Metal Foam failure

Dear All

I'm working on studing the use of metal foam in sandwich structre containing Al or steel plate to overcome an impact shells or plates at differnet impact velocity but the prblem that I face how to define the failure critrion of Meat foam except difine the crushable foam properties, and I've read a paper on using cohesive element but i don'nt know how to use it.

Hopefully some one can help me solving this prblem, by the way I'm using ABAQUS v6.6

Regards