Determination of the longitudinal compressive strength of some laminated composite materials

'Determination of the longitudinal compressive strength of some laminated
composite materials using various classical and innovative tests' by Dr. Frédéric Laurin.
The present study proposed a critical analysis of the available existing tests in order to determine the longitudinal compressive strength of various
unidirectional plies. The (i) standard compressive tests on UD plies, (ii) additional bending tests on UD plies and (iii) an alternative tensile test on a specific lay-up that fails by fibre kinking were considered for different composite materials.
The composites considered are (i) a classic aerospace carbon/epoxy material with standard ply thickness, (ii) another carbon/epoxy material with thin plies in order to study the effect of ply thickness on the strength and finally (iii) a carbon/thermoplastic material to highlight the role of the matrix on the strength studied. All these tests were highly instrumented in order to accurately determine the failure scenario and to ensure that the relevant failure mode was obtained.
In order to analyse such tests (compression, tension and flexure), a
micromechanical model, associated with a damage model defined at the ply
scale, has been proposed. It has been shown that the variation in the longitudinal compressive strength obtained at the UD ply scale for tensile and flexure tests is consistent when the fibre kinking is considered at the microscopic scale, which appears to be the relevant scale of analysis. In addition, the influence of the position of the plies through the thickness has also been considered for compression tests and can again be explained by the use of a micromechanical modelling.