Bending Fatigue Research Articles

Experimental investigation of bending fatigue behaviors for T-shaped welded joint

A fatigue test was conducted on a T-shaped welded joint under three-point bending conditions. Prior to the test, the geometry of the weld toe on both sides of the specimen was observed and measured. The locations of Fiber Bragg Gratings (FBG) strain gauges were determined based on the weld toe’s geometric features. During the experiment, a 2-level load spectrum block of cyclic loading was applied, resulting in distinct beach marks on the fatigue fracture surface. The stress-time history of the weld toe’s geometric features was monitored. After the test, the fatigue fracture was observed and measured, the influence of the crack path on the crack propagation rate was analyzed, and the influence of the crack propagation pattern on the stress evolution in the nearby area was studied. The experimental results show that the multiple cracks initiation positions have strong relationship with the characteristic points of weld toe morphology. Based on the Linear Elastic Fracture Mechanics (LEFM) theory and the concept of varying remote stress, four crack propagation simulation patterns were constructed and carried out. The results show that the varying remote stress has an more important influence on life prediction of welded joints, while the threshold mainly affect the life prediction of the early stage.

Crystal plasticity analysis of fatigue crack initiation site considering crystallographic orientation in Ti–22V–4Al alloy

In this study, plane bending fatigue tests were conducted on Ti–22V–4Al alloy, a β-type titanium alloy, to examine the fatigue crack initiation behavior in detail. In addition, the prediction of fatigue crack initiation points was investigated from the perspectives of the Schmidt factor (SF) and crystal plasticity finite element method (CP-FEM). The slip system contributing to fatigue crack initiation can be accurately predicted by assessing the magnitude relationship of SF. Also, this prediction is already indicated in a lot of paper by using out of component of slip activity. However, the location where the fatigue crack will occur can be not estimated by SF on polycrystalline. Therefore, prediction of grains where fatigue cracks will occur could be achieved with high accuracy by constructing a CP-FEM that considers the mechanical interaction of polycrystals and grain boundary. Utilizing advanced methodologies such as CP-FEM and numerical calculation techniques, it is strictly investigated that the factors influencing fatigue crack initiation in polycrystalline materials. Our research concluded the understanding of fatigue crack initiation on polycrystal grains by considering the mechanical interaction of polycrystals and grain boundary.

Fatigue performance testing and life prediction of welded fuel pipes

The external piping system which connects power devices, valve control devices, actuators, etc. is an essential system on the aero engine. Under the combined effects of high fluid pressure and external vibration, multiaxial fatigue failure is the main factor that seriously affects the safety of the piping system. The objective of this paper is to establish the multiaxial fatigue life model for the typical welded fuel pipe of the piping system by combining fatigue testing, simulation and theoretical analysis which is of great guiding significance for the engineering application of the piping system. Firstly, the fatigue limits of welded fuel pipes under no and 13.5 MPa internal pressure are obtained by rotational bending fatigue tests using the up-and-down method. Three additional stress levels of rotational bending fatigue tests under no internal pressure are supplemented and then the S-N curve is further obtained by the group method. Since the corresponding fracture surface of the specimens locates at the weld toe near the fixed end, peak stress method is adopted to evaluate the fatigue performance of the weld toe on the pipe specimens. In addition, by comparing the fatigue limit with no and 13.5 MPa internal pressured pipes, it is obvious that the equivalent uniaxial stress corrected by Gerber formula is not applicable for the multiaxial fatigue condition which is caused by the combined effect of fluid pressure and displacement load. The local stress concentration factor caused by the weld toe is determined and based on Findley critical plane model, the multiaxial fatigue life model is established which simultaneously takes the local stress concentration effect, mean stress effect and multiaxial stress effect into consideration. The results of rotational bending fatigue tests under 13.5 MPa internal pressure are within the triple error dispersion band and the accuracy of the proposed life model are verified.

Abnormal fatigue behavior of a CoCrW-based wear-resistant alloy

The fatigue characteristics of a CoCrW-based wear-resistant alloy, which underwent hot forging and a solution treatment resulting in ultimate tensile strength (UTS) and yield strength (YS) levels of 911 and 540 MPa respectively, were analyzed through rotary bending fatigue tests at 600 °C. An exceptionally elevated threshold at 107 cycles, measuring 700 MPa, marks a 1.29-fold increase over the YS and a 0.77-fold increase over the UTS. Notably, the observation of strain-induced martensitic transformation in the superficial layer underscored the alloy’s superior fatigue resistance, primarily attributed to its significant work-hardening capacity.

Evaluating and correlating asphalt binder and mixture fatigue properties considering aging conditions

Asphalt fatigue cracking is a critical distress type for flexible pavement. This study utilized the state of practice binder and mixture cracking tests and parameters to investigate how asphalt binders’ and mixtures’ fatigue performance vary between the different mix designs and evaluate their changes with aging. The potential relationships between the measured binder properties and mixture performance were also explored. Five asphalt mixtures with disparate mix designs were evaluated and three different aging conditioning levels were conducted. The binder tests include the traditional time and frequency sweep and linear amplitude sweep test, while the mixture evaluations include the semi-circular bending and cyclic fatigue test. The results indicate that the different fatigue parameters from the tests can evaluate and rank the mixes differently. The correlation analysis using the Spearman correlation coefficient shows that the mixture cracking parameters that are more predominant by asphalt mixture’s flexibility/brittleness show strong correlations (Spearman coefficient larger than 0.8) with binder cracking indices. The LAS fatigue life-related parameters generally do not correlate well with mixture fatigue indices (Spearman coefficient smaller than 0.6). Furthermore, a prediction model to estimate asphalt mixture’s fatigue performance was developed based on linear regression and Artificial Neural Network (ANN) approach, which only requires the mix design info. and binder fatigue property as the inputs, significantly reducing the time and eliminating the effort in preparing and testing the asphalt mixture specimen for mixture fatigue performance measurement.

Fatigue-based process window for laser beam powder bed fusion additive manufacturing

Processing defects remain the primary cause for fatigue failure of laser beam powder bed fusion (PBF-LB) produced components. Accordingly, process mapping methodologies have been extensively developed to identify optimal processing parameters to avoid defects. For structure-critical applications, it is necessary to validate the defect-based process map through fatigue testing. We quantify the defect structure (porosity) process map for PBF-LB Ti-6Al-4V based on defect populations and fatigue properties. The defect populations were measured in samples fabricated at constant power and small increments in scanning velocity using X-ray micro-computed tomography and 2D metallography and analyzed using a number density approach. Furthermore, 4-point bend fatigue testing was used to establish stress-cycles to failure properties. Our results reveal distinct defect populations in both keyhole and lack-of-fusion defect regimes, with continuous variation in defect density. The number density-based defect size quantity strongly correlates with process parameters, peak stress, and initiating defect size, offering a quantitative approach to establish process-defect-fatigue relationships. We conclude that the process window exists just as clearly for fatigue as it does for defects, although more sensitive to variability in defects. Consequently, within this fatigue-based process window, one can expect to consistently produce dense components with superior fatigue properties.

Computerised design, simulation of meshing and stress analysis of bionic logarithmic spiral spur gear drives

Inspired by the inherent properties of logarithmic spiral in nature, a new cylindrical spur gear drives using logarithmic spiral as a gear tooth profile is proposed. The logarithmic spiral property is explored, and then the equation of meshing, conjugate tooth profile and contact path of the proposed gear pairs are derived. The meshing characteristics of the new pair are investigated, such as pressure angle, contact ratio and sliding ratio. Simulation analysis of the strength, transmission error and transmission efficiency are used to validate the performance of the gear pairs before production of the proposed gear, followed by gluing load capacity and bending fatigue strength testing of the fabricated gear pairs. The results show that the pressure angle at any point of the tooth profile on the proposed gear is constant and equal to the logarithmic spiral strike angle. The contact ratio of the gear decreases with the increase of the strike angle. Compared with that of involute gears, logarithmic spiral gears have better performance in terms of strength, transmission error, transmission efficiency and lifetime.

An investigation on bending fatigue in a corrosive environment of dual-phase 1000 sheet steel RSW joints and damage model via experiment and numeric analysis

Fatigue, corrosion, and fatigue damage models are best addressed to improve and understand the service performance of materials, particularly automotive steel. This study is an attempt to experimentally and finite element investigates plain bending fatigue performance and damage model of DP 1000 sheet steel resistance spot welding (RSW) joints in 3% NaCl aqueous corrosive treatment. RSW applications were carried out using different weld currents. The joint samples were then subjected to optical image analysis, tensile shear, and fatigue tests (3% NaCl-aqueous and normal atmosphere). A proper damage model of RSW junctions was developed and corrected by numeric analysis. Besides, RSW nugget formation, tensile shear, and plain bending fatigue tests were also applied. Consequence, fatigue behavior, tensile load carrying capacity, and effective fracture behavior of resistance spot welded joint specimens were evaluated. Results showed that a corrosive environment negatively affected fatigue performance. With the developed model, it was observed that the fatigue life of the samples decreased by 30–35% in the fatigue tests performed in the corrosive environment. Experimental and numerical analysis results of plain bending were compatible.

Reference dynamic power cable of floating offshore wind turbine for thermal and simple fatigue evaluation

With the increased interest in floating offshore wind turbines, there is an increased focus on evaluating the lifetime of the auxiliary systems, such as the mooring lines and the dynamic power cables, because these systems are in-mature compared to bottom-mounted offshore wind farms. This paper proposes a conceptual reference dynamic power cable suitable for the 15 MW NREL reference turbine mounted on the UMaine floater installed at 82 m water depth. This provides a basis for discussing the life evaluation of dynamic cables obtained from aeroelastic simulation of the floating offshore wind turbine platform exposed to the environmental conditions of the South Brittany site in France. An electromagnetic-thermal finite element simulation is used to determine the current capacity of the cable and aeroelastic simulations are used for a simple assessment of the main failure modes as maximum cable tension, minimum bending radius and fatigue damage accumulation.

Research on gear life reliability analysis based on accelerated life test

AbstractAs one of the key components of marine reducer, the life reliability of gear is of great significance to the safe operation of the reducer and even the whole transmission system. However, due to economic and testing constraints, executing extensive fatigue life tests on complex and costly gears presents a formidable challenge, resulting in inadequate reliability assessments. In this paper, the gear life reliability analysis method based on the accelerated life test is proposed. By conducting the gear bending fatigue accelerated life test, the life distribution and failure mechanism are determined based on the accelerated life data. Furthermore, the gear life distribution parameters and acceleration model are solved by least squared method. This allows us to derive a reliability index specific to the service conditions, facilitating the evaluation of gear life reliability. The method proposed in this paper provides data and theoretical support for the accelerated life tests, lays a foundation for the gear reliability evaluation under small samples, and improves the efficiency of the gear fatigue life evaluation. It has significant engineering significance in saving test costs, reducing test times and shortening development cycle.

Fatigue and tensile behaviour of Ti+TiN+Ti+TiVN multilayer nitride films coated on AZ91 magnesium alloy by closed field unbalanced magnetron sputtering

Despite their extensive use in the automotive and aerospace industries, Mg and Mg alloys, which are light metals, exhibit low fatigue and tensile strength. In this study, transition metal-nitride (TMN) multilayer coatings (Ti+TiN+Ti+TiVN) were coated twice on AZ91 Mg alloy using a Confined Field Unbalanced Magnetron Sputtering (CFUBMS) system to increase fatigue and tensile strength. The structural properties of the films were analyzed by using X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectrometry (EDS) methods, and the mechanical properties were analyzed by rotating bending fatigue and tensile testing machines. Ti+TiN+Ti+TiVN multilayer nitride surface coatings on AZ91 Mg alloys showed a dense and columnar microstructure and according to XRD results (111) was the preferred orientation with the dominant peak. The fatigue limit value of the AZ91 base material was fixed at 60.46 MPa, while it increased to 68.48 MPa after being coated with multilayer nitride. Along with the multilayer nitride coating, the tensile strength increased from 169.98 MPa to 175.43 MPa. As a result, the multilayer hard nitride coating with low surface roughness, which fills the defects, notches, and voids on the surface of the AZ91 base material, increased the fatigue and tensile strength in parallel. Based on the outcomes of the research, the literature has been enriched with an innovative approach through the enhancement of fatigue and tensile strengths by applying a CFUBMS coating to lightweight metals and alloys, such as AZ91, especially in the transportation industry where lightness and dynamic load resistance are essential.

Design and manufacturing of rotating bending fatigue test machine

Design and manufacturing of rotating bending fatigue test machine

The effects of 3D printing designs on PLA polymer flexural and fatigue strength

This study assessed the comprehensive assessment of flexural and fatigue strength of the three-dimensional (3D)-printed polylactic acid (PLA) samples across diverse printing designs and parameters. The experiment framework included a diverse array of printing parameters: layer heights, first layer thicknesses, infill densities, top/bottom infill patterns, extruder temperatures, perimeters, and types of solid layer top and bottom. Our findings suggest that there is an interplay between these parameters and the mechanical properties of PLA specimens. Notably, the fatigue strength of PLA printing specimens is more significantly influenced (0.44%) by an increase in the thickness of the first layer compared to flexural strength (87%). The rate of increase in bending strength is lower in cases of layer height (3.55%) and initial layer height (0.44%) in contrast with other factors. Specimens with an initial layer thickness of 0.4 mm reached the highest number of cycles until failure, recording 21 022 cycles. Furthermore, the study identifies the infill pattern’s impact on strength, highlighting that the line infill pattern type case has the highest bending strength of 75.97 MPa and surpasses the honeycomb pattern in bending strength. Compared to the Honeycomb pattern, the rectilinear design has 2.1% higher bending strength. The number of cycles to failure of the rectilinear pattern is greater than those of the honeycomb pattern. In comparison to other patterns, the Rectilinear Top/Bottom infill pattern has a higher interest rate of 27.5% for bending strength and 200.83% for fatigue strength. Additionally, greater bending and flexural strength are obtained by raising the solid layer top, bottom, and perimeter values, respectively. In comparison to the other temperatures, the bending strength and fatigue strength are highest at 200 °C. Therefore, the first layer height of 0.4 mm, the top/bottom rectilinear infill pattern, the extruder temperature of 200 °C, the perimeter value of 3, the solid layer/top value of 3, and the solid layer/bottom value of 3 are the optimal values for the part subjected to at the same time bending strength combined with fatigue strength. This comprehensive study may provide a broader and deeper understanding of individual and combined effects on an overview of the bending and fatigue strength in connection to printing design and printing parameters, as well as the ideal optimal parameters for 3D printing with the PLA material. Manufacturers and designers can use the recommended parameters to optimize the strength of their printed parts, considering both bending and fatigue performance.

Scalable Crystalline Silicon Photovoltaic Fibers for Electronic Textile Applications

AbstractThis study presents a novel method to fabricate scalable photovoltaic fibers (PVFs) by leveraging crystalline silicon (c‐Si) solar cell technology, known for its high‐power conversion efficiency (PCE), stable performance, and low cost. The c‐Si PVF is built on a flexible circuit strip as narrow as 400 µm, and c‐Si cells as small as 0.35 mm2 are surface‐mounted on the strip. The cells are diced from an interdigitated back‐contact c‐Si solar cell (≈153 cm2). A c‐Si PVF including a 1 mm2 cell reaches PCE up to 9.6% and 11.0% under simulated AM 1.5G illumination without and with encapsulation, respectively, the highest reported for c‐Si PVFs, while a 1.5 ft‐long fiber produces ≈37 mW m−1. Additionally, the PVF can tolerate bending fatigue with no sign of performance loss after 8000 bending cycles. To demonstrate practical applicability, the c‐Si PVFs are also woven into textile swatches. They deliver ≈10 mW cm−2 under a halogen lamp and successfully power a light‐emitting‐diode. This PVF technology is scalable with regards to both achieving thin fibers and its compatibility with roll‐to‐roll fabrication processes. The fiber concept presented here can also be extended to any chip‐scale surface mountable devices, enabling cell‐agnostic fiber technologies for multifunctional electronic textiles.

Expanding the Frontiers of nail product evaluation: Novel application of differential scanning calorimetry (DSC) for assessing crosslinking density and predicting nail brittleness and flexibility.

While modern industry advancements have expanded nail beautification options, scientific literature primarily focuses on nail biology and medicine, with limited attention on cosmetic treatments. This study aimed to investigate human nail denaturation properties, including gender impact, blending nails to enlarge the sample pool, nail sensitization through bleaching, and active effectiveness testing. The objective was to understand the DSC and bending fatigue relationship, and define the consumer relevance of the DSC test. Nail clippings were collected from adult female and male volunteers. The wet DSC was employed to validate sample preparation, explore the effects of gender, and assess the potential of using blended nails for claims substantiation testing. Nails were sensitized through bleaching using hydrogen peroxide. The effects were confirmed through DSC and nail flexure tests. Furthermore, the ability of actives to address concerns related to nail softness and brittleness was assessed using these techniques. The results confirmed the viability of equilibrating nails in water for up to 14 h as a standardized testing method. The denaturation temperature results were independent of gender and suitable for claims substantiation testing. Blending nails from different sources did not yield significant variations in denaturation properties. A preliminary study suggested that cadaver nails should be used with caution because they exhibited differences in denaturation temperature, influenced by the sampling location. Bending fatigue tests highlighted the significance of humidity, with higher humidity conditions (80%) enhancing nail flexibility and providing better resolution for claims substantiation. Sensitizing the nails with hydrogen peroxide induced alterations in both DSC and bending fatigue results. Proof-of-principle studies demonstrated an elevation in denaturation temperature and a decrease in the number of cycles to break, indicating a nail-hardening effect when formaldehyde was applied. The use of a nail softener led to an enhancement in nail fatigue resistance due to a notable reduction in nail crosslinking density. The measurement of crosslinking density proved to be a sensitive tool for assessing the effects of cosmetic treatments on nails, particularly in predicting outcomes related to nail brittleness and flexibility.

FE-analytical slice model and verification test for load distribution analysis and optimization of planetary gear train in wind turbine

Load distribution behavior of planetary gear train (PGT) is crucial for the contact and bending fatigue failure of wind turbine transmission system. With the increasing power of wind turbines, the load and failure rate of wind turbine become larger, which leads to the demand of accurate and efficient modeling, analysis and optimization for load distribution of PGT. In this paper, a new efficient and accurate FE-analytical slice model for load distribution analysis and optimization of PGT in wind turbine is proposed, which is explicitly formulated by the geometry slice model of external/internal gear contact, original FE-analytical slice model for local contact deformation, and efficient finite element (FE) model for global structural deformation. In the FE-analytical slice model, geometry errors are effectively descripted by discretizing gears into a series of slices, while gear tooth contact elasticity and structural elasticity are addressed by the FE-analytical method accurately and efficiently. Upon the proposed model, the load distribution behaviors of PGT with coupling effects of elasticity and errors are revealed and optimized by tooth modification and in-phase eccentricity arrangement strategy. The load distribution tests of PGT in wind turbine are conducted, verifying the proposed FE-analytical slice model which is significant to improve the load-bearing capacity and avoid the fatigue failure of wind turbine transmission system.

Critical distance-based fatigue evaluation of welded joints in steel bridge under bending loading

Welded joints are prone to fatigue cracking under bending loading in steel bridges. However, certain design curves for these joints primarily focus on tensile or bending-tension loads, potentially leading to inaccurate assessments. This study conducted bending fatigue tests on fillet welded joints (FWJs), evaluating the suitability of specification methods for assessing their fatigue performance and attempting to determine the strength curves required for fatigue assessment. Furthermore, it validated the feasibility of the traditional theory of critical distance (TCD) in predicting the fatigue life of FWJs under bending loading. On this basis, a TCD assessment method incorporating the welding residual stress (WRS) was proposed. The results indicate that the fatigue design curve of the specifications provides conservative predictions for the fatigue performance of FWJs under bending loading, and FAT112 from Eurocode3 may be suitable for fatigue assessment using hot-spot stress and nominal stress methods. Furthermore, predicting fatigue life for FWJs under bending loading with traditional TCD is feasible. Compared to traditional TCD, the proposed method significantly improves prediction accuracy, with a minimum scatter factor of just 1.5. The proposed TCD not only considers the WRS effect but also reduce the need for numerous fatigue tests to establish the design curve for a specific welded joint.

Effect of salt–fog spray environment on bending fatigue properties of 3D woven composites

In this study, the effect of salt–fog spray corrosion environment on bending fatigue properties of three-dimensional (3D) woven composites was investigated. Three test environmental conditions, namely a normal environment, two cycles of salt–fog spray corrosion environment, and four cycles of salt–fog spray corrosion environment, were designed. In addition, the salt–fog spray corrosion mechanism, the bending fatigue properties, damage mechanisms, and failure modes of 3D woven composites were studied. The results showed that the bending strength and bending modulus decreased by 5.5 and 9.3%, and 2.27 and 3.45% after two and four salt–fog spray cycles, respectively, compared with that of the normal environment. The bending fatigue properties of 3D woven composites were related to the applied stress and salt–fog spray cycles. The salt–fog spray environment was responsible for the degradation of the interface bonding strength. The maximum reduction ratio of bending fatigue life after salt–fog spray treatment exceeded 70%. The brittle fracture characteristics of 3D woven composite yarn were more pronounced with an increase in salt–fog spray aging cycles.

Expediting structure–property analyses using variational autoencoders with regression

We present a machine learning approach that expedites structure–property analysis in materials, bypassing traditional feature extraction and exploratory data analysis techniques. This objective is accomplished by employing a variational autoencoder (VAE) structure that is modified to include a regressor network for property prediction (VAE-Regression). This modification allows for direct linkage of imaged features and quantitative part properties within the VAE latent space. We first demonstrate our approach using 2D optical micrographs and corresponding four-point bend fatigue life data from laser beam powder bed fusion additively manufactured Ti-6Al-4V coupons. The VAE-Regression model extracts spatial features, predicts fatigue life, and identifies features of porosity defect governing fatigue behavior such as pore clusters, pores near sample edges, and jagged pore morphologies. These features corroborate fatigue literature on physics-based modeling and experimentation. We then demonstrate the versatility of our methodology using binder jet additively manufactured WC-Co coupons, where porosity and microstructural discontinuities are known to lower the three-point bend transverse rupture strength, but the interaction between the WC and Co are yet to be completely understood. We attempted to understand these interactions using our VAE-Regression architecture. Within our dataset, we show that coarser WC grains surrounded by larger Co pools indicate lower strength, while finer WC grains with smaller Co pools indicate higher strength. This machine learning approach using image-based data will likely prove to be critical in understanding and identifying structure–property relationships in new materials and manufacturing processes.

Fretting fatigue behavior of helical-torsional contact steel wire in wire rope

Fretting wear and torsional deformation of steel wire can reduce the performance of wire rope and threaten the safety of mine hoisting system. In this study, to explore the influence of different torsional deformation on the fretting fatigue wear behavior under multi-wire spiral contact, an experimental study was conducted on a self-made test apparatus. The results show that the increase of torsional deformation can reduce the breaking force of steel wire by about 2.6%, and reduce the bending fatigue performance by about 36.4%. In addition, the maximum wear depth, wear amount and coefficient of wear increase with the increase of torsional deformation. The torsion and deformation of the pearlite lamellae parallel to the tensile stress direction are the main reasons for the decrease of the wear resistance of the main steel wires. More torsional deformation makes the steel wire produce less furrow morphology in fretting fatigue wear. The main wear mechanism of steel wire with small torsional deformation is abrasive and tribochemical reactions, and the main wear mechanism of steel wire with large torsional deformation is surface fatigue and tribochemical reactions.