Materials Science and Engineering A 384 (2004) 35–46 Self organization of shear bands in stainless steel Q. Xue, M.A. Meyers ∗ , V.F. Nesterenko Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093, USA Received 22 April 2002; received in revised form 12 May 2004 Abstract The spatial distribution of shear bands was investigated in 304L stainless steel through the radial collapse of a thick-walled cylinder under high-strain-rate deformation (∼10 4 s -1 ). The shear-band initiation and propagation were also examined. Self-organization of multiple adiabatic shear bands was observed. The effect of grain size on spacing of shear bands was investigated at four different grain sizes: 30 m, 50 m, 140 m and 280 m. A single crystal with a similar composition was also tested. The experimental results show only a modest variation of shear-band spacing within the investigated grain size range. Three principal mechanisms are considered to be active in initiation: (a) momentum diffusion by stress unloading, (b) perturbation in the stress/strain/temperature fields, (c) microstructural inhomogeneities. The observed shear-band spacing is compared with existing theories; Grady–Kipp and Wright–Ockendon–Molinari theories. These are one-dimensional theories that do not consider the evolution in spacing as the shear bands grow. A discontinuous growth mode for shear localization under periodic perturbation is applied and predicts spacings in good agreement with observations. Self-organized initiation and propagation modes are discussed in relation to the interaction among the nucleus and well-developed shear bands. © 2004 Elsevier B.V. All rights reserved. Keywords: Shear bands; Dynamic deformation; Stainless steel; Self organization 1. Introduction Thermally-assisted shear localization is one of the most important deformation and failure mechanisms in materi- als subjected to high strain rate deformation. Initial pertur- bations lead to a non-uniform distribution of temperature, which promotes localized softening and accelerates catas- trophic failure. Adiabatic shear bands have been extensively studied [1–3] since the mechanism was described by Zener and Hollomon [4]. A significant body of research has been carried out, correlating both the thermomechanical response and metallurgical characteristics with the sensitivity to shear localization. The perturbation analysis [5–8] was success- fully used to model the evolution of localization. This evolu- tion was experimentally investigated under controlled con- ditions by Marchand and Duffy [9], among others. In most studies, isolated bands were investigated. Nev- ertheless, multiple shear bands are often found in dynamic deformation events, such as explosion and impact. The evolution of multiple shear bands exhibits some features of ∗ Corresponding author. Tel.: +1 858 534 4719; fax: +1 858 534 5698. E-mail address: mameyers@mae.ucsd.edu (M.A. Meyers). self-organization. Shear bands were first shown by Bowden [10] to have a characteristic periodic spacing. Shockey [11] used an expanding cylinder accelerated by explosives and were able to determine the spacing of shear bands in steels. Grady [12], Grady and Kipp [13], Wright and Ockendon [14], and Molinari [15] developed theoretical predictions for shear band spacing that represent a beginning of our understanding of their collective behavior. More recently, Nesterenko et al. [16,17] developed an explosive testing method using a thick-walled cylinder specimen, which was successfully used to investigate the spacing of shear bands. This method has been successfully used by Nesterenko et al. in titanium [18,19], copper [17], tantalum [20], and Ti–6Al–4V [21–23]. It was also used to demonstrate the im- portance of shear localization in granular materials [24,25]. This subject is comprehensively reviewed in [26,27]. Pre- liminary results on self-organization of shear bands in 304 SS were recently presented [28,29]. The purpose of this paper is to extend these findings by characterizing the evolution of multiple shear bands in a typ- ical F.C.C. material (stainless steel), to analyze the spacing characters and to compare it with the existing theories. For the first time, the effects of microstructural variables (grain size and annealing) on shear-band sensitivity, nucleation, and 0921-5093/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2004.05.069