Dynamic failure of sandwich beams with fluid-structure interaction under impact loading

Abstract

The objective of this research is to examine the added mass effect that water has on the dynamic response of a sandwich composite under impact, particularly impact leading to failure. Because sandwich composites are much less dense than water, fluid structure interaction plays a large part in the failure. Composite samples were constructed using vacuum assisted transfer molding, with a 6.35 mm balsa core and symmetrical plain weave 6 oz E-glass skins. The experiment consisted of three phases. First, using threepoint bending, strain rate characteristics were examined both in air and under water. After establishing that the medium had no effect on the beam response under different strain rates, but confirming that previously established relationships between strain rate and ultimate strength for axially loaded glass composites can be applies to sandwich construction in bending, the experiment progressed to impact testing where each specimen, again a one inch wide beam, was subjected to progressively increasing force. The data from this phase showed that submerged samples failed at lower drop heights and lower peak forces with a failure mode dominated by center span skin compression failure. Beams in air were able to withstand higher drop heights and peak forces. Dry sample failure mode was dominated by skin compression failure at the clamped support with occasional evidence of shear failure through the core adjacent to the clamped support. The data from this study will increase understanding of sandwich composite characteristics subjected to underwater impact.