Bipedal Impact with Granular Matter
Type of Degreedissertation
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Impact with granular matter has been of great interest to researchers for decades, mainly because the material, as a conglomeration of discrete solids, behaves as a fluid until a solid like behavior becomes established. As a result, a resistance force that would account for these characteristics during impact has been difficult to model. For this study, the resistance force is modeled as a linear superposition of a static (depth-dependent) resistance force and a dynamic (velocity-dependent) frictional force. Impact is defined from the moment the end point of the system comes in contact with the granular matter surface until the moment when the vertical linear velocity of the end point is zero. The variables of interest are the final depth at the end of the penetration phase and the stopping time. The results for two experimental designs: a free round-ended link and a two-link kinematic chain with two points of contact were compared to the results obtained by applying the resistance force formulation developed to corresponding CAD simulation models. The simulation and experimental results revealed that the initial displacement increases with initial velocity, while the stopping time decreases for all models. The sensitivity to impact angle and initial velocity were studied and as a result an improvement to the resistance force was formulated. A series of expressions are proposed for the resistance force coefficients to test the dependency of the impact of the free round-ended link on the initial conditions, specifically impact angle and initial velocity. The resistance force and its components were studied as they reacted during impact. The outcomes of this study have a potentially great significance in robotic design, military applications, and prosthetics design.