A general continuum theory of polycrystalline materials

像冰、岩盐和地幔这样的物质作为高粘性流体在很长一段时间内流动。例如，冰川的流动类似于金色糖浆在厨房桌子上的传播。然而，由于冰和岩石在小尺度上的晶体结构，与正常流体相比，它们以有趣和不寻常的方式流动。这种流动称为多晶流动。这些流动至关重要：冰的流动是海平面上升的主要原因，了解地球地幔的流动是板块构造的核心。了解盐在洞穴中的流动也很重要，因为越来越多的人需要利用这些洞穴来储存氢，作为净零能量转换的一部分。多晶流在小范围内形成晶体结构，这使得它们在某些方向上流动得更快，这取决于晶体的方向。因此，理解和预测晶体结构如何演变是大规模预测这些流动的关键。该提案通过开发一种新的方法来解决这一挑战，该方法制定了可以预测任何多晶材料微观结构的方程和计算机模型。关键的发展是使用对许多晶粒进行平均的统计场来模拟晶体结构，而不是直接模拟晶粒。这种“连续体”方法类似于水和空气等流体的流动可以通过速度和密度等平均量来建模，而不是通过观察单个分子。该方法将模型减少到相对较少的经验参数，这些参数可以使用实验数据进行系统校准。通过避免在模型中解析晶体结构的每个晶粒，连续体方法在准确性和预测能力方面获得了实质性的收益，为多晶流动的高效和高分辨率模拟打开了新的大门。从长远来看，这些结果将支持对未来由于冰盖流动导致的海平面上升的预测，更好地了解地球地幔和板块构造，以及更好地了解其他物质的流动，例如洞穴中的岩盐-帮助过渡到净零。

Materials such as ice, rock salts and the Earth's mantle flow as highly viscous fluids over a long time. For example, the flow of a glacier is similar to the spread of golden syrup over a kitchen table. However, due to the crystal structure of ice and rock at small scales, they flow in interesting and unusual ways compared to normal fluids. Such flows are called polycrystalline. These flows are of critical importance: the flow of ice is the main contributor to sea-level rise and understanding the flow of the Earth's mantle is central to plate tectonics. Understanding the flow of salt in caverns is also important as there is an increasing need to use these caverns to store hydrogen as part of the net zero energy transition.Polycrystalline flows form a crystal structure on a small scale, which allows them to flow faster in certain directions, depending on the orientation of the crystals. Therefore, understanding and predicting how the crystal structure evolves is key for predicting these flows at a large scale. This proposal addresses this challenge by developing a new approach of formulating equations and computer models that can predict the microstructure of any polycrystalline material. The key development is to model the crystal structure using a statistical field that averages over many crystal grains, rather than modelling grains directly. This "continuum" approach is analogous to how flow of fluids like water and air can be modelled by average quantities like velocity and density, rather than by looking at individual molecules. The approach reduces the model to relatively few empirical parameters, which can be systematically calibrated using experimental data. By circumventing the need to resolve each grain of the crystal structure within the model, the continuum approach confers substantial gains in terms of accuracy and predictive capability, opening news doors to efficient and highly resolved simulations of polycrystalline flows. Long-term, the results will support improved predictions for future sea-level rise due to ice-sheet flow, better understanding of the Earth's mantle and plate tectonics, and better understanding of the flow of other materials, such as rock salts in caverns - helping with the transition to net zero.