Delamination effect on vibration and impact behavior of the curved sandwich panels

Sandwich composite materials are used in many areas due to their high strength and stiffness to weight ratio. However, sandwich composites are susceptible to impact is the biggest drawback in the use of these materials. Therefore knowledge of the impact response of these materials is of great importance in the design of structures. Present study deals with the delamination effect on impact response and natural frequency of sandwich composite panels. The face sheets of the sandwich panel were E-glass/epoxy laminates made of four plies oriented 0°/90°/-45°/+45° and the core was PVC foam. Teflon film was used for the creation of delamination between foam and face sheet and cut in 10 and 25 millimeters in diameter and placed on the center of upper and lower surface of specimen face sheet-foam interface. The specimens were prepared by cutting out 100 mm x100 mm in dimension before vibration drop-weight impact tests were performed under different impact energy levels. The effects of parameters like delamination diameter, delamination location, curvature and energy level on impact response and failure modes were investigated. Looking at the relationship between contact force and deflection, information on the failure process were obtained for the sandwich composites specimens. When the curvature of panels increases, the contact force of the upper face sheet of the specimen increases and the contact force in the lower face sheet decreases. Considering the results of vibration test and analyses, natural frequency has increased with the increase of curvature for free, cantilever and fixed support while reducing with delamination. While the increases of delamination in diameter and the position of the delamination in lower face sheet-foam interface reduces the natural frequency. Keywords: Sandwich composites, low velocity impact, delamination, curved panel, natural frequency