Strain rate effects on the shear properties of a highly orientated thermoplastic composite material using a contacting displacement measurement methodology – Part B: Damage evolution

This paper is concerned with the characterisation of the shear mechanical properties of glass-fibre-reinforced thermoplastic composite laminates over a range of strain rates. 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. Twenty-two [±45]2s laid-up specimens each were tested at 5, 50 and 500 (mm/min) crosshead displacement rates, using a universal testing machine. The longitudinal and transverse strains were obtained experimentally using contacting extensometry apparatus and then transformed to the ply axis using Classical Laminate Theory. A rigourous statistical treatment method was proposed for the processing and analysis of the raw data. The shear modulus decreased for increasing strain rate. The shear failure stress increased for increasing strain rate. Semi-empirical linear functions of the shear modulus and shear failure strength were proposed with respect to the logarithm of the shear strain rate. The shear failure strain was independent of strain rate. Finally, the observed opposing trends of in-plane shear modulus and shear failure stress suggested that shear damage evolution is strain rate dependent for the examined material.