Yielding of commercial poly(vinyl chloride) pipe material

Tubular test specimens of commercial poly(vinyl chloride) pipe material wer e tested in biaxial stress systems covering the four quadrants of the plane -stress space. The test rig provided yield stresses at a constant temperatu re and controlled strain rate tension, compression, internal pressure, exte rnal pressure, and torsion combined loading. The experimental yield points fit the von Mises yield criterion. This result was confirmed by the ratio o f compressive to tensile yield stresses; being unity, the density remaining constant with the applied hydrostatic stress, and, finally, the normality of the strain vector to the yield locus at the corresponding stressing poin t. Subsequent yielding loci of previously deformed specimens deviated large ly from the von Mises locus. This deviation may have been caused by craze-v oid interaction. Finally, the viscous behavior, the dependence of yield str esses on the strain rate and temperature, is represented with a generalized phenomenological model based on an Eyring-Ward-type expression. (C) 2001 J ohn Wiley & Sons, Inc.