International Journal of Fracture最新文献

A coupled axisymmetric peridynamics with correspondence material model (CA-PD-CMM) is proposed in this work to predict the heat conduction, plastic and fracture behaviors of metals. In this model, the governing equations of axisymmetric thermo-mechanical problems are derived based on the Euler–Lagrange equation and the separation of the deformations along the in- and out-of-plane directions. The force state and heat flux state are given by the PD linearized theory. The theory of continuum damage mechanics is incorporated into the CA-PD-CMM to effectively describe the ductile damage behaviors. Moreover, a secant line technique based on the uniaxial tensile test curve is developed to obtain temperature-dependent parameters of the damage model. Finally, the validity and performance of the proposed CA-PD-CMM are demonstrated by several representative numerical examples.

The mechanical properties of metal matrix fiber-reinforced composites depend on many aspects of their structure in a complicated way. In this paper, we propose a phase-field-cohesive-zone framework to study interface debonding, matrix cracking, and their competition in metal matrix fiber-reinforced elastoplastic composites by numerical simulation. This approach combines an explicit cohesive zone model for interface debonding and a phase field model for matrix cracking. The features of this framework are: (1) crack propagation and branching can be simulated without the need to track the cracks; (2) the interface debonding is described by the cohesive zone model, and is not directly interfered by the phase field in the bulk; (3) the cohesive interface has zero thickness instead of being regularized; (4) any reasonable cohesive law of interest is readily incorporated with very few constraints; (5) the competition of the two failure mechanisms, namely, matrix cracking and interface debonding, is captured. Accuracy of this framework is verified with existing analytical and numerical results. The proposed framework shows a potential in investigating various complicated crack behaviors in composites.

Dynamic brittle facture in materials with many pores/perforations has been shown experimentally to feature complex evolution of crack morphologies that include crack branching, micro-branches that arrest, cracks restarting from pores and branching soon after. Computational models of these problems need to accurately account for the dynamic interactions between strain waves and stress concentration zones induced by the perforated geometry. In this paper, we aim to improve the predictive capabilities of computational simulations of dynamic brittle/quasi-brittle fracture in samples with complex geometries, like perforated plates, by introducing a discretization method using non-uniform grids near a boundary (NB-NUG) for 2D peridynamic fracture modeling. The NB-NUG avoids the steps and the corresponding artificial stress concentrations created in PD models when using uniform grids over domains with curved boundaries. The new method also reduces numerical errors compared with general non-uniform grids used for PD models. We apply the model for dynamic fracture of thin PMMA plates with different arrangements of periodic pores/perforations. The results match the experimental observations for all of the cases considered. Fine features observed in the experiments (multiple cracks branching and cracks that arrest soon after splitting, number of branching events, etc.) are captured by the new approach and not by the other PD models with different types of grids. The results show that the high strain energy density regions created around perforations attract a nearby crack tip, deflecting the crack path, altering its propagation velocity, and promoting crack branching in its wake, thus dissipating more energy. Nonlocality of damage helps here in allowing its unrestricted evolution in problems in which complex crack morphology is sensitive to small changes in the geometrical arrangement of pores in the structure.

We study multiple transverse cracking of symmetric laminates in the framework of the variational approach to fracture. Considering the Griffith model, we assume that several cracks can appear instantaneously through the whole thickness of the core layer, separating the bar in n elastic segments. We show that the energy minimization implies the bifurcation from solutions with uniform crack spacing to non uniformly spaced solutions, a phenomenon ignored in the literature for perfect systems. The stability of uniformly spaced solutions crucially depends on the concavity of the elastic compliance of each elastic segment as a function of the segment length. We compute this function and its derivatives numerically with domain-derivative techniques for a large set of geometric and material parameters. Our results indicate that the change of concavity and the related instability is a robust qualitative property that becomes quantitatively relevant in the case of laminates with thin and soft outer layers.

This study presents numerical analyses for edge chipping by impact loading. As a numerical analysis method, we extend Particle Discretization Scheme Finite Element Method (PDS-FEM) developed by the authors to be able to simulate fracture due to impact loading. We performed simulations targeting edge chipping of soda-lime glass by impact of rigid steel sphere and examined the crack morphology while varying the diameter of the impactor, the impact velocity, and the impact distance. The proposed method successfully simulates the 3D complex crack pattern on edge chipping such as Hertzian cone crack and conchoidal chip scar. The method also reproduces the change of crack morphologies depending on the impact force and the impact distance. Also, a series of numerical analyses is presented to reveal the effect of the impactor geometry on the chip dimensions. The height of chip is independent of the impactor geometry while the width of chip depends on it. According to the agreement with experimental results, it is confirmed that the proposed method is capable of realizing edge chipping due to impact loading.

The phase-field fracture method (PFM) requires an extremely fine mesh to accurately capture the crack topology, which is computationally expensive. In this work, a new adaptive mesh refinement method is proposed for phase-field fracture. Based on the phase field increment, a volume weighted Quickselect algorithm is used to determine the coarsen region and the refined region. The speed of the crack propagation is predicted to control the size of the refined region, which reduces unnecessary degrees of freedom. Several benchmark numerical examples are simulated and the results demonstrate the efficiency and accuracy of the proposed method. In the numerical examples, the computational time using this method is reduced by about 90% compared with the standard PFM.

Herein, we focus on understanding the microstructure-fracture correlations in a Ti–6Al–4V alloy additively manufactured via electron beam melting (EBM) and subjected to various post-process heat-treatments. Specifically, the as fabricated material is subjected to a sub-transus heat-treatment followed by air-cooling and a super-transus heat-treatment followed by either air- or furnace-cooling. Next, a series of in-situ single edge notch tension (SENT) tests are carried out under a high-resolution digital optical microscope. The panoramic high-resolution images captured during the in-situ tests are then used to characterize the planar deformation on the specimen surface using microstructure-based digital image correlation (DIC). The results of the in-situ SENT tests together with DIC and post-mortem fractographic analyses provided us with a better understanding of the microstructure-fracture correlations in these materials. Our results show that the fracture mechanism of the as fabricated and sub-transus heat-treated materials is essentially the same, while the changes in the microstructure following the super-transus heat-treatments significantly affects the fracture mechanism. In this case, several microcracks of hundreds of microns in length first nucleate away from the deformed notch following extreme plastic deformation at discrete locations. Furthermore, the location of these microcracks in the super-transus heat-treated materials is extremely sensitive to the details of the underlying microstructure.

This study presents an application of bond-associated non-ordinary state-based peridynamics (PD) and the corresponding fatigue theory to predict fatigue crack growth in hydrogel. The constitutive model of the hydrogel is assumed to be the neo-Hookean material. Fatigue process is viewed as a series of quasi-static crack growth and solved by the explicit method. The applied strain energy-based fatigue criterion is obtained from hydrogel fatigue experiments. The fidelity of this model is established by simulating the relevant experiment. Due to the limitation of the test data, only crack growth phase of fatigue life of hydrogel is focused on. The progressive damage predictions by PD agree with that of experiment and capture the general characteristics of the experimentally observed damage patterns.

We introduce a nonlocal model of peridynamic type for fracture evolution in the quasistatic regime. Nonlocal quasistatic fracture evolution is developed and supporting numerical examples are presented. The approach is implicit and is based on local stationary and fixed point methods. Here a smooth cohesive force-strain model is used. Initially the force increases with strain then softens and decreases to zero. It is proved that the fracture evolution decreases stored elastic energy with each displacement step as the cracks advance; provided the displacement increments are chosen sufficiently small. These results apply to any system of multiple cracks. This is also seen in the numerical examples. The numerical examples include evolution of a straight crack, a crack propagating inside an L-shaped domain, and two offset inward propagating cracks.