Crack Propagation by Cohesive Element

Hi everyone,

 I've been working on crack propagation problem by cohesive elements in Abaqus.

 I have a sandwich struture where adhesive bonds two steels together. And I've attached part of my input file in the following.

 I can have the stress and strain distribution, but I really expect the crack will propagate in the midplane of the adhesives. I don't know whether I have to preset a line in the middle of adhesive as existing crac, or I can set some crack interaction to get the crack growth result. 

 I've stuck in this problem for several days, and tried to found out online. However, I've met several similar problems but no solutions provided. I really appreciate that some idea or advice could be given. 

 Thanks a lot,

I set the adhesive property is *Material, name=Mat_Adhe
*Damage Initiation, criterion=QUADS
 3.3e+06, 7e+06, 7e+06
*Damage Evolution, type=ENERGY, mixed mode behavior=POWER LAW, power=1.
330.,800.,800.
*Damage Stabilization
0.001
*Elastic, type=TRACTION
 8.5e+08, 8.5e+08, 8.5e+08

  The step is *Step, name=Step-1, nlgeom=YES, inc=10000
*Static
0.005, 1., 1e-09, 0.01

  And the field output is *Node Output
CF, PHILSM, RF, U
*Element Output, directions=YES
LE, PE, PEEQ, PEMAG, S, STATUSXFEM

 history output is *Node Output, nset=Total-1.Set-1
RF1, RF2, RF3, RM1, RM2, RM3, U1, U2
U3, UR1, UR2, UR3