Engineering Fracture Mechanics最新文献

The introduction of pyrolytic carbon (PyC) interphase in SiC_f/SiC composites significantly improves their toughness, primarily by deflecting matrix cracks, while the underlying toughening mechanisms toward various PyC microstructures remain mysterious due to the challenges in experimentally observing microscopic deformations within PyC. This paper addresses this gap by constructing distinct PyC models based on orientation angle (OA), a key experimental characteristic, and then conducting Mode I loading simulations on SiC_f/PyC/SiC systems by molecular dynamics (MD). Results indicate that as OA increases, the deformation behavior of PyC transits from multilayer sliding to delamination, which correlates to a reduction in the fracture energy of SiC_f/PyC/SiC systems. Energy dissipation models are established for two microscopic deformation patterns as multilayer sliding and delamination based on homogenization theory, with results demonstrating that the energy dissipation caused by multilayer sliding within PyC surpasses that of delamination. Furthermore, mesoscale stochastic simulations of crack propagation in PyC with different textures are carried out to obtain crack path configurations and corresponding energy dissipations. The outcomes highlight the superior toughening effect of high texture (HT) PyC over medium texture (MT) and low texture (LT) PyC due to longer crack path within HT PyC, aligning well with experimental findings. This study provides valuable insights into cracking through PyC with varying textures, offering a foundation for optimizing PyC coating processes in SiC_f/SiC composites to enhance performance.

Mixed-mode crack-tip stress field is different in low and high loading rate conditions, resulting in different mixed-mode stress intensity factors (SIFs) measurements. How to correctly measure mixed-mode SIFs in different loading rate conditions is of critical importance. To this end, mixed-mode SIFs are measured and compared by optical caustics method with high-speed photography, specifically by the interpretation of crack-tip optical image, i.e., caustics pattern which reflects crack-tip stress field. Different mixed-mode caustics patterns in shape are observed in drop weight and blast loading conditions, indicating that corresponding crack-tip stress field and mixed-mode SIFs measurements are different. Under drop weight loading, mixed-mode caustics patterns are consistent with the classical caustics interpretation for SIFs measurements, while those under reflected P wave loading in blasts are not consistent. Therefore, a modified mixed-mode caustics interpretation is proposed and verified to be available for SIFs measurements in blast loading condition. Finally, underlying reasons for different mixed-mode SIFs measurements in low and high loading rate conditions are discussed, and it is concluded that in low loading rate condition, a longer loading time results in crack-tip K-dominated stress field which is suitable for the classical caustics interpretation, while in high loading rate condition, the loading time is too short to form K-dominated stress field in the crack tip, hence a modified caustics interpretation is necessary. This paper benefits correct applications of caustics method to mixed-mode SIFs measurements in different loading rate conditions.

The finite element method can be used to compute accurate stress intensity factors (SIFs) for cracks with complex geometries and boundary conditions. In contrast, handbook solutions act as surrogate SIF models that provide significantly faster evaluation times. However, the development of conventional surrogate SIF models relies on manual development based on low-order parameterizations. This limits surrogate model accuracy and generalizability. In this paper, we develop a framework for the automated development of mechanics-guided handbook SIF solutions by using interpretable machine learning via genetic programming for symbolic regression (GPSR). Formalizing the mechanics-based approach of Raju and Newman, SIF training data is decomposed into multiple subsets. This decomposition enables parallel GPSR model development of subfunctions, each of which accounts for specific geometrical corrections with respect to a known analytical model. Using this mechanics-based approach with GPSR allows for equations to be learned with improved accuracy and reduced complexity relative to the Raju Newman equations while maintaining the inherent interpretability of mathematical expressions. In this paper, we present equations that match the complexity of the Raju Newman equations while having reduced error, as well as equations with similar errors and reduced complexity.

Tensile fractures in deep coal and rock mass can readily trigger dynamic calamities like rock bursts, significantly impacting the safety of coal mining. To enhance our understanding of coal’s tensile failure mechanism, Brazilian splitting failure experiments were conducted on coal samples with prefabricated cracks of different sizes. Acoustic emission (AE), electromagnetic radiation (EMR) and digital image correlation (DIC) techniques were used to analyze the instability failure process and precursor characteristics of coal samples. The results showed that, for coal samples of the same thickness, the tensile strength and peak strain gradually decreased with the increase of coal sample size, whereas the elastic modulus increased gradually, highlighting more pronounced brittleness characteristics and revealing a noticeable size effect. The time-varying evolution of AE energy, EMR energy and VE (virtual extensometer) elongation during the tensile failure process of coal samples is closely correlated to the stress evolution trend, exhibiting distinct characteristics at various loading stages. The failure modes of coal samples of varying sizes exhibited a strong correlation with the spatial distribution of AE events, as well as the strain and displacement field measured by DIC. With the coal sample’s growing size, the percentage of AE high energy events rose while the total number of AE positioning events fell, the proportion of DIC strain concentration area decreased, displacement zoning characteristics became more obvious, and the critical opening displacement of cracks increased. The variance of AE, EMR and DIC related parameters in coal samples showed significant critical slowing down characteristics. Based on their response timescales, EMR energy was identified as an “Early warning”, AE energy as a “Medium warning”, and VE elongation as a “Short-imminent warning”. A comprehensive analysis of multi-parameter monitoring information proved beneficial in accurately pinpointing precursory response points of coal mine dynamic disasters, thereby enhancing monitoring precision.

This paper introduces an adaptive peridynamics with a correspondence material model (A-PD-CMM) to effectively simulate the coupled creep-plastic behavior and the creep crack propagation in metal materials. In this method, to describe the coupled creep-plastic deformation with considering the creep damage, the multiaxial coupled constitutive model that integrates the Wen-Tu creep damage model and the J₂ plastic model is developed. Moreover, a damage associate criterion is incorporated into the peridynamics framework to effectively capture the influence of damage on the force state. To detail the rapid damage evolution during the tertiary creep stage, a time-adaptive solving strategy is proposed. Additionally, the constitutive integration algorithm of the multiaxial coupled model is efficiently realized by decoupling it into two parts, that is, an implicit computation of creep-plasticity and an explicit evolution of creep damage. The efficacy and engineering applicability of the proposed A-PD-CMM are validated through several representative numerical examples, showcasing its potential in addressing complex material behavior.

Accurately predicting the mode I fatigue life of concrete is critical for evaluating the safety of structures. However, due to the stochasticity of fatigue life, it remains a challenge to the deterministic methods in the existing literature. This study presents a probabilistic method for predicting the mode I fatigue life of concrete. The method considers four concrete material parameters in the initial fracture toughness-based crack propagation criterion and the tension-softening constitutive relationship as random variables following a two-parameter Weibull distribution. The detailed procedure for the implementation of the method is elaborated using the notched three-point bending (TPB) beam as an example, and the effectiveness of the method is verified by comparing the predicted fatigue life with the experimental results collected from the literature. Furthermore, the sensitivity analysis shows that the stochasticity of the initial fracture toughness is the most important factor leading to the variability of the fatigue life. Tensile strength stochasticity is the second most important factor. The effects of other material parameters on fatigue life are negligible. The proposed method allows reasonable prediction of fatigue life based solely on prior knowledge of the statistical laws governing the two factors. Meanwhile, the calculation results suggest that the large scatter in fatigue life is due to the high sensitivity to the stochasticity of concrete material parameters. The proposed method is expected to enhance the understanding of the stochastic nature of fatigue life and achieve accurate predictions at different failure probabilities.

In this paper, crack propagation behaviors in a weldment are simulated under cyclic loadings using crystal plasticity finite element coupled with the XFEM. The result shows that the cracks in heat affected zone grow faster than that in the welded zone. Short crack propagation dominated by dislocation activity takes approximately 4 to 5 grains, followed by long crack propagation which is unrelated to dislocation activity and the growth direction kept an angle to the loading direction (45°-51°). Experimentally observed deflections within grains and at grain boundaries, retardation at grain boundaries are captured by the simulation.

Reinforced concrete (RC) hollow piers are inevitably impacted by solar radiation during their service life. However, normal investigation approaches are inadequate for characterizing the long-term degeneration of RC structures under cyclic solar radiation. In this article, a novel elastoplastic-thermodynamic numerical approach has been suggested for evaluating the long-term deterioration behavior of hollow piers during cyclic solar radiation and ambient temperature fluctuations. The findings suggest thermal effect caused by solar radiation and ambient temperature fluctuations might cause the pier surface concrete to crack. The maximum first principal strain of pier surface concrete in July is approximately 1.21 times greater than the concrete peak tensile strain. Tensile damage of pier concrete rises with cyclic times of solar radiation. Tensile damage of surface concrete rose from 0.495 to 0.566 and 0.610, as exposure time increased from 1 to 10 and 100 years. Reducing the surface short wave absorption rate, increasing concrete specific heat, and decreasing pier wall thickness is beneficial to minimizing long-term tensile damage of pier concrete.

Research on creep crack growth in defective materials or structures at high temperatures is essential for structural security evaluations. As the creep displacement rates of the specimens are estimated using the stress intensity factor K_I and plastic J-integral J_P, the traditional ASTM method is essentially an indirect method and some limitations have been discovered in previous studies. Based on the quasi-static load–displacement and creep displacement rate models for specimens with mode-I crack, an indirect method for creep crack growth testing is proposed according to the derived formula of elastic and plastic displacement rate and a direct method that obtains the creep crack growth rate of materials using only the crack length a. Furthermore, an iterative method for obtaining the real-time crack length through displacement–time curves was discussed by combining the indirect and direct methods. The proposed methods were verified using the results of finite element analysis (FEA) and experimental results for various materials. These results show that the direct method for creep crack growth testing is simpler and more effective than the indirect method, and the results predicted by the new methods are consistent with those obtained using traditional and literature-based methods.

The R-curves for transverse cracking could be determined based on the size effect law using SENB specimens, where the R-curves determined by the size effect law were consistent with those determined by the compliance method. The crack growth resistance in the steady-state and the crack extension at the onset of the steady-state of carbon-fiber/epoxy laminates, T800S/2592, were determined to be 0.22 N/mm and 0.36 mm, respectively. The crack growth stability in SENB specimens depended not only on the load control method but also on the specimen geometry, whereas a unique R-curve could be obtained regardless of the crack growth stability.