Indentation study of foam core sandwich composite panels

Due to their high stiffness and strength to weight ratios, composite sandwich structures have proven their usefulness in a large number of applications in various technical fields, especially in aeronautics, automotive and civil engineering. One of the main drawbacks of sandwich structures is the loss of load caring capacity due to indentation damages. The purpose of the present work is the evaluation of the response of foam core sandwich composite panels to indentation. Experimental tests were performed by a spherical indentor using an Instron universal test machine under displacement control at cross-head speed of 2 mm/min. The test specimens were manufactured by using rigid foam Rohacell WF51 with a thickness of 50 mm and glass-fiber reinforced composite face sheets with a thickness of 2.4 mm. The load-displacement response for both loading and unloading steps was recorded during the testing. The diameter of the damaged zone on the face sheet was measured after the unloading. A numerical modeling of the indentation response in axisymmetrical conditions was performed using the ABAQUS finite element computer code. The plastic response of the core material was described by the *CRUSHABLE FOAM HARDENING option. The geometrical nonlinearity was taken into account by using the *NLGEOM option. The main goal of the analysis was to predict the residual stresses and strains, and especially the magnitude of the residual dent. A good match between the finite element modeling and the experimental data was obtained. The present work should be considered as a step towards developing a more sophisticated numerical model capable of describing indentation as well as post-indentation mechanical behavior of sandwich structures.