ties

I am working on a model in which i have a soft layer of material bonded between to rigid layers of material via cohesive elements following a linear separation-traction law based on a critical fracture energy value I determined from experimental and numerical work. I have the interlayer and cohesive elements as one part with a partitioned face and connected to the two adherends via surface-to-surface ties. I have found that my model runs successfully only if the soft interlayer material is made very stiff.