Search Results (1,786)

Acoustic emission (AE) technology was used to monitor the fatigue crack growth process of superalloy. The analysis results show that both the cumulative values and the K-entropy values of AE parameters have good correspondences with the three stages described by fracture mechanics, which makes it possible to characterize the process of fatigue crack growth. Since K-entropy is more sensitive to changes in fatigue state, the turning points between the second stage and the third stage are earlier than those defined by fracture mechanics, indicating that it has an early warning capability. The K-entropy of AE parameter was first proposed to represent the growth rate of fatigue crack. This method not only effectively decreased the large dispersion of change rate of AE parameters but also ensured the similarity with the fatigue crack growth rate, thereby optimizing the characterization of fatigue crack growth. Full article

The fatigue performance of titanium alloys is a critical determinant of the service life and structural integrity for aerospace and marine engineering components. But within the framework of damage tolerance design, resistance to fatigue crack propagation is regarded as a key indicator governing the fatigue performance of these engineering structures. In previous work, while the general fatigue performance of Ti–6Al–4V-0.55Fe alloy has received systematic study, targeted research focusing on its resistance to fatigue crack propagation remains limited. Therefore, in this work, compared with Ti–6Al–4V ELI alloy, the fatigue crack propagation behavior and fracture mechanism of Ti–6Al–4V-0.55Fe alloy with a duplex microstructure were systematically investigated. The results show that when ∆K < 12.75 MPa⋅m^1/2, Ti-6Al-4V-0.55Fe alloy demonstrates superior resistance to fatigue crack propagation. Fractographic analysis indicates that the primary difference between the two alloys lies in the stage of crack initiation and early propagation. This behavior is attributed to the addition of trace Fe, which enhances α/β boundary resistance and thereby retards crack growth. Moreover, crack propagation of TC4-F alloy is also slowed by the increased path length from bypassing the α_p phase. Full article

To investigate the effect of scribing wheel angle on the scribing behavior of LCD glass, an SPH-based numerical model was established in LS-DYNA and validated against experimental results for reaction force and median crack depth. The results show that the model can accurately capture the mechanical response and crack propagation during the scribing process. At a scribing depth of 10 μm, the maximum relative errors between simulation and experiment were 5.17% for reaction force and 2.36% for median crack depth. The results for the 110° scribing wheel indicate that median cracks mainly initiate and propagate rapidly during the penetration stage, while the median crack depth becomes nearly stable after the preset depth is reached, and the subsequent rolling stage has little influence on further crack growth. As the wheel angle increases from 90° to 140°, the experimental mean peak reaction force increases from 2.66 N to 9.97 N, the maximum effective stress increases from 374.4 MPa to 732.8 MPa, and the median crack depth increases from 68 μm to 97 μm. Experimental observations further show that small wheel angles tend to cause debris accumulation and edge chipping, whereas excessively large wheel angles are likely to induce lateral cracks. Overall, a wheel angle of about 110° provides better cross-sectional quality, surface quality, and crack controllability for 0.2 mm-thick LCD glass. Full article

Composite laminates experience static and fatigue delamination, presenting significant challenges for failure prediction. This is critical in curved composites, where delamination behavior is complex to predict. In this study, fatigue tests were conducted on curved composite laminates under non-constant mixed-mode conditions. The testing setup involved a four-point bending test using L-shaped, unidirectional carbon-fiber-reinforced polymer curved beam specimens. A Teflon insert placed at the bend was used to initiate delamination. Experimental data acquisition included digital image correlation (DIC) to monitor delamination length during testing. This is important since it enhances subsequent model correlation. A virtual crack closure technique (VCCT)-based method for simulating fatigue-driven delamination under variable mixed-mode conditions was validated against experiments. Delamination growth was modeled using a Paris-like power–law relationship based on the strain energy release rate. The approach was implemented in Abaqus as a user subroutine, incorporating load ratio and mode mixity effects through VCCT-based mode separation. This study demonstrates accurate fatigue delamination prediction and highlights the role of optical measurements in experiments. The model improves our understanding of delamination propagation under varying mode mixity and contributes to structural integrity analysis. The results show how mode mixity influences delamination, impacting the performance and lifecycle of composite structures. Full article

In this study, La-doped TiO₂-SiO₂ composite films were deposited on glass substrates by radio-frequency magnetron sputtering. The evolution of microstructure and macroscopic properties was systematically investigated across an annealing temperature range of 350–650 °C. The results show that the La-doped TiO₂-SiO₂ composite structure effectively suppresses abnormal grain growth and delays the anatase-to-rutile phase transition, thereby improving the films’ high-temperature structural stability. Notably, the composite film annealed at 550 °C (LS-550) exhibits the highest anatase crystallinity and forms a dense, smooth (RMS = 1.37 nm), crack-free nanocrystalline network. In terms of wettability, the improved hydrophilicity is attributed to the combined effects of La incorporation and hydrophilic silanol (Si-OH) groups in the amorphous SiO₂ phase. As a result, the water contact angle of the LS-550 film decreases dramatically to 28.0°, indicating excellent hydrophilicity. Moreover, the LS-550 film demonstrates an optimal photocatalytic degradation efficiency of approximately 76% for methylene blue, significantly outperforming the pure TiO₂ film. Furthermore, the enhanced mechanical performance is associated with the combined effects of the SiO₂-containing amorphous phase and the finer microstructure induced by La incorporation. Consequently, the critical load (Lc) of the LS-550 film reaches 75.64 mN, significantly exceeding that of the pure TiO₂ film annealed at the same temperature (61.25 mN). In summary, the composite film annealed at 550 °C concurrently achieves high crystallographic thermal stability, robust interfacial mechanical durability, excellent surface hydrophilicity, and enhanced photocatalytic activity, thereby offering practical guidance for developing TiO₂-based coatings with self-cleaning potential for high-rise building curtain walls. Full article

To investigate the shear performance of steel fiber-reinforced high-strength concrete (SFRHSC) corbels subjected to concentrated loading, an experimental program was executed on six specimens featuring welded anchorage for the upper longitudinal reinforcement. The control variables included shear span-to-depth ratios of 0.2 to 0.5 and steel fiber volume fractions of 0%, 0.75%, and 1.50%. During the testing phase, strain evolution within the steel reinforcement and concrete matrix was monitored to analyze the structural deformation sequence and ultimate failure modes. Anchored in the Mohr–Coulomb failure criterion and the foundational strut-and-tie model (STM) framework, a softened strut-and-tie calculation approach for corbel shear capacity was formulated; this method explicitly accounts for the softening effect of the steel fiber-reinforced concrete (SFRC) and incorporates a size effect correction. The established shear capacity calculation model, alongside STM-based provisions from ACI 318-19, EN 1992-1-1, and CSA A23.3-19, was deployed to forecast the shear capacities of the six fabricated specimens and 18 additional units sourced from existing literature. Ultimately, a rigorous comparative analysis was conducted between the theoretical predictions generated by each method and the empirical test data. The results indicate that the failure process of the SFRHSC corbels primarily involves three distinct stages: initial cracking, through cracking, and ultimate failure. The addition of steel fibers can alleviate stress concentration at cracks and limit crack growth, thereby improving the tensile performance of the cracked concrete. Test results indicate that the strain in the longitudinal tensile reinforcement increased with the shear span-to-depth ratio but decreased as the steel fiber volume fraction increased. At the point of specimen failure, all longitudinal tensile reinforcement had reached the yield strength, while the horizontal stirrups only partially yielded. The concrete strain distribution across the normal section of the corbel did not follow the plane section assumption. Furthermore, incorporating steel fibers increased both the cracking load and the ultimate load of the corbel normal sections. The mean value of the experimental-to-predicted ratios obtained from the STM provisions of various international codes was 1.453, with a variance of 0.029, indicating conservative calculation results. In contrast, the mean value of the experimental-to-predicted ratios for the calculation model developed in this study was 1.048, with a variance of 0.004, demonstrating closer agreement with the experimental results and less dispersion. Simultaneously, by explicitly considering the softening effect in SFRHSC and the size effect, it provides a better prediction for the shear capacity of corbels. Full article

Given the depletion of conventional oil and gas resources, oil shale represents a promising alternative source of hydrocarbons that can be recovered through pyrolysis. This study examines the thermal decomposition of raw oil shale from the Tarfaya deposit and its decarbonized concentrate, studied by thermogravimetric analysis at different heating rates (5, 10, 20 and 40 °C/min). Pretreatment with acetic acid enabled the selective removal of calcite, confirmed by elemental, XRF, and XRD analyses, which revealed a relative enrichment in silica and dolomite in the oil shale concentrate. Pyrolysis of the raw shale occurs primarily between 300 and 500 °C, with a conversion rate of approximately 30%. In contrast, for the oil shale concentrate, the pyrolysis process begins at a relatively low temperature, within a wider temperature range (260–520 °C). Kinetic analysis based on Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods shows that at a conversion rate of 60%, the activation energy achieves 14.09 kJ/mol and 10.78 kJ/mol, respectively. The results indicate that the selective removal of calcite by acetic acid treatment facilitates kerogen pyrolysis by reducing mineral–organic interactions. Indeed, calcite dilutes the reactive organic fraction and can act as a physical barrier limiting heat and mass transfer within the oil shale. Its removal improves, on the one hand, the accessibility of kerogen to thermal cracking and promotes its decomposition, and on the other hand, reduces the amount of residue after pyrolysis. In addition, the kinetic analysis based on Criado master curves reveals changes in the reaction mechanism after decarbonation treatment depending on the heating rate (β). A shift from a two-dimensional Avrami–Erofeev model (A2) to a three-dimensional model (A3) was observed at a low heating rate (β = 5 °C/min), suggesting a change in nucleation and growth dynamics during kerogen decomposition. At high heating rates (10, 20 and 40 °C/min), the thermal decomposition of kerogen combines several reaction mechanisms depending on the temperature range considered. Full article

In high-cycle fatigue, the majority of fatigue life is spent in the crack initiation stage. However, current models fail to accurately capture the fatigue life consumed in the crack initiation stage, resulting in discrepancies in predictions. Here, we propose a fatigue life prediction model based on the crack tip plastic zone, combined with a multi-stage crack growth approach. To quantify the crack initiation life, a modified Tanaka–Mura model is developed by incorporating the effects of localized plastic deformation at the crack tip. The proposed model demonstrates good agreement with experimental observations. Furthermore, a reliability-based fatigue evaluation framework is established by introducing a fatigue safety factor formulation. The results show that the safety factor decreases with increasing applied stress levels, attributed to the reduced standard deviation and lower scatter of fatigue life at higher stresses. The findings provide a practical and physics-informed methodology for fatigue life and safety assessment of aluminum alloy components under complex cyclic loading conditions. Full article

Residual grit particles introduced during grit blasting are important process-induced defects that can significantly affect the interfacial damage evolution of thermal barrier coatings (TBCs) under thermal cycling; however, the coupled effects of thermally grown oxide (TGO) amplitude, grit size, and grit position on crack propagation in the bond coat (BC) remain insufficiently understood. In this work, a two-dimensional finite element model containing residual alumina grit particles was established to investigate the influence of these three factors on the radial stress distribution and crack growth behavior in the BC, and their individual contributions and interaction effects were further quantified using response surface methodology. The results showed that TGO morphology and interfacial grit defects jointly controlled the stress concentration and crack propagation behavior in the BC. Increasing the TGO amplitude intensified the radial tensile stress concentration in the BC and gradually shifted the critical stress region during thermal cycling. Larger grit particles further aggravated the local stress concentration near the grit tips, while the movement of grit particles toward the TGO peak led to a more pronounced increase in stress concentration and crack propagation tendency. The crack growth behavior was found to be consistent with the corresponding stress evolution characteristics. Response surface analysis further revealed that grit size and grit position had much stronger effects on crack propagation than TGO amplitude, and their interaction was the most significant among all factor combinations. The minimum crack length in the BC layer was obtained at a TGO amplitude of 0.01 mm, a grit size of 20 μm, and a position parameter of 0.752, and the predicted value agreed well with the finite element result. This study provides a comparative basis for interfacial damage assessment and grit-blasting parameter optimization in TBCs containing residual grit defects. Full article

This study evaluates fatigue crack growth in marine high-manganese steel LNG (Liquefied Natural Gas) storage tanks under cryogenic conditions. A 3D simulation framework using the M-integral for stress intensity extraction and the VCTD (Vertical Crack Tip Displacement) criterion for path prediction was developed. Parametric simulations showed that crack propagation is strongly directional, with the surface growth rate exceeding the depthwise rate. Fatigue life decreased with increasing initial crack surface length and maximum load but increased with crack inclination angle. In addition, the Mode I stress intensity factor along the depthwise path converged during propagation and rose sharply when the crack depth approached 90% of the wall thickness. An XGBoost-based dual-target model further achieved accurate prediction of crack depth and residual life. Full article

Metal magnetic memory (MMM) is a promising non-destructive evaluation method for ferromagnetic materials, allowing early detection of stress concentration and micro-defects under weak geomagnetic excitation. However, current magneto-mechanical coupling models are computationally complex and insufficient to characterize the full-cycle evolution of mesoscale physically short cracks. This work proposes a magnetic dipole model and its decomposed formulation for V-shaped cracks. Combined with theoretical derivation, finite element simulation, and in situ three-point bending tests on Q345 steel, the magneto-mechanical coupling mechanism and magnetic signal evolution during crack propagation are investigated. Results show that the MMM normal component exhibits obvious peak-peak features at the crack tip, while the tangential component shows a single-peak characteristic. Two critical signal mutations are observed at crack lengths of about 100 μm and 3000 μm, corresponding to micro-meso and meso-macro crack transitions, respectively. The model is verified with relative errors of 15.2% for H_x and 17.6% for H_y. This study reveals the quantitative correlation between MMM signals and full-lifecycle crack growth, supporting damage assessment and fatigue life prediction for ferromagnetic engineering structures. Full article

Concrete structures frequently experience sustained loading during service, which may lead to crack propagation and eventual failure. In this study, three-point bending beams with heights of 200 mm and 300 mm were subjected to sustained load levels of 0.82, 0.84, and 0.86 of the peak load. The crack propagation process was monitored using the Digital Image Correlation (DIC) technique to capture full-field displacement and strain distributions. Analysis of the crack opening displacement (COD) and the fracture process zone (FPZ) revealed that concrete exhibits brittle fracture behavior under sustained loading, with the FPZ not fully developed at creep failure. The crack propagation process was further characterized into three stages. In the initial stage, crack development is mainly governed by viscoelastic deformation. In the intermediate stage, both viscoelasticity and the gradual decay of cohesive stresses within the FPZ contribute to crack growth. In the final unstable acceleration stage, crack propagation is dominated by cohesive stress degradation. Importantly, the crack length at creep failure closely matches the corresponding crack length on the descending branch of quasi-static loading, indicating a direct link between time-dependent creep fracture and quasi-static post-peak behavior. These results provide new insights into the time-dependent fracture mechanics of concrete, revealing the evolution of damage under long-term loading. The study emphasizes material behavior, including FPZ development and stage-wise crack propagation, offering a mechanistic understanding of creep fracture beyond the evaluation of measurement techniques. Full article

Focusing on the R&D demand for green earthen building materials in coastal high-temperature and high-humidity areas, this study explores the biocolonization control mechanism of raw earth–rubble walls, taking the traditional raw earth–rubble walls of ancient buildings in Sanfang Qixiang, Fuzhou, as the research subject. FTIR, XRD, Raman, and SEM-EDS combined technologies were employed for characterization. The results show that the raw earth is rich in proteins, amino acids, and other nutrients, which provide the nutritional basis for plant growth. The raw earth and rubble share homologous mineral components. The rubble is fired from raw earth mixed with iron minerals such as hematite, with carbonaceous substances generated during the firing process. Iron, carbon, and potassium released from the weathered rubble may inhibit the growth of plant roots. The raw earth is relatively looser than the rubble, and the two form a dense–loose alternating structure. Combined with the secondary calcification mechanism in the raw earth, this structure resists the expansion and cracking of the wall and improves the viscosity and hardness of the wall. It is concluded that in a high-temperature and high-humidity environment, the raw earth first releases nutrients to promote plant growth. As time progresses, the relevant substances released by the rubble continuously inhibit root growth. Combined with the structural characteristics of the wall with high firmness and crack resistance, plants growing on the wall will not damage the wall structure. This finding provides a theoretical basis for the biocolonization control mechanism of raw earth–rubble walls and also offers practical references for the protection and sustainable reuse of raw earth buildings in similar areas. Full article

The intralaminar and interlaminar mode I initiation fracture toughness of unidirectional IM7/8552 carbon/epoxy composites were re-evaluated using only the published experimental data. Classical statistics, two-parameter Weibull analysis (location fixed at zero), non-parametric kernel density estimation (KDE), bootstrap resampling (10,000 replications), and bootstrap-based uncertainty quantification were applied to the fatigue-precracked (FPC) initiation values (n = 12) and the corresponding R-curves. The pooled FPC mean initiation toughness was 0.1982 kJ/m² (COV = 8.50%). Weibull fitting yielded a shape parameter β = 12.33 and scale η = 0.2058 kJ/m², providing a B-basis value of 0.1715 kJ/m² (90% reliability) and an A-basis value of 0.1417 kJ/m² (99% reliability). The Kolmogorov–Smirnov test confirmed statistical equivalence between intralaminar and interlaminar groups (p > 0.05), validating the use of a single initiation toughness for both crack planes when sharp fatigue-precracked starter cracks are employed. Intralaminar R-curves exhibited significantly steeper propagation, rising to approximately 0.385 kJ/m² at Δa = 30 mm due to extensive fiber bridging, whereas interlaminar R-curves reached a near-plateau after 12–15 mm. Bootstrap 95% confidence bands quantified the higher uncertainty associated with the intralaminar R-curve. Teflon-insert data produced artificially high initiation values and unstable growth, confirming that only fatigue-precracked results are suitable for design allowables. This study demonstrates that a single, statistically robust initiation toughness (B-basis = 0.1715 kJ/m²) can be used interchangeably for intra- and interlaminar cracking in progressive-damage models and preliminary design analysis of IM7/8552 structures. The open-source statistical workflow (KDE + bootstrap) developed here is transferable to other small-sample composite datasets, though the numerical B-basis value (0.1715 kJ/m²) is specific to IM7/8552 and should not be generalized without validation. Full article