International Journal of Fracture最新文献

Dynamic crack involves instabilities promoted by either external perturbation or intrinsic front oscillation. In an effort to decipher fracture surface markings of brittle materials, crack roughness of Wallner lines promoted by shear waves and surface corrugations induced by spontaneous front oscillations was investigated with silicon single crystal. The statistical distribution of surface height variations and the corresponding roughness exponents were determined. The Wallner lines are found to be self-affine with a Gaussian distribution and a roughness exponent of 0.8, which are consistent with the surface flaws giving rise to shear waves. In contrast, the surface corrugations do not exhibit self-affinity, due to their scale invariant characteristic shape. Interestingly, specific instabilities, which appear at very high speed and exhibit similar physical properties as front waves, render the crack roughness self-affine with a Gaussian distribution and a roughness exponent of 0.5. The findings of the present work will help to understand the origin of fracture surface markings for brittle materials, especially for single crystalline ceramics.

This article aims to discuss and complete the avalanche representations of the failure process of quasi-brittle materials. Paper was used as a model material. We proposed an original method to determine avalanches extracted directly from the force drops in the post-peak regime of experimental force–displacement curves. We studied the avalanche distributions on notched and unnotched samples, taking into account the measurement noise. From these experimental tests, two regimes in the avalanche distribution were observed during the propagation of a macrocrack, in particular with a well-defined power law at small scale, that was consistent with other avalanche distributions based on other methods and other materials in literature. A single regime power-law distributed was found for a diffuse damage (without a significant macrocrack propagation) using the Mazars’ damage model. Our results showed that the post-peak regime of tensile curves contained the statistical signature of the propagation of a macrocrack during the rupture of paper.

The focus of this study was prevented disasters caused by the breaking of high hard roofs (HHRs) in mines. A model of the mining load-bearing capacity of a HHR cantilever beam structure (HHRCBS) was developed based on elastic foundation beam theory. The evolution of mining load-bearing capacity and energy aggregation and dissipation in HHRs were analyzed. Additionally, the dynamic working resistance experienced by hydraulic supports was quantitatively decomposed from an energy perspective. The findings indicated that (1) during mining operations, the pressure and strength of the working face were primarily governed by the stability of the HHRCBS. (2) The cantilever length significantly influenced the evolution of mining load-bearing capacity and energy aggregation and dissipation in the HHR. By reducing the length of the cantilever beam in the HHR, the effects of roof breakage on the cantilever beam structure were significantly decreased. (3) The dynamic load of the overburden and the energy released by the breakage of the HHR corresponded to 7536.1 kN, while the static load generated by the breaking of low rock blocks was 8348.3 kN. We then analyzed an integrated surface control technology for HHRs and conducted a field test in the Datong Mining District. The measured dynamic working resistance showed that the proposed integrated surface control technology could effectively prevent strong pressure during mining.

Owing to their excellent biocompatibility and capability of large deformation, hydrogels have attracted extensive attention for promising applications. When subjected to cyclic loads, hydrogels are susceptible to fatigue. To ensure their durability, it is crucial to have a deeper understanding on the fatigue mechanisms of hydrogels. However, there is a lack of study in the literature for predicting the fatigue damage of hydrogels under the coupling of large deformation and water diffusion. This work aims to formulate a fatigue life predictor for characterizing the crack nucleation of single-network hydrogels and unveil the effects of water diffusion on fatigue. Borrowing the concept of fatigue crack nucleation for rubber-like materials, the fatigue life predictor is developed within the framework of configurational mechanics. With the proposed predictor, the contributions of stretching and mixing to the fatigue damage of hydrogels are identified. Case studies with different swelling conditions are conducted to further distinguish various effects, including chemical potential, loading rate, and cyclic stretching amplitude, on both stretching and mixing induced damage. It is concluded that the fatigue damage accumulation in hydrogels under cyclic loading is the competing result of stretching and water diffusion. As the proposed predictor is capable of predicting the spatial fatigue damage of hydrogels, the current research can provide guidance on designing loading profiles to improve the fatigue life of hydrogels. In addition, by incorporating self-healing mechanism and multiphysics coupling, the proposed modeling framework can be further expanded to investigate the fatigue of other hydrogels, like double-network and stimuli-sensitive hydrogels.

Lattice metamaterials have been attracting wide research interests due to their excellent mechanical properties. Most of meta-properties have been implemented by proper geometric designs of microstructures. In this study, we examine another way to obtain outstanding properties, which has been relatively less explored. That is, we aim to adjust the loading bearing capability of lattices by periodically introducing prestress into particular lattice segments. Based on existing related works, we focus on the following two problems deserving further investigations. First, results have been provided based on a single cell with/without taking into account the interactions between each two of neighboring individual cells. Second, it is interesting to search for the optimal distribution of prestress in lattices subjected to a specific load. For the former, we propose a set of constraint equations for implementing periodic boundary conditions (PBC) on a periodic unit cell and validate the method. The significance of PBC related to rotational degrees of freedom is emphasized. We then use the proposed method to calculate the initial damage surface of four kinds of prestressed lattice unit cells under PBC. For the latter, we build a new optimization algorithm with the help of the so-called Symbiotic-Organisms-Search technique (SOS), to calculate the optimal prestress setting corresponding to the requested properties. As an example, the optimal prestress setting is found to almost double the critical load to failure of the lattice in a special direction. This work may be helpful to design lattice metamaterials with programmable strengths.

The peridynamic (PD) theory is a nonlocal reformulation of mechanics with various advantages over common approaches, mainly local continuum mechanics and molecular dynamics (MD). PD theory can capture phenomena at different dimensions, including nanoscale. However, limited studies have been performed by this theory in nanoscale, which have generally focused on the feasibility and accuracy of using PD in atomic-scale modeling. In the present study, based on the ordinary state-based peridynamic method, we investigate the fracture of pre-cracked single layer graphene sheets (SLGSs) under uniaxial tension. By simulating the exact atomic model of graphene, the failure strain and crack growth pattern in the zigzag and armchair directions in PD are compared with MD. We show that by considering some restrictions, these two methods have a good consistency with each other. Afterward, we study two different coarse-grained PD models and demonstrate this method can simulate the failure of graphene with acceptable accuracy. A significant reduction in simulation cost is an excellent point of the PD compared to the MD simulation model. Under these conditions, a massive atomic model with several million atoms can be easily simulated.

Hydrogels exhibit rate-dependent fracture behavior, due to solvent diffusion, rearrangement of the polymer network, and other mechanisms. To explore rate-dependent fracture behavior, a series of creep fracture experiments were performed on gelatin-based hydrogels under different controlled humidity, and load conditions. The crack tip boundary condition was controlled to non-immersed and fully water-saturated conditions. Additionally, full-field measurements of the displacement field were performed with digital image correlation. From these experiments, we show that humidity influences the crack initiation time but not the growing crack speed, and that water on the crack tip will significantly influence the fracture properties of the failure zone. Schapery’s viscoelastic J-like integral was adopted for analysis of the experimental measurement to distinguish bulk viscoelastic dissipation from the fracture process zone dissipation. We show that viscoelastic J-like integral is path-independent and can serve as a characterizing parameter for quasistatic crack growth, which provides a way to predict crack growth speed in the simulations.

Repurposing existing natural gas pipelines for hydrogen transport requires an accurate assessment of the distribution of hydrogen (H) atoms at defects, such as dents, under frequent pressure fluctuations experienced by gas pipelines. In this work, a 3-dimensional finite element-based model was developed to determine the stress/strain and H atom concentrations at an unconstrained dent on an X52 steel pipe which experienced denting, spring-back and cyclic loading processes. As expected, stress and strain concentrations generate at the dent center. However, the cyclic loading reduces the stress level and shifts the stress concentration zone from the dent center along the circumferential direction. As the dent depth increases, the maximum H atom concentration is further shifted from the dent center to the side. There are no certain relationships among the maximum H atom concentration, von Mises stress, hydrostatic stress, and plastic strain in terms of their distributions and quantities. Pressure fluctuations decrease both the stress and H atom concentrations at the dent, providing a beneficial effect on reduced risk of the dented pipelines to hydrogen embrittlement in high-pressure hydrogen gas environments. The indenter size has little influence on the H atom distribution in the dent area.

This paper aims to study the Mode-I penny-shaped crack problem of an infinite body of one-dimensional hexagonal piezoelectric quasicrystal. The problem is transformed into a mixed-boundary value problem in the context of electro-elasticity of quasicrystals, and the corresponding integro-differential equations are analytically solved. Two extreme cases of electrically impermeable and permeable crack surface are considered. By virtue of the generalized potential theory method, the three-dimensional complete analytical solutions of three-dimensional crack problems under symmetric concentrated and uniform loads are expressed in terms of elementary functions. Important parameters in fracture mechanics are explicitly derived, such as crack surface displacements, the distributions of generalized stresses at the crack tip and the corresponding generalized stress intensity factors. The validity of the proposed solutions and the coupling effect of phonon-phason-electric fields are investigagted through numerical examples.

Environmental aging induces a slow and irreversible alteration of the rubber material’s macromolecular network. This alteration is triggered by two mechanisms which act at the microscale: crosslinking and chain scission. While crosslinking induces an early hardening of the material, chain scission leads to the occurrence of dangling chains responsible of the damage at the macromolecular scale. Consequently, the mechanical behavior as well as the fracture properties are affected. In this work, the effect of aging on the mechanical behavior up to fracture of elastomeric materials and the evolution of their fracture properties are first experimentally investigated. Further, a modeling attempt using an approach based upon a micro-mechanical but physical description of the aging mechanisms is proposed to predict the mechanical and fracture properties evolution of aged elastomeric materials. The proposed micro-mechanical model incorporates the concepts of residual stretch associated with the crosslinking mechanism and a so-called “healthy” elastic active chain (EAC) density associated with chain scission mechanism. The validity of the proposed approach is assessed using a wide set of experimental data either generated by the authors or available in the literature.