Yield behavior and failure response of an aliphatic polyketone terpolymer subjected to multi-axial stress states

The yield behavior of an engineering thermoplastic under biaxial stress sta tes has been investigated. The material considered is an aliphatic polyketo ne terpolymer. Multiaxial testing was performed on thin-walled hollow cylin ders at four different temperatures and three strain rates. Various stress states were applied in order to develop failure envelopes. Within each enve lope, the nominal strain rate along the octahedral shear plane, (gamma)over dot (oct), was held constant. These tests were performed at 0, 20, 50 and 80 degrees C at (gamma)over dot (oct) = 0.05 min(-1). At 20 degrees C, samp les were also tested at (gamma)over dot (oct) = 0.005 and 0.5 min(-1). Belo w the T-g of 12 degrees C, failures in all stress states investigated, exce pt axial compression, were brittle. At temperatures of 50 and 80 degrees C, all failures were ductile. At 20 degrees C, both ductile and brittle failu res were observed. Although the rate affected the yield strength of the mat erial, it had little effect on the mode of failure. In contrast, the temper ature had a significant effect on the yield strength and mode of failure. W hile the effect of strain rate on yield strength was greater in the hoop di rection than axial, the opposite was true for the effect of temperature. It was also observed that the state of stress played a significant role in th e material failure. (C) 2000 Kluwer Academic Publishers.