Compressive behavior of laminated composite structures

Physical testing of laminated structures has indicated that the compressive strength is often considerably lower than that predicted by analytical methods. Poor testing techniques and poorly constructed materials seem to be possible reasons for the premature failure. However, since many of the failures are characterized by delamination of the structures, the cause of the failure may be due to local buckling of the composite plies. In this dissertation, a ply buckling model is studied to assist in the understanding of the failure mechanisms. In order to find the failure envelope, inplane fracture and overall buckling are assumed as the failure modes of these structures. The classical theory of elasticity for thin shells, including transverse shear deformation, is used in the derivation. Then, the relations between the predicted failure stresses and laminate orientations can be obtained. A simple optimum design procedure for laminate orientation and hoop/helical ply thickness ratio is proposed by using the previous two failure theories. The optimal point may be defined as the highest intersection of the various failure criteria. Results are presented in the form of a parametric study for three stacking sequences. Finally, the comparison of the failure stresses between the laminates with and without an inside hoop layer is discussed