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

开发镁微观结构感知本构模型的多尺度方法

• 批准号: 2283233
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2283233
• 关键词: Multi; scale; Approach; Development; Microstructure

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.

与EPSRC的战略和研究领域保持一致：该项目属于EPSRC材料工程-金属及合金研究领域，并与“通过提高资源效率来减少材料需求，通过更好地了解微观结构/加工/性能三角关系来减少产品开发周期”的战略重点保持一致。模型和实验方面的进展是该项目的预期成果，促进了跨学科合作，并进一步使其与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，使其成为高性能环境中潜在的减轻重量的替代品。应用包括飞机中的部件，在这些部件中，重量更轻的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；其有限的滑移系统和高的各向异性导致了以位错滑移、孪生和再结晶为特征的复杂且往往是竞争性的变形模式。这意味着镁的加工性能较差，导致在常规成形过程中早期失效。近年来，熔体剪切和严重塑性变形等新的前后处理技术在改善镁的加工性能和块体力学性能方面显示出良好的前景。这些技术改变了材料的微观结构和纹理，以促进更均匀的变形，并最终延缓破坏。然而，这些技术对高应变率特性的影响在很大程度上仍不清楚。该项目旨在更好地了解镁合金的变形机制，以及它们对机械载荷(应变率、应力状态)、热环境(升高、冷却温度)和微观结构(晶粒度、织构)的敏感性。该项目将包括几项关键活动：1.整体本构特征使用牛津大学撞击工程实验室的一套机械加载设备(准静态加载框架、分离式霍普金森压杆、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射线衍射仪监测机械加载过程中织构(颗粒旋转和孪生)的变化。动态失效识别塑性变形的主要机制(如滑移和孪生)作为温度、速率、应力状态等的函数，并了解微观结构如何鼓励/阻止失效。推断触发绝热剪切的条件。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，绝热剪切破坏更加频繁。模型开发上述活动的结果将用于补充镁的新本构模型和失效模型的开发。这些模型将以基于晶体塑性的有限元方法模拟为基础，这些模拟本身通过升级方法来获得主体本构模型的数值信息预测。以这种方式导出这些模型，为利用统计方法和机器学习方法为镁合金中的微观结构量身定做设计提供了可能性。一旦开发了这些模型，就有可能与布鲁内尔大学的研究人员合作，他们开发了MCAST技术，以产生具有统一微观结构的镁合金的新织构；因此，为该项目提供了直接应用。