The auxiliary fields could be applied to the method for computation of SIFs for a dynamically propagating crack

Hi all,

Recently, I have read the paper "Dynamic crack propagation under mixed-mode loading- Comparison between experiments and X-FEM simulations" published in IJSS, 44 (2007), 6517-6534. I have met some questions on the choice of auxiliary fields for calculating the SIFs.  Could someone give me some details including the auxiliary velocity fields, the auxiliary displacement fields and the auxiliary stress fields. Thanks.

regards