Development of an S-specimen geometry for shear testing of woven thermoplastic composites

A fundamental understanding of pure shear failure is important in elucidating the failure characteristics of woven thermoplastic composites. This work presents a novel S-specimen design and an associated methodology for testing pure in-plane shear failure in composites. The technique has been experimentally tested with woven thermoplastic composites which have complex failure evolution in shear due to their weave architecture. Four different composites were considered to demonstrate the scope of the technique application, with various combinations of weave (plain, satin, twill), matrix (Polypropylene — PP, Polycarbonate — PC, Polyetheretherketone — PEEK), and fibre (glass, carbon, PP). A Digital Image Correlation (DIC) system integrated with the hemispherical testing device validated that shear strain was the dominant strain in the failure region. From this work, it is evident that shear failure morphology varies between the tested composites based on the differences in their weave architecture and fibre and matrix properties. Additional Finite Element Analysis (FEA) showed that neither bending nor friction hindered the tests ability to produce pure shear in the specimen. This new shear specimen provides a means of inducing shear failure utilising the hemispherical dome apparatus currently used for composite forming studies and failure analysis of other deformation modes between uniaxial and equi-biaxial tension.