Damage assessment of compression loaded debond damaged sandwich panels

Sandwich composites with face sheets of fiber-reinforced plastics (FRP) and cores of polymer foam offer a lightweight construction that is well suited to wind turbine blades, naval and other vessels for high-speed operation or where payload considerations require that the structural weight be minimized. Some of these applications involve the use of highly optimized sandwich solutions. Studies are under way to establish how the structural performance is influenced by the presence of production defects or in-service damage. This paper deals with the failure of compression loaded sandwich panels with an implanted circular face/core debond. Compression tests were conducted on intact sandwich panels and panels with an implanted circular face/core debond with three different types of foam core materials (PVC H130, PVC H250 and PMI 51-IG). The strains and out-of-plane displacements of the debonded region were monitored using digital image correlation (DIC) measurements. Mixed mode bending (MMB) fracture characterization tests were conducted to determine the fracture toughness of the face/core interface in the panels. Finite element analysis and linear elastic fracture mechanics were employed to determine the critical buckling load and ultimate compression strength of the panels. Modeling approaches and failure criteria are discussed. Tentative strength reduction curves are presented, but uncertainties concerning the intact strengths of the materials examined need to be further addressed before these can be used with confidence.