The development of multiscale constitutive models for powder processing: from particles to products

在许多工业部门，如制药、化工、食品、陶瓷和粉末冶金，干燥粉末的加工是制造产品的一般途径。由于材料性质和加工条件的复杂性和多样性，使用这种加工技术制造高质量的产品是一项具有挑战性的任务。这些行业的快速增长和扩张以及激烈的竞争要求高效和严格的质量控制过程。传统的经验设计路线，通常采用试错方法，不能满足这些要求。迫切需要一个严格的模型来准确地预测粉末在加工过程中的行为和最终产品的性能，特别是在产品开发的早期阶段的小批量。提出的项目的主要目标是开发鲁棒的多尺度本构模型，该模型将基于不同的数值方法：离散和连续。前者将用于微观尺度上的模型，在微观尺度上，粉末被视为相互作用的单个颗粒的集合。后者将被开发为探索粉末行为和产品在宏观尺度上的性能的平台，其本构系数将基于离散方法的模拟来确定。上述工业中使用的粉末种类繁多，有弹性的、弹塑性的、粘弹性的和粘塑性的，并且具有不同的粘合机制，如通过范德华力粘合或由于界面能的存在而粘合。为了使待开发的多尺度模型能够考虑这些因素，还将开发并将这些颗粒之间的严格接触规律纳入多尺度模型，以便分析颗粒的材料性质和键合机制的影响，并将所开发的模型用于各种应用。此外，大多数工业加工都是在空气中进行的。在加工的早期阶段，粉末从一个设备输送到另一个设备，在粉末的快速流动中，气流可能是重要的。为了探索这种影响，还将开发数值模型来模拟气固两相流。这样就可以确定气流对粉末性能和最终产品性能的影响。开发的模型将通过使用正电子发射粒子测试（PEPT）的实验测试进行定量验证，这是伯明翰大学开发的一种方法。所开发的多尺度模型将增强对粉末加工的理解，并将成为许多行业中工艺设计和产品开发的宝贵工具。

In a number of industrial sectors, such as pharmaceuticals, chemicals, food, ceramics and powder metallurgy, processing of dry powders is a general route to making products. To manufacture high quality products using this processing technique is a challenging task because of the complexity and diversity of material properties and processing conditions. Rapid growth and expansion in these industries and intensive competition demands high effectiveness and stringent quality control of the process. Conventional empirical design routes, which generally employ trial-and-error approaches, cannot meet these requirements. A rigorous model is urgently needed to accurately predict the powder behaviour during processing and the performance of final products from the properties of the constituent particles, especially of small quantities in the early stages of product development. The primary goal of the proposed project is to develop robust mufti-scale constitutive models which will be based upon combining different numerical methods: discrete and continuum. The former will be used to model at micro-scale, in which the powder is treated as a assembly of individual particles interacting each other. The latter will be developed as a platform to explore the powder behaviour and the performance of the product at the macroscale, for which the constitutive coefficients will be determined based upon simulations with the discrete methods. The powders used in various industries mentioned above are of various types, such as elastic, elastoplastic, viscoelastic and viscoplastic, and with different bonding mechanisms, such as bonding through van der Waals' force or adhesion due to the presence of interfacial energy. In order that the mufti-scale model to be developed can take these factors into account, rigorous contact laws between these particles will also be developed and incorporated into the mufti-scale models, so that the influence of materials properties of the particles and the bonding mechanisms can be analysed and the developed model can be used in a variety of applications. Furthermore, most industrial processing is carried out in air. During the rapid flow of powder in the early stages of processing, where the powder is delivered from one apparatus to another, the air flow may be important. To explore this effect, numerical models will also be developed to simulate the gas/solid two phase flow. This allows the effects of air flow on the powder behaviour and the performance of the final products to be identified. The developed model will be quantitatively validated by experimental testing using Positron Emission Particle Testing (PEPT), a method developed at the University of Birmingham. The mufti-scale model developed will enhance understanding of powder processing and will be a valuable tool for process design and product development in a number of industries.