The Development of a New Compression Test Specimen Design for Thick Laminate Composites

Abstract

A new specimen design for determining the compression strength of thick unidirectional laminate composites has been developed using finite element simulations and validated by experimental testing. The computational models included parts of the testing fixture. The materials used for experiments were carbon fibre/epoxy T300/914 from Hexcel Composites and IM7/8552. An understanding has been developed to explain why, using the standard, parallel sided design, for testing specimens in compression and using the ICSTM fixture, specimens using a laminate thicker than 2 mm do not fail in an acceptable way. Initially, simulation and experimental parametric studies were carried out to investigate the effects of loading and design conditions on the fixture and specimen in order to change the stress distribution in the 2 mm thick, parallel sided, 10 mm x 10 mm gauge section specimen. In addition, in order to optimise the specimen itself, different adhesives for bonding end tabs to the laminate were investigated, as were the end tab design and material used in their manufacture. Subsequent simulations showed that the use of an extended and waisted gauge length of either circular or s-shaped profile both caused thick laminate specimens to fail close to the centre of the gauge length. The predicted strength being similar to that measured for a 2 mm thick, parallel sided specimen using the optimised design. Experimental compression strength data from thick laminate specimens with the circular and s-shaped profiles machined into the gauge section validated the finite element results; the strengths achieved being almost identical to those for the 2mm thick laminates. Results from the analysis of the standard design and some preliminary work on the waisted design were presented at a conference [52]. Results for further work on the waisted design and experimental details have been reported in [51] and [75].