A Crystal Plasticity Approach for Shear Banding in Hot Rolled High-Strength Steels
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I.
INTRODUCTION
LOCALIZATION of deformation to shear bands is one of the most important sources of failure in materials that are subjected to high strains and high strain rates. The characteristics of the materials affect their tendency to develop localized deformation bands, initiating for example from the inhomogeneities of the microstructure. The martensitic wear-resistant steels are widely used in applications requiring high initial strength combined with reasonable ductility, such as in various mining processes. One of the most important factors affecting the shear banding propensity is the materials strain hardening capability.[4,10,34,41] The limited strain hardening capability of quenched and tempered martensite tends to lead to the development of strain localization bands at large plastic deformations. In general, martensitic steels are not very strain rate sensitive, but the high strain rate conditions are still found to cause shear banding more easily also in these materials.[3,26,33] For example, in impact wear-related applications, the tendency to shear banding can be a significant challenge, since shear bands can cause severe damage in the parts and components already during manufacturing,[24] as well as be a major contributor to the failure processes during the use of the parts.[27]
MATTI LINDROOS and ANSSI LAUKKANEN are with the VTT Lifecycle Solutions, Espoo, Finland. Contact e-mail: matti.lindroos@vtt.fi VELI-TAPANI KUOKKALA is with the Department of Materials Science, Tampere Wear Center, Tampere University of Technology, Tampere, Finland. Manuscript submitted April 21, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Great interest has been placed on developing initiation and propagation models for shear banding, especially related to the macroscopic scale simulations of forming and cutting operations and dynamic failure of materials.[32] The finer scale models focusing on the microstructure level are more scarce. Crystal plasticity models[12,13,15,17,36] have been used to seek the fundamental reasons for localization arising from the microstructure level. Quite recent research activities in this field involve special alloys,[16,37] focusing on the microstructural heterogeneity and size effects,[7,11,29,43] and research beyond finite element solvers for easier implementation of material failure propagation.[39] All these efforts underline the importance of shear localization to the failure in various types of materials, especially in the thermomechanically processed ultrahigh-strength steels. Despite the still limited understanding of the details of the strain localization mechanisms in high-strength steels, recent crystal plasticity studies[25,35,40] have shown the potential of developing the steel microstructures by virtual design tools, which could also take into account the shear banding phenomenon. Alternatives for the conventional crystal plasticity approaches to shear localization have been suggested for example by Anand and Su,[1] who considered the deformation of amorphous glasses by virtua
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