Static and dynamic stressing of elastic, plastic and viscous granules

几乎完全弹性的粘弹粘塑性模型颗粒将分别进行单轴静态压缩和正常动态低速冲击(自由落体)试验，分别记录相应的力-位移-时间和冲击-回弹事件。从压缩试验中，力-位移和力-位移率行为将使用适当的接触模型来近似，以获得微观力学特性，如微观屈服强度、刚度等。宏观断裂(由于同时作用于法向应力和剪应力)导致的产品失效将以断裂概率函数的形式来表示，并且将描述瞬时和疲劳破坏的机理。研究了粘结剂含量和循环加水卸载对微屈服和宏观破坏概率的影响。此外，还将考察位移控制加载速度对粘性细观力学性能的影响。从冲击和反弹过程中记录的数字图像可以得到冲击和反弹速度，由此可以确定冲击次数，即恢复系数。将研究在冲击过程中接触时水层和粉末层的层厚度的影响。我们预计，到第一个资助期(24个月)结束时，上述多尺度试验将圆满结束，为将在第二个资助期(12个月)进行的数值模拟铺平一条明确的道路。采用离散单元法，利用PFC3D软件进行三维数值模拟。该项目的成果将极大地改善控制和减少颗粒(由微米范围内的初级颗粒组成的毫米范围内的颗粒集合体)的不受欢迎的变形和破碎，方法是确定具体的能量限制，以优化未来颗粒的工业处理，并建立质量标准，为利基市场和高价值加工(农业、食品和制药)行业的设计师产品造粒。

Almost perfectly elastic to viscoelasto-viscoplastic model granules will be experimentally tested (individually) by uniaxial static compression and normal dynamic low-velocity impact (free-fall) tests; the corresponding force-displacement-time and the impact-rebound events will be recorded respectively. From the compression tests, the force-displacement and the force-displacement rate behavior will be approximated using suitable contact models to arrive at the micro-mechanical properties such as micro-yield strength, stiffness, etc. Product failure by macro-breakage (resulting due to simultaneously acting normal and shear stresses) will be expressed in terms of breakage probability functions and moreover the mechanism in case of instantaneous and fatigue failure will be described. The influences of binder content and cyclic moisture loading-unloading on the micro-yield and macro-breakage probability will be studied. Furthermore, the influence of displacement-controlled loading velocity on the viscous micro-mechanical properties will be examined. From the recorded digital images during the events at impact and rebound, the impact and rebound velocities can be arrived at, from which the impact number i.e. the coefficient of restitution will be determined. The influence of layer thickness of moisture and powder layers at contact during impact will be investigated. We expect that by the completion of the first funding period (24 months), the above described multi-scale experimentation would successfully conclude, paving a well-defined path to the numerical simulations which will be performed during the second funding period (12 months). Three dimensional numerical simulations will be performed according to the discrete element method using the software PFC3D. The outcome of this project would provide an excellent improvement towards controlling and reducing undesired deformation and breakage of granules (particle collectives in the millimeter range composed of primary particles in the micrometer range), by defining specific energetic limits to optimize future industrial handling of granules and establish qualitative standards to granulate designer products for niche markets and high value process (agricultural, food and pharmaceutical) industries.