A Multi-scale Approach to the Development of Microstructure-aware Constitutive Models for Magnesium

与EPSRC的战略和研究领域保持一致：该项目属于EPSRC材料工程-金属和合金研究领域，符合“通过资源效率减少材料需求，通过对微观结构/加工/性能三角的更深入了解来缩短产品开发的前置时间”的战略重点。在建模和实验方面的进步是这个项目的预期成果，促进跨学科合作，并进一步与EPSRC的愿景保持一致。项目描述：与其他结构金属相比，镁合金具有最高的强度重量比之一，使其成为高性能环境中潜在的减重替代品。应用包括飞机上的部件，其中更轻的重量替代品可以显著节省燃料和成本。尽管有这些优点，但镁的广泛使用受到其复杂变形行为的限制；它的有限滑移系统和高各向异性导致复杂且经常竞争的变形模式，其特征是位错滑移、孪生和再结晶。这意味着镁的可加工性很差，导致在常规成形过程中早期失效。近年来，新的预处理和后处理技术，如熔体剪切和剧烈塑性变形，显示出改善镁的可加工性和整体力学性能的希望。这些技术改变了材料的微观结构和织构，以促进更均匀的变形，最终延缓失效。然而，这些技术对高应变率性能的影响在很大程度上仍然未知。该项目旨在提高对镁合金变形机制的理解，以及镁合金对机械载荷（应变率、应力状态）、热环境（升高、冷却温度）和微观结构（晶粒尺寸、织构）的敏感性。该项目将包括几项关键活动：使用牛津大学冲击工程实验室的机械加载设备（准静态加载框架，Split- Hopkinson压力棒，单级气枪）和领先的诊断技术（高速成像，DIC，测速）来表征镁合金的本构行为。原位织构演化利用ESRF的动态x射线衍射来监测机械加载过程中织构（晶粒旋转和孪生）的变化。动态失效识别塑性变形的主要机制（如滑移vs孪生）作为温度，速率，应力状态等的函数，并了解微观结构如何促进/阻止失效。推导引起绝热剪切的条件。绝热剪切是低对称性金属（镁、钛）的主要破坏模式，随着应变率的增加，绝热剪切的发生频率更高。上述活动的结果将用于补充镁的新本构和破坏模型的开发。这些模型将以基于晶体塑性的有限元方法模拟为基础，这些方法本身通过升级方法来达到体本构模型的数值预测。以这种方式导出这些模型，可以利用统计方法和机器学习方法来定制镁合金的微观结构设计，以满足组件的特定需求。一旦这些模型被开发出来，就有可能与布鲁内尔大学的研究人员合作，他们已经开发了MCAST技术来生产具有均匀微观结构的镁的新纹理；因此，为这个项目提供了一个直接的应用。

Alignment to EPSRC's strategies and research areas:This project falls within the EPSRC Materials engineering - metals and alloys research area and aligns with the strategic focus of 'reducing material demand through resource efficiency and reducing lead times to product development through greater understanding of the microstructure/processing/performance triangle.' Advances in modelling and experimentation are expected outcomes of this project, promoting interdisciplinary collaboration, and further aligning it with the EPSRC's vision.Description of Project:Magnesium alloys enjoy one of the highest strength-to-weight ratios compared to other structural metals, making them potential weight savings alternatives in high-performance environments. Applications include components in aircraft, where lighter weight alternatives can represent significant fuel and cost savings. Despite these advantages, widescale use of magnesium has been limited by its complex deformation behaviour; its limited slip systems and high anisotropy lead to complex and often competitive deformation modes characterised by dislocation slip, twinning, and recrystallisation. This means magnesium suffers from poor workability, leading to early failure during conventional forming processes.In recent years, novel pre- and post-processing techniques such as melt shearing and severe plastic deformation have shown promise in improving both the workability and bulk mechanical properties of magnesium. These techniques alter the microstructure and texture of the material to promote more uniform deformation and ultimately delay failure. The effect of these techniques on high strain-rate properties however remains largely unknown. This project seeks to develop an improved understanding of the mechanisms of deformation in magnesium alloys, and their sensitivity to mechanical loading (strain-rate, stress state), thermal environment (elevated, cooled temperatures), and microstructure (grain size, textures). The project will comprise several key activities:1. Bulk constitutive characterisationCharacterise the constitutive behaviour of magnesium alloys using the suite of mechanical loading equipment (quasi-static load frames, Split- Hopkinson pressure bars, single-stage gas guns) and leading diagnostic techniques (high-speed imaging, DIC, velocimetry) within the University of Oxford's Impact Engineering Laboratory.2. In-situ texture evolutionUtilise dynamic X-ray diffraction at ESRF to monitor changes in texture (grain rotations and twinning) during mechanical loading.3. Dynamic failureIdentify the primary mechanisms of plastic deformation (e.g. slip vs twinning) as a function of temperature, rate, stress-state, etc. and understand how microstructure can encourage/discourage failure.Deduce the conditions which trigger adiabatic shear. Adiabatic shear is a primary mode of failure in low symmetry metals (magnesium, titanium), and is encountered more frequently with increasing strain-rate.4. Model developmentResults from the aforementioned activities will be used to complement the development of new constitutive and failure models for magnesium. These models will be underpinned by crystal plasticity based finite element method simulations that are themselves put through upscaling methodologies to arrive at numerically informed predictions of the bulk constitutive models. Deriving these models in this manner opens the potential to utilise statistical methods and machine learning approaches to tailor the design of microstructure in magnesium alloys for the specific needs of a component.Once these models are developed, there exists the possibility to collaborate with researchers at Brunel University who have developed the MCAST technique for producing new textures of magnesium with uniform microstructure; thus, providing a direct application for this project.