The videos below show the results of the MbDFEM simulation.
Note the stress distribution and the location of the peak stress in the "mass" part (right video). This stress results from the inertial forces, and so its maximum occurs when maximum acceleration takes place, this is, when the mass stops going "down" and starts moving "up", due to the spring force. Note also that, at the other peak acceleration, this is, when the part stops moving up and starts going down; there is no stress. Internal stress appears only when tensile force is transmitted through the material of the part. This simulation demosntrates de capability of the software to capture stresses resulting from inetial forces.