Initiation of adiabatic shear bands from a microstructural standpoint
Shmuel Osovski (University of North Texas), Daniel Rittel (), peri Landau (), Arie Venkert ()
Dynamic Behavior of Materials
Tue 2:40 - 4:00
Salomon 101
It has been recently shown that dynamic shear failure of crystalline solids can be initiated by local microstructural changes (dynamic recrystallization, DRX), instead of the commonly assumed thermal softening mechanism. The driving force for the microstructural evolution leading to DRX was identified as the dynamic stored energy of cold work. However, for many materials, deformation twinning is another major deformation mechanism whose role must also be considered. Furthermore, the emergence of DRX in different materials was shown to occur at a wide range of strains (normalized to the failure strain) and thus having different contributions to the process of shear localization with respect to the thermal effects. In this work, we assess the contribution and interplay of both DRX and twinning to the initiation of dynamic shear localization, by means of combined transmission electron microscopy and numerical modeling. Controlled dynamic shear experiments, carried out on commercially pure Titanium, show extensive twinning which largely precedes the occurrence of DRX. Distinct areas of the sheared section contain either twins or DRX islands. A grain-scale finite element model illustrates the interplay between twinning, DRX, and associated thermal effects. This study shows the relative evolution of each mechanism and its contribution to the overall shear localization process, in full agreement with the experimental observations. The calculated local and global temperature elevations show that until failure, the maximum local temperature rise remains modest. This work elucidates the physical micro-mechanisms underlying the propensity to shear localization of crystalline materials, in which the role of local temperature variations is not as crucial as commonly thought of.