International Journal of Fracture最新文献

Efficient and accurate prediction of chloride concentration distribution in concrete is extremely important for evaluating the durability of reinforced concrete (RC) structures in the coastal region. A peridynamic (PD) framework for chloride diffusion–reaction is proposed to explore the mechanisms of the long-term chloride ingress in concrete. Specifically, the improved intermediately homogenized peridynamic (IH-PD) method is substituted for the solid modeling method of the interface transition zone (ITZ), with the consideration of the mesoscopic characteristics of concrete and great computational efficiency. In addition, considering the effect of concrete mesostructure, an effective chloride diffusion coefficient is constructed based on the Mori–Tanaka method, in which the proportion of various bonds is determined by the statistics. To verify the reliability of the proposed model, the numerical results are compared with the third-party experiments data. From the results, the randomness of concrete mesostructure leads to the randomness of chloride concentration at the same ingress depth, following the normal distribution. Moreover, the chloride diffusion performance which reflects the speed of chloride diffusion is significantly improved with the increase in the water-cement ratio. Noteworthily, the ITZ thickness can be appropriately increased without affecting the reliability of the results.

The peridynamic correspondence model (PDCM) provides the stress–strain relation that can introduce many classical constitutive models, however, the high computational consumption and zero-energy mode of PDCM certainly limit its further application to practical engineering crack problems. To solve these limitations and exploit the advantage of PDCM, we propose a simple and effective method that adaptively couples dual-horizon peridynamic element (DH-PDE) with finite element (FE) to simulate the quasi-static fracture problems. To this end, a stabilized dual-horizon peridynamic element for DH-PDCM is firstly developed that the peridynamic strain matrices for the bond and material point are constructed respectively. The nonlocal ordinary and correctional peridynamic element stiffness matrices are derived in detail and calculated by the proposed dual-assembly algorithm. Subsequently, a unified variational weak form of this adaptive coupling of DH-PDE and FE is proposed based on the convergence of peridynamics to the classical model in the limit of vanishing horizon. Therefore, the integrals of the peridynamic element and finite element in this coupling method are completely decoupled in the viewpoint of numerical implementation, which makes it easier to realize the proposed adaptive coupling by switching integral element. Moreover, the proposed adaptive coupling is implemented in Abaqus/UEL to optimize the calculational efficiency and real-time visualization of calculated results, which has potential for dealing with the engineering crack problems. Two-dimensional numerical examples involving mode-I and mixed-mode crack problems are used to demonstrate the effectiveness of this adaptive coupling in addressing the quasi-static fracture of cohesive materials.

A multi-phase-field approach for crack propagation considering the contribution of the interface energy is presented. The interface energy is either the grain boundary energy or the energy between a pair of solid phases and is directly incorporated into to the Ginzburg–Landau equation for fracture. The finite difference method is utilized to solve the crack phase-field evolution equation and fast Fourier method is used to solve the mechanical equilibrium equation in three dimensions for a polycrystalline material. The importance of the interface (grain boundary) energy is analyzed numerically for various model problems. The results show how the interface energy variations change the crack trajectory between the intergranular and transgranular fracture.

Brittle material Mode I fracture may be characterized by the double cleavage drilled compression test. For linear elastic materials, the critical energy release rate, or fracture toughness, can be estimated simply using the linear elastic fracture mechanics. For other types of constitutive behavior, the material parameter has to be determined with numerical fracture modeling. In this paper, we have used two approaches, the phase-field damage model and the cohesive elements, in order to estimate the critical energy release rate of an elastoplastic material. Firstly, we assessed the numerical models and discussed their parameters by comparison of available data from double cleavage drilled compression experimental tests run on a silica glass. Both phase-field damage and cohesive zone models were able to reproduce fracture initiation at the observed macroscopic stress for the linear elastic material. However, the material toughness could not be predicted by the phase-field approach due to the result dependence on the model regularization parameter. Secondly, an elastoplastic methyl methacrylate polymer was submitted to the compression test in our lab. Both models were then extended for elastic-perfectly plastic materials. Crack initiation was obtained at the observed macroscopic strain for similar critical energy release rate ranges for both approaches, providing good confidence in the estimated material toughness.

Brittle materials are known for their violent and unpredictable cracking behavior. A behavior which is dictated by a combination of microscopical material defects and the competition between the potential energy of the system and the surface energy of the material. In this study, we present the implementation of a dynamic fracture phase-field model with a new crack driving force into a commercial finite element (FE) solver and examine its behavior using three different tension-compression splits. After validating the implementation, we use the model to investigate its predictive capacity on quasi-statically loaded L-shaped soda-lime glass specimens with varying critical load levels. The dynamic fracture phase-field model predicted similar crack propagation to what was found in the literature for quasi-static and dynamic validation cases. By varying the critical load level for the L-shaped soda-lime glass specimens using the new crack driving force, the model predicted a positive correlation between the initial crack propagation speed and the critical load level, similar to what was seen in the experiments. However, the predicted crack propagation speed decreased quicker than the experimental crack propagation speed. The tension-compression splits had an impact on the predicted crack propagation paths. Overall, the proposed crack driving force used in the dynamic fracture phase-field model seems to capture the relation between critical load and initial crack propagation speed and thus enables crack predictions for specimens of varying strength.

Intermittent beading is a novel design that holds great potential for simultaneous improvement of strength and toughness of composites. Despite the progress in fabrication of beaded fiber composites, the mechanisms of fracture in such composites are largely unknown. In this study, calculations are carried out for interfacial debonding in a beaded fiber composite subjected to tensile loading. The post-yield strain softening followed by strain hardening of polymer matrix, and debonding of the fiber-bead, bead-matrix and fiber-matrix interfaces are accounted for in the numerical analyses. It is found that interfacial debonding can activate plastic deformation in the bead and polymer matrix, contributing to toughening of the beaded fiber composite. We have identified that the bead-matrix interfacial debonding is the major mechanism controlling plastic deformation in the matrix. The low cohesive strength of the bead-matrix interface plays a role in suppressing development of shear bands in the polymer matrix, enhancing plastic dissipation of the composite. The high toughness of the bead-matrix interface enables large plastic zone in the matrix, promoting plastic dissipation. For the fiber-bead interface, there is an increase in plastic dissipation of the composite with decreasing cohesive strength, while high interface toughness can amplify plastic dissipation. In addition, we reveal that weak fiber-matrix interface is capable of spreading plastic deformation in the matrix, increasing plastic dissipation of the composite. The findings of this study can shed new light on the fracture mechanisms of beaded fiber composites.

Hydride precipitation ahead of a crack is examined under conditions of hydrogen chemical equilibrium, steady-state heat conduction and linear elastic metal behavior. The limiting conditions are approached via the interaction of the operating physical mechanisms of material deformation, hydrogen diffusion and energy flow. Analytical relations are presented for the distributions of hydrogen concentration in solid solution, hydride volume fraction and stress components, as well as for the hydride precipitation zone boundary. It is shown that there is an annulus, within the hydride precipitation zone, where stresses, although vary according to (1/sqrt{r})—singularity, deviate significantly from the well-known K-field, being smaller, according to the difference of hydrostatic stress before and after hydride precipitation. The hydride precipitation zone increases with crack-tip constraint, given by T-stress. In addition, temperature gradient affects hydride precipitation zone size, by controlling stress trace distribution.

The Pure Shear (PS) crack specimen is widely employed to assess the fracture toughness of soft elastic materials. It serves as a valuable tool for investigating the behavior of crack growth in a steady-state manner following crack initiation. One of its advantages lies in the fact that the energy release rate (J) remains approximately constant for sufficiently long cracks, independent of crack length. Additionally, the PS specimen facilitates the easy evaluation of J for long cracks by means of a tension test conducted on an uncracked sample. However, the lack of a published expression for short cracks currently restricts the usefulness of this specimen. To overcome this limitation, we conducted a series of finite element (FE) simulations utilizing three different constitutive models, namely the neo-Hookean (NH), Arruda-Boyce (AB), and Mooney-Rivlin (MR) models. Our finite element analysis (FEA) encompassed practical crack lengths and strain levels. The results revealed that under a fixed applied displacement, the energy release rate (J) monotonically increases with the crack length for short cracks, reaches a steady-state value when the crack length exceeds the height of the specimen, and subsequently decreases as the crack approaches the end of the specimen. Drawing from these findings, we propose a simple closed-form expression for J that can be applied to most hyper-elastic models and is suitable for all practical crack lengths, particularly short cracks.

A global energy minimization criterion based on Griffith’s theory is introduced for the node-splitting lattice spring model. The fracture criterion is computed by both direct numerical simulations of energy release rate G and through a J-integral formulation for comparison and validation. For mode I fractures, the standard implementation of J-integral formulation yields very good estimations of the energy release rate, but for mixed mode fracture the estimations deviates from the direct calculated energy release rate. The reasons for this discrepancy are elucidated and an approach to best approximate the J value is given. This method is compared with the more standard maximum tip stress threshold crack criterion, and shows a much better prediction of the energy release rate and is more robust under grid refinement.

Underground rocks in coal mining and oil exploration are usually subjected to in-situ stress and dynamic loading. In this paper, the tensile fracture behaviors of brittle rocks under coupled in-situ stress and dynamic loading are investigated numerically via the simulation of Brazilian disc (BD) tests of the modified split Hopkinson pressure bar (SHPB). To achieve this purpose, a cohesive zone model in the framework of the finite element method is used to model the cracking of the rock Brazilian disc under confining pressure. The pressure-dependent property of the rock is considered using the recently proposed bi-linear constitutive law. Dynamic Brazilian disc tests of the SHPB with two impact velocities of a striker are simulated for the rock. Comparisons between the simulated results and the reported experimental ones show a good agreement, demonstrating the accuracy and validity of the simulation models and the numerical approach. Due to the existence of holes in the rock in underground rock engineering practices, a pre-hole is inserted in the BD rock specimen in the modified SHPB tests to more realistically consider the rock fracture. The effects of the in-situ stress, the pre-hole size, and the pre-hole position on the dynamic fracture characteristics of the rock are numerically investigated using the modified SHPB test for BD rock specimen.