International Journal of Fracture最新文献

Despite the extensive research on crack propagation in brittle solids, numerous unexplored problems still necessitate in-depth study. In this work, we focus on numerical modeling of multi-crack growth, aiming to explore the effect of material heterogeneity and multi-crack interaction on this process. To do this, an improved singular-finite element method (singular-FEM) is proposed with incorporation of heterogeneity and crack interaction. An efficient algorithm is proposed for simulating multi-crack propagation and interaction. Stress singularity near crack tip is reproduced by the singular elements. The singular-FEM is convenient and cost-effective, as the zone far away from crack tips is directly discretized using linear elements, in contrast to the quadratic or transition elements utilized in traditional FEM. Next, the proposed method is validated through benchmark study. Numerical results demonstrate that the superiority of the singular-FEM, which combines the merits of low cost and high accuracy. Then, the mechanics of crack growth are explored in more complex scenarios, accounting for the effects of crack interaction, loading condition and heterogeneity on crack trajectory, stress field and energy release rate. The findings reveal that the combined effect of heterogeneity and crack interaction plays a critical role in the phenomenon of crack growth, and the proposed method is capable of effectively modeling the process.

The study of fracture mechanics is usually within the paradigm of a failure mode that needs to be avoided. However, both in nature and in modern technology, there exist several situations where an ability to fracture is essential. In this work, we consider the problem of machining highly ductile and strain-hardening metals, such as annealed Cu, Al and Ta. These metals are known by the moniker “gummy metals” due to the large forces and poor surface finish associated with machining them. We investigate a chemo-mechanical technique involving adsorption of organic monolayers on the metal surfaces that causes the metals to become relatively brittle. This transition from ductile to brittle results in > 50% drop in the cutting force and an order of magnitude improvement in the surface finish. Molecular dynamics simulations of the phenomenon show the organic monolayers impose a surface stress on the metal surface which results in arresting of the dislocations close to the surface. The results suggest that a deeper understanding of the underlying mechanism has implications in environment-assisted cracking, stress-corrosion cracking and hydrogen embrittlement.

Ductile materials exhibit rate-dependent behaviors when subjected to different loading rates, particularly during impact and explosion events. In order to investigate the high strain rate behaviors of metal materials, a phase field model considered the rate-dependent threshold for effective plastic work is proposed. And the presented model couples the influences of the stress triaxiality and Lode angle parameter on failure behaviors. Later, a single element is modeled to demonstrate the impacts of the model in predicting stress-strain relations under varying loading rates. To illustrate the impacts of the Lode angle parameter on load-displacement responses, rectangular notch specimens are used. Next, the presented model is employed to mimic the shear fracture of hat-shaped specimens at different strain rates based on the split Hopkinson pressure bar tests, and the model parameters are calibrated by comparing the strain waveforms between the simulations and experiments. The numerical results indicate the developed model is capable of accurately reproducing the shear ductile fracture of the hat-shaped specimens under high strain rates.

Micro-crack propagation in polycrystalline materials can strongly depend on the defect size and its ratio to specimen size, and local variation in the microstructural features such as grain orientation, size, etc. While the dependencies are understood heuristically, the use of mechanistic models to capture the effect of various factors influencing micro-crack propagation can enable accurate prediction of fracture properties of polycrystalline materials and their engineering. To this end, a crystal plasticity coupled to damage model for micro-crack propagation on cleavage planes has been developed in this work and is shown to successfully capture the grain orientation dependent growth. In order to identify a suitable integration scheme for the coupled model, a one-dimensional model is developed and a detailed comparative analysis of three different schemes is performed. The analysis shows that the coupled explicit–implicit scheme is the most suitable and is a key finding of this work. Subsequently, a two-scale multi-scale method has been developed to include the interaction between the defect, its surrounding microstructure and the specimen. The two-scale method along with the coupled crystal plasticity-damage model has been applied to perform finite element method based micro-crack growth simulations for a microstructurally short and physically long crack with two different microstructures with random orientation and texture. Such a study comparing microstructural effects on crack growth from pre-existing defects of drastically disparate sizes hasn’t been performed before and is a novelty of this work. The analyses clearly show that though the micro-crack path from long crack is different depending on the orientation distribution, the rates are nearly independent of the local behavior. Moreover, the micro-crack propagation rate from long crack is significantly larger at the initial stages, with the latter showing significant acceleration after a small growth. Overall, the influence of microstructure on the crack growth behavior is stronger for short cracks, which conform with experimental observations and is successfully captured by the proposed model.

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.