Video microscopy of granular deformation and strain localisation in partially-solid alloys

该项目寻求首次使用视频显微镜来观察和测量部分固态合金的变形机制。重点放在糊状区力学中最少被研究的领域之一，即当多个等轴晶体接触但粘聚力可以忽略的时候，固体中间组份的流变学。这些显微组织在工业铸造过程中经常发生变形，例如汽车底盘零件的铝合金和镁合金的高压铸造。研究发现，当严重变形与凝固同时发生时，铸态组织和缺陷与大多数教科书中的组织和缺陷明显不同。最近的研究表明，这是因为凝固过程中的变形导致合金变形为颗粒状材料。颗粒状材料只是我们每天遇到的颗粒的无序集合，从花园里的土壤到厨房桌子上的盐。然而，颗粒材料的力学可能是复杂的，出现在离散颗粒之间的机械相互作用中，而这些相互作用往往与颗粒本身的力学无关。例如，筒仓中的小麦颗粒与土壤中的砂粒具有明显不同的力学性质，但每个大桩的变形行为有许多力学相似之处。颗粒材料在物理科学和工程中都很重要，颗粒力学的应用是研究(I)土木工程中的土力学，(Ii)地球科学中的板块构造和地震，(Iii)农业中的谷类作物的流动和储存，以及(Iv)化学工程中的药粉和膏体处理的核心。该项目试图提供直接的实验证据，证明部分固体合金也应被视为一种颗粒状材料。最终目的是为了使视频显微镜所揭示的现象和机制成为未来部分固态合金变形的粒状理论的基础。为了使这些科学进展成为可能，将开发一种直接原位测量糊状区变形的创新装置。方法是同时测量(I)原位晶体尺度上的现象和(Ii)全球力学数据。来自土力学和地球科学平行学科的颗粒变形知识将被用于开发该仪器并解释结果。这项研究将产生在晶体尺度上运行的变形机制的知识，并将微观机制与全球流变学定量联系起来。研究还将研究部分固态合金中颗粒剪切带的形成和生长。

This project seeks to use video microscopy to observe and measure, for the first time, the deformation mechanisms in partially-solid alloys. The focus is on one of the least studied areas of mushy-zone mechanics, rheology at 'intermediate' solid fraction, when multiple equiaxed crystals are in contact but have negligible cohesion. These microstructures are commonly deformed during industrial casting processes, for example the high-pressure die-casting of Al- and Mg-alloy automotive chassis components. It has been found that, when severe deformation occurs at the same time as solidification, the as-cast microstructure and defects are markedly different to those in most textbooks. Recent research has suggested that this is because deformation during solidification causes the alloy to deform as a granular material.Granular materials are simply the disordered assemblies of particles we encounter every day from the soil in the garden to salt on the kitchen table. However, the mechanics of granular materials can be complex, emerging from the mechanical interactions between discrete particles which are often unrelated to the mechanics of the particles themselves. For example, grains of wheat in a silo have markedly different mechanical properties to the grains of sand in a soil, yet the deformation behaviour of large piles of each share many mechanical similarities. Granular materials are important across the physical sciences and engineering and the application of granular mechanics is central to research on (i) soil mechanics in Civil Engineering, (ii) plate tectonics and earthquakes in Earth Science, (iii) the flow and storage of cereal crops in Agriculture, and (iv) the handling of pharmaceutical powders and pastes in Chemical Engineering. This Project seeks to provide direct experimental proof that partially-solid alloys should also be considered a form of granular material. The ultimate aim is for the phenomena and mechanisms revealed by video-microscopy to form the foundation for future granular theories of partially-solid alloy deformation.To enable these scientific advances, an innovative apparatus for the direct in-situ measurement of deformation in the mushy-zone will be developed. The approach is to simultaneously measure (i) phenomena at the scale of the crystals in-situ and (ii) global mechanical data. The knowledge of granular deformation from the parallel disciplines of Soil Mechanics and Earth Science will be used in developing the apparatus and in interpreting the results. The research will generate knowledge of the deformation mechanisms operating at the scale of the crystals, and quantitatively link the micromechanisms with the global rheology. Research will also study how granular shear bands form and grow in partially-solid alloys.