With the release of 10.0 and the new cohesive zone elements, an interest in modeling the adhesive properties has arisen. We have contacted our adhesives material supplier to perform testing but they have indicated that they are not sure how to gain the necessary parameters, (normal/shear separation and max normal stress). Can you provide any published works on how these parameters can be obtained from empirical techniques? Also, please clarify the meaning of the material constants for the CZM material model.
Here is further explanation of the three material parameters:
C1 (sigma_max) is simply the peak value of tension stress, and C2 (delta_n_bar) is the corresponding deflection at peak stress in a tension-only test.
C3 (delta_t_bar) is sqrt(2)*delta_t, where delta_t is the deflection that corresponds to peak shear value.
We don't know of any formal test standards that describe the procedure for running these tests.
If the user knows the fracture energy and max tension stress prior to fracture, then they can get delta_n_bar based on the following relationship:
phi_n = e * sigma_max * delta_n_bar
Since the amount of energy for normal-only and shear-only are assumed to be the same in our implementation,
phi_n = phi_t = sqrt(e/2) * tau_max * delta_t_bar
Hence, tau_max and sigma_max are related by
tau_max = sqrt(2*e) * sigma_max * delta_n_bar / delta_t_bar
The third constant delta_t_bar can then be obtained if they have an idea of what tau_max (peak shear value) should be.
In many cases, a user knows (a) fracture energy, (b) max tension stress, and (c) max shear stress. Thus, even if the deflections at peak stress were not measured, they could still get the 3 constants using the equations above.