On the effect of inter-laminar contact on the dynamics of locally delaminated FRP strengthened walls

The paper studies the effect of the inter-laminar contact and its temporal variation on the behavior of FRP strengthened walls with delaminated regions. The paper adopts an analytical approach that unifies the displacement and stress fields of sub-regions where the delaminated faces are in contact with ones where the layers are free of contact. This is achieved by means of a Robin type of condition at the delaminated interface and a 2D time dependent Heaviside function that automatically switches between contact states. The model is converted into a finite element form that utilizes the high order displacement fields, overcomes the obstacles due to the scatter of geometric scales, avoids the need to mesh through the thickness of the layers, and simplifies the implementation in a broader finite element framework. The role of the inter-laminar contact non-linearity is demonstrated through the study of the dynamic behavior triggered by the geometrically non-linear snap-out of a delaminated layer in a shear wall strengthened with FRP. The analysis quantifies the impact of the 2D time dependent contact map on the snap-out load, the dynamic post-buckling behavior, and the interfacial stresses. The paper closes with conclusion regarding the delaminated wall as well as many other laminated, adhesively bonded, or sandwich structural forms that are prone to delamination, dynamic instabilities, and the combination of the two.