Abstract
Adiabatic shear band (ASB) formation in textured HCP polycrystals has been investigated under regimes of high rate compression and shear loading using dynamic thermo-mechanically coupled, dislocation-based crystal plasticity modelling. The balance between rate of plastic dissipation leading to internal heat generation versus rate of thermal diffusion at a crystallographic length scale has been shown to be pivotal for the formation or otherwise of ASBs. Micro-texture has been found to have a key role in both advancing and inhibiting shear band growth, and its control offers the possibility of new alloys with higher impact strength over strain rate range1 × 10−2 to 1 × 105 s−1. Texture has been found to lead to wide variations in applied macroscopic strain at which ASB formation occurs, such that strain level in isolation is inappropriate as a universal indicator of ASB onset.High-rate shear loading is found to lead to lower onset strains for ASBs compared to high rate compression, but the dependence of both on texture leads to considerable variation in strain level for ASB formation. A preliminary map demarcating ASB onset has been established over regimes of applied strain and texture for dynamic shear and compression.
Highlights
Adiabatic shear band (ASB) formation remains an important phenomenon in a range of technological and industrial application areas, including that of foreign object damage in aero-engines
In the present work, we address the onset of ASB formation with full consideration of internal heat generation, the resulting heat transfer, and local thermally-driven strain softening in the ratesensitive crystal model
It is interesting to find that the shear band onset strain is around 4.5% on average and this is much higher than the 3.7% that occurs under shear loading
Summary
Adiabatic shear band (ASB) formation remains an important phenomenon in a range of technological and industrial application areas, including that of foreign object damage in aero-engines. It is a highly complex process involving dynamic deformation, high-rate plasticity, internal heat generation, thermal transients with big local temperature excursions, and very localised slip. The short loading duration acts to inhibit the local heat conduction, which in turn is argued to be a contributory factor in ASB formation by virtue of highly localised temperature increases, enhancing local softening, potentially followed by void growth and failure (Wright, 2002), in particular for materials with low coefficient of thermal conductivity, low specific heat, and high density (Antolovich and Armstrong, 2014). It is reasonably difficult to find ASBs in copper where the material’s high thermal conductivity is sufficient to conduct heat away from localisation regions
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