The extremely narrow bands of localised shear deformation known as Adiabatic Shear Bands (ASBs) appear in metals and alloys subject to intense, high strain rate loading such as ballistic impacts or high rate manufacturing. Despite their reduced dimensions, the bands act as dramatic weak spots because their microstructure and morphology is radically different from the surrounding material. ASBs form suddenly and unexpectedly, and predicting them is difficult. Their sudden appearance while in-service invariably leads to the catastrophic failure of aerospace and defence systems (turbine blades, armour,...). Equally, ASBs dominate high rate manufacturing (machining, additive manufacturing, forming): efficiency calls for the sort of high rate, fast loads that tend to introduce undesired ASBs, greatly weakening the manufactured piece be- low specification. Owing to the huge volumes of manufactured pieces and to the high cost of design cycles in the defence and aerospace industries, predictive methodologies able to address ASB formation would lead to vast cost savings and efficiencies. Despite decades of research, the micro- and mesoscopic processes that cause ASB remain elusive. Whereas their growth and ultimate failure are relatively well-understood as thermomechanical instabilities, ASB initiation takes places at pico- and sub-micron scales that fall beyond current experimental measurement capabilities. Equally so, the inherently dynamic (time-dependent) loading conditions under which ASBs form have hitherto precluded the theoretical modelling of the phenomenon.

Across three work packages (WP), this project addresses the inherent difficulties in modelling the initiation of ASBs by developing an ambitious, truly dynamic, multiscale modelling protocol with which to study and predict the conditions (loading, composition, microstructure) that promote the onset of ASBs in cubic and hexagonal metals. WP1 Microscale delivers a fundamental understanding of the physical source of the instability that gives rise to ASBs, by employ atomistic models (MD & lattice dynamics) with which to study sources of dislocation generation and dislocation motion under loads known to promote ASB. WP2 Mesoscale develops an entirely new formulation of thermo-elastodynamic dislocation dynamics (DD) with which to model ASB initiation and emergence at the mesoscale; this formulation addresses all current modelling limitations unable to account for the materials' inertia and thermal effects long since postulated to play a dominant role in the initiation of ASBs. WP3 Multiscale then combines WP1 and WP2 to develop a predictive multiscale model for ASB with which to study formation conditions (loading, composition, microstructure) in target metallic systems (Ti6Al4V, W, Al) of high scientific interest and industrial relevance. The resulting modelling protocol will enable the study of ASBs at the mesoscale for the first time, and produce a methodology with which to (1) predict and diagnose ASB failure in metallic systems, and (2) guide materials selection so as to select the most desirable microstructures with which to avoid or promote ASB formation. These tools will streamline the design cycle of aerospace and defence pieces subject to impacts, and optimise manufacturing operations reliant on minimising ASB formation (additive manufacturing, machining).