Cohesive zone models for the shear creep life assessment of bonded joints

Epoxies are the most common structural adhesive type in bonded joints. They are viscoelastic materials that show time and temperature dependent behavior under creep. Cohesive zone models (CZM) are often used to model the adhesive bonds, but rarely to model the creep behavior of adhesive bonds. The application of creep load to end notched flexure (ENF) samples leads to a change in the shear fracture energy, which depends on both creep time and creep load. Accordingly, in order to model the creep behavior in ENF joints, fracture energies must be accessed for each time increment along the simulation. For this purpose, the proposition of functions must be addressed, which must contain two variables including creep load level and creep time. The current research presents two different functions to determine the shear fracture energies according to the different creep times and creep loads. The function parameters are obtained by linear and nonlinear regressions. The models were validated and then used in a numerical analysis as part of the adhesive constitutive behavior, using CZM. Very good agreement between the numerical and experimental creep curves was observed.