HSUEH-LEE SYNOPSISMethods to measure the plane strain fracture toughness (I&) of PVC pipe material, valid according to linear elastic fracture mechanics (LEFM), have been developed. As in metals practice, the crack tip plastic zone must be small compared to initial crack length, section thickness, and other specimen dimensions to achieve validity. Other conditions of test rate and temperature also must be fulfilled. K I , values vary from 2.8 to 4.0 MN m-.3R. Quantitative micromechanical analyses of the plastic flow regions on the fracture surfaces account for only a fraction of the measured toughness. Other deformation mechanisms (crazing) below but near the surfaces have been observed; apparently they absorb the balance of the work required to drive the stable crack. Under catastrophic, rapid crack propagation, only a single craze exists ahead of the crack tip; the multiple crazes disappear. Thus the dynamic fracture toughness may be several factors less than the static or stable value. tion rate), and temperature in addition to the material property itself [4].