An improved contact algorithm for the material point method and application to stress propagation in granular material

Contact between deformable bodies is a difficult problem in the analysis of engineering systems. A new approach to contact has been implemented using the Material Point Method for solid mechanics, Bardenhagen, Brackbill, and Sulsky (2000a). Here two improvements to the algorithm are described. The f irst is to include the normal traction in the contact logic to more appropr iately determine the free separation criterion. The second is to provide nu merical stability by scaling the contact impulse when computational grid in formation is suspect, a condition which can be expected to occur occasional ly as material bodies move through the computational grid. The modification s described preserve important properties of the original algorithm, namely conservation of momentum, and the use of global quantities which obviate t he need for neighbor searches and result in the computational cost scaling linearly with the number of contacting bodies. The algorithm is demonstrate d on several examples. Deformable body solutions compare favorably with sev eral problems which, for rigid bodies, have analytical solutions. A much mo re demanding simulation of stress propagation through idealized granular ma terial, for which high fidelity data has been obtained, is examined in deta il. Excellent qualitative agreement is found for a variety of contact condi tions. Important material parameters needed for more quantitative compariso ns are identified.