A method to determine composite material residual tensile strength in the fibre direction as a function of the matrix damage state after fatigue loading

Abstract

The phenomenon of residual strength in composite laminates after fatigue loading has been studied for decades but is generally expressed as a function of the number of cycles applied to the specimens. henomenological laws deduced from these tests are therefore loading dependent and identifying a valid model for any loading condition of a given laminate requires long fatigue testing campaigns. To overcome this difficulty, a testing procedure is proposed to express the residual tensile strength of a unidirectional ply in the fibre direction, as a function of its matrix damage. The resulting behaviour is then independent of the imposed loading and can be etermined by only a few fatigue tests. Experimental results obtained on glass-epoxy non-crimp fabric laminates are presented and analysed.