Mesh distortion can arise from several sources. The following list are some possible reasons. The user should check his input deck against each of them.
Too coarse a blank mesh (and sometimes too coarse a tool mesh);
Too infrequent an adaptive refinement increment;
Too large a time step;
Bad contact treatment;
Hourglassing and possibly incorrect hourglass control;
There are several commonly ways to reduce hourglass mode, i.e.
a) Use element type 16. The element type 2 (BT element) only has one integration point in the plane of the element and it is easier to excite an hourglass mode. Element type 16 has four integration points in the plane of element and isis more resistant to the hourglass mode
b) Use hourglass control (the card of *HOURGLASS).
c) Use a suitably fine mesh to prevent overpenetration;
d) Increase the adaptive frequency
e) Use small time step
f) Change to a different contact formulation.