Sorry, i didn't understand it the first time. So, to elaborate again, i am doing some double cantilever beam testing to find out critical energy release rate of PDMS like material on glass.

the left highlighted portion is the crack and the right side edges are shared. then i applied some displacement to let the crack propagate, the energy release found this way should be critical energy release rate, right? 

problem is when i vary the amount of displacement at the top left vertex, the energy release rate varies much. 

can you please tell me what i'm doing wrong?