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

该项目首次尝试使用视频显微镜来观察和测量非固态合金的变形机制。重点是糊状带力学研究最少的领域之一，“中间”固体部分的流变学，当多个等轴晶体接触但具有可忽略不计的内聚力时。这些显微组织通常在工业铸造过程中变形，例如铝和镁合金汽车底盘部件的高压压铸。研究发现，当凝固同时发生剧烈变形时，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。颗粒材料就是我们每天遇到的颗粒的无序组合，从花园里的土壤到厨房餐桌上的盐。然而，颗粒材料的力学可以是复杂的，来自于离散颗粒之间的力学相互作用，而这些相互作用通常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特性，但两者的大桩的变形行为在力学上有许多相似之处。颗粒材料在物理科学和工程中都很重要，颗粒力学的应用是以下研究的核心：(1)土木工程中的土壤力学，(2)地球科学中的板块构造和地震，(3)农业中谷物的流动和储存，以及(4)化学工程中药物粉末和糊状物的处理。该项目旨在提供直接的实验证明，部分固体合金也应被视为颗粒材料的一种形式。最终目的是通过视频显微镜揭示的现象和机制，为未来的部分固体合金变形的颗粒理论奠定基础。为了实现这些科学进步，将开发一种创新的仪器，用于直接原位测量糊状带的变形。该方法是同时测量(i)晶体原位尺度上的现象和（ii）全球力学数据。来自土壤力学和地球科学平行学科的颗粒变形知识将用于开发设备和解释结果。该研究将产生在晶体尺度上运行的变形机制的知识，并定量地将微观机制与全局流变学联系起来。研究还将研究颗粒剪切带如何在非固态合金中形成和生长。

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.