Flexural and impact properties of sandwich panels used in surfboard construction

Surfboards represent a particularly simple example of sandwich panel construction and are conventionally made from a preshaped low density polyurethane foam core encased in an E-glass/polyester skin. They are made to minimum weight and thickness and as a result suffer durability problems. The boards are particularly prone to denting due to impact damage, causing principally cosmetic problems. More importantly, they frequently snap under normal service conditions. Recently, there has been considerable interest in the use of higher performance materials for the skins, notably S-glass and epoxy resin, to improve the durability of surfboards. This work examines the failure of simple parallel faced panels fabricated to simulate a section of a surfboard. It is shown that when loaded in four point bending, the panels fail by compression of the core and that this mode of failure produces the same characteristics as seen in service failures. Further, the flexural strength is dominated by the behavior of the core and is not improved appreciably by the use of S-glass or epoxy resin. On the other hand, the impact resistance is improved by the use of S-glass and further improved if epoxy resin is used as the matrix.