Shear frame standardization for stamping of thermoplastic woven fabric composites

Thermoforming of commingled thermoplastic/glass woven fabric relies on material deformation at temperatures above the matrix melting temperature. The resistance to deformation depends not only on the matrix viscosity, but also on the fabric architecture. These woven materials exhibit shear deformation with concomitant area changes, enabling them to take on shapes of double curvature. This makes them a great candidate for thermoforming of structural parts [1,3]. To improve the viability of this manufacturing process, simulations and design tools are needed. A standardized test method must be devised to ensure accurate material characterization for finite element models. Therefore, extensive testing with the use of a trellis shear frame is discussed. Testing shows significant non-repeatability, introducing great concern for modeling purposes. Reasons for inconsistency include: fiber tension, alignment and manufacturing. Correlation between test fixtures of different sizes was established by normalizing the data with respect to area. These results suggest that the number of crossovers, as represented by the area, within the material is critical. Two distinct areas of concern addressed in this paper include: the change in fabric temperature during stamping and the material response at these temperatures.