Aide Needed in crack propagation with ANSYS

Hello,I'm a student in engineering.  I wannto do simulation of the process of a cracked plate which is subjected to  tensile stress at the each end of the plate and perpendicular to the crack plane. with ansys .( crack type I )

i've read some the the posts here, some people give solution by creating  cohesive elements in the symmetry line , so once the failure criterion is satisfied, the crack will propagate . however it's propagating along the preset path-- the symmetry line.  but i'm so interested in how to predict the path, which means  wherever failure criterion is satisfied , elements began to separate,this process goes on and on until the plate is torn apart.  in this way i can  simulate the crack propagation step by step .   

I've thought about that first mesh the plate ,then separate all elements ,after add cohesive elements between every elements . Is this correct? And someone knows how to realize it ? if my idea is not correct , please tell me why and your suggesion .

salutsun@yahoo.com.cn 

Thanks alot!

dan