dimples on the adhesion strength of textured coating interfaces. Different diameters or texture area ratios of micro-dimples were prepared on the sample surface using a picosecond laser, followed by PVD coating deposition. Scratching tests and indentation tests were then conducted on the textured coating surface. The adhesion strength and crack propagation behavior of the coating on the surface of different samples were studied under dynamic and static contact conditions. The results showed that under dynamic contact conditions, the critical load for coating failure of most textured samples was higher than that of non-textured samples. As the depth and diameter of the micro-dimple's topography increased, the critical load first increased and then decreased, with the maximum critical load being 14.9% higher than that of the non-textured samples. Under static contact conditions, almost no coating spalling was observed around the indentation on the surface of the micro-dimple's topography textured coating, while the spalling areas of non-textured samples were mainly at the edges and surrounding areas of the indentation. In contrast, the spalling regions of the textured samples were primarily concentrated at the edges of the texture. It can be seen that the dimpled texture hinders crack propagation and reduces the interlocking network of cracks, thereby reducing coating spalling. The research results provide important theoretical guidance for the design and optimization of textured coatings on mold surfaces. [ABSTRACT FROM AUTHOR]

Overloaded traffic is one of the major effects that cause more early damage to asphalt pavement than regular traffic. Moving overloaded traffic not only needs to consider dynamic coefficient and axle load coefficient when carrying out pavement mechanics calculations, but also accelerates pavement failure and boosts the cost of construction and maintenance. Although asphalt pavement of a stabilized base with inorganic binder has a strong bearing capacity, the shortcoming of reflective cracking also seriously restricts its performance. This paper describes the mechanical response and crack propagation of asphalt pavement of stabilized base with inorganic binder which has a crack, under the coupling effect of moving overloaded traffic and temperature. Extended finite-element method (XFEM) was conducted to simulate reflective cracks propagating freely from a stabilized base with inorganic binder to asphalt overlay. Dynamic analysis was also carried out by varying the axle weight and tire pressure, which could help highway builders understand the stress distribution of pavement under design traffic and the crack propagation law of pavement structures. Results indicated that the mechanical response of asphalt pavement was comprehensively related to tire pressure, axial weight, and its active position and that overloaded traffic accelerates crack propagation more than regular traffic. This research achievement contributes to providing roadway engineers with a more profound perception to potentially advance pavement design practitioners for specific traffic characteristics. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate the application of 3D printing technology, particularly using sand-type materials, in the creation of artificial rock models for rock mechanics experimentation. Design/methodology/approach: Using a comprehensive analysis, this research explores the utilization of 3D printing technology in rock mechanics. Sand-type materials are specifically investigated for their ability to replicate natural rock characteristics. The methodology involves a review of recent achievements and experimentation in this field. Findings: The study reveals that sand-type 3D printing materials demonstrate comparable properties to natural rocks, including brittle characteristics, surface roughness, microstructural features and crack propagation patterns. Research limitations/implications: While the research establishes the viability of sand-type 3D printing materials, it acknowledges limitations such as the need for further exploration and validation. Generalizability may be constrained, warranting additional research to address these limitations. Originality/value: This research contributes insights into the potential application of sand-type 3D printing materials in indoor rock physics experiments. The findings may guide future endeavors in fabricating rock specimens with consistent structures for practical rock mechanics applications. [ABSTRACT FROM AUTHOR]

The peridynamics (PD), as a promising nonlocal continuum mechanics theory, shines in solving discontinuous problems. Up to now, various numericalmethods, such as the peridynamicmesh-free particle method (PD-MPM), peridynamic finite element method (PD-FEM), and peridynamic boundary element method (PD-BEM), have been proposed. PD-BEM, in particular, outperforms other methods by eliminating spurious boundary softening, efficiently handling infinite problems, and ensuring high computational accuracy. However, the existing PD-BEM is constructed exclusively for bond-based peridynamics (BBPD) with fixed Poisson's ratio, limiting its applicability to crack propagation problems and scenarios involving infinite or semi-infinite problems. In this paper, we address these limitations by introducing the boundary element method (BEM) for ordinary state-based peridynamics (OSPD-BEM). Additionally, we present a crack propagationmodel embeddedwithin the framework of OSPD-BEM to simulate crack propagations. To validate the effectiveness of OSPD-BEM, we conduct four numerical examples: deformation under uniaxial loading, crack initiation in a double-notched specimen, wedge-splitting test, and threepoint bending test. The results demonstrate the accuracy and efficiency of OSPD-BEM, highlighting its capability to successfully eliminate spurious boundary softening phenomena under varying Poisson's ratios. Moreover, OSPDBEMsignificantly reduces computational time and exhibits greater consistencywith experimental results compared to PD-MPM. [ABSTRACT FROM AUTHOR]

Cylindrical shell structures have excellent structural properties and load-bearing capacities in fields such as aerospace, marine engineering, and nuclear power. However, under high-pressure conditions, cylindrical shells are prone to cracking due to impact, corrosion, and fatigue, leading to a reduction in structural strength or failure. This paper proposes a static modeling method for damaged liquid-filled cylindrical shells based on the extended finite element method (XFEM). It investigated the impact of different initial crack angles on the crack propagation path and failure process of liquid-filled cylindrical shells, overcoming the difficulties of accurately simulating stress concentration at crack tips and discontinuities in the propagation path encountered in traditional finite element methods. Additionally, based on fluid-structure interaction theory, a dynamic model for damaged liquid-filled cylindrical shells was established, analyzing the changes in pressure and flow state of the fluid during crack propagation. Experimental results showed that although the initial crack angle had a slight effect on the crack propagation path, the crack ultimately extended along both sides of the main axis of the cylindrical shell. When the initial crack angle was 0°, the crack propagation path was more likely to form a through-crack, with the highest penetration rate, whereas when the initial crack angle was 75°, the crack propagation speed was slower. After fluid entered the cylindrical shell, it spurted along the crack propagation path, forming a wave crest at the initial ejection position. [ABSTRACT FROM AUTHOR]

The stress intensity factor (SIF) distribution of a semi‐elliptical surface crack is often used for evaluating the fatigue strength of structures. Virtually exact distributions of SIFs FISE,FIISE,FIIISE can be provided along the crack front by solving the hypersingular integral equation of the body force method. In this paper, to create a very accurate SIF variation formula, the elliptical crack SIF solutions FIE, FIIE, FIIIE are used and the SIF ratios FISE/FIE, FIISE/FIIE, FIIISE/FIIIE are mainly focused. Paying attention to the corner point singularity, by applying the least squares method to the ratio FISE/FIE, FIISE/FIIE in the whole range of parametric angle β, FISE and FIISE formulas can be proposed. Instead, FIIISE formula can be proposed by applying the method of least squares to the ratio of FIIISE/FIIIE in the range β≥15° but applying directly to FIIISE in the range β≤15°. In this way, all of formulas proposed in this paper provide the SIFs with better than 1.0% accuracy. Highlights: Accurate SIF formulas for semi‐elliptical surface cracks were created within 1% error.Similar to solving the HIEM, closed form solutions of an elliptical crack were utilized.This formula assume the crack front intersects the free surface at an angle θS≅100.5°.Using singularity r‐0.5 along the crack front, the shape FISE(β)≈const. was investigated. [ABSTRACT FROM AUTHOR]

This paper presents a numerical approach for investigating fatigue delamination propagation in composite stiffened panels loaded in compression in the post-buckling field. These components are widely utilized in aerospace structures due to their lightweight and high-strength properties. However, fatigue-induced damage, particularly delamination at the skin–stringer interface, poses a significant challenge. The proposed numerical approach, called the "Min–Max Load Approach", allows for the calculation of the local stress ratio in a single finite element analysis. It represents the ratio between the minimum and maximum values of the stress along the delamination front, enabling accurate evaluation of the crack growth rate. The methodology is applied here in conjunction with the cohesive zone model technique to evaluate the post-buckling fatigue behavior of a composite single-stringer specimen with an initial delamination. Comparisons with experimental data validate the predictive capabilities of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of the R-curve effect in delamination propagation in composite materials. The R-curve effect refers to the phenomenon whereby resistance to crack propagation increases with the advancement of the delamination, due to toughening mechanisms, such as fiber bridging. Numerical models often neglect this effect assuming a constant value of the fracture toughness. A numerical approach based on cohesive elements and on the superposition of two bilinear traction-separation laws is adopted here to accurately predict the R-curve effect in skin-doubler composite specimens subjected to three-point bending tests. The carbon-epoxy material presents two different sensitivities to the fiber bridging phenomenon resulting in two different R-curves. Comparisons with literature experimental data, in terms of load and delaminated area vs. applied displacement, and ultrasonic C-scan images show the effectiveness of the adopted approach in simulating the R-curve effect. The predicted numerical stiffness aligns with the experimental scatter, although the maximum load is slightly underestimated by approximately 15% compared with the average experimental results. The numerical model accurately predict the R-curve effect observed in the experimental data, demonstrating a 31% increase in the maximum load for the material configuration exhibiting greater sensitivity to fiber bridging. [ABSTRACT FROM AUTHOR]

Sixteen-head automatic tape laying of non-crimped carbon-fibre-reinforced plastic is performed, and the fibre alignment is compared with that produced via hand laying. The effect of fibre alignment is tested via quasi-static and cyclic three-point bending tests. Using the Fill Multilayer (a 16-head tape-laying machine), precision fibre laying of unidirectional fabrics is performed with deliberate misalignment to examine the effect of fibre orientation and investigate the random effect on longitudinal misalignment. The automatic tape-layered coupons are compared with hand-layered carbon fibre tapes to investigate the relationship between the fibre alignment and the flexural strength. A 52% reduction in the fibre alignment scatter is achieved via the Fill Multilayer. Fibre orientation increases lead to a higher flexural strength of 16.08% for Fill Multilayer-made coupons compared with hand-layered samples. An investigation of the correlation between fibre alignment and flexural strength shows that shear-based failure increases exponentially as the alignment decreases. Fill Multilayer-made coupons have a higher void concentration due to ultrasonic welding, but also the highest modulus and flexural strength, as fibre misalignment is reduced to 1.68°, with a modulus degradation of 1.4%. [ABSTRACT FROM AUTHOR]

Patching is a common technology used in repairing asphalt-pavement potholes. Due to the differences in material properties between patched- and unpatched-asphalt mixtures, significant strain and stress concentrations could be induced; thus, further cracks and interfacial debonding distress could be caused. As a remedy, the strain and stress concentrations can be alleviated by utilizing optimum patching shapes. Therefore, this paper employed finite element methods (FEM) to deeply analyze the mechanical performance of patched-asphalt pavements embedded with different patching shapes. Three patching shapes, these being rectangular, stair, and trapezoid, were considered for use in pavement pothole repairs based on two- and three-dimensional finite element models. In the two-dimensional models, Top-Down and Bottom-Up crack propagations were simulated to assess the anti-damage performance of the patched pavements with different patching shapes. In addition, the thermal stress behaviors within patched-asphalt pavements were simulated using the two-dimensional model to analyze the performance of the patched pavements during the cooling process in construction. In addition, interface-debonding performance was simulated for the patched-asphalt pavements using three-dimensional models. In light of the simulation results, engineers are expected to better understand the mechanism within patched pavements and to improve the quality of the pavement patching. [ABSTRACT FROM AUTHOR]

The failure of premature thermal cycling spalling off is the bottleneck problem currently faced by yttrium oxide partially stabilized zirconia (YSZ) ceramic-based sealing coatings. Studies on the thermal cycling performance of coatings with "brick-mud" structures were carried out by experimental and simulation methods in this paper. The results showed that, as the thickness of "mud" layer increased, the bonding strength of the "brick-mud" structure coatings gradually decreased. When the thickness of the "mud" layer was about 3 μm and 10 μm, the thermal cycling lives of the T1 and T2 coatings were improved by 90.0% and 135.7%, respectively, compared with conventional coating (T0 coating), while that of the T3 coating (containing thick "mud" layers of about 20 μm) was decreased by 81.4%. The stress field of M2 "mud" layers with different thicknesses was subjected to a comprehensive effect by thermal mismatch stress and pores in "brick" layer. Compared with the medium and thick "mud" layers, the thin "mud" layer sustained obvious larger σ 22   m a x and σ 12   m a x , indicating its potential for the preferential initiation of transverse microcracks. In addition, the thin "mud" layer withstood the largest σ 11   m a x and had the strongest potential for longitudinal crack growth. Both transverse and longitudinal cracking could consume energy during thermal cycling and reduce the stress concentration at the top coating/bond coating interface. These were the main reasons for the improvements in the thermal cycling performances of the T1 and T2 coatings. The degree of crack deflection and the capacity of energy dissipation in the "mud" layer increased significantly with its thickness. However, the propagation length of transverse cracks also gradually increased in the meantime. Especially when the "mud" layer was 20 μm, the length of the transverse cracks increased rapidly. Thus, early interlayer delamination failure occurred in the T3 coating during thermal cycling. [ABSTRACT FROM AUTHOR]

According to the traditional blasting theory and practice, the slotted cartridge blasting can form straight cracks extending along the slot direction and achieve directional fracture. In this paper, an experimental study has been carried out to determine the influence of incident stress waves and reflected stress waves. Under the influence of stress waves, the propagation path of the main crack in slotted cartridge blasting is not straight, and the directional fracture effect is inadequate. Under the experimental conditions in this paper, the propagation of main cracks mainly experienced three stages: directional propagation stage, counterclockwise deflecting propagation stage, and clockwise deflecting propagation stage. The difference between incident stress waves and reflected stress waves results in the difference in the deflecting direction, transforming the main crack into a wing shape. In rock roadway drilling and blasting engineering, the propagation path of main cracks produced by peripheral boreholes using the slotted cartridge blasting is also affected by the incident and reflected stress waves. These stress waves are inevitably generated from free faces and adjacent boreholes; however, these are rarely considered in the design of blasting parameters. Therefore, the design and optimization of blasting parameters considering the interaction of stress waves and main cracks in the slotted cartridge blasting need to be further developed. [ABSTRACT FROM AUTHOR]

The growth of cracks between plies, i.e., delamination, in continuous fibre polymer matrix composites under cyclic-fatigue loading in operational aircraft structures has always been a very important factor, which has the potential to significantly decrease the service life of such structures. Whilst current designs are based on a 'no growth' design philosophy, delamination growth can nevertheless arise in operational aircraft and compromise structural integrity. To this end, the present paper outlines experimental and data reduction procedures for continuous fibre polymer matrix composites, based on a linear elastic fracture mechanics approach, which are capable of (a) determining and computing the fatigue crack growth (FCG) rate, da/dN, curve; (b) providing two different methods for determining the mandated worst-case FCG rate curve; and (c) calculating the fatigue threshold limit, below which no significant FCG occurs. Two data reduction procedures are proposed, which are based upon the Hartman-Schijve approach and a novel simple-scaling approach. These two different methodologies provide similar worst-case curves, and both provide an upper bound for all the experimental data. The calculated FCG threshold values as determined from both methodologies are also in very good agreement. [ABSTRACT FROM AUTHOR]

In this paper, a method of crack propagation analysis based on adaptive extension finite element is proposed. This method combines adaptive mesh reconstruction technology with the extended finite element method (XFEM). Firstly, the model of the engineering structure is discretized with the help of mesh generation software, and the initial mesh is divided. Secondly, the Construction of the XFEM model and the tip of the crack strengthening function are introduced to describe the physical field properties of the crack tip. The integral equation is solved to obtain the crack tip parameters. Then, the adaptive mesh reconstruction technology is built to refine the mesh of the crack tip area through the error estimation of the crack tip. Finally, the SIFs at the crack tip were calculated using the interaction integral, and the path direction of crack growth was determined using the maximum circumferential tensile stress criterion. Thus, the propagation path can be well traced. [ABSTRACT FROM AUTHOR]

Rivets are usually used to connect the skin of an aircraft with joints such as frames and stringers, so the skin of the connection part is a porous structure. During the service of the aircraft, cracks appear in some difficult-to-detect parts of the skin porous structure, which causes great difficulties in the service life prediction and health monitoring of the aircraft. In this paper, a secondary development subroutine in PYTHON based on ABAQUS-XFEM is compiled to analyze the cracks that are difficult to monitor in the porous structure of aircraft skin joints. The program can automatically analyze the stress intensity factor of the crack tip with different lengths in the porous structure, and then the residual fatigue life can be deduced. For the sake of safety, the program adopts a more conservative algorithm. In comparison with the physical fatigue test results, the fatigue life of the simulation results is 16% smaller. This project provides a feasible simulation method for fatigue life prediction of porous structures. It lays a foundation for the subsequent establishment of digital twins for damage monitoring of aircraft porous structures. [ABSTRACT FROM AUTHOR]

The vertical ice breaking of marine structures in ice-covered areas involves the deformation and failure of an ice sheet. Different from the existing conventional scenarios where the ice sheet is used as a transportation and support medium, the damage to the ice sheet will be more severe when a structure penetrates the ice sheet from below, due to the lack of elastic support from the fluid above the ice sheet. In order to investigate the failure mode of the ice sheet and the ice load characteristics during vertical penetration, a mesh-free bond-based peridynamic method is used in this paper to simulate the mechanical behaviors of the ice sheet. The cracks simulated in this study exhibit a higher level of similarity to experimental results, which improves the accuracy of the ice load. The numerical model established shows satisfactory applicability for the analysis of penetration failure of an ice sheet. In addition, the influence of ice thickness, impact velocity, and cylinder diameter on the failure characteristics of the ice sheet and breakthrough load are analyzed. The results of a parametric study indicate that the relationship between ice thickness and breakthrough load, as well as the relationship between load area and breakthrough pressure, can both be fitted using quadratic functions. [ABSTRACT FROM AUTHOR]

Nominated for Eurosteel 2021 Best Paper Award The fatigue design of shear connectors for composite girders is based on fatigue strength curves (with 95% survival probability) derived from tests with one or just a few connectors. According to the Eurocodes, the lifetime of a girder can then be limited by failure of the shear connector with the highest fatigue utilization. The failure probability of a component is thus determined by the failure probability of one shear stud or composite dowel, although a composite girder is an internally highly statically indeterminate system with the capability of redistributing forces in the composite joint. This paper outlines how considering crack propagation, the residual capacity of shear connectors with cracks and the redistribution of forces towards less stressed and damaged connectors can have positive effects on the lifetime of a girder. The failure probability of a girder is determined by several Monte Carlo simulations using a simplified FE lamella model with incremental calculation of the degradation of the connectors. The input parameters with the greatest influence on the fatigue behaviour of the girder are evaluated. Furthermore, the results show the economic potential of a future global safety concept for composite girders, especially those with composite dowels. [ABSTRACT FROM AUTHOR]

Fatigue design of composite girders and in particular shear connectors according to Eurocode 4 is based on fatigue strength curves. Therefore, the lifetime of a girder can be limited by failure of a critical shear connector. The failure probability of a component is thus determined by the failure probability of one shear stud or composite dowel, although a composite girder is an internally highly statically indeterminate system with the possibility of redistributing forces in the shear connection. This paper outlines the positive effects on the lifetime of a girder by considering crack propagation and residual capacity of shear connectors with cracks as well as redistributing forces towards less stressed and damaged connectors. The failure probability of a girder is determined by a Monte Carlo simulation using a lamella model with incremental calculation of the degradation of the shear connection. The results show the economic potential of a future global safety concept for composite girders especially with composite dowels. [ABSTRACT FROM AUTHOR]

This research paper reviews the recent works on the rolling contact fatigue of rail wheels. The topic covered includes the mathematics equations of rail-wheel contact stress and fatigue, RCF defects in the rail, the development of cracks, and the strategies used to reduce the rate of RCF defects. Therefore, the main understandings of RCF as they currently stand are crucial for the improvement and mitigation on rail fatigue failures in the future. This research paper has not been published yet and has not been discussed yet by the Malaysia Railway Network. [ABSTRACT FROM AUTHOR]

Lightweight design has had an important role to play in recent gear developments. One way of reducing gear weight is to apply a shot-peening process in addition to the usual case-hardening because the higher compressive residual stresses within the material mean that the same torque values can be transmitted with smaller gears. However, due to the compressive residual stresses, fisheye failures at non-metallic inclusions can occur, which have an effect on the endurance fatigue strength of high-strength gears, especially in the very high cycle fatigue range. This paper presents a detailed FEM simulation of the stress state at a non-metallic inclusion in the tooth root fillet of such high-strength gears. The aim is to explain certain fracture characteristics, which differ from fisheye failures of standard specimens. With the results of the simulation und taking into consideration the fracture characteristics determined in a SEM, a fracture analysis for fisheye failures in the tooth root fillet of high-strength gears is carried out that links different theories found in the literature. Subsequently, this analysis and the influence of residual stresses are compared with data and further fracture analyses from experimental investigations found in the literature. [ABSTRACT FROM AUTHOR]

Most of the structures in service are subjected to cyclic loading of variable amplitude. The effect of load interaction is necessary to accurately predict the fatigue life of components in design phase. In the present paper, a fatigue damage methodology under complex loading history is proposed considering two stages of damage process and considering the effect of sequence of loading. This is further modified by considering opening stress in crack propagation stage. The proposed methodologies are compared with the linear damage rule by illustrating an example of dynamically induced stress in a slender bar under uniform axial time varying force. The effect of various influencing parameters on fatigue life of bar is also studied. The proposed methodologies are further validated using experimental fatigue test results. The comparison shows a good agreement between theoretical and experimental results. It is found that conventional Miner's rule estimates higher damage index compared to the proposed methodology. [ABSTRACT FROM AUTHOR]

How to simulate fracture mode and crack propagation path in a plate with multiple cracks is an attractive but difficult issue in fracture mechanics. Peridynamics is a recently developed nonlocal continuum formulation that can spontaneously predict the crack nucleation, branch and propagation in materials and structures through a meshfree discrete technique. In this paper, the peridynamic motion equation with boundary traction is improved by simplifying the boundary transfer functions. We calculate the critical cracking load and the fracture angles of the plate with multiple cracks under uniaxial tension. The results are consistent with those predicted by classical fracture mechanics. The fracture mode and crack propagation path are also determined. The calculation shows that the brittle fracture process of the plate with multiple cracks can be conveniently and correctly simulated by the peridynamic motion equation with boundary conditions. [ABSTRACT FROM AUTHOR]

• A new damage quantification based on peridynamic theory has been established. • This new approach tackles the complex crack initiation plane, which is unsolved. • The new technique has been validated by experimental case studies. • The predictions exhibit very good agreements with experiments. • Crack propagation patterns can be accurately predicted using this new approach. This paper proposes a novel approach to evaluate the damage in Peridynamic simulations to identify the crack initiation and propagation, based on the physical meaning of the bond network. The most commonly used criterion to assess the damage in Peridynamic simulations is the nodal damage value, a ratio of the broken bonds to number of unbroken bonds for each point. There is no consensus on the magnitude of nodal damage value within the literature. In most cases, the assessment is conducted visually via damage contours. Rarely, researchers calculate nodal damage value by counting the bonds that pass through a crack plane and must be broken to initiate a crack. Despite being widely-used, the application of nodal damage value is questionable since it neglects the likelihood of broken bonds that are irrelevant to a crack. In other words, the applied value of the nodal damage value might not give the information about the crack whether it emerges or not. This paper shows the influence of the nodal damage value on damage assessments and compares the proposed method with the nodal damage value in different scenarios. The results exhibit that the proposed method is robust, effective, and more importantly provides a single outcome for Peridynamic simulations. [ABSTRACT FROM AUTHOR]

Fatigue failure is a typical failure mode of welded structures. It is of great engineering significance to predict the remaining fatigue life of structures after a certain period of service. In this paper, a two-stage hybrid deep learning approach is proposed only using the response of structures under fatigue loading to predict the remaining fatigue life. In the first stage, a combination of convolutional neural network (CNN), squeeze-and-excitation (SE) block, and long short-term memory (LSTM) network is employed to calculate health indicator values based on the current measured data sequence. In the second stage, a particle filtering-based algorithm is utilized to predict the remaining fatigue life using the previously calculated health indicators. Experimental results on different welded specimens under the same loading conditions demonstrate that the hybrid deep learning approach achieves superior prediction accuracy and generalization ability compared to CNN, LSTM, or CNN-LSTM models in the first stage. Moreover, the average relative deviation between the predicted and actual fatigue life is less than 6% during the final quarter of the crack propagation and fracture stage. [ABSTRACT FROM AUTHOR]

The response characteristics of the mesostructure and macro-characteristics of the soil–rock mixture under repeated freeze–thaw action have an important influence on the safety and stability of the dump slope in low-temperature environments. In order to further understand the multi-scale response behavior of a soil–rock mixture under freeze–thaw cycles, this paper carried out indoor freeze–thaw cycles, uniaxial compression, and electrochemical impedance spectroscopy tests on a soil–rock mixture taken from a graphite mine dump in Jixi City, Heilongjiang Province, China. Combined with the simulation calculation of discrete element numerical software (PFC2D 7.0), the effects of freeze–thaw cycling on electrochemical impedance spectrometry (EIS) mesoscopic parameters, uniaxial compressive strength, and crack propagation of soil–rock mixtures were analyzed. The intrinsic relationship between mesoparameters and macroscopic mechanical properties was established. The results showed that as the number of freeze–thaw cycles increases from 0 to 15, the mesopores inside the soil–rock mixture gradually increase, and the angular similarity of distribution characteristics increases by 5.25%. The uniaxial compressive strength and the peak secant modulus increase exponentially with the increase in the number of freeze–thaw cycles, the uniaxial compressive strength decreases by 47.62%, and the peak secant modulus decreases by 75.87%. The peak strain and pore compaction stage showed an exponential increase and an increasing trend, respectively, and the peak strain increased from 2.115% to 4.608%. The failure mode was basically similar in different cycles; the failure cracks extended from the corners to the middle and lower parts before the failure finally occurred. The types of failure cracks were mainly tensile cracks, followed by tensile shear cracks and the fewest compression shear cracks. The similarity and uniaxial compressive strength conformed to a good linear relationship with the number of freeze–thaw cycles, with the uniaxial compressive strength decreasing linearly with the increase in similarity. [ABSTRACT FROM AUTHOR]

The randomness of sea conditions and loading sequences are among the key contributing factors that affect our ability to accurately predict the fatigue crack growth in ships. Climate change may alter the long-term characteristics of these factors along the service life of existing or newly constructed ships. This paper presents a framework for quantifying the impact of climate change on crack propagation in ship hulls. A probabilistic fatigue crack propagation approach is developed to account for uncertainties associated with material properties and loading conditions; specifically, those affected by climate change. Global Climate Models (GCMs) are used to quantify the long-term effects of climate change on the sea conditions and the resulting ship loading time histories. The proposed approach is applied to a tanker ship operating within predefined routes in the Atlantic Ocean. The results show that the effect of climate change on the crack propagation depends on the navigation route. [ABSTRACT FROM AUTHOR]

Crack propagation leads to rock instability and failure, which seriously influence the safe and efficient operation of coal mines. According to the characteristics of fracture development and expansion, this paper takes a fractured rock with different crack numbers as the research background and studies the effects of the grouted arrest measure, anchored crack arrest measure, and grouted anchored arrest measure on the mechanical properties, energy evolution, crack expansion, and progressive instability of the fractured rock. The sensitivity of different crack arrest measures to the peak strength, elastic modulus, total crack number, and impact tendency of the fractured rock are analyzed based on the sensitive percentage. The experimental results show that the more cracks in the rock, the greater the increase of peak stress of grouted rock and grouted anchored rock, and the smaller the increase of peak stress of anchored fractured rock. With the increase of the crack number, the total crack number in anchored fractured rock specimens gradually decrease, the total crack number in grouted rocks, and grouted anchored rock specimens gradually increase. The anchored fractured rock with more cracks produces a lower total crack number when it is destroyed. The grouted rock and grouted anchored rock with more cracks produce a higher total crack number when it is destroyed. The pre-peak energy of anchored single-fractured rock is larger, the pre-peak energy of grouting multi-fractured rock is larger, and the grouted rock has a strong impact tendency. The grouted arrest measure is an important sensitive parameter to the impact energy index; the anchored crack arrest measure is the primary sensitive parameter to the peak stress, elastic modulus, and total crack number; and the grouted anchored arrest measure is an important sensitive parameter to the elastic modulus. The research results of this paper provide some guidance on the selection of crack arrest parameters and scheme design in practical rock engineering. [ABSTRACT FROM AUTHOR]

Ceramics are commonly used as high-temperature structural materials which are easy to fracture because of the propagation of thermal shock cracks. Characterizing and controlling crack propagation are significant for the improvement of the thermal shock resistance of ceramics. However, observing crack morphology, based on macro and SEM images, costs much time and potentially includes subjective factors. In addition, complex cracks cannot be counted and will be simplified or omitted. Fractals are suitable to describe complex and inhomogeneous structures, and the multifractal spectrum describes this complexity and heterogeneity in more detail. This paper proposes a crack characterization method based on the multifractal spectrum. After thermal shocks, the multifractal spectrum of alumina ceramics was obtained, and the crack fractal features were extracted. Then, a deep learning method was employed to extract features and automatically classify ceramic crack materials with different strengths, with a recognition accuracy of 87.5%. [ABSTRACT FROM AUTHOR]