Mode I Failure of Laminated Polymeric Composites

A mechanical model for the prediction of mode I delamination failure of a laminated double cantilever beam (DCB) type specimen is presented. The volume of material ahead of the crack tip that experiences high stresses due to the presence of the crack tip was replaced by a nonlinear elastic spring foundation. The volume undergoing global deformation due to the external loading was replaced by a beam. The spring foundation was characterized by a covalent interatomic force law as a constitutive law and a non-uniform strain distribution throughout the spring length. Experimental data of fracture toughness for PEEK adhesive joints were used to partially characterize the spring foundation. Experimental results from mode I fracture tests performed to verify the current model are presented. The current model matched the experimental results closely for PEEK and BP907 adhesive joints for a wide range of adhesive layer thickness. It also reproduced load vs displacement curves of E7TI/G40 and E719/IM7 composite specimens very closely. The work presented contributes a new fracture model for prediction of delamination of laminated composite structures.