Modeling Of Fracture Behavior Research Articles

Dynamic recrystallization based ductile fracture modeling in hot working of metallic materials

Ductile fracture is a key factor to the workability of metallic materials undergoing hot deformation. The ductility of materials at elevated temperature is closely related to dynamic recrystallization (DRX). To systematically investigate the DRX based ductile fracture, hot tensile experiments, microscopic observations and modeling of fracture behavior were conducted for 316LN steel. Based on the experimental results, a monotonic increasing relationship between ductility and the percentage of DRX (Xdrx) was figured out and identified to be attributed to the DRX influenced void evolution. With the softening effect caused by DRX, the local stress concentration, which serves as the driving force of void nucleation, void growth as well as void coalescence of the material, is highly relieved and the behaviors of voids thus change. To describe the DRX based void evolution and predict ductile fracture in hot working process, an extended damage model was established by introducing Xdrx into the void-based GTN-Thomason ductile fracture model, which is termed as the extended GTN-Thomason model in this research. In modeling of the ductile fracture considering DRX, the void nucleation strain, which represents the strain with the highest nucleation rate, and the critical void size ratio, which articulates the onset of void coalescence were figured out to increase with Xdrx. In addition, the strain rate sensitivity and the temperature dependency are involved in representing the kinetics of DRX and the flow stress applied in the model. The developed model was then implemented into finite element (FE) simulation and its related parameters were calibrated via a hybrid experiment and simulation method. Finally, the specific validation experiments were designed and conducted and the predicted fractures agree well with experimental results. This research thus offers an in-depth understanding of the DRX based ductile fracture and further facilitates and supports the design of hot working process by avoiding ductile fracture occurrence.

Modeling of fracture behavior in polymer composites using concurrent multi-scale coupling approach

ABSTRACTEmbedded statistical coupling method was originally developed to provide computational efficiency, to decrease coupling complexities, and to avoid the need to discretize the continuum model to atomic scale resolution in concurrent multi-scale modeling. An embedded statistical coupling method scheme is relatively easy to implement within a conventional finite element method code and has been tested in standard solid lattice structures. However, this method encounters difficulties when being implemented for amorphous materials like polymers, due to the fact that they lack specific ordered lattice structure and atoms may not be covalently bonded with each other, which are the requirements of common coupling schemes. Therefore, a new approach needs to be developed to resolve this problem. In this article, details of a modified embedded statistical coupling method approach for atomistic-continuum coupling developed to perform simulations of macroscale crack growth in polymers is presented. The presence of the continuum domain surrounding the molecular dynamics region allows for the application of far field loading, and prevents stress wave reflections from the external boundary impinging back on the crack tip. In our approach, a material point method, which is a meshless particle-in-cell method based on an arbitrary Euler-Lagrange scheme and has been proven to have good performance in large deformation problems, is used to model the continuum domain. It is concurrently coupled with molecular dynamics, a widely used method in atomistic simulations, using a so-called handshake region. Anchor points, the equilibrium positions of the constrained particles, which are designed to transmit displacements and forces between nanoscale and macroscale model, are defined in the handshake region. A concurrently coupled material point method-molecular dynamics simulation of crack propagation inside a polymer is performed to verify this new coupling approach, thereby providing a better understanding of the fracture mechanisms at the nanoscale to predict the macro-scale fracture toughness of a polymer system. Results are presented for concurrently coupled simulation of crack initiation and crack propagation in a di-functional cross-linked thermoset polymer, EPON 862.

Modelling of fracture behaviour in biomaterials

One of the most frequent causes of degradation and failure of quasi-brittle biomaterials is fracture. Mechanical breakdown, even when not catastrophic, is of particular importance in the area of biomaterials, as there are many clinical situations where it opens the path for biologically mediated failures. Over the past few decades the materials/biomaterials community has developed a number of numerical models, but only with limited incorporation of brittle failure phenomena. This article investigates the ability of a non-linear elastic fracture mechanics (NLEFM) model to reliably predict failure of biomaterials with a specific focus on the clinical settings of restorative dentistry. The approach enables one to predict fracture initiation and propagation in a complex biomechanical status based on the intrinsic material properties of the components. In this paper, we consider five examples illustrating the versatility of the present approach, which range from the failure of natural biomaterials, namely dentine and enamel, to a restored tooth, a three unit all ceramic bridge structure and contact-induced damage in the restorative layered materials systems. It is anticipated that this approach will have ramifications not only to model fracture events but also for the design and optimisation of the mechanical properties of biomaterials for specific clinically determined requirements.