Taking mode I loading as an example, I want to study the influence of T-stress on fracture toughness of materials, so I consider the following displacement loading for the boundary nodes. My question is: for a given T-stress, how are the u1 and u2 components updated in abaqus? I know that the updates of u1 and u2 can be achieved by setting small K increments, but due to the presence of T-stress, how to keep T constant while updating u1 and u2?