Failure Criteria for Fiber Analysis

Hello,

I am trying to include a failure criteria for a single yarn in a plain- weave fabric model.The yarns behave as elastic-brittle( That is there is no plastic deformation)
I have the failure stresses and strains data in both fiber and transverse directions.I have  included the following properties:

Material definition
Density
Elastic : engineering constants
Viscoelastic: Relaxation test data

I have tried to use the suboptions in elastic behavior (fail stress and fail strain) ,but it doesnt include material degradation.The only way to include an element deletion is through a VUMAT.Please let me know if I can use a VUMAT only for the failure criteria.Also it would be very helpful if somebody has sample VUMATs for defining simple tensile failure.

Thanks