To support simulations of blast loading from explosives using the Material Point Method (MPM), preliminary studies of gas expansion in MPM using the recently developed Convected Particle Domain Interpolation (CPDI) integrator, as well as established integrators based on the Generalized Interpolation Material Point (GIMP) method, show that prevailing algorithms for updating the deformation gradient produce results that are often grossly inconsistent with the update of the particle positions. Mapping of velocity to boundary background nodes is analyzed and demonstrated to induce large errors in problems involving large velocities and rapidly changing velocity gradients (common in blast and penetration applications). The error in the velocity cascades to ultimately corrupt other variables, especially the velocity gradient and stress on which it depends. A well-respected code verification process (the method of manufactured solutions) is used to quantify the errors in the update of variables in the MPM using the CPDI interpolator. Different methods based on linear extrapolation were tested for their potential to improve the mapping of the large-deformation velocity fields in blast and penetration, but with only isolated successes in some cases that often worsened results in other cases
