Interface Fracture Mechanics

Hello everybody,

                          I am trying to perform a harmonic analysis of a material sample (say a simple 2D plate) with an edge crack in it using 'Ansys R16'. I see that under sinusoidal loading condition, the two crack faces open or close and interpenetrate (after closing which is not possible practically).

          1.  I believe, stiffnesses of the crack faces change during interpenetration and so the results are not credible anymore.