Fatigue & Fracture of Engineering Materials & Structures最新文献

The synergistic mechanism between crack network evolution and energy release in deep coal mine roof sandstone is a critical factor triggering rock burst disasters. This study combined acoustic emission (AE) monitoring with digital image correlation (DIC) technology to conduct uniaxial compression tests on double-flawed sandstone, systematically analyzing how rock bridge dip angle regulates crack propagation paths and damage evolution. A mechanical criterion for mixed-mode crack propagation was developed based on stress intensity factor theory, optimizing traditional crack classification standards. Results show that as rock bridge dip angle increases, crack penetration length shortens, energy dissipation channels decrease, and AE energy accumulation intensifies. Under low rock bridge angles, tensile stress drives crack initiation with predominantly mixed I/II propagation modes, whereas at high angles, cracks initiate via shear slip, dominated by mixed III modes. The regulatory mechanism of rock bridge dip angle on crack network configuration and energy release paths is revealed, providing a theoretical basis for achieving directional energy release in roof rock through active optimization of rock bridge angles.

The fatigue life of plain concrete under uniaxial stress reversal loading conditions has been scarcely addressed in the literature. Predicting the fatigue life of plain concrete under different stress reversal loading conditions provides valuable insight during the design phase of any major project. After combining the fatigue test results of 40 years of experimental data into one comprehensive database, a simple model is proposed in this study to estimate the shape and scale parameters of a two-parameter Weibull distribution that appropriately describes the fatigue life of concrete in uniaxial stress reversal. The model was developed considering 201 experimental data points and uses only the maximum stress level as an input, simplifying its application and use. The model's validity is checked against experimental data available in the literature. The comparison shows a good agreement between the results, showing a mean absolute percentage error below 12% for all stress levels. A methodology is also presented to modify the model based on the number of available experimental tests. This is particularly useful for cases where the safety level is paramount and a more conservative result is desired. The efficacy of the proposed adjustment is tested against experimental data not used for model development. The results indicate the method's capability to yield conservative fatigue life estimations with reasonable efficacy.

This study systematically investigates the anisotropic failure behavior of extruded Al-Cu-Li alloys under very high cycle fatigue (VHCF) conditions. Ultrasonic fatigue testing reveals that, after aging, specimens loaded along the extrusion direction (ED) exhibit significantly longer fatigue lifetimes than those along the transverse direction (TD) and normal direction (ND), with all orientations achieving VHCF performance. A detailed analysis of < 100 > and < 111 > fiber textures demonstrates their pronounced influence on fatigue crack initiation sites, propagation paths, and fracture modes. Finite element analysis and microstructural characterization are combined to establish a mechanism chain linking texture evolution, slip behavior, stress localization, and fatigue crack growth. The results show that the < 111 > texture promotes orientation-dependent slip constraint and stress accumulation at grain boundaries and unfavorably oriented slip systems, thereby governing the formation of anisotropic fatigue failure modes. These findings provide key mechanistic insight into the fatigue failure behavior of Al-Cu-Li alloys and lay a theoretical foundation for their reliable structural application.

This study investigates the influence of hybrid-treated coconut fiber (HTCF) content on the mechanical and fracture properties of high-strength concrete (HSC) with a target strength of 60 MPa. The fibers were treated by boiling for 1 h, followed by immersion in a 1% NaOH solution, enhancing their surface morphology and composition, as confirmed by SEM and XRD analyses. The dry density of HSC increased at 0.25% fiber content (FC) but decreased at higher levels. Pulse velocity peaked at 1% FC, surpassing the control mix by 2.27%. At 0.5% FC, compressive strength and elastic modulus increased by 5.22% and 2.85%, respectively, while tensile strength improved by 33.31% at 1% FC. At 0.75% FC, $�K_{\mathrm{IC}}$ and $�J_{\mathrm{IC}}$ increased by 5.12% and 12.40%. $�G_F$ and $�G_A$ peaked at 0.25% FC, improving by 42.19% and 73.62%. $�{\text{CTOD}}_{\mathrm{IC}}$ decreased with fiber addition. These results underscore the significance to optimize HTCF content for enhanced HSC performance.

The underground coal gasification (UCG) method might convert potentially abandoned sources of coal to utilizable mines. In this study, the effect of stress and configuration of two pre-existing cleats in a brittle coal on the mechanism of secondary crack propagation and cavity growth rate has been investigated using the linear parallel bond model (LPBM). The numerical modeling results showed that the best situation for the coalescence phenomenon is at the cleat's tip to tip angle of 20°, the bridge angle and the step angle equal to 15° and 90°, respectively. Also, the rock bridge lengths had no effect on the geomechanics parameters. If cleats' spacing was almost equal to half of the initial crack length, the highest wing crack length would be achieved. On the other hand, samples fragmentations and number of cracks increase as the confining pressure increases; this is the more appropriate condition for the cavity growth rate.

Uniaxial fatigue testing at room temperature was employed to investigate the fatigue characteristics of 7075 high-strength aluminum alloy under very high cycle fatigue (VHCF) conditions across different processing states. Specimens subjected to surface mechanical rolling treatment (SMRT) exhibited smooth and continuous S-N curves, demonstrating three distinct failure modes depending on applied stress amplitudes: surface-induced failure (S-mode), internal crack initiation without fine granular area (FGA) formation (I-mode), and internal failure accompanied by FGA (IFGA-mode). In contrast, welded SMRT specimens and untreated 7075-T651 alloy counterparts displayed only two failure modes (S-mode and IFGA-mode). Notably, fatigue lives in IFGA-mode failure showed processing-independent characteristics across different material conditions. The stress intensity factor range (ΔK) was systematically applied to elucidate the mechanisms underlying these failure mode transitions and the characteristic trends observed in S-N curves.

The notched semi-circular bend (NSCB) specimen incorporating the split Hopkinson pressure bar (SHPB) is the only suggested dynamic mode I fracture testing method of rocks by the International Society for Rock Mechanics and Rock Engineering (ISRM). Constrained by current experimental techniques, the instantaneous fracture propagation details have yet to be fully elucidated. In this work, we re-evaluate the dynamic transient propagation fracture properties of the NSCB specimen by discrete element method (DEM). Numerical results show that the complete crack propagating process can be well described by the logistic model. The moment tensor (MT) analysis results indicate that the tensile fracture mechanism dominates the whole fracture process. Detailed energy analysis shows that previous averaged propagation fracture toughness may be overestimated. The fracture propagation toughness is affected by both loading rate and crack velocity. These new insights provide significant implications for disaster prevention in rock engineering.

The low cycle fatigue (LCF) life for the GH4169 inertia friction welding joints is predicted through deep learning approaches. Experiments are conducted to obtain three types of LCF datasets for convolutional neural network (CNN) establishment, including deformation images, average strain, and combined average strain and damage fraction. The role of dataset types and sizes on the CNN accuracy in LCF life prediction is discussed, utilizing 1222–2397 deformation images and 1175–2585 numerical values (including average strain and damage fractions). Results show the dataset of strain and damage fraction brings higher $�R^2$, especially under a larger dataset (0.9560). This data-physics integrated approach innovatively utilizes peak strain features as the CNN model input, and it demonstrates that higher accuracy of LCF life prediction for nickel-based materials can be achieved after introducing a physics model. The method is promising for non-destructive supervision of in-service equipment and structures.