Predictive Multiscale Modelling Protocol of Adiabatic Shear Band Initiation in Manufacturing and Aerospace Materials

局部剪切变形的极窄带称为绝热剪切带(ASB)，出现在承受高应变率加载的金属和合金中，例如弹道撞击或高速制造。尽管尺寸降低了，但这些带仍然是一个引人注目的弱点，因为它们的微观结构和形态与周围的材料完全不同。ASB的形成是突然和意外的，预测它们是困难的。它们在服役期间突然出现，总是会导致航空航天和防御系统(涡轮机叶片、装甲等)的灾难性故障。同样，ASB在高速制造(加工、附加制造、成形)中占据主导地位：效率要求高速率、快速的负载，这往往会引入不需要的ASB，大大削弱了低规格的制成品。由于国防和航空航天工业制造的零件数量巨大，设计周期成本高，能够解决ASB形成问题的预测性方法将带来巨大的成本节约和效率。尽管进行了数十年的研究，但导致ASB的微观和中观过程仍然难以捉摸。虽然它们的生长和最终失效被相对较好地理解为热机械不稳定性，但ASB的启动发生在皮微米和亚微米尺度，超出了目前的实验测量能力。本项目通过三个工作包(WP)，通过开发一个雄心勃勃的、真正动态的、多尺度的建模方案，解决了在模拟立方和六方金属中ASB开始的条件(载荷、成分、微结构)方面的固有困难。通过使用原子模型(MD和晶格动力学)来研究在已知促进ASB的载荷下位错的产生和位错运动的来源，WP1微观尺度提供了对引起ASB的不稳定性的物理来源的基本理解。WP2介观尺度发展了一种全新的热弹动力学位错动力学(DD)公式，用来模拟ASB在中尺度上的启动和涌现；该公式克服了目前所有无法解释材料的惯性和热效应的建模限制，长期以来一直被认为在ASB的启动中起主导作用。然后，WP3多尺度将WP1和WP2结合起来，开发了ASB的预测多尺度模型，用于研究具有高度科学意义和工业意义的目标金属系统(Ti6Al4V，W，Al)的形成条件(载荷、成分、微观结构)。由此产生的建模方案将首次能够在中尺度上研究ASB，并产生一种方法，用来(1)预测和诊断金属系统中的ASB故障，以及(2)指导材料选择，以选择最理想的微观结构来避免或促进ASB的形成。这些工具将简化受影响的航空航天和国防部件的设计周期，并优化依赖于最大限度地减少ASB形成(添加制造、机械加工)的制造操作。

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).