Fatigue Life Research Articles

New insights into fatigue anisotropy of an additively manufactured medium-entropy alloy: from the perspectives of crack initiation and crack propagation

ABSTRACT The present work investigates anisotropic fatigue properties of an additively manufactured (AM) medium-entropy alloy (MEA). The fatigue properties of the materials in 0°, 45° and 90° orientations with respect to the build layers were measured. In order to discover the dominant factors for stress level-dependent fatigue anisotropy, crystal plasticity finite element simulations and fatigue crack growth (FCG) experiments were used to evaluate crack initiation and crack propagation behaviours, respectively. The main conclusions are summarised as follows: First, in comparison to grain anisotropy, the difference in fatigue initiation stage is controlled by defect anisotropy. Second, the direct cause of the difference in the FCG rate is considered to be the differences in deflection angle, affected by the incompatibility of the slip planes between adjacent grains. Third, the AM-MEA displays a stress level-dependent fatigue anisotropy. At high-stress level, the fatigue life of the MEA-45° specimen is significantly higher than that of MEA-0° and MEA-90°, while at low-stress levels, the fatigue resistance of MEA-0° is similar to that of MEA-45°. Stress level-dependent fatigue anisotropy is controlled by different ratios of crack initiation and crack propagation. Our work proposes a novel research strategy that qualitatively evaluates fatigue anisotropy of AM materials.

Reliability and fatigue life prediction of GFRP pipes by continuum damage mechanics-based damage elastic–plastic bridging model

Reliability and fatigue life prediction of GFRP pipes by continuum damage mechanics-based damage elastic–plastic bridging model

A Study of the Effect of Graphene on Fatigue Life of CuAlNi Shape Memory Alloy

A Study of the Effect of Graphene on Fatigue Life of CuAlNi Shape Memory Alloy

Study on the improvement of fatigue and crack resistance of semi-flexible pavement materials using the mixing -molding method

This study focuses on two significant issues pertaining to conventional grout-molded semi-flexible pavement material (P-SFP): the difficult of achieving a high grouting rate and the limited scope for enhancing asphalt content, both of which contribute to the poor crack resistance of the SFP. To address these problems, the Mixed-Molding Method Semi-Flexible Pavement Material (M-SFP) is proposed, which utilizes a combination of mixed-molding method to enhance the crack resistance and fatigue life of SFP. In order to investigate the effects of asphalt film thickness and gradation type, four different gradations and five different asphalt contents of M-SFP were designed based on the volume filling theory. The effects of asphalt film thickness and gradation type on the cracking resistance and fatigue life of M-SFP were investigated through various tests, including low-temperature bending, semi-circular bending tensile, and four-point bending fatigue test. The results were then compared with those of the control P-SFP. The test results show that the strain energy density of M-SFP is increased by 24.9 % and the fracture energy is increased by 52.1 % compared with the conventional P-SFP; the number of fatigue life times under 200με, 225με, and 250με microstrain are increased by 53.6 %, 41.3 %, and 47.3 %, respectively. Based on crack resistance test results, it is recommended that the design asphalt film thickness of M-SFP exceed 10μm. Furthermore, measurements of the air void content reveal that the M-SFP exhibits significantly better compactness compared to the P-SFP. In conclusion, it shows that the Mixing-Molding method can be used to obtain semiflexible pavement materials with higher asphalt dosage, better cracking resistance, better degree of compactness, and longer fatigue life. In addition, the correlation analysis between the cracking resistance results and the rigid-flex ratio indicates that the recommended design rigid-flex ratio for SFP should be less than 2.06.

Developing a Sitting Simple Baduanjin program for advanced cancer patients with the fatigue-sleep disturbance symptom cluster: A feasibility study.

We describe a development and feasibility study of a Sitting Simple Baduanjin program for advanced cancer patients suffering from the fatigue-sleep disturbance symptom cluster. This study was to evaluate the practicality and safety of the Sitting Simple Baduanjin intervention and determine its preliminary efficacy. This work employed a single-arm mixed-methods approach. The primary outcome measures were feasibility (i.e., recruitment, adherence, and satisfaction) and safety. Validated self-report questionnaires were used to evaluate the preliminary effects of the program, including fatigue, sleep quality, and quality of life at the 4th, 8th, and 12th weeks of the intervention. Qualitative interviews were also conducted after the program. A total of 30 participants were enrolled, of which 23 (77%) completed the 12-week Sitting Simple Baduanjin program. The mean adherence rate was 88% and no adverse events were reported. Statistically significant improvements were observed in terms of fatigue, sleep quality, and quality of life after program completion. Four themes emerged from the qualitative interview data: (a) acceptability of the Sitting Simple Baduanjin technique, (b) perceived benefits of exercise, (c) barriers, and (d) facilitators. The findings support the feasibility of the Sitting Simple Baduanjin program for advanced cancer patients and show promise in improving patients' levels of the fatigue-sleep disturbance symptom cluster and quality of life.

Prediction of rotational bending fatigue life of bearing steel based on damage mechanics

Based on the theory of continuous damage mechanics, this paper proposes a fatigue damage evolution model and numerical calculation method considering the influence of vacuum chemical heat treatment process, and studies the rotational bending fatigue damage analysis and life prediction method of M50NiL bearing steel. Firstly, the constitutive model, fatigue damage evolution equation and material parameter calibration method in the theoretical model are given. Secondly, based on the ABAQUS platform, the damage mechanics-finite element numerical calculation method of fatigue damage analysis considering the influence of hardened layer is realized by writing the UMAT subroutine; then, the rotational bending fatigue test of M50NiL bearing steel treated by vacuum chemical heat treatment of quenching and tempering, carburizing and carbonitriding is carried out, and the influence of heat treatment process on fatigue performance is analyzed; finally, based on the proposed fatigue damage model and numerical calculation method, the rotational bending fatigue life of M50NiL bearing steel is predicted, and the results are compared with the experimental results to verify the correctness of the proposed method.

Numerical Simulation of Rubber Concrete Considering Fatigue Damage Accumulation of Cohesive Zone Model.

Rubber concrete (RC) has been used in fatigue-resistant components due to its durability, yet the numerical simulation of its fatigue properties remains in its early stages. This study proposes a cohesive zone model (CZM) that accounts for the accumulation of fatigue damage at the mesoscale to investigate the fatigue performance of RC. The model integrates static and fatigue damage in the CZM, effectively capturing damage caused by fatigue loading. Validation was conducted using experimental data from the existing literature. Based on this validation, four concrete beams with varying rubber replacement rates (0%, 5%, 10%, and 15%) were tested. The CZM was employed to describe the mechanical behavior of the interface transition zones (ITZs) and the mortar interior, which were simulated and analyzed under different stress levels. The results demonstrate that the model accurately simulates crack propagation paths, interface damage evolution, and the fatigue life of RC beams under fatigue loading. A functional relationship between fatigue life and stress level was established for various rubber replacement rates. This study provides a reference model for numerical simulations of RC under fatigue loading conditions and introduces new approaches for analyzing the fatigue performance of other materials.

Numerical characterizations of the thermomechanical response of power modules with ceramic substrates and lead-free bonds

PurposeThe present paper aims to study the influence of the substrate system on the thermomechanical response of various lead-free die attach materials used in power electronics using nonlinear finite element simulations.Design/methodology/approachParticularly, three ceramic substrate systems, including direct copper bonded (DCB) and aluminum nitride (AlN) – as well as silicon nitride (Si3N4) –based insulated metal substrate (IMS) configurations are examined in this study. Additionally, three die attach systems, namely, silver-tin transient liquid phase (TLP), sintered silver (Ag) and sintered copper (Cu) are included in the analysis. ANSYS software is employed to build the finite element models of the power modules and to conduct the nonlinear thermomechanical investigations.FindingsThe simulation results revealed that the IMS, Si3N4 and DCB-based power modules end up with significantly lower interconnect inelastic strains and inelastic strain energies suggesting better fatigue life performance. Additionally, the bonding layer stresses and expected failure mechanism are not influenced by the substrate configuration rather than the bond material. For instance, the silver-tin TLP joints develop high stresses and hence brittle failures are expected. Nonetheless, the sintered Ag and sintered Cu have significantly lower stresses which could lead to fatigue-induced failures.Originality/valuePower electronics use various ceramic-based substrate systems because of their improved thermal conductivity, electrical insulation and heat resistance properties. The proper selection of the substrate structure could highly enhance the thermal fatigue of the power modules. Markedly, the findings of this research are useful for designing highly reliable and effective power modules continuously subjected to thermomechanical loadings.

The Corrosion Fatigue Behavior and Mechanism of AerMet 100 Steel in 3.5% NaCl at Room Temperature.

AerMet 100 steel is a new type of double-hardened high-strength steel, which is often used as landing gear material in amphibious aircraft. In the present paper, the corrosion fatigue behavior and mechanism of AerMet 100 high-strength steel in a 3.5% NaCl solution was studied by stress-controlled fatigue tests and a series of subsequent characterizations of the fracture surface, microstructure, and cracks. The results indicated that the fatigue life of AerMet 100 high-strength steel decreased with a decrease in the stress level in a 3.5% NaCl solution, satisfying the relationship lgN = -2.69 × 10-3 σ + 6.49. The corrosion fatigue crack usually initiated from the corrosion pit and propagated across the martensitic flat noodles. Meanwhile, the corrosion fatigue crack tip was filled with Cr2O3, Fe2O3, and amorphous material; it propagated in the transgranular mode by a slip dissolution mechanism. This study provides some engineering significant for the fatigue performance of AerMet 100 steel in a 3.5% NaCl solution.

Fatigue analysis on flax-epoxy composites: insights and implications

This study investigates the performance of flax fiber and epoxy resin composites, focusing on fatigue testing, which is scarcely reported in the literature. Fatigue behavior is evaluated under full reverse bending loading conditions: R = −1. Apart of the definition of the classic S-N curve, the analysis deeply investigated the evolution of the hysteresis leaf generated during each cycle over the entire fatigue life. This approach allows evaluating interesting parameters such as the evolution of the loss factor and the apparent modulus over life, being these informations fundamental for practical application of natural-fiber composites in engineering applications.

Fatigue life assessment and verification of turbine joints: current status and prospects

The research status of fatigue life assessment technology for turbine joint structures is introduced. The progress, shortcomings and development trends of existing research are discussed from the aspects of multi-field load analysis, crack initiation life assessment, crack propagation simulation and test technology. The evaluation methods of service life and damage tolerance of turbine joint structures are discussed in detail. The results show that the existing analysis and test methods can basically realize the fatigue life assessment of turbine joints, but due to various limitations, the engineering applicability needs to be improved urgently. Robust load reduction analysis methods, life assessment methods based on physical mechanisms and data-driven, load history-related crack propagation life assessment methods and test technologies under complex thermal environments are still needed to establish a fatigue life assessment and verification system for advanced aero-engine turbine joint structures.

Effect of granulated blast furnace slag on uniaxial compression fatigue properties of engineered geopolymer composites

Engineered geopolymer composites (EGCs), emerging as a novel eco-friendly cementitious material, exhibit considerable potential in diverse applications. Granulated blast furnace slag (GBFS) is a by-product of the blast furnace ironmaking process. Owing to its exceptional cementing properties, GBFS is frequently incorporated into geopolymer materials to enhance strength and stability, while also achieving slurry solidification at ambient temperature. The study examined the effect of different rates of GBFS replacement on the fatigue behavior of EGCs using uniaxial compression fatigue testing, with a particular focus on the changes in fatigue life and fatigue deformation. The results indicate that the fatigue life of EGC conforms to a Weibull distribution. While a higher GBFS replacement rate can improve the compressive strength of EGC, it has a detrimental effect on the fatigue life. Furthermore, when subjected to fatigue loading, the total strain accumulation, residual strain, and fatigue stiffness of EGC exhibited a three-stage evolutionary pattern, and remained constant during the secondary creep stage. Therefore, the comprehensive effect of adding GBFS to EGC on material strength and fatigue properties should be taken into account. This study uncovers the potential negative impacts of GBFS on the fatigue properties of EGC, contradicting the previous belief that GBFS could enhance the mechanical properties of geopolymers. Therefore, a comprehensive and meticulous assessment is necessary when contemplating the use of GBFS as a reinforcement material for EGC.

Probabilistic risk assessment method considering machining-induced random residual stress

The aero-engine disks inevitably have manufacturing-induced anomalies and machining-induced random residual stress (RS) in localized and critical areas, which cause a severe threat to the safety of the aircraft. Traditional structural design of the disks fails to establish a quantitative correlation between the machining process and the failure risk. Therefore, this paper proposes a probabilistic model considering random RS to quantify the influence of machining RS subjected to low-cycle fatigue. The RS dispersion is quantified using a scaling parameter, obtained by X-ray diffraction measurements and orthogonal cutting simulations. The crack life database under varying RSs is established for efficient probability calculations. Results show that the coefficient of variation (COV) of the RS on the same machined surface with the same processing parameters is 7.62 % in the local area and 13.74 % in the whole machined surface. The risk results show that the probability of failure (POF) considering the deterministic RS is 2–4 % lower than the POF without RS, owing to the extension of fatigue life by compressive RS. Furthermore, the POF considering the random RS is almost the same (difference <0.6 %) as the POF considering the deterministic RS because the depth of the machining RS is around 0.2 mm. The proposed method predicts the POF more accurately and is thus valuable for the safety assessment of an aero-engine titanium disk.

A Hybrid Mechanism and Data‐Driven Approach for Predicting Fatigue Life of MEMS Devices by Physics‐Informed Neural Networks

ABSTRACTOur research group has focused on the long‐term performance degradation of micro‐electro‐mechanical systems (MEMS) devices under mechanical, thermal, and electrical stresses. We previously used physics‐based models for performance prediction, but the diverse materials, structures, and environmental conditions of MEMS devices affect their long‐term stability. Traditional physics‐based models struggle to account for these factors, limiting practical application. To address this, we employ data‐driven methods to include more variables. This paper introduces a hybrid approach combining physical principles with data‐driven techniques, specifically physics‐informed neural networks (PINN), to model and analyze performance degradation in MEMS resonators. We compare this method with previous physics‐based and data‐driven approaches (support vector machine and random forest) under identical conditions. The hybrid method not only provides accurate predictions but also considers more operating conditions, enhancing practical application.

An adaptive acceleration scheme for phase-field fatigue computations

Abstract Phase-field models of fatigue are capable of reproducing the main phenomenology of fatigue behavior. However, phase-field computations in the high-cycle fatigue regime are prohibitively expensive due to the need to resolve spatially the small length scale inherent to phase-field models and temporally the loading history for several millions of cycles. As a remedy, we propose a fully adaptive acceleration scheme based on the cycle jump technique, where the cycle-by-cycle resolution of an appropriately determined number of cycles is skipped while predicting the local system evolution during the jump. The novelty of our approach is a cycle-jump criterion to determine the appropriate cycle-jump size based on a target increment of a global variable which monitors the advancement of fatigue. We propose the definition and meaning of this variable for three general stages of the fatigue life. In comparison to existing acceleration techniques, our approach needs no parameters and bounds for the cycle-jump size, and it works independently of the material, specimen or loading conditions. Since one of the monitoring variables is the fatigue crack length, we introduce an accurate, flexible and efficient method for its computation, which overcomes the issues of conventional crack tip tracking algorithms and enables the consideration of several cracks evolving at the same time. The performance of the proposed acceleration scheme is demonstrated with representative numerical examples, which show a speedup reaching up to four orders of magnitude in the high-cycle fatigue regime with consistently high accuracy. Graphical abstract

Research on the microstructure, mechanical and fatigue performance of 7075/6061 dissimilar aluminum alloy fusion welding joint treated by nanoparticle and post-weld heat treatment

The microstructure and mechanical properties of 7075/6061 high-strength dissimilar aluminum alloy fusion welds, after TiC nanoparticle-assisted welding and heat treatment, were discussed, and their fatigue performance was analyzed. The results indicate that the significant increase in hardness at the weld zone with T6 treatment compared to T5 is due to the solution treatment providing supersaturated solid solution for subsequent aging precipitation. T5 treatment causes the precipitation in the heat affected zones, thereby increasing the hardness of these regions. The joints exhibit excellent yield strength and tensile strength after heat treatment, with the elongation performance being optimal in T6 state. The fatigue performance of dissimilar aluminum alloy joints treated with nanoparticle and heat treatment is superior to the joints with single riveting. Porosity defects and microcracks generated during welding are prone to stress concentration, with interconnected pores and easily propagating cracks forming fatigue sources for pores and cracks. The crack propagation behavior is influenced by the pinning effect of TiC nanoparticles at the grain boundaries, and the second phase particles hinder crack propagation along the grain boundaries, forcing cracks to extend towards the 6061 side or the HAZ of the lower strength 6061 matrix. It demonstrates that the method of combining nanoparticle-assisted melt inert-gas welding and T6 heat treatment improves the fatigue life of 7075/6061 dissimilar aluminum alloy joints.

Fatigue life modeling for a low alloy steel after long-term thermal aging

Fatigue failure of materials has a considerable impact on the safety of equipment in service. In this study, axially tensile and low cycle fatigue tests were conducted on a low alloy steel after accelerated thermal aged at 450 °C for 10,000 h. The experimental results indicate that the ultimate and yield strengths increase moderately, while the fatigue life of specimens experience a slight decrease in this circumstance. The fracture analysis demonstrates that the bainite breaking facilitates the fatigue crack initiation and propagation after thermal aging, which is accompanied by a decrease in plastic strain amplitude. Therefore, the plastic strain amplitude is considered as an indicator of thermal aging in fatigue life modeling for the low alloy steel. Finally, a novel life model that incorporates both aging time and temperature was proposed for rapid prediction of low cycle fatigue life. It is assumed that this model promotes reliable fatigue life prediction in low alloy steels under various thermal aging circumstances, as well as the extrapolation of fatigue performance of the material in service.

FEM Investigation of the Roughness and Residual Stress of Diamond Burnished Surface

Characterization of surface integrity is possible with three critical metrics: microstructure, surface roughness, and residual stress. The latter two are discussed in this paper for low-alloyed aluminum material quality. Ball burnishing is a regularly used finishing procedure to improve surface roughness, shape accuracy, and fatigue life, taking advantage of the fact that it can favorably influence the variation in stress conditions in the material. The effect of burnishing is investigated using finite element simulation with DEFORM 2D software using the real surface roughness of the workpiece. The FEM model of the process is validated with experimental tests, the surface roughness is measured using an AltiSurf520 measuring device, and the residual stress is analyzed with a Stresstech Xstress 3000 G3R X-ray diffraction system (Stresstech, Vaajakoski, Finland). The results indicate that the burnishing process improves the surface roughness and stress conditions of AlCu6BiPb low-alloyed aluminum, and the study shows that there is good agreement between the FE and experimental results, further revealing the effect of the process parameters on the distribution of the compressive residual stress.

Aircraft joint structure lightweight design

PurposeThe purpose of this article is to carry out a lightweight design of the joint structure according to the service condition of the joint.Design/methodology/approachThe finite element analysis techniques are used along with the variable density structure topology optimization method, the multi-island genetic algorithm for structural dimension optimization and the fatigue life analysis method.FindingsUtilizing the topology optimization method and size optimization method, the mass of the optimized model for the A100 material model is 9.67 kg. Compared to the pre-optimized model, the mass decreases by 8.23 kg, representing a weight reduction of 46.0% in the optimized model; the fatigue life of the aircraft joint is predicted to be a maximum of 1,460,017 cycles.Originality/valueThe originality of this study is that it provides new design ideas for the lightweight design of aircraft load-bearing structures.

Fatigue Behavior of H-Section Piles under Lateral Loads in Cohesive Soil

Most structures supporting solar panels are found on thin-walled metal piles partially driven into the ground, optimizing costs and construction time. These pile foundations are subjected to repetitive lateral loads from various external forces, such as wind, which can compromise the integrity of the pile-soil system. Given that the expected operational lifespan of photovoltaic solar plants is generally 20–30 years, predicting their service life under fatigue loads is crucial. This research analyzes the response of H-section piles to lateral fatigue loads in cohesive rigid soils through four field tests, subjected to load cycles of 55%, 72%, and 77% of the static failure load, corresponding to maximum loads of 25 kN, 32 kN, and 35 kN, respectively. Additionally, the effect of load cycles on the degradation of pile-soil adhesion is studied through two pull-out tests following cyclic tests. This study reveals that soil fatigue does not occur under repetitive loads and that soil stiffness remains constant once the cycles causing soil compaction have been overcome. Nevertheless, the accumulated plastic deflection of the soil increases steadily once soil compaction occurs due to cyclic loading. The implications of these results on the fatigue life of photovoltaic solar panel foundations are discussed.