Dynamic recrystallization and adiabatic shear localization

Abstract

It has recently been reported that, in alloys exhibiting early dynamic recrystallization (DRX), the onset of adiabatic shear bands (ASB) is primarily related to microstructural transformations, instead of the commonly assumed thermal softening mechanism as shown by Rittel et al. (2006Rittel et al. ( , 2008 and Osovski et al. (2012b). Further, the dominant role of microstructural softening in the necking process of dynamically stretching rods showing DRX has been verified using linear stability analysis and finite element simulations by Rodríguez-Martínez et al. (2014). With the aim of extending this coupled methodology to shear conditions, this paper presents an analytical solution to the related problem of ASB in a material that undergoes both twinning and dynamic recrystallization. A special prescription of the initial and loading conditions precludes wave propagation in the specimen which retains nevertheless its inertia, allowing for a clear separation of material versus structural effects on the localization process. A parametric study, performed on the constants of the constitutive model, permits the identification of their relative role in the onset of the dynamic instability. The main outcome of the analysis confirms the strong destabilizing effect played by the development of DRX, consistently with the former statement regarding ASB, and contributes to rationalize the observations of other authors.

Mechanical behavior of ultrafine-grained materials under combined static and dynamic loadings

“…5(a). The two-step or three-step dynamic loading also affects the failure strain, which is different from results of other researchers (10,(16)(17). It should be noted that static loading itself did not lead to any catastrophic failure of UFG Ti.…”

A Universal Equation Governing Engineering Stress-strain Curves of Polycrystals

“…[46][47][48][49] In Fig. 2(a), the decrease in Lüders strain with decreasing grain size is therefore attributed to the faster saturation in dislocation density with decreasing grain size after the critical grain size.…”

Dynamic shear instabilities in metallic sheets subjected to shear-compression loading

“…with the equivalent strain in the material, see Fig. 5 in Section 5), is generally used as an indicator of the material stability in shear band problems: the greater the critical instantaneous grow rate, the more prone the material is to develop shear localization (see also the works of Molinari (1997) and Rodríguez-Martínez et al (2015)). An alternative indicator of the stability of the solution was proposed by Fressengeas and Molinari (1994) who defined a cumulative instability index,Î = t 0ηε used by several authors to predict the formation of necks at high strain rates (see Petit et al (2005), El Maï et al (2014 and N'souglo et al ( 2020)).…”

“…Other recent works that have used the linear stability theory to investigate the formation of shear bands in metallic materials are the papers of Rodríguez-Martínez et al (2015) and Longère (2018), who analyzed the respective roles of thermal softening and dynamic recrystallization in the initiation of shear bands in Ti6Al4V, and the article of Gurrutxaga-Lerma (2018), who studied the conditions that dislocation generation and motion must fulfill to promote the development of adiabatic shear bands in crystalline metals. In addition, Arriaga et al (2015Arriaga et al ( , 2016 recast the stability analysis as a generalized eigenvalue problem that can be implemented in a finite element code to determine the onset of shear localization, damage and fracture, at the element level, in general multidimensional applications.…”

“…The theoretical model extends the linear stability analysis for simple-shear formulated by Molinari (1997) to shear-compression loading. The numerical simulations have been performed in ABAQUS/Explicit (2016) using a unit-cell model based on the work of Rodríguez-Martínez et al (2015) in which the shear band formation is favored introducing geometric and material imperfections. Moreover, we have developed a calibration procedure for the stability analysis that enables to make qualitative and quantitative comparisons with the finite element calculations.…”