Recently, a few users asked similar questions on obtaining shear stresses between discretely-modeled layers of a composite material or two bonded materials.

In ANSYS 11.0, cohesive zone model (CZM) was introduced for use with contact elements (in 10.0, CZM was used only with INTER20x interface elements). However, if a user is only interested in determining the shear stresses between two layers, CZM need not be used, although contact elements can still provide the requested information.

Because maximum shear stress reported at a surface may not reflect the interlaminar shear stress, looking at stress values for the parts may not suffice, especially if the parts have curvature. If, on the other hand, contact elements are used, frictional stress can provide the requested information, as it acts tangential to the two mating surfaces.

Max shear stress between two blocks

Max shear stress between two blocks

A simple test case (Workbench 11.0 .dsdb file) is attached.  In this example, two blocks are modeled both as multibody parts and via contact.  The max shear stress is shown in the figure “Max shear stress between two blocks.”

Frictional Stress Between Two Blocks

Frictional Stress Between Two Blocks

Similar results are obtained for frictional stress, as shown in “Frictional Stress Between Two Blocks.”

The user may wish to change the material properties or change the loading.  In other scenarios, the two will not be equal to each other, although the frictional stress output allows one to determine the stresses acting tangential to the mating surfaces.

Even without the use of the CZM constitutive relationship, output of bonded contact elements can provide users with information from a design perspective of whether separation may occur.  Including CZM allows one to perform failure analysis to see delamination and its propagation; however, for design purposes, simply neglecting the CZM material law may be sufficient to determine if failure may occur at the interface.