Simulation of the thermostamping of woven composites: determination of the tensile and in-plane shearing behaviors

The numerical simulation of the thermostamping process for fabric-reinforced thermoplastic composites requires an accurate characterization of the fabric material properties. To capture the interaction of the yarns comprising the woven fabric and the thermoplastic resin of the matrix, the characterization process of these thermoplastic composites requires tensile and shear tests. In this paper, the experimental investigation of three Twintex® fabrics which are being characterized as part of an international benchmark program is presented. The tensile stiffness is determined by unaxial tensile tests of single yarns. The in-plane shear behaviour is characterized by shear-frame tests at room temperature and at 175°C. Shear-frame testing of these Twintex fabrics has been found to be very sensitive to the test methodology as evidenced by the large discrepancy for shear-frame test data from the various research groups using different testing setups. The different methods are reviewed to achieve an understanding of the test. The possible sources of uncertainties are discussed, and in light of this analysis, an appropriate test, using in particular a mechanical conditioning method, is proposed. Three-dimensional Digital Image Correlation (DIC) is used to measure the strain field and to evaluate the actual shear angle and the homogeneity of the shearing within the specimen.