Dear Divyansh,

a general answer cannot be given to your question. Johnson Cook is only a phenomenological fracture criterion with decreasing fracture strains for increasing stress triaxiality. It was shown to fit for many materials, however, it does not fit in general. Please specify your question.

Dear A. Morasch ,

Thank you for your reply,

I am working on the incremental sheet metal forming process in which mostly shear dominant fracture is occurred. As far i know, in shear dominant state the triaxiality is very low.  In J-C (Johnson cook) model strain is a function of stress triaxiality but not the lode parameter which is used to define the stress state with stress triaxiality.

Dear Divynash,

as Wierzbicky showed, the Johnson Cook model is limited for covering low triaxilaty failure in sheet metal. His publication is:

T. Wierzbicky, Y. Bao, Y.W. Lee and Y. Bai: Calibration and evaluation of seven fracture models". Int. J. Mech. Sci., 47:719-743, 2005.

I highly recommend it to you.

Regards,

A. Morasch

Dear A. Morasch,

Thank you ,my confusion is clear now.