Shear Bands in Materials Processing: Understanding the Mechanics of Flow Localization From Zener's Time to the Present

Abstract

Shear banding is a material instability in large strain plastic deformation of solids, where otherwise homogeneous flow becomes localized in narrow micrometer-scale bands. Shear bands have broad implications for materials processing and failure under dynamic loading in a wide variety of material systems ranging from metals to rocks. This year marks 75 years since the publication of Zener and Hollomon's pioneering work on shear bands (Zener and Hollomon, J Appl. Phys., 15, 22–32, 1944), which is widely credited with drawing the attention of the mechanics community to shear bands and related localization phenomena. Since this landmark publication, there has been significant experimental and theoretical investigation into the onset of shear banding. Yet, given the extremely small length and time scales associated with band development, several challenges persist in studying the evolution of single bands, postinitiation. For instance, spatiotemporal development of strain fields in the vicinity of a band, crucial to understanding the transition from localized flow to fracture, has remained largely unexplored. Recent full-field displacement measurements, coupled with numerical modeling, have only begun to ameliorate this problem. This article summarizes our present understanding of plastic flow dynamics around single shear bands and the subsequent transition to fracture, with special emphasis on the postinstability stage. These topics are covered specifically from a materials processing perspective. We begin with a semihistorical look at some of Zener's early ideas on shear bands and discuss recent advances in experimental methods for mapping localized flow during band formation, including direct in situ imaging as well as ex situ/postmortem analyses. Classical theories and analytical frameworks are revisited in the light of recently published experimental data. We show that shear bands exhibit a wealth of complex flow characteristics that bear striking resemblance to viscous fluid flows and related boundary layer phenomena. Finally, new material systems and strategies for reproducing shear band formation at low speeds are discussed. It is hoped that these will help further our understanding of shear band dynamics, the subsequent transition to fracture, and lead to practical “control” strategies for suppressing shear band-driven failures in processing applications.

Photoelastic characterization of shear‐bands in mechanically stretched polymeric fibers

“…In terms of energy, in homogeneous processes such as shear bands and crazing would absorb energy (Donald & Kramer, 1982). This knowledge enhances the design of new materials and increases the endurance of existing materials to extreme working conditions, which is the focus of recent research activities (Tang et al, 2018;Viswanathan, Yadav, & Sagapuram, 2020;Wang et al, 2018).…”

Determining large-strain metal plasticity parameters using in situ measurements of plastic flow past a wedge

“…A potential complication is that certain multi-phase engineering alloys (e.g. high-strength steels, Ti and Ni alloys) are prone to shear localization, especially at high V0 [10,11,49]. While this is not a fundamental limitation, in that the proposed parameter estimation method is independent of the nature of the flow, this will, however require the use of special imaging techniques with even better spatial/temporal resolution to accurately capture the localized flow; some of our preliminary work [26,27] touches upon full-field measurement issues in the presence of shear localization.…”

“…In these applications, the material deformation is well into the plastic regime and often characterized by extreme strains of several hundreds to thousand percent, strain rates in the range of 10 to 106/s, and significant plastic heating. Other examples which involve large plastic deformation and flow, albeit over small localized volumes, include tribological contacts [4], erosion [5], indentation [6,7] and deformation fields in the vicinity of a fast-running ductile crack or a shear band [8–11]. For computational finite-element models to provide accurate predictions of the material behaviour and flow kinematics, it is imperative that the parameters of the material’s constitutive law ‘the law that relates the flow stress to plastic strain, strain history, strain rate and temperature’ be calibrated under relevant large deformation conditions.…”

Role of Si Minor Addition on Glass Formation and Flow Stress Characteristics of a Zr-Based Metallic Glass

“…However, poor room-temperature ductility of MGs under tensile loading is a big challenge to apply them in engineering structures 4,5 . Several works have been done to identify mechanism of flow stress behavior of MGs under tensile loading and few studies have succeeded to improve tensile flow characteristics in amorphous alloys [6][7][8] . Tensile loading sensitivity is so high that even the MG composites are exposed to the brittle fracture 9,10 .…”

“…In another work, a failure mechanism based constitutive model for bulk metallic glass was proposed, in which the nucleation and coalescence of nano-voids during the deformation was estimated 21 . Another study presented a thermodynamically constitutive model of MGs by extending an infinitesimal deformation approach, in which the multiplicative decomposition of deformation gradient and additive decomposition of free energy was considered 22 . Yao et al 23 developed a size-dependent constitutive model of MGs and found that the size effect is a crucial factor in micro forming processes.…”