An Improved Contact Algorithm for the Material Point Method and Application to Stress Propagation in Granular Material

Contact between deformable bodies is a dif- cult problem in the analysis of engineering systems. A new approach to contact has been implemented us- ing the Material Point Method for solid mechanics, Bar- denhagen, Brackbill, and Sulsky (2000a). Here two im- provements to the algorithm are described. The rst is to include the normal traction in the contact logic to more appropriately determine the free separation crite- rion. The second is to provide numerical stability by scaling the contact impulse when computational grid in- formation is suspect, a condition which can be expected to occur occasionally as material bodies move through the computational grid. The modications described preserve important properties of the original algorithm, namely conservation of momentum, and the use of global quantities which obviate the need for neighbor searches and result in the computational cost scaling linearly with the number of contacting bodies. The algorithm is demonstrated on several examples. Deformable body so- lutions compare favorably with several problems which, for rigid bodies, have analytical solutions. A much more demanding simulation of stress propagation through ide- alized granular material, for which high delity data has been obtained, is examined in detail. Excellent quali- tative agreement is found for a variety of contact con- ditions. Important material parameters needed for more quantitative comparisons are identied.