Determination of Axial Stress and Deformation Variations in a Cylindrical Bed of Granular Material with Applications in Space

Granular material beds have significant space application, especially in the Advanced Life Support Systems (ALSS). Long-term space missions are possible by using ALSS that facilitate in successively recycling vital life sustaining elements, like water, thereby preventing high re-supply costs. This paper presents results from analytical, computational, and experimental studies of a dry granular bed media of activated alumina enclosed in a cylinder to determine the variation of axial stress and displacement along the bed medium due to applied loads at one end of the bed. A set of closed form analytical expressions has been developed to predict the axial stress and displacement variations based on equilibrium equations, appropriate boundary conditions, and other relevant relations among normal and shearing stresses in the medium. This model takes into account the friction between the media and the walls of the housing cylinder, and considers the fact that the bed is of finite length. The computational model utilizes the finite element method. The bed media and the cylinder walls are modeled using axi-symmetric continuum elements. Frictional contact between the cylinder walls and the bed media is considered. In the experimental study, under the action of an axial applied load at on end, the axial stress in the granular bed was measured at various depth using a load/pressure sensor. The axial stress and deformation results from the experiments, analytical method and computational model are found to match relatively well among each other.