Search Results (71)

The quality of SLM formed parts is one of the key factors of the promotion and application of additive manufacturing technology. The scanning strategy fundamentally affects the fatigue life of SLM 316L stainless steel parts by regulating residual stress, defect distribution, and microstructure. Three different scanning strategies (meander scanning, stripe scanning, and chessboard scanning) were adopted to prepare the specimens. High cycle fatigue loading was applied to SLM 316L stainless steel specimens prepared by different scanning strategies. The thermal conductivity characteristics during the SLM part forming process were analyzed based on scanning electron microscopy observations of microstructure of SLM specimens, and the mechanism of residual stress and internal defect generation were revealed. The scanning direction determines the growth direction of the grains, thereby affecting the anisotropy and overall fatigue performance of SLM 316L stainless steel parts. The scanning path determines the overlap and lap joint of the melt pool, directly affecting the number, size, and location of pores and incomplete fusion defects. The scanning strategy affects the distribution and magnitude of residual stresses by changing the path of heat source movement. Theoretical analysis and experimental verification results indicate that the selection of a scanning strategy is an effective method for optimizing the fatigue performance of SLM parts. Full article

The article presents an analysis of the mechanical properties of S700MC steel, which represents advanced low-alloy high-strength steels. The influence of microstructure, shaped by a controlled thermo-mechanical rolling process, on the strength, ductility, and resistance to cracking and fatigue of the material is discussed. Particular attention is paid to the anisotropy of mechanical properties resulting from the orientation relative to the rolling direction, manifested by variations in yield strength, tensile strength, and total elongation of the specimens. The analysis also includes the material’s behavior under dynamic conditions, where the steel’s strength increases with the strain rate. Experimental investigations conducted using the digital image correlation (DIC) method enabled a detailed assessment of local strains and fracture characteristics of specimens subjected to both static and dynamic testing. The results showed that specimens cut along the rolling direction exhibited, on average, 6.4% higher tensile strength and 6.8% higher yield strength compared to those cut transversely. Moreover, dynamic loading led to an increase in load-bearing capacity of over 10% compared to static tests. The obtained data are highly relevant from the perspective of structural design, where the selection of material orientation and the consideration of strain rate effects are crucial for ensuring the reliability of components made from S700MC steel. Full article

Selective laser melting (SLM) offers a novel approach for manufacturing intricate structures, broadening the application of titanium alloy parts in the aerospace industry. After the build period, heat treatments of annealing (AT) and hot isostatic pressing (HIP) are often implemented, but a comparison of their mechanical performances based on the specimen orientation is still lacking. In this study, horizontally and vertically built Ti6Al4V SLM specimens that underwent the aforementioned treatments, together with their microstructural and defect characteristics, were, respectively, investigated using metallography and X-ray imaging. The mechanical properties and failure mechanism, via fracture analysis, were obtained. The critical factors influencing the mechanical properties and the correlation of the fatigue lives and failure origins were also estimated. The results demonstrate that the mechanical performances were determined by the α-phase morphology and defects, which included micropores and fewer large lack-of-fusion defects. Following the coarsening of the α phase, the strength decreased while the plasticity remained stable. With the discrepancy in the defect occurrence, anisotropy and scatter of the mechanical performances were introduced, which was significantly alleviated with HIP treatment. The fatigue failure origins were governed by defects and the α colony, which was composed of parallel α phases. Approximately linear relationships correlating fatigue lives with the X-parameter and maximum stress amplitude were, respectively, established in the AT and HIP states. The results provide an understanding of the technological significance of the evaluation of mechanical properties. Full article

The application of additive manufacturing technology in the field of nuclear power is becoming increasingly promising. The low-cycle fatigue behavior of Z2CN19-10 controlled-nitrogen-content stainless steel (SS) was investigated by fatigue equipment, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), including additive manufactured (AM) and forged materials. The results showed that the microstructure of the AM material exhibited anisotropy for the X, Y, and Z directions. The tensile and impact properties of the X, Y, and Z directions in AM material were similar. The fatigue life (N_f) of X- and Y-direction specimens was better than that of Z-direction specimens. The tensile, impact, and fatigue properties of all AM materials were lower than those of the forged specimens. The Z direction specimens of AM material showed the best plastic strain by the highest transition fatigue life (N_T) during the fatigue strain amplitude at 0.3% to 0.6%. The forged specimens showed the best fatigue properties under the plastic strain amplitude control mode. Fatigue fracture surfaces of AM and forged materials exhibited multi- and single-fatigue crack initiation sites, respectively. This could be attributed to the presence of incompletely melted particles and manufacturing defects inside the AM specimens. The dislocation morphology of AM and forged fatigue specimens was observed to study the low-cycle fatigue behaviors in depth. Full article

This paper investigates the effect of mean shear stress on short-beam shear fatigue in a GLARE 1-3/2 commercial fiber–metal laminate (FML). This study explores three shear stress ratios (${\mathit{R}}_{\mathit{\tau }}$ 0.1, 0.3, and 0.5) and two material orientations (longitudinal and transversal) under constant amplitude fatigue. Different stress levels for each ${\mathit{R}}_{\mathit{\tau }}$ value were explored to obtain failures between 10³ and 10⁶ load cycles. The experimental results reveal anisotropy, with transversal specimens exhibiting lower performance and increased scatter. The mean shear stress effect is discussed herein, with insights into the critical role of mean shear of fatigue performance. ${\mathit{R}}_{\mathit{\tau }}$ 0.1 was the most severe condition and ${\mathit{R}}_{\mathit{\tau }}$ 0.5 was the least severe. The ${\mathit{R}}_{\mathit{\tau }}$ 0.3 condition produced steeper S-N curves, indicating that the combined effect of mean shear stress and shear stress amplitude led to a higher rate of damage accumulation. The fractographic analysis investigated the failure modes and confirmed the damage dominated by Mode II, supporting the test methodology employed. Full article

Fatigue endurance anisotropic behavior was evaluated for an API 5L X42 pipeline steel through axial force-controlled fatigue tests amongst Longitudinal, Diagonal, and Circumferential directions. This study shows that fatigue life anisotropy is mainly controlled by pearlite banding degree (A_i) and ferritic grain orientation (Ω₁₂). Also, it is foreseen that the observed behavior can be related to the dislocation arrays generated by the cyclic loading in relation to microstructure orientation, and the interactions of the fatigue crack tip with the microstructure during the crack propagation stage. Full article

This paper presents the results of an analysis of the mechanical properties of the S420M steel samples collected both perpendicular and parallel to the rolling direction. The scope of the analysis included the following: a static tensile test, a hardness measurement, a low-cycle fatigue test, and a microstructure analysis of the analysed material. During the analysis, it was found that the rolling direction had little effect on the most important strength parameters determined in the static tensile test, but had a significant effect on the fatigue properties. During fatigue testing, a significant reduction in fatigue life (from 50% to almost 300%) was observed for samples perpendicular to the rolling direction. The largest reduction in fatigue life was observed at the ε_ac = 0.25% strain level (almost 300%), while the smallest was at ε = 0.25% (50%). A comparative analysis of the results of constant-amplitude and programmed fatigue tests confirmed the validity of using accelerated life tests to determine the low-cycle fatigue properties of construction materials. The results of the experimental verification of the Palmgren–Miner linear hypothesis of fatigue damage accumulation confirmed the significant influence of the material data on the results of fatigue life calculations. Full article

Aero-engine turbine vanes made from directionally solidified nickel-based superalloys often fail with crack formation from the external wall of cooling channels. Therefore, this study simulates the compressive load on the external wall of the vane and conducts a sequence of creep–fatigue evaluations at 980 °C to investigate the creep–fatigue damage mechanisms of a directionally solidified superalloy and to assess its life. It is found that at low strain ranges, creep damage is dominant, with creep cavities forming inside the specimen and fatigue sources mostly distributed in the specimen interior. As the strain range increases, the damage mechanism transitions from creep-dominated to creep–fatigue coupled damage, with cracks nucleating preferentially on the surface and exhibiting a characteristic of multiple fatigue sources. In the longitudinal (L) specimen, dislocations in multiple orientations of the {111}<110> slip system are activated simultaneously, interacting within the γ channels to form dislocation networks, and dislocations shear through the γ′ phase via antiphase boundary (APB) pairs. In the transverse (T) specimen, stacking intrinsic stacking faults (SISFs) accumulate within the limited {111}<112> slip systems, subsequently forming a dislocation slip band. The modified creep–fatigue life prediction model, incorporating strain energy dissipation and stress relaxation mechanisms, demonstrates an accurate fatigue life prediction under creep–fatigue coupling, with a prediction accuracy within an error band of 1.86 times. Full article

The heel pad, located under the calcaneus of the human foot, is a hidden treasure that has been subjected to harsh mechanical conditions such as impact, vibration, and cyclic loading. This has resulted in a unique compartment structure and material composition, endowed with advanced biomechanical functions including cushioning, vibration reduction, fatigue resistance, and touchdown stability, making it an ideal natural bionic prototype in the field of bionic materials. It has been shown that the highly specialized structure and material composition of the heel pad endows it with biomechanical properties such as hyperelasticity, viscoelasticity, and mechanical anisotropy. These complex biomechanical properties underpin its advanced functions. Although it is known that these properties interact with each other, the detailed influence mechanism remains unclear, which restricts its application as a bionic prototype in the field of bionic materials. Therefore, this study provides a comprehensive review of the structure, materials, biomechanical properties, and functions of the heel pad. It focuses on elucidating the relationships between the structure, materials, biomechanical properties, and functions of heel pads and proposes insights for the study of bionic materials using the heel pad as a bionic prototype. Finally, a research idea to analyze the advanced mechanical properties of heel pads by integrating sophisticated technologies is proposed, aiming to provide directions for further in-depth research on heel pads and inspiration for the innovative design of advanced bionic materials. Full article

This study aims to assess the mechanical tensile properties of Polyamide produced via selective laser sintering (SLS). The research focuses on the effects of post-processing, positional dependency, anisotropy, and the repeatability of SLS print jobs on material properties. Understanding this anisotropy is crucial for reliable component simulation. A design-appropriate simulation method is developed. A total of 27 identical specimens were fabricated in various orientations and positions within the build chamber, repeated across three print jobs, alongside standard specimens for different post-processing treatments and tempering durations. The mechanical tensile properties were evaluated through tensile tests and compared with simulation outcomes. A new material modeling concept was formulated in the finite element (FE) program ANSYS, employing an orthotropic approach based on linear elastic initial deformation. The Hill Yield Criterion was utilized to model the transition to the plastic region, characterized by a nonlinear strain hardening curve. The print direction was integrated into the FE simulation mesh via a local material coordinate system. Surface treatment via glass bead blasting resulted in slight increases in mechanical response, while tempering had a minor influence. Significant anisotropy was observed, with only the z-position in the build chamber affecting mechanical properties. Successful mapping of anisotropy in structural simulations was achieved. This research did not address optimization of the printing process, recyclate effects, powder aging, or fatigue. The findings provide a comprehensive analysis of the mechanical behavior of SLS-printed specimens, serving as a foundation for treatment methodologies and simulation strategy development. Full article

Residual stress (RS) in laser powder bed fusion (LPBF) additive manufactured structures can significantly affect mechanical performance, potentially leading to premature failure. The complex distribution of residual stresses, combined with the limitations of full-field measurement techniques, presents a substantial challenge in conducting damage tolerance analyses of aircraft structures. To address these challenges, this study developed a comprehensive simulation framework to analyze the 3D distribution of residual stresses and fatigue crack growth in LPBF parts. The 3D residual stress profiles of as-built samples in 15° and 75° build directions were computed and compared to experimental data. The fatigue crack propagation behavior of the 75° sample, considering 3D residual stress, was predicted, and the effects of residual stress redistribution under cyclic loading were discussed. It shows that the anisotropy of residual stress, influenced by the build direction, can lead to mixed-mode fracture and subsequent crack deflection. Tensile residual stress in the near-surface region and compressive stress in the inner region can cause an inverted elliptical crack front and accelerate fatigue crack growth. Full article

Al-Mg alloy wire modified by Sc and Zr additions was used to prepare a high-strength, non-heat-treated Al-Mg alloy component by wire arc additive manufacturing (WAAM) technology in the present work, and the microstructure, mechanical properties, fatigue resistance, as well as their anisotropies of the deposited Al-Mg-Sc-Zr alloy component were studied. The results show that the microstructure of the as-deposited alloy is composed of fine equiaxed grains with an average grain size of around 8 μm, and nanosized Al₃(Sc, Zr) particles (~5 nm) are also evident. The tensile properties and fatigue resistance of the deposited alloy showed significant anisotropy, and the performance of the traveling direction is always better than that of the deposition direction. The ultimate strength, yield strength, elongation, and critical fatigue life (cycles) of the as-deposited alloy along the traveling direction (0° direction) are 362 ± 7 MPa, 244 ± 3 MPa and 24.8 ± 0.3%, and 1.72 × 10⁵, respectively. The presence of weak bonding areas and high tensile (positive) residual stress between the deposition layers deteriorate the tensile properties and critical fatigue life of the sample along the deposition direction. Full article

Single crystal nickel-based superalloys are extensively used in turbine blade applications due to their superior creep resistance compared to their polycrystalline counterparts. With the high creep resistance, high cycle fatigue (HCF) and low cycle fatigue (LCF) become primary failure mechanisms for such applications. This study investigates the fatigue life prediction of CMSX-4 using a combination of crystal plasticity and lifetime assessment models. The constitutive crystal plasticity model simulates the anisotropic, rate-dependent deformation behavior of CMSX-4, while the modified Chaboche damage model is used for lifetime assessment, focusing on cleavage stresses on active slip planes to include anisotropy. Both qualitative and quantitative data obtained from HCF experiments on single crystal superalloys with notched geometry were used for validation of the model. Furthermore, artificial neural networks (ANNs) were employed to enhance the accuracy of lifetime predictions across varying temperatures by analyzing the fatigue curves obtained from the damage model. The integration of crystal plasticity, damage mechanics, and ANNs resulted in an accurate prediction of fatigue life and crack initiation points under complex loading conditions of single crystals superalloys. Full article

The paper presents the original results of cyclic testing of materials that are identical in chemical composition but produced by two different technologies: conventional metallurgy and additive manufacturing. For the aluminium alloy AlSi10Mg and the austenitic steel 316L, tensile curves, tension–compression and torsion alternating fatigue curves are experimentally obtained and presented. The experimental results are compared for two fabrication technologies—conventional metallurgy and additive DLMS technology. The results indicate a significant effect of anisotropy on the fatigue performance of the AM materials and a different slope of the fatigue life curves in the cyclic torsion versus cyclic tension–compression. The static and, in particular, the fatigue properties of both materials are discussed in relation to the microstructure of the materials after conventional production and after additive manufacturing. This comparison allowed us to explain both the causes of the anisotropy of the AM materials and the different slope of the curves for normal and shear stresses under cyclic loading. Using the example of the strength assessment of bicycle frames, the possibility of progressively wider use of additive manufacturing for load-bearing structures is presented. Full article

Fatigue crack growth behavior of additively manufactured Ti metal matrix composite with TiB particles at room temperature was studied using a compact tension specimen and at the stress ratio of 0.1 (R = 0.1). The composite studied in this work was manufactured with a unique additive technique called plasma transferred arc solid free-form fabrication, which was designed to manufacture low-cost near-net-shaped components for aerospace and automotive industries. The fatigue crack growth rate experiments were carried perpendicular and parallel to the additive material build, aiming to find any fatigue anisotropies at room temperature. The findings reveal that additively manufactured Ti-TiB composite shows isotropic fatigue properties with respect to fatigue crack growth. Furthermore, the fatigue crack growth mechanisms in this additive composite material were identified as void nucleation/coalescence and the bypassing of particles and matrix, depending on the interparticle distance. Full article