Search Results (189)

Aluminum alloy is a lightweight, high-strength material based on aluminum matrix with the addition of elements such as copper, magnesium, silicon, zinc, manganese, or lithium. Featuring low density, high specific strength, excellent formability, and outstanding corrosion resistance, it is widely applied in the fields of aerospace, rail transit, automotive lightweighting, and additive manufacturing. In the aerospace sector, fatigue failure constitutes the primary failure mode of load-bearing components. This paper reviews the influence mechanisms of various strengthening technologies, namely shot peening (SP), laser shock processing (LSP), physical vapor deposition (PVD), micro-arc oxidation (MAO), anodic oxidation (ANO), additive manufacturing, casting, extrusion, and heat treatment, on the fatigue properties of aluminum alloys; analyzes the regulatory effects of process principles, coating compositions, and microstructures (grains, phase composition, and interfacial bonding) on crack initiation and propagation; discusses the synergistic effect between plastic deformation strengthening and coating functionality; summarizes the key material and process factors affecting the fatigue life of aluminum alloys; and finally prospects the technical development trends driven by high-reliability service requirements. Full article

Finely dispersed Al–Ca–Ti composite alloys with a set of remarkable properties can be considered as new promising structural materials. For wider use of these alloys, data on their fatigue behavior are needed. In this work the comparative study of the low-cycle fatigue strength of hot-rolled Al–xCa–0.2Ti alloys with different eutectic fractions determined by different calcium contents was conducted. The fatigue tests were carried out according to a single-plane bending scheme using a dynamic mechanical analyzer. A symmetrical loading cycle (asymmetry coefficient R = −1) with a constant stress amplitude was used. The maximum number of cycles was 20,000. It was found that increasing the eutectic fraction from 40% to 80% led to a 75% increase in the fatigue limit—from 80 to 140 MPa—which directly correlated with the alloy’s yield strength. The fatigue crack propagation occurred with the formation of a scaly fracture surface, whereas final static rupture was associated with a ductile dimple fracture. The microstructural mechanisms of alloy fatigue failure were discussed. It was found that increasing the total length of the eutectic particles/aluminum matrix interphase boundaries changed the failure mechanism to a more brittle one. Full article

Laser shock peening (LSP) is an advanced surface modification technique that significantly enhances the fatigue resistance of metallic components through the synergistic implantation of deep compressive residual stresses (CRSs) and gradient microstructural refinement. Existing investigations have shown that LSP can generate strengthening layers extending from several hundred micrometers to approximately 1 mm in depth, with affected zones reaching 5–6 times the depth typically achieved by conventional shot peening in representative titanium alloys. In specific cases, LSP has increased the fatigue limit from 483.2 MPa to 593.6 MPa, corresponding to an improvement of approximately 22.8%, while optimized treatment of Ti-17 compressor blades has extended fatigue life by more than two orders of magnitude. This review systematically elucidates the anti-fatigue strengthening mechanisms of LSP across a range of metallic systems, with emphasis on three key aspects: (i) the mechanistic retardation of fatigue crack initiation and propagation, mediated by CRS-induced reductions in the stress intensity factor and enhanced crack closure effects; (ii) the parametric sensitivity of surface integrity and stress field homogeneity to laser energy density, spot overlap ratio, and multiple-impact sequencing; and (iii) the process-specific characteristics of emerging LSP variants, including laser peening without coating, warm laser shock peening, and cryogenic laser shock peening. Furthermore, we critically evaluate the role of multiscale numerical simulations—encompassing macroscopic finite element analysis, mesoscopic crystal plasticity modeling, and molecular dynamics—in optimizing process parameters and predicting fatigue life. By integrating experimental, computational, and theoretical perspectives, this review establishes a coherent process–structure–property framework to guide the rational design of LSP protocols for targeted fatigue performance enhancement. Full article

Purpose—The flexspline of a harmonic drive constitutes a thin-walled structure with discontinuous gear rim and cylinder configuration, where cyclic stresses induce stress concentration, followed by crack initiation, propagation, and ultimately fatigue failure. This paper reviews advancements in understanding its mechanical properties and fatigue failure mechanisms, aiming to establish a foundation for enhancing operational longevity and guiding future research. Design/Methodology/Approach—The study integrates meshing theory, tooth shape parameters, cylinder stress influencers, and assembly/meshing stress considerations. Theoretical analysis, finite element simulations, and experimental methods are employed to examine stress patterns and fatigue dynamics. Structural parameters and tooth profiles are systematically analyzed for their impact on stress distribution and fatigue life. Findings—Flexspline fatigue failure arises from tooth root stress concentration and cylinder bending stress accumulation. The double-circular-arc tooth profile boosts load capacity by 35% relative to the involute profile, yet demands high-precision machining to preserve meshing performance. Increasing cylinder length mitigates stress concentration but reduces torsional stiffness, while optimized root fillet radii can lower the stress concentration coefficient by 28%. Assembly interference and meshing contact stress accelerate crack initiation, as validated by transient dynamics simulations. Surface strengthening processes (e.g., shot peening) enhance fatigue life by up to 66% through residual compressive stress regulation. Originality/Value—This paper synthesizes multi-scale research on flexspline design, structural optimization, and fatigue mechanisms, proposing novel approaches such as “manufacturability-oriented optimization” and digital twin-driven monitoring. By linking dynamic loads, material properties, and geometric parameters, it bridges theoretical gaps and provides actionable insights for high-precision harmonic drives in robotics and aerospace, advancing reliability in precision transmission systems. Full article

This paper addresses the challenges of life prediction and reliability assessment for ball screws under complex operating conditions by proposing a reliability prediction model that incorporates full-life fatigue damage. First, a full-life fatigue life prediction model encompassing the three stages of crack initiation, propagation, and fatigue cumulative spalling is developed. This model comprehensively considers the effects of material properties, geometric parameters, and loading history, enabling a systematic description of the fatigue process of ball screws from initial use to final failure. Based on this life prediction model, an enhanced adaptive Kriging–Monte Carlo simulation (E-AK-MCS) method is introduced to construct a surrogate model, which efficiently solves the high-dimensional nonlinear limit state function, thereby enabling accurate reliability assessment and parameter sensitivity analysis. Experimental results demonstrate that the proposed model achieves an average life prediction accuracy of 94.15% for the 8020 and 5005 specification ball screws, indicating its preliminary engineering applicability under the tested conditions. Reliability analysis indicates that ball diameter fracture toughness, and initial crack size are key factors influencing service reliability. This research provides systematic theoretical methods and technical support for the accurate life prediction, reliability design, and process optimization of ball screws. Full article

TA15 titanium alloy fabricated by Laser Powder Bed Fusion (L-PBF) exhibits high strength but poor ductility due to its fine acicular α′ martensitic microstructure. This study systematically investigates the effects of post-annealing treatments (800–950 °C for 0.5–4 h) on the microstructural evolution and mechanical performance of L-PBF-built TA15. Results show that with increasing temperature and time, the metastable α′ martensite decomposes into a progressively coarser lamellar (α + β) structure. This transformation leads to a decrease in strength and hardness but a significant improvement in ductility, with elongation increasing from (8.5 ± 0.5)% (as-built) to (19.4 ± 1.1)% (900 °C/2 h) as the ultimate tensile strength (UTS) decreased from (1100 ± 29) to (895 ± 37) MPa. However, annealing at 950 °C, which approaches the β-transus temperature, induces a coarse Widmanstätten structure in the alloy. Although this structure yields a relatively high elongation (23.8 ± 3)%, it also leads to excessive strength loss, with an ultimate tensile strength of only (833 ± 23) MPa, rendering it less desirable for structural applications requiring high load-bearing capacity. Moreover, such coarse lamellar structures are generally associated with poor fatigue resistance, as cracks tend to propagate along prior β grain boundaries. An optimal strength-ductility synergy is achieved by annealing at 900 °C for 0.5 h, yielding an ultimate tensile strength of (951 ± 13) MPa and an elongation of (18.8 ± 1.7)%. These findings provide crucial guidance for tailoring the mechanical properties of L-PBF-fabricated TA15 alloy through post-processing heat treatments. Full article

Nickel-based single-crystal superalloys are key materials for manufacturing aero-engine turbine blades. Different grain boundaries are inevitably formed during the production of superalloys and weaken the fatigue performance of the alloys. Systematic exploration of the effect of grain boundary misorientation (GBM) on the fatigue properties of superalloys is of great significance. Available research cannot fully illustrate the influence of GBM on the high-cycle fatigue (HCF) damage mechanism of superalloys, especially its coupling with inherent casting defects. In this study, bicrystal specimens with misorientations of 4°, 8° and 12° were fabricated from a second-generation nickel-based single-crystal superalloy. The influence mechanism of misorientation variation on HCF performance was systematically investigated. The test results show that the HCF life of the alloy decreases obviously as GBM rises from 4° to 8° and then declines slowly. Fracture analysis indicates that fatigue damage is closely associated with GBM and casting defects. A 4° grain boundary promotes coordinated deformation and inhibits cracking, whereas misorientations over 8° cause dislocation pile-up and speed up crack propagation. Based on the significant effects of GBM and casting defects on fatigue damage behavior, as well as the analysis of the two key parameters in the Basquin model, a linear correlation is established between the fatigue strength coefficient (σ′_f) and misorientation; a coupling relationship is constructed among the fatigue strength exponent (b), misorientation, and defect size. Prediction results confirm that the model achieves higher accuracy by incorporating casting defect parameters. Full article

This paper investigates the influence of surface ultrasonic rolling treatment on the fatigue performance of Mg-3Al-1Zn extruded alloy and systematically analyzes the evolution laws of fatigue life and mechanical properties with the thickness of the surface removed layer. The results show that after ultrasonic rolling treatment, the fatigue life of the alloy at a stress amplitude of 240 MPa changes significantly and reaches a peak at a specific removal thickness: when the 80 μm surface layer is removed, the fatigue life reaches 7.79 × 10⁶ cycles, which is much higher than that of the untreated sample (3.87 × 10⁴) and the sample only subjected to ultrasonic surface rolling processing (1.8 × 10⁴). With the increase in the removal thickness, the fatigue life shows a trend of first increasing and then decreasing, and a second increase occurs within the range of 400–500 μm. Microstructure analysis indicates that at a depth of 80 μm from the surface, the strength is enhanced due to grain refinement and the peak hardness, thereby inhibiting the initiation of fatigue cracks, while within the depth range of 400–500 μm, there exist high-density dislocations and deformation layers, which also effectively hinder crack propagation. This study reveals the key role of surface state and subsurface microstructure in the fatigue behavior of magnesium alloys, providing a theoretical basis for improving the fatigue performance of magnesium alloys through surface modification. Full article

Fatigue failure in scaffolding components poses significant risks to worker safety, particularly in high-altitude construction environments. This study investigates the fatigue behavior of scaffolding stirrups, a critical structural element prone to premature failure. The objective is to analyze the fatigue damage mechanisms in stirrups through a combined experimental and numerical approach. Mechanical characterization and micro-hardness testing were conducted to assess the material properties of the stirrup, while finite element modeling (FEM) was employed to simulate its performance under cyclic loading. The Johnson–Cook material model was utilized to compare experimental hysteresis curves with FEM results, validating the numerical approach. Additionally, the Extended Finite Element Method (XFEM) was applied to model crack initiation and propagation. Results reveal that material hardening and fatigue crack growth are the primary causes of stirrup failure, with distinct fatigue zones and crack paths identified. The study quantifies the relationship between crack growth stages and stirrup bending, providing insights into the failure process. These findings contribute to improving the safety and lifespan of scaffolding systems by identifying key factors influencing stirrup durability. Full article

Titanium alloys exhibit exceptional strength-to-density ratios, high hardness, and outstanding resistance to elevated temperatures, making them indispensable structural materials in aerospace engineering, marine construction, and biomedical applications. In aerospace systems specifically, fatigue failure represents the predominant failure mode for titanium alloy components. This review systematically examines prevalent surface treatment techniques for titanium alloys—including shot peening, ultrasonic rolling treatment, hot isostatic pressing (HIP), physical vapor deposition (PVD), micro-arc oxidation (MAO), and thermal spray processes—and critically evaluates their respective effects on fatigue performance. The underlying mechanisms of each technique are concisely outlined, with emphasis on stress state evolution, near-surface microstructural refinement, and interfacial integrity. Building upon the characteristic surface-dominated fatigue fracture behavior of titanium alloys, this work focuses on how coating composition, architecture (e.g., graded, multilayer, or nanocomposite designs), and interfacial bonding strength govern fatigue resistance. A unified analysis is presented on the distinct yet complementary roles of substrate deformation strengthening (e.g., residual compression, grain refinement) and coating-mediated protection (e.g., barrier function, crack deflection, stress redistribution) during fatigue crack initiation and propagation. Key determinants of fatigue performance, including residual stress distribution, coating/substrate adhesion, thermal mismatch, and environmental degradation susceptibility, are rigorously assessed. Finally, emerging research frontiers are identified, including intelligent process–structure–property mapping, in situ monitoring of fatigue damage at coated interfaces, and design of multifunctional gradient coatings that synergistically enhance strength, wear resistance, and fatigue endurance of titanium alloy components. Full article

Stellite alloys are widely used in the aerospace field owing to their excellent high-temperature strength and thermal fatigue resistance. However, with the rapid development of the aerospace industry, there is an urgent demand to further enhance the mechanical properties and thermal fatigue resistance of Stellite alloys. In the present study, we prepared a conventional CoCrW alloy (classified as a Stellite alloy) and a novel CoCrWAlNi alloy, which was formulated by introducing aluminum and nickel into the CoCrW matrix, using the direct laser deposition technique. Their microstructural characteristics, mechanical properties, and thermal fatigue performance were systematically investigated. The results indicated that the additions of aluminum and nickel contribute to stabilizing the γ-Co phase. Compared with the CoCrW alloy, the CoCrWAlNi alloy exhibited higher elongation at fracture. In situ observation was employed to study the initiation and propagation of thermal fatigue cracks. Meanwhile, the effects of oxidation on thermal fatigue resistance were analyzed through experimental tests and theoretical calculations based on the Huntz model. Finally, an optimized thermal fatigue mechanism tailored for cobalt-based alloys was established, which yields deeper insights into the failure mechanisms of these alloys under complex thermal-cycling fatigue conditions. Full article

This study investigates the effect of microstructure on water-induced embrittlement of dual-phase austempered ductile iron (ADI). Dual-phase ADI materials were produced by austenitization at 780, 800, 820, and 840 °C followed by austempering at 400 °C/1 h, resulting in microstructures composed of varying fractions of free ferrite and ausferrite. Tensile properties were evaluated under dry conditions and in distilled water. The embrittlement zones were observed in all samples investigated; however, they were not critical in all cases. The results indicate that free ferrite is less sensitive to water-induced embrittlement, whereas increasing ausferrite content promotes the formation and growth of the embrittlement zone. Elongation was identified as the most sensitive mechanical parameter, showing statistically significant reductions of up to ~80% for microstructures containing more than ~65% ausferrite, while proof strength remained largely unaffected. Fracture surface analysis revealed fatigue-like striation features within the embrittlement zone, indicating cyclic crack initiation and propagation. Based on correlations between tensile behavior, fracture morphology, and microstructural features, a water-induced embrittlement mechanism involving cyclic local chemisorption and surface-initiated crack growth is proposed. These findings highlight the critical roles of phase type, volume fraction, and spatial distribution in controlling the resistance of dual-phase ADI to embrittlement in aqueous environments. Full article

Additive manufacturing (AM) of Ti-6Al-4V alloy is widely used in aerospace and medical fields due to its excellent strength and corrosion resistance. However, the microstructural heterogeneity induced by the AM process often results in fatigue properties inferior to those of their forged counterparts. Synchrotron Radiation Computed Tomography (SR-CT) was employed to conduct an in situ three-dimensional investigation of fatigue damage evolution in Ti-6Al-4V alloy fabricated via laser powder bed fusion (LPBF). Experimental results revealed phenomena of crack bridging and deflection, accompanied by the consistent presence of local high-density zones (LHDZs) throughout the fatigue damage progression. Combined with quantitative analysis of crack propagation rates, the influence of LHDZs on fatigue damage evolution was analyzed, and the relationship between AM processes, LHDZs, and fatigue damage was discussed. The results indicate that the basket-weave α-phase microstructure in Ti-6Al-4V prepared by LPBF exhibits a high correlation with the distribution of LHDZs, and the orientation of LHDZs aligns with the crack propagation direction. By adjusting process parameters such as cooling rate and temperature gradient, the formation of LHDZs can be modified, thereby influencing the fatigue properties of the material. This provides theoretical support for achieving process optimization of the fatigue properties of Ti-6Al-4V alloy prepared via LPBF. Full article

This paper investigates the fatigue and residual strength behavior of recycled carbon fiber reinforced plastics (rCFRPs) with different fiber architectures in an epoxy resin matrix: a unidirectional (UD) rCFRP and a non-crimp fabric (NCF) composite. Due to the research gap in fatigue testing of recycled carbon fiber-reinforced plastics with quasi-continuous fiber reinforcement, their fatigue properties are investigated in this article. The objective of the present study is to contribute to the broader goal of integrating recycled carbon fibers as quasi-continuous fiber reinforcement in structural applications by understanding their failure behavior. To determine suitable stress levels for fatigue testing, quasi-static tensile tests are conducted first. Subsequently, fatigue tests are performed with a stress ratio of 0.1. Damage evolution is documented by a continuous recording of the stiffness degradation. For the unidirectional material, an S-N_f curve is created based on three stress levels. The curve can be described with a logarithmic equation. Fatigue testing of the NCF laminate is performed at a single stress level. Subsequent residual strength tests using standard specimens show no clear correlation between the number of load cycles of pre-cycling and residual strength, but indicate a sudden-death behavior for both composites. For further investigation of the damage behavior, in situ residual strength tests are carried out using a combination of acoustic emission analysis and micro-computed tomography (µCT) imaging. This investigation is intended to illustrate crack initiation and propagation three-dimensionally after pre-cycling and during residual strength tests. The results demonstrate a significant influence of the microstructure on the failure behavior. Full article

The following paper aims to provide the results of an innovative structural crack detection technique using printed adaptive sensors. They were manufactured using conductive ink with silver microparticles and polymer insulators. The technique leveraged the unique properties of Direct Ink Write additive manufacturing combined with domain knowledge in the field of technical condition monitoring. The goal was to achieve high sensitivity and precision in detecting fatigue-crack-induced changes in structural components. The sensors’ fabrication repeatability, output stability, and crack detection capabilities were investigated. Based on preliminary measurements of the sensors’ output characteristics, the analyzed data showed that a tolerance in the range of 5% can be obtained for batch production. Damage size estimation using this new crack gauge during a fatigue crack growth test was high compared to the reference, with less than 1 mm precision over 30 mm of crack length. Throughout the fatigue test of up to 1.5 million cycles, all CCPSs remained fully functional, with no failure-related changes in their output signal patterns. The proposed sensor has proven its reliability for the detection of fatigue cracks and propagation monitoring and is a good alternative to other SHM technologies for this purpose. Full article