Micromechanics stress–strain behavior prediction of dual phase steel considering plasticity and grain boundaries debonding H. Hosseini-Toudeshky a , B. Anbarlooie a,⇑ , J. Kadkhodapour b,c a Fatigue and Fracture Mechanics Lab., Department of Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran b Department of Mechanical Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran c Institute for Materials Testing, Materials Science and Strength of Materials (IMWF), University of Stuttgart, Stuttgart, Germany article info Article history: Received 24 September 2014 Accepted 10 December 2014 Available online 18 December 2014 Keywords: Dual phase steel Cohesive zone Stress–strain Interface debonding Ferrite and martensite interfaces abstract Stress–strain response of multiphase materials similar to dual phase (DP) steel depends on the elastic– plastic and damage behavior of all ingredient phases. DP steels typically contains of ferrite and martensite phases, but the grain boundaries of martensite phase may act as important location with possible occur- rence of damage or debonding under static loading. The focus of this paper is consideration of ferrite and martensite interface debonding in addition to the elastic–plastic behavior of ferrite and martensite to predict the stress–strain behavior of DP steel using a finite element (FE) micromechanical approach. For this purpose the micromechanics representative geometry is selected from scanning electron micros- copy (SEM) images and the finite element mesh is generated based on the real shape of grains. Interface elements based on the cohesive zone modeling are also used for consideration of damage or debonding on the ferrite and martensite interfaces. Therefore, the developed micro mechanic finite element model is based on the real microstructure, uses cohesive elements between martensite islands and ferrite matrix and also considers the elastic–plastic behavior of ferrite and martensite phases. Handling of such simu- lation procedure with two source of material nonlinearity (plasticity and cohesive zone damage) is not an easy task. It is shown that the obtained stress–strain behaviors are in well agreement with the experi- mental results. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Recently, automotive industries explore a material solution for lightweight and crash-safe designs. Dual phase steels are among the most important advanced high strength steel (AHSS) products recently developed for the automotive industry. This group of steels is very interesting for light weight constructions because it combines a high ultimate strength with a high fracture strain [1]. Dual phase steels consisting of hard martensite islands within a ferrite matrix have received considerable attention due to their continuous yielding behavior, high work hardening rate and ductil- ity [2]. The key microstructural characteristics for DP steel are the amount, strength and distribution of the martensite islands [3]. One approach for the commercial production of dual phase steel is the continuous annealing approach, where hot or cold rolled steel strip is uncoiled and annealed intercritically to produce the desired microstructure [4]. Irrespective of the chemical composi- tion of the alloy, the simplest way to obtain a ferritic–martensitic steel is intercritical annealing of the ferritic–pearlitic microstruc- ture, followed by a sufficiently rapid cooling to enable the austen- ite to martensite transformation. The microstructure and the final amount of ferrite and martensite in DP steel can be controlled by the holding time, intercritical temperature, and the cooling rate [5,6]. Microstructural components of DP steels are under three dis- tinct deformation processes in the mechanical response up to the failure point. In the first stage both the ferrite matrix and martens- ite particles deform elastically. In the second stage the ferrite phase deforms plastically while the martensite phase continues to deform elastically. In the third stage both the ferrite and martens- ite phases deform plastically [7,8]. Then, the voids nucleation in the microstructure may leads to the failure of component. In the failure procedure of dual phase steel during the necking and local- ization, large deformation, rotation and displacement occur in the ferrite matrix and subsequently rotation and displacement trans- mit to the martensite grains [9]. SEM microstructure analysis of dual phase steel reveals three distinctive mechanisms of voids nucleation: cracking of the martensite, de cohesion at ferrite and martensite interface, and separation of adjacent martensite regions [10,11]. http://dx.doi.org/10.1016/j.matdes.2014.12.013 0261-3069/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +98 9127893574. E-mail address: anbarluei@aut.ac.ir (B. Anbarlooie). Materials and Design 68 (2015) 167–176 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes