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

被称为绝热剪切带（asb）的极窄的局部剪切变形带出现在金属和合金中，这些金属和合金受到强烈的、高应变率的载荷，如弹道冲击或高速率制造。尽管它们的尺寸减小了，但由于它们的微观结构和形态与周围的材料完全不同，这些带成为了引人注目的弱点。asb的形成是突然和意外的，预测它们是困难的。它们在服役期间的突然出现总是会导致航空航天和国防系统（涡轮叶片、装甲等）的灾难性故障。同样，asb主导着高速率制造（机械加工、增材制造、成型）：效率要求高速率、快速负载，这往往会引入不需要的asb，大大削弱了低规格的制造件。由于国防和航空航天工业中制造零件的数量庞大，设计周期的成本很高，因此能够解决ASB形成的预测方法将大大节省成本并提高效率。尽管经过数十年的研究，引起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破坏相对来说被很好地理解为热机械不稳定性，但ASB的起始发生在微米和亚微米尺度上，这超出了目前的实验测量能力。同样，asb形成的固有动态（时间相关）加载条件迄今为止排除了该现象的理论建模。通过三个工作包（WP），该项目通过开发一个雄心勃勃的、真正动态的、多尺度建模协议来研究和预测促进立方和六边形金属中asb发生的条件（载荷、成分、微观结构），解决了模拟asb发生的固有困难。WP1 Microscale通过采用原子模型（MD和晶格动力学）来研究已知促进ASB的载荷下位错产生和位错运动的来源，从而对产生ASB的不稳定性的物理来源有了基本的了解。WP2中尺度发展了一种全新的热弹性动力学位错动力学（DD）公式，用于模拟ASB在中尺度的发生和出现；该公式解决了目前所有的建模限制，无法解释材料的惯性和热效应，因为长期以来假定在asb的启动中起主导作用。然后，WP3 Multiscale将WP1和WP2结合起来，开发出ASB的预测多尺度模型，用于研究具有高科学兴趣和工业相关性的目标金属体系（Ti6Al4V、W、Al）中的地层条件（载荷、成分、微观结构）。由此产生的建模协议将使ASB首次在中尺度上的研究成为可能，并产生一种方法，用于(1)预测和诊断金属系统中的ASB故障，以及(2)指导材料选择，以便选择最理想的微观结构，以避免或促进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，并通过最小化ASB形成（增材制造、机械加工）来优化制造操作。

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).