Fatigue & Fracture of Engineering Materials & Structures最新文献

This article highlights the importance of “opening strain,” which quantifies the amount and direction of net cyclic plastic deformation, in describing the ratcheting behavior of materials. Ratcheting experiments were conducted on P91 steel at 823 K with varying stress amplitude (290–380 MPa) and mean stress (0–120 MPa). Analysis revealed that ratcheting occurs due to unequal cyclic tensile and compressive plastic strains, leading to non-closure of hysteresis loops, quantified as “opening strain.” The ratcheting behavior of P91 steel exhibited an initial quasi-stable phase followed by an acceleration phase before failure. Transmission electron microscopic investigation of interrupted test specimens highlighted that dislocation tangles, forests, and networks were associated with minimal strain accumulation in the stable phase. Further investigation of the failed specimens confirmed that the formation of incipient dislocation cells and recrystallized subgrains provided strain-free paths for dislocation motion and significant strain accumulation in the acceleration phase.

This study investigates the effect of thermal cycling and loading modes on the fracture behavior of dolomite, a strong magnesium-rich rock. Forty-eight dolomite specimens (semicircular bend [SCB] and intact Brazilian disks) were subjected to 0, 50, 100, and 500 heating–cooling cycles between 20°C and 60°C and then tested under Pure Mode I, Mixed Mode I/II, and pure Mode II loading conditions. Results indicated that thermal cycling enhanced dolomite's strength properties—fracture toughness, fracture speed, and acceleration—up to ~300–400 cycles, after which these properties deteriorated. These changes correlated with variations in sound wave velocity and porosity, suggesting microstructural alterations. Intact Brazilian disks showed tensile strength and fracture toughness comparable to SCB specimens under Pure Mode I but demonstrated a higher tensile modulus across all loading conditions. A direct correlation was observed among fracture load, absorbed energy, fracture velocity, and fracture toughness, with faster fracture associated with higher toughness.

The paper introduces a new modification to Walker's mean stress correction model in terms of torsional loading conditions. In order to derive the new modified version the authors have performed a wide literature research as well as their own experimental fatigue tests. The paper presents the results of fatigue test of own experimental research for inter alia AA5754-H24 and AA2007-T3 aluminum alloys for full cross section and hollow specimens under pure shear torsional state and other materials. The obtained fatigue results have been used in order to calculate the equivalent stresses and compared with other popular mean stress correction models. The model proposed by the authors does not require knowledge of many material constants, but is related to the loading parameters used to estimate fatigue life. The comparison between the computation models has shown that the authors' model has the smallest scatter band which proves its high stability in terms of fatigue life estimation.

Nuclear-grade pipelines are essential for nuclear safety, and their failure can lead to severe accidents. Traditional deterministic methods tend to be overly conservative, overlook uncertainties in key factors, and struggle to accurately assess reliability under complex conditions. This paper aims to present a probabilistic fracture mechanics methodology to evaluate the reliability of circumferential cracks in primary piping welds under transient loads. A dedicated software tool, developed based on this method, calculates rupture and leakage probabilities by incorporating parameter uncertainties alongside deterministic fracture models. Furthermore, the influence of various in-service inspection schedules on weld reliability is examined through case studies. The results indicate that excessively long inspection intervals result in actual failure probabilities at 60 years that exceed the safety goal of 10⁻⁶ failures per year. In accordance with current ASME Code, Section XI, the first inspection should occur by the 10th year, while subsequent intervals may be optimized to every 20 years. Sensitivity analyses reveal that the initial crack depth and crack half-angle have the greatest impact on probabilities, followed by the tensile strength, the safety factor, the yield strength, and the probability of detection model.

In situ small fatigue crack growth experiments at 500°C, combined with pretest and posttest electron backscatter diffraction analysis, were conducted to investigate the growth behavior of FGH96. High-temperature fatigue loading reduced the average texture intensity and induced a pronounced {111} plane normal alignment along the loading direction, forming a localized strong texture. Significant local lattice rotations and geometrically necessary dislocation accumulation occurred in the crack region, both decreasing with distance. Crack growth was predominantly transgranular and strongly influenced by crystallographic orientation. Intragranular crack path deflection occurred with similar frequencies toward slip systems of higher and lower Schmid factors. The experimental results demonstrated that under certain conditions, high-angle grain boundaries substantially impeded transgranular crack propagation. Three types of crack growth resumption behaviors induced by grain boundaries were identified. Overall, crystallographic orientation and grain boundaries jointly govern the small crack growth. These findings enable high-precision life prediction of small fatigue cracks.

This study investigates the mixed-mode fracture behavior of asphalt concrete using Single-Edge Notched Beam (SENB) specimens subjected to various combinations of tensile and shear stresses. Five stress conditions were achieved by adjusting the support positions and fracture tests were conducted to obtain load line displacement (LLD) curves and key fracture parameters. Three representative loading conditions were further simulated using the cohesive zone model (CZM) in ABAQUS to examine damage evolution and crack propagation. The experimental results indicate that as the loading condition transitions from pure tension (Mode I) to mixed tension-shear and then to pure shear (Mode II), the fracture behavior changes from ductile to brittle, accompanied by increases in fracture energy, peak load, and displacement at peak load, while the mixed-mode fracture toughness initially decreases and subsequently increases. The simulations confirm that the CZM can accurately model mixed-mode (I–II) fracture and capture the evolution of tensile and shear stress distributions during loading.