查看更多>>摘要：The complex geometrical configuration of shaped film cooling holes (FCHs) enhances the cooling efficiency of turbine blades, while the stress concentration at the shaped FCH edge and the manufacturing defects usually leads to high-cycle fatigue (HCF) failure under the service conditions. In this study, HCF tests at 900℃ were conducted on DD6 single-crystal superalloy containing dustpan and dovetail FCHs. The effect of shaped FCHs and manufacturing defects on the HCF strength was investigated, and the related HCF failure mechanism was analyzed using SEM, EDS, and EBSD. The results show that manufacturing defects including pores, recast layer, and polycrystalline microstructure region exist around the shaped FCH edge. The stress concentration of defective pores promotes the plastic deformation and oxidation at high temperatures, leading to crack initiation. The oxide layer thickness in the high stress area of the dovetail FCH specimen is 3.44μm thicker than that of the dustpan specimen, and correspondingly the fatigue strength of the dovetail FCH specimen is 13.96MPa lower than that of the dustpan specimen (304.93 MPa vs. 318.89 MPa). The fatigue strength of these two kinds of FCH specimens is lower than that of the traditional cylindrical FCHs due to the existence of the manufacturing defects, indicating the necessity to consider the effect of manufacturing defects in the evaluation of the HCF strength of components with the shaped FCHs.
查看更多>>摘要：Materials with a negative Poisson's ratio have gained attention for their unique mechanical properties, enabling applications in aerospace, construction, and medicine. However, the complex geometry of such structures poses challenges for traditional manufacturing. 3D printing offers a solution, allowing precise fabrication of these intricate designs. This study uses 3D printing to create three types of structures from PLA: concave hexagonal, four-directional chiral, and biomimetic feather structures. Tensile testing revealed that the concave hexagonal structure outperformed the others in mechanical strength. Finite element simulations confirmed its superior load-bearing capacity during fracture. Additionally, fractal analysis showed the concave hexagonal structure had the highest fractal dimension in crack propagation, further validating its mechanical superiority. These findings highlight the concave hexagonal structure's advantages through experimental, numerical, and fractal analyses.
查看更多>>摘要：This study investigates the effect mechanism of water jet peening (WJP) on the surface integrity and fatigue performance of CoCrFeNiAl/Al6061 laminate composites. Through experiments and finite element simulations, the following results were obtained: At a jet velocity of 300mm/s, significant plastic deformation was observed in the core layer, and the maximum residual compressive stress increased from 679 MPa at 250 mm/s to 802 MPa, indicating that higher jet velocity promotes the development of residual stress. Core layer thickness plays a crucial role in fatigue life; specimens with a 1-mm-thick core layer exhibited lower fatigue life, while a 2-mm-thick core layer showed significant improvement. The jet velocity of 300 mm/s was the most effective in enhancing fatigue life.
查看更多>>摘要：Threaded fasteners are prone to fatigue fracture under axial alternative load conditions. Recent studies demonstrated that the pitch difference between bolt and nut can significantly impact the fatigue life. Currently most standards specify equal nominal pitch for bolt and nut that can be one of the reasons of their low fatigue resistance. Choosing optimal pitch difference value can enhance fasteners durability. However, the exact relationship between the pitch difference and the fatigue life remains unclear. This study analytically demonstrates that the relationship between stress concentration level under static load and the pitch difference follows inverse normal distribution. Then, based on the experiments under alternative load, we divided fatigue life into two stages: the initial fatigue life and the residual fatigue life. The results show that the stress concentration level and initial fatigue life exhibit a geometrically inverse relationship, i.e., when the stress concentration is minimized, initial fatigue life is maximized. Finally, we propose a novel mathematical model based on the pitch difference-stress concentration level-fatigue life relationship. The model offers a practical solution for improving fatigue resistance in engineering applications without incurring any additional cost.
查看更多>>摘要：This paper presents an integration of the hierarchical quadrature element method (HQEM), characterized by p-convergence, with the virtual crack closure method (VCCM) for evaluating stress resultant intensity factors of through-cracked plates. A HQEM formulation, free from shear locking and applicable to both thin and moderately thick plates, is developed based on the Mindlin-Reissner plate theory. Building upon the conventional framework of VCCM, a universal formula for calculating fracture parameters is derived for the proposed element formulation with an arbitrary number of boundary nodes. Both the calculation formula and its corresponding numerical implementation are simple and straightforward. Several representative numerical examples demonstrate the accuracy and effectiveness of combining HQEM and VCCM for fracture parameter calculation in through-cracked plates. Furthermore, the results indicate that a relatively coarse mesh is sufficient to obtain highly accurate moment and shear force intensity factors for cracked plates, whether thin or thick, thereby greatly simplifying the preprocessing procedure.
Mattia MeleDario CroccoloMassimiliano De AgostinisStefano Fini...
2883-2893页
查看更多>>摘要：The effect of part build orientation on the fatigue properties of additively manufactured parts has been demonstrated to be highly influenced by the type or composition of the raw material. In this study, an experimental campaign was carried out to investigate this effect in the case of CX maraging steel processed by laser powder bed fusion. For this purpose, specimens were manufactured with vertical, horizontal, and 45° inclined orientations. First, the dimensional accuracy, surface finishing, density, and hardness of specimens were characterized to determine the role of part build orientation. Then, the specimens were tested to determine the fatigue curve and limit. Finally, the fracture region was observed via scanning electron microscope. The results reveal that the effect of build orientation on the fatigue strength in the finite life domain is not statistically significant. Conversely, the build orientation affects the achievable surface finishing of parts after machining and, consequently, the fatigue limit of the material. The highest fatigue resistance is observed in specimens inclined at 45°, while vertical specimens showed the lowest limit.
查看更多>>摘要：The cohesive failure between the asphalt pavement and the rail wrapping material around the tram track is the one diseases of the new embedded tram track structure. A time-dependent viscoelastic cohesive zone model (CZM) was employed to characterize interface behavior between asphalt pavement and rail wrapping materials. By integrating Maxwell rheological elements into a bilinear CZM framework, the model captures time-dependent traction-separation behavior. Key features include distinct stiffness evolution during elastic deformation and relaxation-driven traction variations under different loading rates (10-300 mm/min). An Elman neural network surrogate model was developed to inversely identify five critical interface parameters from experimental load-displacement curves, achieving high accuracy (RMSE: 0.0143-0.2384, R~2>0.9). Validation via interface pull-off test demonstrated strong agreement between simulated and experimental results, confirming the model's efficacy in predicting viscoelastic interface degradation. This framework provides a robust tool for analyzing time-sensitive cohesive failures in urban rail infrastructure.
Kazuki MatsudaEmanuel dos SantosPaulo Costa AssuncaoHamid Jahed...
2908-2918页
查看更多>>摘要：The fatigue strength of wire arc additive manufactured (WAAM) nano-particle enhanced AA 7075 material was investigated. The material could be deposited without solidification cracks to form a slender wall; however, the fatigue strength was lower than AA 7075 produced by either additive cold spray deposition or rolling. Most of the fatigue cracks initiated from the surface or near-surface porosity. The microstructure of the additive manufactured AA 7075 consisted of fine and equiaxed grains, with an average grain size of 10.4μm. SEM observation revealed agglomerated TiC clusters with sizes > 1 μrn located along the grain boundaries. A method for estimating the equivalent defect-free S-N curve was proposed by using a √area parameter. It is suggested that the defect-free WAAM material would be comparable to that of solutionized cold spray deposited AA 7075.
查看更多>>摘要：Semi-flexible pavement material (SFPM) is an asphalt paving composite that incorporates cement-based grout injected into the large voids of asphalt concrete. The damage to the interface under fatigue conditions is a primary concern for SFPM, primarily due to the weak interfacial bonding between cement and asphalt. Therefore, it is essential to understand the damage mechanisms of the cement-asphalt interface under fatigue conditions. The fatigue characteristics of SFPM are investigated using semicircular bending tests. Subsequently, microscopic damage mechanisms are examined through scanning electron microscopy, energy dispersive spectroscopy, and nanoindentation tests. The effects of asphalt binder and interfacial modifiers on interface damage are also analyzed. Results indicate that high-viscosity asphalt exhibits the optimal interfacial thickness, strong adhesion, a minimal number of interfacial micropores, high interfacial strength, and superior fatigue resistance. Additionally, the incorporation of emulsified asphalt promotes the continuous precipitation of hydration products within the asphalt phase, thereby enhancing fatigue resistance.
查看更多>>摘要：Fretting phenomenon contributes significantly to the failure of steel wire ropes. The fretting occurs in two modes: partial slipping and gross sliding at the trellis point of contact where the material experiences high contact pressure and relative slipping of wires. A new damage model has been developed incorporating the fatigue-induced residual modulus of elasticity as the fretting parameter. This newly developed model has been applied to the simplified two-wire model previously. This paper presents the application of the novel damage model on the steel wire rope strand. The damage model is coded in the UMAT subroutine, and FEA has been carried out in Abaqus Software. The wire rope strand experiences the gross sliding condition using a coefficient of friction = 0.2 and 0.8. The damage response and residual modulus on the trellis point of contact have been extensively evaluated and found to follow Ruiz's fretting parameter, thus conforming the fretting condition with gross sliding.
NETL
NSTL
Wiley