Strain field inhomogeneities and stiffness changes in GMT containing voids

During compression moulding of glass mat thermoplastics (GMT), voids may fo rm. However, it is not clear whether voids are as critical to mechanical pe rformance in GMT as in thermoset composites. The present investigation also considers the general problem of damage mechanisms in GMT. Conventional te nsile tests, acoustic emission, a stiffness degradation test and a speckle technique for strain field measurements are used as well as optical microsc opy of polished cross-sections. The void content (up to 5%) does not signif icantly influence the strength or stiffness degradation process. The reason is the large inhomogeneity of the strain fields in GMT. Failure occurs in locally soft regions and void effects are of secondary importance. Details of the failure process are discussed, emphasising the large local strains i n matrix-rich regions. (C) 2001 Published by Elsevier Science Ltd.