13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Mesh Dependence of Transverse Cracking in Laminated Stainless Steel with both High Strength and High Ductility Xiang Guo1, 2, Wenjun Zhang3, Jian Lu4,* 1 School of Mechanical Engineering, Tianjin University, Tianjin 300072, China 2 Tianjin Key Laboratory of Nonlinear Dynamics and Chaos Control, Tianjin 300072, China 3 School of Civil Engineering, Tianjin University, Tianjin 300072, China 4 Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong * Corresponding author: jianlu@cityu.edu.hk Abstract A combination of surface mechanical attrition treatment (SMAT) and co-rolling can produce large-scale laminated nanostructured stainless steel (SS) with both high strength and high ductility. Recent numerical results based on the cohesive finite element method have revealed that brittle nanograined interface layer can enhance the ductility of the co-rolled SMATed SS. Here, numerical investigation focuses on effects of both shape of the bilinear cohesive law and mesh size and shows that the larger thickness of the phases in uniform state allows the use of coarser meshes. Keywords Laminated nanostructured metals, cohesive finite element method, bilinear cohesive law, mesh dependence 1. Introduction Surface mechanical attrition treatment (SMAT) and co-rolling can be combined to produce large-scale laminated nanostructured metals with both high strength and high ductility [1]. Therefore, it is believed to have a good future to be applied in structural engineering. Through the SMAT, a nano-crystalline surface can be generated for various metals to enhance their yield stress and fatigue life. The co-rolled SMATed metals with nanograined interface layers (NGILs) can be produced. This approach can generate laminated nanostructured 304 stainless steel (SS) with tensile yield stress 878 MPa and failure strain 48% [1]. A computational framework for fracture analysis is in need to investigate the toughening mechanism. The main concern is on the nucleation and the propagation of non-localized microcracks into coarse-grained layer (CGL). Therefore, the cohesive finite element method (CFEM) is appealing to investigate the cracking. The CFEM can model damage initiation/evolution and fracture processes explicitly and has been used to investigate brittle and ductile fracture extensively. The intrinsic CFEM embeds cohesive elements along boundaries of all volumetric elements as part of the physical model [2]. It was adopted in our former studies [3,4]. Our studies have shown that both the critical energy release rate and the thickness of the NGIL play critical roles in determining the overall ductility of the co-rolled SMATed 304SS. However, the dependences of the results on both shape of the cohesive law and the mesh have not been addressed. 2. Mesh dependence issue and numerical framework Many cohesive laws have been developed [5]. The bilinear cohesive law was used in [3,4], as shown in Fig. 1. max T , cohesive strength, is the stress at which the damage initiates and the
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