In this paper, the mechanical behaviour of an ideal dry granular material under both evolving and steady conditions has been studied. Triaxial loading both constant volume and constant pressure Discrete Element (DEM) tests on periodic cells have been performed. The role played by strain rate, void ratio and imposed pressure has been analysed. The aim of the paper is to obtain a numerical data set, at present totally absent in the literature, useful for the definition of constitutive relationships capable of reproducing phase transitions (from solid-to-fluid and vice versa) taking place in granular materials. The novelty of the data set obtained derives also from the type of loading tests performed, referred as heating, cooling and cyclic, in which different strain rate histories are imposed, inspired to what locally occurs in flowing granular masses, accelerating and decelerating according to the slope inclination. The numerical results are interpreted by considering state variables (granular temperature and fabric) and the energies evolution (elastic and kinetic fluctuating) to put in evidence phase transition processes. Again, this interpretation of the results is fundamental to conceive upscaled constitutive relationships based on thermodynamic theories. The numerical results have allowed to highlight the role of the strain acceleration/deceleration, and the evolution of the directional properties of the microstructure even in the collisional regime (never described up to now). Cooling constant volume tests results provide a description, not available in the literature, of the evolving response of the material under pure collisional conditions.

本文研究了理想的干燥粒状材料在不断变化和稳定条件下的力学行为。在周期性电池上进行了恒定体积和恒定压力的三轴加载离散元素（DEM）测试。分析了应变率，空隙率和施加压力所起的作用。本文的目的是获得目前在文献中完全不存在的数值数据集，可用于定义能够再现相变的本构关系。（从固体到流体，反之亦然）发生在粒状材料中。获得的数据集的新颖性还源于所执行的载荷测试的类型，称为加热，冷却和循环，其中施加了不同的应变率历史，从而启发了在流动的颗粒状物质中局部发生的变化，并根据该变化进行了加速和减速。坡度。通过考虑状态变量（颗粒温度和织物）和能量演化（弹性和动力学波动）来解释数值结果，以证明相变过程。同样，对结果的这种解释对于基于热力学理论构想高阶本构关系至关重要。数值结果突出了应变加减速的作用，甚至在碰撞状态下（迄今为止都没有描述）的微观结构的方向性的演变。恒定体积冷却试验结果提供了在纯碰撞条件下材料演变响应的描述（文献中未提供）。