Fracture toughness of short fiber/thermoplastic matrix composites, compared on the basis of different test methods

A variety of thermoplastic matrices, including Polyethersulfone (PES), Polyoxymethylene (POM), and toughness modified Polyethylenterephthalate (PET), and their short glass fiber reinforced composites have been tested with respect to their impact resistance. Test methods applied, all characterize in some respects the "toughness" of these materials. It turns out, however, that the ranking order of their toughnesses varies quite remarkably, depending on the particular testing procedure. In a fracture mechanics test with compact tension specimens, the fracture toughness of Polyethersulfone, for instance, is very low compared to the other thermoplastics and to their short fiber reinforced versions. This is due to the very sharp notches used in this kind of toughness test, and due to the high notch sensitivity of PES. In a falling dart test with a CEAST® modular falling weight device, and the use of unnotched plates, PES proves to be, on the other hand, much better than all the other competitive materials. The results are discussed with respect to the content of infor mation of the individual tests on the "toughness" profile of the different polymers and com posite materials studied