International Journal of Fracture最新文献

Two dimensional intergranular brittle cracks propagating through a microstructured material produce fracture profiles which, at scales larger than the microstructural length scale, are anti-persistent and close to directed random walks with Hurst exponent (sim 0.5). The extent of intergranularity is controlled by the ratio of the toughness of the grain boundaries to that of the grain interior. However, experiments suggest [e.g. Ponson et al. (Phys Rev Lett 97(12), 2006)] that even when transgranular crack propagation is possible, the fracture profile is still close to a random walk. In this work, generating fracture profiles in a material with an idealised honeycomb microstructure using a phase field based model of crack propagation, we show that the competition between inter and transgranular fracture manifests in a manner that is more nuanced than what the experiments suggest. While the fracture profile is indeed always anti-persistent, transgranularity resulting from toughening the grains leads to profiles that can have roughness exponents much lower than 0.5. Moreover, in such cases, the overall toughness of the specimen scales with the Hurst exponent. On the other hand, transgranularity resulting from weakening the grain boundaries, without changing the toughness of the grain interior, always lead to fracture profiles close to the random walk.

To understand the effects of laminar structure on fracture propagation and proppant transportation intuitively, an improved true triaxial fracturing device with a proppant pumping unit was used to carry out sand-laden fracturing on shale oil reservoir samples with multiple lithological-combination and different laminar structures. Based on high-precision CT scanning technology and acoustic emission (AE) monitoring technology, the propagation mechanism of hydraulic fractures (HFs) and proppant transportation characteristics were analyzed, and the critical condition for lamina slip was proposed. The results show that laminas with initial width tend to be activated by fracturing fluid, resulting in diversion or offset. Closed laminas tend to be penetrated by HFs and are hardly activated by fracturing fluid. Rock with dense initial width laminas tends to form “#” shaped fractures interwoven with activated laminas and vertical fractures. In contrast, rock with closed laminas tends to form simple fractures dominated by vertical HFs. The width of HFs varies greatly from the perforation layer to the neighboring layer. As the difference in tensile strength between the interlayer and the perforated layer increases, the degree of decline in HF width significantly increases. Intensive AE activity was monitored at the intersection of vertical HFs and activated laminas, indicating that decreased fracture width causes proppants to bridge and block at the diversion and offset. Therefore, most proppants are filled in wide fractures near perforation, blocking the diversion and offset; there is almost no proppant in activated laminas. Reducing proppant diameter is conducive to placing the proppant in the activated laminas and interlayer HFs. Compared with placing 200 mesh and 120/140 mesh with similar fracture morphology samples, the proppant placement volume ratio of 400 mesh proppant placing samples increased by 7%. The findings significantly improve the scheme decision-making and parameter design of fracturing technology for thin interlayered shale oil reservoirs.

A composite of a woven fabric embedded in a soft matrix exhibits the attributes of both constituents. The fabric is strong in tension but flexible in bending. The soft matrix impedes fluid penetration. Applications of such composites include tents, rain coats, and wound closure patches. How such a composite tears under cyclic load remains unclear. Here we embed a woven fabric of ultrahigh molecular weight polyethylene in a soft matrix of thermoplastic polyurethane, and tear each specimen of the composite with cyclic energy release rate of a fixed amplitude, G. Two thresholds are identified, G_a and G_b. When G < G_a, the composite does not tear. When G_a < G < G_b, the composite tears by yarn slip without yarn break, and then tearing arrests after yarns jam. When G_b < G, the composite tears, without arrest, by a combination of yarn slip and yarn break. We then prepare a composite with strengthened fabric-matrix interface, and find that G_a increases but G_b decreases. We interpret these findings in terms of stress deconcentration along the yarns. It is hoped that this study will aid the development of fatigue-resistant composites.

In this work, the 3D nature of stationary mixed-mode (I & II) notch tip fields in shape memory alloys, initially in austenite phase, under small scale transformation and yielding conditions is studied through finite element simulations. An isotropic constitutive model which represents the combined effects of superelasticity and plasticity is employed. The effects of the above factors and temperature on the evolution of transforming and plastic zones as well as the spatial distribution of near-tip stresses, plastic strain and martensite volume fraction are analyzed. The results show that at a temperature above the austenite finish temperature, (A_f), plasticity occurs before phase transformation takes place near the tip, whereas it does so only in the fully transformed martensite phase at a temperature well below (A_f). By contrast, the transforming zone is much smaller at higher temperature, which is attributed to impediment caused by plastic deformation. Under mixed-mode loading, hydrostatic stress is tensile near the stretched or blunted part of the notch, and compressive close to its sharpened portion. The plastic strain and martensite volume fraction are higher at the latter side. The thickness variations of field quantities become insignificant at distances from the tip of 0.25 to 0.5 of the specimen thickness.

An extension of the coupled criterion (CC) of finite fracture mechanics is proposed in order to assess brittle crack initiation considering plasticity. The main change compared to the classical linear elastic approach consists in considering the plastic strain energy variation due to crack initiation. The proposed approach enables assessing quasi-brittle failure at singularities or stress concentrators in materials exhibiting plastic deformation. It is illustrated on V-notch steel specimens subjected to bending. If plastic deformation is disregarded, the CC underestimates the failure force compared to those measured experimentally. Considering plasticity yields a better representation of failure force variation as a function of the V-notch angle.

This study is aimed at investigating the crack growth behavior of 2A12 aluminum alloy under constant amplitude loads and various single peak overload conditions, with a focus on the effects of different load ratios and overload ratios on the crack growth rate. Due to the complexity and numerous parameters involved in traditional physical models, we proposed a whale optimization algorithm-backpropagation neural network-based model for predicting crack growth rate. By comparing results on datasets of 2A12 aluminum alloy and QSTE340TM steel, including Wheeler, Huang, WOA-SVM, and WOA-RBF models, our study demonstrates that our model achieves higher predictive accuracy. Finally, the paper calculated the crack growth life using the cycle-by-cycle method and conducted a detailed comparison and analysis of the prediction errors of various models. This research holds significant theoretical and practical value for enhancing understanding of material crack behavior and developing more accurate models for predicting crack growth rates.

We perform experiments and peridynamic simulations to understand the evolution of cracks in a thin glass plate, backed by a polycarbonate plate, impacted by a small projectile at 150 m/s. We use the peridynamic model to investigate how various types of crack systems are generated by the impact event and how they evolve in time. The detailed investigations of wave interactions and the different cracks and failure types they generate, performed using the peridynamic model, are unique. Post-mortem analysis of glass fragments allows comparisons with the computational results in terms of the kind and location of crack systems. Fractography results provide information about the growth direction for some of the edge cracks and the peridynamic results are used to explain the particular wave interactions leading to the observed behavior. The model captures, in an average sense, some wispy/very fine cracks (surface roughness) experimentally observed on fragments coming from the ends of the Hertzian-cone crack. This is the first attempt at using a computational model to predict the fine details and complex mechanisms of the origin and time evolution of fracture and full fragmentation in a glass plate from impact.

Fracture toughness is the material property characterizing resistance to failure. Predicting its value from the solid structure at the atomistic scale remains elusive, even in the simplest situations of brittle fracture. We report here numerical simulations of crack propagation in two-dimensional fuse networks of different periodic geometries, which are electrical analogs of bidimensional brittle crystals under antiplanar loading. Fracture energy is determined from Griffith’s analysis of energy balance during crack propagation, and fracture toughness is determined from fits of the displacement fields with Williams’ asymptotic solutions. Significant size dependencies are evidenced in small lattices, with fracture energy and fracture toughness both converging algebraically with system size toward well-defined material-constant values in the limit of infinite system size. The convergence speed depends on the loading conditions and is faster when the symmetry of the considered lattice increases. The material constants at infinity obey Irwin’s relation and properly define the material resistance to failure. Their values are approached up to (sim 15%) using the recent analytical method proposed in Nguyen and Bonamy (Phys Rev Lett 123:205503, 2019). Nevertheless, the deviation remains finite and does not vanish when the system size goes to infinity. We finally show that this deviation is a consequence of the lattice discreetness and decreases when the super-singular terms of Williams’ solutions (absent in a continuum medium but present here due to lattice discreetness) are taken into account.

The catastrophic fracture of the ceramics limits their utilization in industrial applications. Particularly despite the wide potential of the Tantalum carbide (TaC) it is prone to sudden fracture due to its brittleness. Therefore, covering it with the ductile graphite (Gr) shell could improve its toughness as a shock absorber. In this regard, a percolation-based image processing framework is developed to quantify the area, periphery, and tortuosity of the generated cracks, as a measure for the crack deflection, from three distinct methods and correlate it to the shell fraction, stacking mode, and the fracture energy. As well, defining equivalent material for the core–shell composition, finite element simulations were carried out to project the local (i.e. real state) shape function versus the crack progress which has led to the estimation of the critical crack size in flexural leading. The results are useful for quantifying and optimization of the design parameters for the core–shell composites and their arrangements versus the specified application.

Three-dimensional characterization of internal defects in Ti–6Al–4V alloy fabricated by Laser Engineered Net Shaping (LENS) was conducted by utilizing synchrotron X-ray imaging technology. Subsequently, the statistical analysis of defect size, quantity, and morphology characteristics was performed. Additionally, high cycle fatigue tests were conducted to analyze the high cycle fatigue performance of LENS Ti–6Al–4V alloy and elucidate the causes of its anisotropic behavior. Furthermore, based on the multi-stage crack growth model, the high cycle fatigue life of LENS Ti–6Al–4V alloy was predicted. The results showed that the quantity and size of internal defects were small, with defects predominantly spherical pores and no lack of fusion defects detected. Longitudinal specimens exhibited significantly higher fatigue life at high stress levels compared to transverse specimens. The anisotropic behavior of high cycle fatigue performance of LENS Ti–6Al–4V alloy at high stress levels was mainly attributed to the anisotropic distribution of its microstructure, and defects had no impact on the fatigue performance of LENS Ti–6Al–4V alloy. As stress levels decreased, the fatigue life of both types of specimens approached each other, with fatigue strengths of 650 and 656 MPa at 2 × 10⁶ cycles for longitudinal and transverse specimens respectively, showing minimal difference. In addition, the predictions from the multi-stage crack growth model aligned well with experimental results, effectively predicting the high cycle fatigue life of LENS Ti–6Al–4V alloy.