Effect of Boundary Conditions on the Cantilever Bending of Thick Glass Fiber Reinforced Polymer (GFRP) Composite Plates

Abstract

The use of composite materials in highly loaded structural applications continues to increase due to their highly desirable combination of low weight, high strength and durability. This also applies to their use in flexural bending applications, such as for a helicopter’s main rotor yoke. Understanding and predicting the behaviour of such a part first requires a thorough understanding of the behaviour of thick composite plates of uniform thickness, for which limited research has been done, and the majority of which is from a theoretical standpoint. This study examines experimentally the behaviour of thick glass fiber reinforced polymer (GFRP) composite plates in quasi-static flexural bending. 80-layer unidirectional samples were tested in cantilever bending. These results are compared to samples that are tested in similar fashion, albeit with both ends of the sample clamped (clamped configuration) to examine the effect of boundary conditions on the failure load and displacement. The displacement results are compared to theoretical classical laminate theory calculations. Finally, the experimental results of strains measured from strain gauges on the surface of the samples are compared to finite element analysis (FEA) results from ANSYS. It was found that clamping the loaded end reduces the displacement to failure and changes the way the strains progress along the length of the sample by preventing the sample from deflecting naturally. It was also found that the clamped configuration increases the failure load, meaning the sample behaves more stiffly. The strains at locations where the strain gradient was high did not correlate well between experimental and FEA results, such as with interlaminar shear strains on the thickness side of the specimen close to the edge of the fixed support. However, where the strain gradient was low, there was good agreement between experimental and FEA results. Also, the FEA strain profile along the surface of the specimen correlated well with the interpolated strain profile resulting from the strain gauge measurements on the experimentally tested specimens.