An experimental protocol to measure the parameters affecting the compressive strength of CFRP with a fibre micro-buckling failure criterion

Understanding axial compressive failure mechanisms and estimating the related strength in continuous fibre composites is of paramount importance in the design of their parts. The mechanism at stake is the micro-buckling instability of fibres, which is contained by the matrix. In experimental measurements, compressive strength in bending is consistently higher than in axial compression. Indeed, the induced strain gradient provides an additional containment, namely structural effect. The characterisation of all geometrical and materials properties is usually lacking for models describing these combined mechanisms. A comprehensive experimental protocol is proposed in this paper to measure all the input parameters involved in a design oriented failure criterion. An epoxy matrix/high-modulus carbon fibre composite material illustrates this protocol. The influence of some key parameters, including the initial misalignment of the fibre, is discussed, thanks to additional experimental results.