Determining the through-thickness properties of FRP materials

Abstract

Confidence in using fibre-reinforced polymer (FRP) composite materials for primary engineering structures is now widespread within industry. In most applications to date (aerospace, military and sporting equipment), FRPs have been used in modest thicknesses (typically less than 10mm) to carry what are essentially 2-D in-plane loads. As a consequence, design and testing procedures were developed which reflect the need to understand the in-plane response of the material. More recently, engineers have begun to use FRPs in thicker sections, where an understanding of the through-thickness response is paramount in designing a reliable structure, particularly where the through-thickness strength has a controlling influence on the overall structural strength of the component. This requirement has exposed a shortfall in materials characterisation skills—there are no agreed methods for measuring the through-thickness properties of FRPs. In addition, or perhaps as a consequence, there is a dearth of through-thickness data, which means that designers are lacking key information. This paper describes the development of a test specimen to characterise the through-thickness properties of FRPs, and includes results from a range of commonly used materials. It is believed that the specimen could form the basis for a new standard method.