13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Finite Element Simulation of Interfacial Fracture between Fe3C and α-Fe Based on Cohesive Zone Law Deriving from Molecular Dynamics Taolong Xu1, Xiangguo Zeng1, Anlin Yao2,*, Yi Liao1, Rongpeng Xu1,3 1 College of Architecture and Environment, Sichuan University, Chengdu 610065, PR China 2 School of Petroleum Engineering, Southwest Petroleum University, Chengdu 610500, PR China 3 School of Engineering, Alfred University, Alfred, NY, USA 14802 * Corresponding author: yaoalt@sina.com Abstract Once the cohesive zone model (CZM) is used to describe material behavior near crack front zone, it was convenient to simulate crack propagation by using finite element. Actually, the cohesive zone model is depicted by means of the traction-separation relation. But, It is very difficult to determinate such a relation, i. e, the traction-separation relation, through experiment, respectively. The traction-separation laws of most previous work are often assumed rather than predicted. First of all, in order to parameterize and obtain a traction-separation (T-S) law, Molecular dynamics (MD) simulations via Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) are carried out at atomic scale for the deformation and fracture of Fe3C-α-Fe interface in tensile loadings at different temperatures in our study. Then, the generated parameterized traction-separation law is implemented in the finite element model with the behavior of the CZM described by traction-separation (T-S) law. Finally, the ABAQUS finite element commercial software is employed to simulate the crack propagation behavior for X70 pipeline steel CT specimen. Keywords Crack propagation, Cohesive zone model, Molecular dynamics, Parameterized traction-separation law 1. Introduction After more than ten years of construction and development, the length of high pressure gas pipeline made of X70 steel has over 8,000 kilometers in China. As a structure material, X70 pipeline has high excellent strength and toughness. The research of mechanical properties, deformation and fracture mechanism of X70 steel become more and more important. Metallographic analysis show that X70 steel mainly consists of ferrite and a small amount of pearlite[1]. Physics-based modeling of fracture begins at nanometer length scales in which atomic simulation is used to predict the formation, propagation and interaction of fundamental damage mechanisms[2,3]. In recent years, in this research field, great attentions have been paid to use the cohesive zone model (CZM) to set up the leaking between atomic-scale and macro-scale near crack front zone. The theory of cohesive zone model may be traced back to the early works by Dugdale[4] and Barrenblatt[5], in which both concepts of atomistic de-cohesion and the defect process zone are established. Xu and Needleman[6,7] first related the cohesive zone model (CZM) with finite element analysis, and they developed the cohesive finite element method and successfully applied it to simulate crack propagation problems. Cohesive elements that possess zero volume in an undeformed state are inserted between bulk elements. They are particularly appropriate when the crack propagation path can be well-reasoned. Cohesive zone law defines the relation between traction and crack opening displacement. Because it is difficult to direct experimentally quantify the relation, construction of such a law has been a challenging task in the past decade[8,9]. The traction-separation (T-S) relationship in a CZM is generally parameterized through empirical data, such as by using the macroscopic fracture toughness of the material or by conducting nanocrystalline experiments to obtain the stress-strain data[10]. The problem with inputting macroscopic/empirical values of fracture toughness is that these are aggregate responses of hundreds of thousands of grains applied to the location where fracture occurs[11]. This paper simulated a compact tension fracture mechanics specimen through cohesive elements whose T-S relation between Fe3C and α-Fe was derived from MD simulations. These results enable
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