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].