Fatigue Failure Characteristics Research Articles

Study on the Properties and Fatigue Characteristics of Glass Fiber Composites Due to Porosity

A study was conducted on the changes in mechanical properties and fatigue failure characteristics due to voids, one of the fabrication defects in composite materials. This study was primarily based on glass fiber fabrics applied to wind turbine blades and their material properties were predicted through micro and meso modeling of composite materials by simulating random defects including voids. As the wind turbine blades become larger, various defects develop. The fundamental changes in the materials’ properties due to voids were predicted through homogenization methods and Representative Volume Element (RVE), and the failure properties were obtained through progressive failure analysis by applying virtual coupons according to ASTM D3090 and ASTM D6641. The progressive failure was identified using the Matzenmiller–Lubliner–Taylor (MLT) failure condition, and the fatigue failure characteristics were assessed through the Tsai–Hill 3D load.

The fatigue behavior of TC17 titanium alloy under different test environments: The effect of saltwater on fatigue failure characteristics and life estimation

The study of fatigue behavior in saltwater for TC17 titanium alloy has become a potential research issue in practical engineering and theoretical scientific research. In this study, it is found from the designed fatigue test that the corrosiveness of the test environment has a significant negative effect on the fatigue life of titanium alloy, and the distributions of fatigue life in 3.5%NaCl solution and 5%NaCl solution are similar. Typical surface failure characteristics and obvious corrosion traces are detected due to the coupling effect of corrosion and fatigue load. Then, electron back scatter diffraction (EBSD) is performed to figure out the change of micro grains from fine grains to coarse grains with the test environment changes from water to NaCl solution, and the strain concentration regions are detected at grain boundary and internal of coarse grains. Finally, the comparison of S-N curve with different models are carried out, Basquin model is proved to be suitable for the S-N curve estimation of TC17, and S-N models for different test environments are established. The micro test results provide a clear understanding of the corrosion fatigue failure behavior, and the newly established model considering the corrosiveness of test environment is novel and essential to the further fatigue study in theoretical research and engineering practice.

Dynamic cyclic fatigue resistance of RACE EVO in S-shaped canal with different angles of access: An in vitro study

Abstract Introduction: Nickel–titanium instruments annually undergo improvements to enhance the cyclic fatigue lifespan, especially with challenging canals. This study examines RACE EVO instrument in an S-shaped double-curvature canal in different angles of insertion 0°, 20°, and 40° to investigate the behavior of the heat-treated instruments in challenging canals. Materials and Methods: A total of 30 instruments were assigned to three groups (Group 0°, Group 20°, and Group 40°). RACE EVO instruments were tested in artificial canals. The canals had two curvatures: an apical one which its parameters are 70° angle and 2 mm radius and a coronal one which its parameters are 60° angle and 5 mm radius. The test was done using a cyclic fatigue apparatus. A statistical study was done by one-way analysis of variance groups, and Tukey’s honestly significant difference/Tukey–Kramer with a level of significance (α) was adjusted to 0.05. Results: The time until failure was reduced by the increase in the angle of insertion; however, Group 20° and Group 40° were not significantly different. All the instruments were broken apically. The scanning electron microscopic analysis showed typical characteristics of cyclic fatigue failure. Conclusions: Increasing the inclination during the insertion reduced the resistance of the RACE EVO instruments to cyclic fatigue failure despite the surface heat treatment of the instrument.

Ultra-low cycle fatigue test study of bolted spherical joints in steel grid structures

During a catastrophic earthquake, bending and failure were exhibited in the bolted spherical joints, and these phenomena have obvious ultra-low cycle fatigue (ULCF) failure characteristics. To study the failure characteristics, hysteresis behavior, stiffness degradation, and energy consumption of bolted spherical joints, the ULCF test of bolted spherical joints specimens was carried out. The experimental study showed that the high-strength bolts experienced an ULCF failure process of bending, crack initiation, crack propagation, and instantaneous failure, and the fatigue life of the specimens was less than 20 times. The pinch phenomenon in the hysteresis curve of the specimen was significant, indicating that its energy consumption was poor. The energy-damage model of the specimens under cyclic displacement was derived based on the cumulative energy consumption. A damage assessment method for the specimen was proposed based on the energy-damage model and angle change characteristics of the specimen. This method provides a reference for damage assessment and repair design of bolted spherical joint grid structures after an earthquake.

Prediction of fatigue lives for steel beams and steel reinforced concrete beams

With the wide application of steel reinforced concrete (SRC) beams, the problem of fatigue has become increasingly prominent. To deeply understand the fatigue performance of SRC beams, a finite element analysis (FEA) about fatigue failure process of SRC beams was performed. The internal H-steel inside SRC beam (SRCH-steel) was shown to possess similar fatigue failure characteristics to steel beam and exert a deciding influence on the fatigue resistance of SRC beam in previous experiments. Therefore, FEA of fatigue crack growth (FCG) was conducted using a fully-automated remeshing technique for steel beam first. Comparisons were made and a good agreement was found between predicted and experimental fatigue lives. The average value of ratio between predicted and experimental fatigue lives for the five steel beams is 1.149, which verifies the accuracy of FEA model. Then, based on the FEA model of steel beam, rebars and external concrete were included to simulate fatigue failure process of SRC beams. The results suggest that the average value of ratio between predicted and experimental fatigue lives for SRCH-steels inside the thirty-nine SRC beams is 1.191, and the average value for tensile rebars is 1.212, which indicates that the numerical model is accurate and reliable. At last, further analysis about influences of critical parameters on fatigue performance of SRC beams was conducted, such as nominal stress range, steel ratio of SRCH-steel, steel ratio of tensile rebars, fatigue strength of tensile rebars, shear span-to-depth ratio, concrete strength grade and stirrup ratio.

Investigation of the High-Temperature Low-Cycle fatigue failure characteristics of P91 steel weld joints and their fatigue strength reduction factors under various load control regimes

Low cycle fatigue tests are conducted on the base metal, weld metal, a welded joint under the condition that the strain control region is the joint (WJWJ) and a welded joint under the condition that the strain control region is the base metal (WJBM) of P91 steel at 500℃ using different total strain ranges. The cyclic stress response is highest for the weld metal, followed by the base metal, and is relatively similar for WJWJ and WJBM. At 2.0 % total strain range conditions, the materials generally exhibit non-Masing behavior and dynamic strain hardening aging. At all total strain ranges, WJWJ failed in the heat-affected zone, and WJBM broke in the base metal. For the difference in fatigue life between base metal and welded joints, the fatigue strength reduction factor of P91 steel welded joints at 500 °C is given as a suggested value. The fatigue behavior of P91 steel welded joints is verified based on a hybrid hardening model and a modified damage model. This study presents a theoretical framework for analyzing the fatigue strength reduction factors of weldments and comparatively analyzes the effects of different geometrical features.

Characterizing fatigue damage evolution in asphalt mixtures using acoustic emission and Gaussian mixture model analysis

The identification and investigation of fatigue crack evolution and damage modes in asphalt mixtures are crucial for understanding the corresponding mechanisms and characteristics of fatigue failure. In this study, the four-point bending fatigue tests were performed on the asphalt mixture specimens with precast joints using the acoustic emission (AE) technique to analyze the damage evolution. The failure modes of the asphalt mixtures were identified using the Gaussian mixture model (GMM). The results revealed that the fatigue damage of the asphalt mixtures can be categorized into four stages: Stage I (void compaction), Stage II (microcrack initiation and stable propagation), Stage III (crack aggregation and unstable propagation), and Stage IV (complete fracture). This division was defined based on the inflection points of the axial displacement curves, the cumulative number of AE events, and the cumulative ringing counts. The evolution of the AE b value was found to be correlated with the crack propagation. The rapid decline in the b value in Stage III was considered a harbinger of the eventual complete fracture in the asphalt mixtures. The GMM clustering analysis indicated that the fatigue damage of the asphalt mixtures primarily involved tensile damage (90%), and shear damage made a small contribution of 10%. Existing AE studies have focused on the quantitative evaluation of AE parameters, while research on clustering identification algorithms for these parameters is scarce. The analytical methods and findings of this study enable an effective identification of fatigue damage in asphalt mixtures at the laboratory scale and offer insights into the fatigue damage mechanisms of asphalt mixtures.

Fatigue-sensitive feature extraction, failure prediction and reliability-based design optimization of the hyperloop tube

Hyperloop research focuses on investigating the design and limitations of its complex subsystems. However, the existing literature overlooks the fatigue failure characteristics of the Hyperloop tube, leaving future engineers without informed estimates of its reliability. To address this gap, this study examined the occurrence and prediction of fatigue failure in the Hyperloop system. The findings revealed that both the underground and above-ground configurations showed resistance to fatigue failure, with the underground system showing greater resilience. Additionally, sensitivity analysis highlighted support spacing, tube ultimate tensile strength, and tube radius as the most influential design variables affecting fatigue sensitivity. Moreover, a reliability-based design cost optimization was performed, taking into account demand uncertainty and utilizing insights from previous analyses to determine ideal design parameters. This research sheds light on critical design aspects of the Hyperloop tube that require intensified attention to effectively mitigate the risk of fatigue failure.

Fatigue Behavior and Mechanism Study on Lugs of TC18 Titanium Alloy

Aerospace structural components are in a complex stress state when they undertake load due to their specific geometric construction. Their fatigue behavior is quite different from the materials that undertake the standard stress state. The research on fatigue behavior of aircraft structures was the foundation of their design and life prediction. Lugs are one of the important connected components of aircrafts. In this paper, the mathematical mechanics’ method was used to calculate the structural feature parameters of TC18 Titanium alloy lugs under several specific loads. The design reference values of structural feature parameters were put forward for lugs. The fatigue behavior and fatigue failure characteristics under specific loads were studied experimentally. The fatigue experiment was conducted to verify the criterion, and the validity of the criterion mentioned above was confirmed by the test results. The fatigue life S-N curves under different loading forms and different mean stresses were researched. The fatigue failure characteristics, such as fatigue crack initiation, propagation, and final fracture, were also studied. These studies provided theoretical support for the anti-fatigue damage design of lugs.

Fatigue behavior of full-shear-connection steel–concrete composite continuous beams under high-cycle loading

Under cyclic loading, the mechanical performances of steel–concrete composite continuous beams (SCCCBs) and steel–concrete composite simply supported beams are different. The development of SCCCBs is hindered by the still unclear fatigue performances of SCCCBs. To study the fatigue failure characteristics of SCCCBs, the scaled full-shear-connection test beams were designed based on an original bridge. Generally, the test results showed that the stress amplitude affected the fatigue performance and fatigue life of an SCCCB. The fatigue failure of the full-shear-connection SCCCBs was controlled by the steel beams. The displacement, relative slip, bending stiffness, and bending moment all degraded in three stages with the increase in the number of loading cycles. In addition, the numerical simulations and parametric analysis with the rain-flow counting method and the linear cumulative damage criterion were carried out to analyze the fatigue behavior of SCCCBs. The validity of the numerical model was verified with experimental results. The influence of the steel nominal strength, span–height ratio, and load amplitude on the bending moment redistribution coefficient was further analyzed via the established numerical model. Compared with the stress amplitude, the nominal yield strength of steel and the span–height ratio had more significant effects on the redistribution of the SCCCB bending moment. Moreover, upon approaching fatigue failure, the redistribution coefficient of the section bending moment changed sharply, which is one of the key issues that should be considered in the fatigue performance study of SCCCBs.

Evaluation of Fatigue Failure Characteristics by Thickness of SheetAl2024-T3Alloy

Evaluation of Fatigue Failure Characteristics by Thickness of SheetAl2024-T3Alloy

Effects of non-symmetric non-uniformly distributed welding residual stress on fatigue failure initiation and propagation in a hydropower generator shaft

PurposeThis article aims to investigate and model the effects of welding-generated thermal cycle on the resulting residual stress distribution and its role in the initiation and propagation of fatigue failure in thick shaft sections.Design/methodology/approachExperimental and numerical techniques were applied in the present study to explore the relationship(s) between welding residual-stress distribution and fatigue failure characteristics in a hydropower generator shaft. Experimental techniques included stereomicroscopy, optical and scanning electron microscopy (SEM), chemical analysis and mechanical testing. Finite element modelling (FEM) was used to model the shaft welding cycle in terms of thermal (temperature) history and the associated development of residual stresses within the weld joint.FindingsExperimental analyses have confirmed the suitability of the used material for the intended application and confirmed the failure mode to be low cycle fatigue. The observed failure characteristics, however, did not match with the applied loading in terms of design stress levels, directionality and expected crack imitation site(s). FEM results have revealed the presence of a sharp stress peak in excess of 630 MPa (about 74% of material's yield strength) around weld start point and a non-uniform residual stress distribution in both the circumferential and through-thickness directions. The present results have shown very close matching between FEM results and observed failure characteristics.Practical implicationsThe present article considers an actual industrial case of a hydropower generator shaft failure. Present results are valuable in providing insight information regarding such failures as well as some preventive design and fabrication measures for the hydropower and other power generation and transmission sector.Originality/valueThe presence of the aforementioned stress peak around welding start/end location and the non-uniform distribution of residual-stress field are in contrast to almost all published results based on some uniformity assumptions. The present FEM results were, however, the only stress distribution scenario capable of explaining the failure considered in the present research.

Investigation of fatigue failure and energy characteristics of rock exposed to complicated stress disturbance paths: Cyclic stress amplitude effect

AbstractTo deeply reveal the differences in geomechanical responses of rock during mining exposed to complicated stress disturbance of excavation unloading and cyclic loading conditions, cyclic triaxial fatigue loads with four cyclic stress amplitude (CSA) (60, 100, 130, and 160 MPa) were performed on deeply buried rock. Results show that rock deformation, energy evolution, and failure modes are all influenced by the CSA. Additionally, it is found that all the strain energy increases with increasing CSA during rock failure. Especially, the dissipated energy increases greatly at the confining stress unloading stage (CSUS) than the fatigue loading stage (FLS), indicating the influence of unloading on rock damage accumulation. Moreover, a damage evolution model reflecting a first slow and then quick increase pattern was established using the dissipated energy. Finally, a transition failure mode from the dominant tensile‐shear to pure shear is found. It is suggested that much more energy needs to be consumed to induce shear cracks than tensile cracks.

The high cycle fatigue behavior, failure characteristics, and fatigue life empirical relationship of 9% Cr steel under different stress ratios at 630 °C

During the startup and shutdown processes of the steam turbine rotor, the fatigue failure behavior caused by asymmetric stress is introduced. To study the effect of mean stress on the fatigue failure behavior of 9% Cr steel at high temperatures, the high cyclic fatigue tests are conducted under different stress ratios (R = −1, 0.1, 0.5, and 0.7) at 630 °C. The results indicate three fatigue failure modes: surface crack initiation failure, sub-surface crack initiation failure, and necking induced failure. With the increasing stress ratio, the surface and sub-surface crack initiation failure modes gradually change to necking induced failure mode. Moreover, the oxide intrusive-extrusion mechanism primarily determines the surface crack initiation failure and promotes surface defect formation. Meanwhile, the inhomogeneous microstructure induces sub-surface crack initiation failure, wherein the crack propagates along the martensitic lath boundary or through the martensitic lath. The attenuation of mechanical properties and the increase in mean stress level are the critical factors affecting the necking induced failure under 630 °C. In addition, the mean stress sensitivity factor (MR) is proposed to explain the effect of the stress ratio on fatigue performance. Furthermore, the mean stress sensitivity factor (MR) can be used to quantitatively analyze the effect of mean stress on fatigue properties under different stress ratios. Finally, the fatigue life empirical relationship considering the mean stress sensitivity factor (MR) is constituted.

Macro-meso fatigue failure characteristics of a bimsoil under multistage cyclic triaxial loads with different frequencies

The dynamic mechanical response of block-in-matrix-soils (bimsoils) is crucial to the long-term stability predication of constructions and building structures made of bimsoils. Although the dynamic failure behaviors of bimsoil under cyclic loads have been widely understood, the influence of loading frequencies on the macro-meso structural deterioration governing localized band propagation have not been well understood. Herein, multistage cyclic triaixal tests and post-test X-ray computed tomography (CT) scanning have been performed on bimsoil with various loading frequencies (f = 0.1 Hz, 0.2 Hz, 1.0 Hz, and 2.0 Hz). The cyclic triaxial tests simulated the behavior of bimsoil material under varied velocities of passing vehicle herein. The macro-meso fatigue failure characteristics were analyzed in terms of stress-strain responses, stiffness degradation, and meso-structural changes. Testing results show that the applied loading frequency alters the coupling degree of soil matrix and rock blocks, and damage develops fully within bimsoil under relatively low loading frequency. In addition, the failure mode of bimsoil changes from bulging failure to shear failure with the increases of loading frequency, and the volumetric deformation is the largest for a bimsoil sample subjected to low loading frequency. Moreover, post-test CT scanning reveals the meso-structural degradation within bimsoil, the multiple interface damage and cracking contribute a lot to the strength, volumetric deformation and failure modes. It is suggested the contact, interlocking, occlusion, and separation among the rock blocks promote the volume dilatancy when subjecting to low loading frequency.

Mechanical Properties of Soft Rocks Subjected to Water‐Rock Reaction and Cyclic Pressure

Studying the mechanical properties of soft rocks subjected to water and cyclic loading would contribute to a better understanding of the stability analysis of soft rock engineering under the conditions of storm and carrier dynamics. In this paper, two soft rocks from Southwest China (i.e., muddy siltstone and silty mudstone) were selected as test samples. Uniaxial compressive tests were applied to investigate the strength and deformation characteristics under water‐rock reactions. Meanwhile, triaxial tests were carried out to analyse the fatigue damage and failure characteristics by applying cyclic axial loading under different confining pressures. The results indicated a reduction in the uniaxial compressive strength (UCS) under saturated conditions, which is correlated with the disintegration resistance of soft rocks. Moreover, the samples exhibited a softening phenomenon due to water absorption and rock expansion, decreasing the elastic modulus. The triaxial tests demonstrated that axial strain accumulated with the number of loading cycles due to fatigue and even failed when applying increased cyclic loading with certain cycles. The cohesion decreased during cyclic loading, but the friction angle was relatively independent of the number of cycles. In addition, reductions in the dynamic elastic modulus and shear modulus decreased with increasing loading time. This study indicated that water and cyclic loadings could cause significant degradation of the strength and stiffness of soft rocks, which need to be considered carefully during the engineering utilization of such materials.

Numerical investigation on the fatigue failure characteristics of water-bearing sandstone under cyclic loading

Numerical investigation on the fatigue failure characteristics of water-bearing sandstone under cyclic loading

Solder Joint Reliability Risk Estimation by AI-Assisted Simulation Framework with Genetic Algorithm to Optimize the Initial Parameters for AI Models

Solder joint fatigue is one of the critical failure modes in ball-grid array packaging. Because the reliability test is time-consuming and geometrical/material nonlinearities are required for the physics-driven model, the AI-assisted simulation framework is developed to establish the risk estimation capability against the design and process parameters. Due to the time-dependent and nonlinear characteristics of the solder joint fatigue failure, this research follows the AI-assisted simulation framework and builds the non-sequential artificial neural network (ANN) and sequential recurrent neural network (RNN) architectures. Both are investigated to understand their capability of abstracting the time-dependent solder joint fatigue knowledge from the dataset. Moreover, this research applies the genetic algorithm (GA) optimization to decrease the influence of the initial guessings, including the weightings and bias of the neural network architectures. In this research, two GA optimizers are developed, including the “back-to-original” and “progressing” ones. Moreover, we apply the principal component analysis (PCA) to the GA optimization results to obtain the PCA gene. The prediction error of all neural network models is within 0.15% under GA optimized PCA gene. There is no clear statistical evidence that RNN is better than ANN in the wafer level chip-scaled packaging (WLCSP) solder joint reliability risk estimation when the GA optimizer is applied to minimize the impact of the initial AI model. Hence, a stable optimization with a broad design domain can be realized by an ANN model with a faster training speed than RNN, even though solder fatigue is a time-dependent mechanical behavior.

Fretting fatigue behavior and failure characteristics of 35CrMoA steel under elliptical loading path

Purpose This study aims to understand the multiaxial fretting fatigue, wear and fracture characteristics of 35CrMoA steel under the elliptical loading path. Design/methodology/approach By keeping the contact pressure and torsional shear cyclic stress amplitude unchanged; the axial cyclic stress amplitude varied from 650 MPa to 850 MPa. The fretting fatigue test was carried out on MTS809 testing machine, and the axial cyclic strain response and fatigue life of the material were analyzed. The fretting zone and fracture surface morphology were observed by scanning electron microscope. The composition of wear debris was detected by energy dispersive X-ray spectrometer. Findings In this study, with the increase of axial stress amplitude, 35CrMoA steel will be continuously softened, and the cyclic softening degree increases. The fretting fatigue life decreases unevenly. The fretting scars in the stick region are elongated in the axial direction. The area of fracture crack propagation zone decreases. In addition, the results indicate that wear debris in the slip region is spherical and has higher oxygen content. Originality/value There were few literatures about the multiaxial fretting fatigue behavior of 35CrMoA steel, and most scholars focused on the contact pressure. This paper reveals the effect of axial cyclic stress on fretting fatigue and wear of 35CrMoA steel under the elliptical loading path.

Mechanical behavior and fatigue failure analysis of standing seam aluminum alloy roof system under temperature effect

Standing seam metal roof systems with universal high-strength, lightweight, and thin-walled characteristics have been applied worldwide in massive large-span landmark buildings, such as gymnasiums, airports, and railway stations. The existing research focuses on the wind uplift design, but there are few studies on the mechanical properties under the temperature effect. In this paper, the temperature effect of the standing seam aluminum alloy roof (SSAAR) system was studied. To be familiar with the mechanical and deformation characteristics of the SSAAR system, the static loading tests under different temperatures and boundary constraints were carried out. Two specimens, one with anti-wind clips and the other without anti-wind clips, were further tested under cyclic loading to evaluate and quantify the fatigue failure characteristics of the roof system. The testing results indicate that the stress concentration, thermal expansion displacement, and wear of the SSAAR system are significant. The slab rib stress is the largest, accounting for about 83.7% of the yield strength, followed by the slab surface stress, and the slab bottom stress is the smallest. The horizontal displacement is greater than the vertical displacement, and the maximum is about 20.42 mm. The boundary constraint mainly affects the support stress and vertical displacement to increase by 47.2% and 79.3% respectively. The anti-wind clips mainly increase the wear thickness of the roof slab, which is increased by 67.5%.