Simulation of micromechanical damage to obtain mechanical properties of bimodal Al using XFEM H. Hosseini-Toudeshky ⇑ , M. Jamalian Department of Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran article info Article history: Received 4 January 2015 Received in revised form 10 June 2015 Available online 25 June 2015 Keywords: Bimodal AL5083 XFEM Fracture Microscale Crack abstract In this paper, we focus on the stress–strain behavior prediction of the bimodal bulk Al5083 series which are comprised of Ultra-Fine Grains (UFG) separated by Coarse Grain (CG) regions. This material is selected due to the availability of the required data in the litera- ture. The CGs in the UFG matrix effectively prevents microcracks from propagation, leading to enhance ductility and toughness while the strength remains high. In this work, initially the dependency of stress–strain behavior of the model on the CG distribution in constant volume fraction is investigated by extraction of RVEs from optical microscopy (OM) images of the real material. Then, XFEM is implemented for bimodal materials considering various fracture criteria for brittle and ductile phases in maximum traction and cohesive law. The solution convergence of such a problem with irregular geometry, plasticity and crack ini- tiation–propagation without any defined pre-cracks demanded extreme effort that accom- plished by refining and arranging meshes and adding damage stabilizations. As a result of the above procedures, the sensitivity of the modeling procedure to various RVEs is obtained, the crack initiation–propagation pattern in microscale is predicted and conse- quently, the global stress–strain behavior result is obtained. It is shown that the predicted results are in good agreement with the available experimental results. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Automotive and aerospace structures are complex engi- neering systems in which it is impossible to completely avoid the occurrence of flaws such as cracks; therefore material strength and damage tolerance investigations in the presence of cracks plays an important role in designing reliable structures. In these structures, the use of light- weight materials with fail-safe designs is extremely impor- tant (Vajragupta et al., 2012). Modern materials science suggests that the analysis of damage tolerance is useful in improvement of components’ mechanical performance (Hedayati, 2014). Development of high strength and fatigue resistant alu- minum alloys is currently one of the main concerns in these industries (Tokarski, 2013). In polycrystalline materi- als, reducing the grain size to the nanometer scale, results in a substantial increase of strength and hardness (Youssef et al., 2006). Bulk nano/UFG crystalline and multiscale microstructure alloys provide the opportunity to improve the performance of lightweight structures; however, a comprehensive understanding of the deformation and fracture of nano/UFG crystalline materials is still emerging. nano/UFG crystalline materials are generally known to have low ductility, but it has been shown that generating a microstructure of coarse grains in a matrix of nano/UFG crystalline grains can substantially improve ductility (San Marchi et al., 2006). However, the ductility of these fine grained materials often shows a reduction. Such effects can be eliminated by means of a grain size distribution http://dx.doi.org/10.1016/j.mechmat.2015.06.015 0167-6636/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: Hosseini@aut.ac.ir (H. Hosseini-Toudeshky). Mechanics of Materials 89 (2015) 229–240 Contents lists available at ScienceDirect Mechanics of Materials journal homepage: www.elsevier.com/locate/mechmat