Fatigue & Fracture of Engineering Materials & Structures最新文献

Laser powder bed fusion (LPBF)–printed Co-Cr-Mo alloy is widely used in biomedical implants and aerospace parts. In LPBF, scanning speed is crucial for melt pool formation and defect prevention, which in turn affects the fatigue behavior of the material. The present study investigates the influence of scanning speeds (600, 750, and 900 mm/s) on the fatigue properties of LPBF Co-Cr-Mo alloy. High-cycle fatigue (HCF) tests were performed to determine the maximum stress at which run-out occurred for each scanning speed. The failure mechanisms in fatigue specimens were explored through field emission scanning electron microscopy. Furthermore, microstructural analysis of fatigue fracture specimens was carried out using transmission electron microscopy. This study demonstrates that scanning speed influences the tensile and HCF performance of LPBF Co-Cr-Mo alloy. The findings of this study will aid in selecting LPBF scanning speeds for Co-Cr-Mo alloy to minimize defects and achieve the desired fatigue properties for medical and aerospace applications.

This paper introduces the influence of the depth, shape, and size of inclusions on crack initiation in RE (La, Ce) rail. A very novel auxiliary strain measuring fixture and an interesting precrack innovative method are used to study the crack and strain at the sharp corner of inclusions. With the increase of RE content (wt%) from 0.030% to 0.130%, the density and size of inclusions first decrease and then increase. The shape of inclusions tends to spheroidize first and then sharpen. Cracks initiate at the sharp corners of long, triangular, irregular, and shallow, large (> 20 μm) inclusions. Precrack deeper than the wear layer will promote the formation of a spiral plastic flow zone at the crack tip and the merger of multiple cracks. These findings provide new insights into the relationship between microstructural features and cyclic loading that could lead to different mechanisms of noninclusion-induced crack initiation.

Segmental bridges, consisting of interconnected segments linked by prestressed tendons, are vital for modern infrastructure but face significant durability challenges due to fatigue from cyclic loading, environmental conditions, and material degradation. Although design and construction have advanced, current standards lack comprehensive methods to assess fatigue under these complex conditions, leading to potential performance and safety concerns. A 3% traffic growth can cut fatigue life from 80 to 44 years, cracking may shorten it by 68 years, and corrosion can reduce reliability from 100 to 44 years, underscoring the need for durability-focused design. This review synthesizes research on fatigue mechanisms, design guidelines, and material innovations in segmental bridges. The paper highlights key findings, such as improvement in fatigue resistance through high-performance concrete and posttensioning techniques, but also identifies gaps in current fatigue life assessment methods. The study emphasizes the need for real-time monitoring systems, advanced predictive models, and innovative retrofitting strategies to enhance long-term bridge resilience. Future research should refine fatigue assessment techniques, integrate real-time data for maintenance, and explore sustainable materials and retrofit solutions to ensure the safety and durability of segmental bridges under increasing traffic and environmental stresses.

The 316L/Q420qENH composite bridge steel, designed for the challenging Qinghai-Tibet Plateau environment, exhibits excellent mechanical properties and superior weathering resistance. However, its fatigue performance in structural engineering remains poorly understood. This work comparatively investigates the fatigue behaviors and life of a novel 316L/Q420qENH composite under high-cycle fatigue (HCF) conditions at a load ratio of R = −1. The findings indicate that the HCF failure of the composite is predominantly due to non-inclusion-induced crack initiation (NIICI) on the softer Q420qENH side. At the microstructural level, slip in the ferritic {110} < 111 > system results in a dense network of low-angle grain boundaries (LAGBs), increasing the kernel average misorientation (KAM) and promoting intergranular fatigue crack initiation. Fatigue limits for smooth and notched specimens are 426 and 291 MPa, respectively, with notches significantly reducing fatigue resistance. The experimental data support a proposed crack initiation mechanism for the 316L/Q420qENH composite under HCF loading.

The objective of this study is to analyze the dynamic propagation of Mode I collinear cracks in a prestressed monoclinic crystalline strip subjected to punch loading. The study focuses on the combined effect of horizontal and vertical prestress on fracture parameters in anisotropic materials. Within the framework of linear elastic fracture mechanics, the moving boundary value problem is formulated using the Galilean transformation and reduced to coupled Cauchy-type singular integral equations, solved analytically through the Hilbert transform. Explicit expressions for crack opening displacement and stress intensity factors are derived. Results show that prestress strongly modifies fracture behavior, with anisotropy, crack velocity, and loading type (localized versus uniform) significantly influencing the response. Localized loading produces stronger effects in anisotropic crystals compared to isotropic ones. The novelty of this work lies in its analytical treatment of dynamic fracture in prestressed anisotropic crystals, offering insights for the design and reliability of micro-electro-mechanical systems (MEMS), acoustic devices, and biosensors.

This study investigates a specific powertrain rubber suspension bushing using an N60 rubber material to develop dumbbell-shaped specimens. Uniaxial tensile fatigue tests were conducted at 23°C, 60°C, and 90°C. Fatigue life prediction models were developed using four damage parameters: peak Green–Lagrange strain $�{\epsilon }_G$; peak Almansi–Euler strain $�{\epsilon }_A$, peak engineering strain $�{\epsilon }_E$, and peak logarithmic strain $�{\epsilon }_l$. The model based on the Green–Lagrange strain showed the highest fitting accuracy. The study also investigated the impact of elevated temperature on rubber fatigue behavior, including a high-temperature fatigue test on the bushing. A simulation using ABAQUS replicated actual operating conditions, and results were combined with the fatigue life prediction model. The predicted fatigue life, with the Green–Lagrange strain as the damage parameter, deviated from the experimental value by only 11.92%, demonstrating the model's effectiveness for evaluating durability under high temperature and reducing testing cost and time.

This study investigates the impact of surface machining quality on the fatigue life of ductile cast iron, with particular emphasis on the inner bore wall quality, which is critical for enhancing the service life of diesel engines. A ring-shaped specimen, matching diesel engine cylinder dimensions, was machined at boring spindle speeds of 90 to 150 r/min. The results demonstrate that the average fatigue life of the specimen increased by 1.3 to 7.1 times at high spindle speeds, owing to the enhanced surface hardness, refined grain structure, and decreased surface tensile residual stress. Additionally, the analysis indicates that increased spindle speeds lead to a thicker hardened surface layer, delaying crack propagation. Fatigue life predictions using Paris' law aligned closely within a threefold error band. This research enhances our understanding of the relationship between surface machining quality and fatigue life in ductile cast iron.

Carbon fiber reinforced composites (CFRCs) are widely used in engineering due to their excellent mechanical properties; however, the transverse tensile mechanical behavior and fiber-matrix interfacial failure mechanisms of CFRCs remain insufficiently investigated. To address this gap, this study employed combined in situ microcomputed tomography (μCT) and digital volume correlation (DVC) characterization on CFRC specimens under transverse tensile loading. Incremental load-dependent in situ μCT datasets were processed to reconstruct three-dimensional (3D) models of specimens, quantify internal pore distribution, analyze porosity evolution, and characterize crack initiation and fracture morphology. Concurrently, DVC was applied to resolve the 3D full-field strain distribution within the loaded specimens. Key results show that CFRCs exhibit an initial porosity of 1.4%, which increases by 3.69 times to 5.16% prior to fracture—indicating rapid internal damage accumulation. More importantly, DVC successfully identified localized strain concentration zones, enabling precise prediction of the ultimate fracture locations. This study innovatively establishes a link between the microscale pore evolution and macroscale fracture behavior of CFRCs under transverse tension through the integration of μCT and DVC. The combined characterization approach not only clarifies the transverse failure mechanism of CFRCs but also provides a reliable technical basis for the structural optimization and performance improvement of CFRC-based components.

This study investigates the fatigue crack behavior of H13 Cr-Mo steel under both untreated and ultrasonic nanocrystal surface modification. Three distinct crack propagation mechanisms were identified: (1) Surface Inclusions: When inclusions were present on the surface, fatigue cracks initiated and propagated as single dominant cracks, resembling those observed in artificial pit specimens. (2) Absence of Surface Inclusions: In the absence of inclusions, fatigue life was governed by the initiation, growth, and coalescence of multiple small fatigue cracks (MSFCs). These cracks exhibited depth-wise propagation, influenced by the formation of large elliptical crack tips where stress concentration occurred, accelerating internal crack growth. (3) Fracture Characteristics: The final fracture behavior of both surface and internal cracks was found to be similar, characterized by rapid crack growth near the end of fatigue life. Notably, fisheye cracks accounted for approximately 93%–95% of the total fatigue life, a result consistent with previous findings and validated through comparative analysis.