Simulation of shear failure in dual phase steels using localization criteria and experimental observation J. Kadkhodapour a,⇑ , B. Anbarlooie b , H. Hosseini-Toudeshky b , S. Schmauder c a Department of Mechanical Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran b Department of Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran c Institute for Materials Testing, Materials Science and Strength of Materials (IMWF), University of Stuttgart, Stuttgart, Germany article info Article history: Received 14 November 2013 Received in revised form 23 February 2014 Accepted 27 February 2014 Available online xxxx Keywords: Dual phase steel Shear localization Stress strain Micro-crack Micro-structure abstract Failure in dual phase (DP) steels is a phenomenon that has been extensively investigated in the last dec- ade through experimental tests and simulation methods. Experimental procedures have shown that fail- ure has a ductile pattern and that shear failure is dominant in these materials. In this research, both experimental and numerical methods were employed to investigate shear failure in dual phase steels. Scanning electron microscopy (SEM) images of the specimens depicted the voids and shear driven voids growth in regions of localized plastic strain in the ferrite matrix. In the simulation section, mechanisms of shear failure in DP steels were simulated by a micro-struc- tural ductile damage model. Solution and convergence of a finite element (FE) problem with irregular geometry, plasticity and ductile progressive damage was a challenging task. The criteria for shear local- ization were implemented in a FE model of a DP steel microstructure by ANSYS parametric design lan- guage (APDL) code to investigate pattern of shear failure. On the other hand, global stress strain behavior was investigated and compared with experimental results. It was concluded that localization criteria could reliably predict shear failure of DP steels. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Recently, automotive industries investigate application of ad- vanced materials like dual phase (DP) steels in vehicle structures. Dual phase steel has many important factors for automobile indus- try applications including less fuel consumption, less manufactur- ing costs, less amount of pollution and higher standards for crash safety [1]. Micro-structure of DP steel consists of hard martensite islands in a soft ferrite matrix. With respect to different phases of dual phase steel structure, a particulate composite model is able to describe material behavior on the micro-scale with good accu- racy [2]. Grain size reduction is effective in improvement of mate- rial behavior [3]. SEM microstructure analyses of DP steels [4] revealed three dis- tinctive mechanisms of void nucleation: cracking of martensite, decohesion at ferrite and martensite interfaces and separation of adjacent martensite regions. The majority of voids formed at ferrite and martensite interfaces were located between closely spaced martensite particles. The voids nucleated at a ferrite/martensite interface by decohesion and formed by particle separation were elongated in the direction of applied load in higher strain values. Moreover, plastic deformation in the adjacent ferrite grains was re- ported and, with increasing strain, the voids grew longitudinally along the grain boundaries. Propagation of ductile cracks occurred by the coalescence of voids along shear bands [4]. Shear bands were formed inside ferrite grains while martensite was hardly deformed and the deformation was localized in the fer- rite matrix [5]. For dual phase steels with high martensite volume fractions, shearing of the ferrite and martensite interface occurred and the deformation extended into the martensite islands. In-situ SEM testing was carried out recently to observe the deformation field in dual phase steels and the same result was obtained in [6]. Avramovic-Cingara et al. [7] performed quantitative measure- ments to determine rate of ductile damage accumulation during in situ SEM tests. They reported that rate of development of the void population with strain was initially low and then increased at large strains. They observed that voids mostly initiated on the interfaces normal to the tensile axis and grew along ferrite grain boundaries. According to the investigations by Marvi-Mashhadi et al. [8] on initiation and relative orientation of the plastic strain localization, failure mode of dual phase steels was also shear dominated. Plastic strain localization occurred in shear band at an angle of 40°–50° http://dx.doi.org/10.1016/j.commatsci.2014.02.046 0927-0256/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +98 21 22970052. E-mail address: j.kad@srttu.edu (J. Kadkhodapour). Computational Materials Science xxx (2014) xxx–xxx Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci Please cite this article in press as: J. Kadkhodapour et al., Comput. Mater. Sci. (2014), http://dx.doi.org/10.1016/j.commatsci.2014.02.046