International Journal of Fracture最新文献

This paper investigates the contact problem of an elastic layer that is perfectly attached to a porous half-space by two rigid flat punches with collinear symmetry. Using integral transformation, the problem is condensed to a singular integral equation of the Cauchy type. Then, the exact expressions for the surface contact stress and surface interface displacement are provided. By using the Gauss–Chebyshev technique, the integral equations are solved numerically, and the variations of the unknown contact stresses and deformations for different parameters are addressed. The results indicate that stress concentration is typically higher on the outer edge of the contact area compared to the inner edge. This also explains why surface damage is more likely to occur on the outer edge in elastic and poroelastic materials. Due to the interaction between the two punches, there will be a superposition of normal displacements at the center. The deformation or bulging at the center can be managed by adjusting the parameter values, allowing the engineered material to fulfill its intended purpose. The potential applications of these research findings encompass safeguarding porous structures against contact-related deformation and damage.

The single cleavage drilled compression specimens of sandstone were impacted by the large-diameter split Hopkinson pressure bar, during which the whole model-I dynamical fracture process was successfully observed. A crack propagation gauge is used to monitor the key time moment of dynamic initiation, propagation, arrest and re-initiation, respectively. The fractal crack extension model is used to analysis the propagation speed of the tortuous crack, and with further combination of the experimental–numerical-analytical method, to determine the dynamic initiation toughness, dynamic propagation toughness, dynamic arrest toughness, and dynamic re-initiation toughness of sandstone. The results show that in the process of crack propagation, the crack propagation path is torturous; and for this curved path, the value of the universal function, which is characterized by the crack’s velocity, is smaller than that with a straight path. The dynamic propagation toughness thus obtained is closer to its real value by using the fractal model. Sandstone’s dynamic initiation toughness is greater than the dynamic arrest toughness, and the dynamic initiation toughness is slightly bigger than the dynamic re-initiation toughness.

The present work aims at investigating crack shielding and size effect related to a cracked slab under tensile loading. For this purpose, experimental tests are carried out on PMMA cracked samples. Three different geometries are taken into account, presenting one, two or three parallel edge cracks, and assuming their distance equal to their initial length. Results are interpreted through the coupled stress and energy criterion of Finite Fracture Mechanics (FFM). The approach is implemented numerically, and parametric finite element analyses are carried out to evaluate the normal stress field and the stress intensity factor for each configuration. It is found that asymmetric crack propagation has to be preferred according to the energy balance. The matching between FFM failure predictions and experimental data reveals to be satisfactory.

Sheet metals subjected to biaxial plane stress loading typically fail due to localized necking in the thickness direction. Classical plasticity models using a smooth yield surface and the normality flow rule cannot predict localized necking at realistic strain levels when both the in-plane principal strains are tensile. In this paper, a recently developed multi-surface model for porous metal plasticity is used to show that the development of vertices on the yield surface at finite strains due to microscopic void growth, and the resulting deviations from plastic flow normality, can result in realistic predictions for the limit strains under biaxial tensile loadings. The shapes of the forming limit curves predicted using an instability analysis are in qualitative agreement with experiments. The effect of constitutive features such as strain hardening and void nucleation on the predicted ductility are discussed.

A novel fatigue model under Cosserat peridynamic framework is proposed to investigate concrete fatigue performance. In this model, a novel cyclic bond failure criterion is established to measure the combined tension/compressive-shear fatigue failure in concrete, which is derived from the Bresler-Pister criterion. Three benchmarks with different fatigue crack modes in concrete are designed. Results show that the mode I and mixed mode I-II fatigue crack patterns are predicted. In the three-point-bend beam fatigue test, the numerical result matches well with the experimental result, in the uniaxial compressive fatigue test, the effects of Cosserat parameters on fatigue crack patterns are discussed. Results found that the Cosserat parameters reflect the effects of concrete microstructures on crack patterns, and the larger Cosserat shear modulus accelerates the fatigue crack propagation process.

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.