Adiabatic shear banding (ASB) is a synonym for a unique dynamic uncontrolled failure mechanism. It implies a concentrated shear deformation mode that ultimately results in catastrophic failure after violent impacts or high-speed machining for example.
The leading paradigm is that a competition between strain (rate) hardening and thermal softening determines the onset of the failure. But more important is the fact that adiabatic shear is universally considered as an instability (material or structural), and therefore modeled on the premise of stability analyses. As an instability, ASB is hardly controllable or even predictable to some extent.
However, as opposed to this purely mechanistic approach, it has recently been shown that instead of thermal softening mechanisms, microstructural softening transformations such as dynamic recrystallization (DRX) are responsible for adiabatic shear failure. Those transformations are dictated by the stored energy of cold work, so that energy considerations can be used to macroscopically model the failure mechanism.
Yet, one question persists, namely how is the shear band formed? What are the initial mechanisms that will later lead to final failure? And most of all, is adiabatic shear failure an abrupt instability or rather a gradual transition as would be dictated by microstructural evolutions?
This paper reports fine scale microstructural characterizations that clearly show the gradual character of the phenomenon, best described as a nucleation and growth failure mechanism, and not as an abrupt instability as previously thought. These observations are coupled to a simple numerical model that illustrates them.
