International Journal of Fracture最新文献

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.

In fracture mechanics, polyacrylamide hydrogel has been widely used as a model material in experiments due to its optical transparency, the brittle nature of its failure, and low Rayleigh wave velocity. Indeed, linear elastic fracture mechanics has been used successfully to model the fracture of polyacrylamide hydrogels. However, in soft materials such as hydrogels, the crack opening can be extremely large, leading to substantial geometric and material nonlinearity at the crack tip. Furthermore, poroelasticity may also modify the local mechanical state within the polymer network due to solvent migration. Direct characterization of the kinematic fields and the poroelastic response at the crack tip is lacking. Here we use a hybrid digital image correlation—particle tracking technique to retrieve high-resolution 3D particle trajectories near the tip of a slowly propagating crack, and measure the near-tip 3D kinematic fields in-situ. With this method, we charactherize the displacement fields, rotation fields, stretch fields, strain fields, and swelling fields. These measurements confirm the complex multi-axial stretching near the crack tip and the substantial geometric nonlinearity, particularly in the wake of the crack, where material rotation exceeds (30^{circ }). Comparison between the measured fields and the corresponding prediction from linear elastic fracture mechanics highlights an increasing disagreement in the direct vicinity of the crack tip, particularly for displacement component (u_x) and the through-thickness strain component (varepsilon _{zz}). Significant swelling occurs due to solvent migration, with a strong correlation to the local stretch.

The increasing use of architected materials has broadened the possibilities of mechanical behaviour. In this article, we aim to explore these new possibilities in terms of in-service behaviour, especially in terms of crack propagation by performing an in-depth study in the framework of Linear Elastic Fracture Mechanics (LEFM). The specific configuration studied here is the case where the architected zones are symmetrically positioned adjacently to the crack path and no propagation occurs within the zone. This problem is addressed both numerically and experimentally. Numerically, an path-following algorithm is used to simulate the crack propagation. Different toughening aspects of the addition of architected zones are identified. First, a temporary increase in crack propagation resistance is shown. It comes from a temporary increase of stored elastic energy in the architected zones, thus acting as mechanical springs. Second, a snap-back instability appears, linked to the release of the previously stored energy. It leads to a higher energy dissipated by the crack propagation process. Experimentally, we evidence the possibility to reproduce the theoretical results using 3D printing. A good quantitative comparison is obtained between numerical and experimental approaches. This study shows that it is possible to improve crack propagation resistance while lightening the component by addition of architected zones outside the crack path. This opens up the way to tune finely, through the use of optimization tools, the crack propagation response.

The hydrogen embrittlement (HE) characteristics of various stainless steels were investigated. In this study, as-received, heated (1100 °C, 15 h), and cold-rolled (30% strain) γ-austenite (AS), α-ferrite (FS), α′-martensite (MS), and γ–α duplex (DS) stainless steels were employed. For as-received stainless steels, severe HE occurred for DS and MS with static tensile loading, while no clear and weak HE was observed for AS and FS, respectively. This could be attributed to the different extent of hydrogen diffusivity in the stainless steel. A large amount of hydrogen penetrated to (i) lattice vacancy with low atomic density for body-centered cubic FS, DS, and MS, compared to that for face-centered cubic (AS); (ii) the phase boundary between γ-austenite and α-ferrite for DS; and (iii) the boundary between the Cr base precipitate and the martensite matrix for MS. HE also occurred strongly for heated-DS owing to the grain growth, i.e., a high hydrogen concentration in grain and phase boundaries. Although no clear HE was detected in as-received AS with static loading, HE occurred in cold-rolled AS, where hydrogen penetrated lattice vacancies and α′-martensite formed through strain-induced martensite. Owing to strain-induced martensite created during cyclic loading, HE was detected even for as-received AS, which is dissimilar to the result of the tensile test. Details of HE characteristics of the strainless steels were examined using the four stainless steels with different microstructures, diferent strain level and oxide layer. Moreover, those were investigated under different loading conditions, such as constant, static, and cyclic loading.

A computational model is formulated for studying dynamic crack propagation in quasi-brittle materials exposed to time-dependent loading conditions. Under such conditions, inertial effects of structural components play an important role in modelling crack propagation problems. The computational model is proposed within the theory of regularised cracks which uses a damage-like internal variable. Here, fracture considers phase-field damage which gives rise to a material degradation in a narrow material strip defining the regularised crack. Based on the energy formulation using the Lagrangian of the system, the proposed computational approach introduces a staggered scheme adopted to solve the coupled system and providing it in a variational form within the time stepping procedure. The numerical data are obtained by quadratic programming algorithms implemented together with a finite element code.

The importance of developing simple relationships for interpreting crack growth rate test results and a practical approach to predicting crack propagation under thermo-mechanical fatigue conditions based on readily available data is emphasised by many authors. In this study, a damage impact parameter was introduced to predict the crack growth rate and durability under isothermal and thermo-mechanical fatigue conditions. To validate the model, we used a single-edge notched specimen made of polycrystalline coarse-grained nickel-based alloy XH73M. The specimen was subjected to loading conditions that included in-phase and out-of-phase thermo-mechanical fatigue at a temperature range of 400–650 °C, as well as isothermal fatigue at 26 °C, 400 °C and 650 °C. A numerical analysis was used to simulate the material deformation behaviour at the crack tip according to a nonlinear kinematic hardening model. Numerical and experimental stress–strain state parameters based on strain energy density were used to formulate and estimate the damage impact parameter. Based on the correlation between the crack growth rate and the introduced damage impact parameter, a method for predicting crack propagation is proposed. The accuracy of the proposed method was experimentally validated.

We develop a computational framework to model damage and delamination in laminated polymer composite structures incorporating the effects of temperature and moisture content. The framework is founded on a recently developed comprehensive multi-layer thin-shell formulation based on Isogeometric Analysis, which includes continuum damage, plasticity and cohesive-interface models. To incorporate hygrothermal effects in the modeling, we propose a scaling law that is based on the Arrhenius equation and material glass transition temperature that establishes the dependence of the intra- and interlaminar material properties on the temperature and moisture content. We compute several classical test cases using a combination of environmental conditions and demonstrate that the resulting modeling approach shows a good agreement with the experimental data, both in terms of failure loads reached as well as failure modes predicted.