Strain rate dependency of the shear properties of a highly oriented thermoplastic composite material using a contacting displacement measurement methodology—Part B: shear damage evolution

Abstract

This paper is the second part of a two-part series on the strain rate dependency of the shear properties of a glass/polypropylene composite laminate material. In this study the Ladevéze composite material model is used to characterise the shear damage evolution for crosshead displacement rates varying over three orders of mag-nitude. The research was carried out as part of the DTI/EPSRC-funded CRACTAC programme, which was part of the FASMAT Foresight Vehicle suite of projects. 22 [±45]2s laid-up specimens are each tested at crosshead displacement rates of either 5, 50 or 500 [mm/min], using a universal testing machine. The experimental longitu-dinal and transverse strains were obtained using contacting extensometry, and then the stresses and strains were transformed to the fibre axis using Classical Laminate Theory. The damage evolution of the shear properties is found to be strain rate dependent. The critical shear damage limit (an inversely proportional measure of the rate of the degradation of shear modulus) increases for increasing strain rate. The elementary shear damage limit (proportional to the energy required for failure) increased for increased strain rate. The onset of shear modulus degradation (measured as the shear damage energy release rate) increased for increasing strain rate. Finally, the initial shear damage limit was found to be an inappropriate measure of the onset of shear modulus degradation within this thermoplastic composite system.