Identifiability of the parameters contained in a cyclic cohesive zone model for CFRP-to-steel bonded joints

The application of externally bonded CFRP reinforcements has shown its effectiveness in reducing crack growth and extending fatigue life of steel elements subjected to cyclic loadings. Failure usually occurs due to cohesive debonding within the adhesive interface and therefore the interfacial behavior is crucial in guaranteeing the effectiveness of the bonded system. The adoption of cohesive zone models represents a valid approach for the description of interfaces between two adherends (i.e. CFRP and steel substrate), providing a useful tool for the analytical and numerical investigation of CFRP-to-steel bonded systems. An important issue generally associated with the use of a cohesive model is the correct calibration of its parameters, necessary to guarantee a reliable use of the model. Therefore, this work proposes a robust inverse analysis procedure to investigate the identifiability of the parameters governing the fatigue behavior of an exponential cyclic cohesive zone model. Single-lap direct shear tests are considered for the numerical investigation of the interfacial bond behavior. The input data chosen for the inverse algorithm are the axial strain measurements in a discrete number of points along the bonded interface and the values of relative displacement between the two adherends measured at peak and valley of each cycle at the specimen loaded end (i.e. the global slip). Virtual data perturbed by different levels of noise are used and a meta-model reduction technique is adopted to reduce the computational cost of the forward operator and to solve the inverse problem in a stochastic context through a Monte Carlo like procedure.