Alan Whittle

Assessment of strength and toughness of modified PVC pipes

Abstract A series of modified PVC pipes, with different concentrations of chlorinated polyethylene, was manufactured under carefully controlled processing conditions. The strength and toughness of each pipe was measured by a variety of methods including uniaxial tensile strength, notched C-ring, essential work of fracture, strain energy release rate, fracture toughness, and impact tests. Over the range of compositions tested, all of the quantitative measures of toughness and strength suggest an approximately linear relationship with modifier concentration. For pipe of the dimensions used in this study, the yield strength is overestimated when determined via the net section stress on the notched C-ring.

The Frequency Effects on Fatigue Threshold of PVC-M and PVC-U in Air and Water Medium

The cyclic fatigue threshold value (Kth) of PVC materials with (PVC-M) and without (PVC-U) impact modifier was determined and compared in air and water environments. The PVCM specimens contain 6 pphr of chlorinated polyethylene (CPE) impact modifier. The testing was undertaken at a stress ratio of R=0.1 and fatigue threshold was evaluated at 3 different frequencies: 1Hz, 7Hz and 20Hz. Frequency noticeably affected the fatigue threshold value; regardless of the testing environment; at low frequency the fatigue threshold of PVC-M was below PVC-U, however, this difference gradually decreased with increasing frequency as Kth of PVC-M increased but Kth of PVC-U remained constant. This trend was accelerated in water where a higher of fatigue threshold, Kth, was also observed. A lower fatigue threshold of PVC-M than PVC-U is associated with the presence of CPE particles. The absorption of water into the PVC matrix was evident with the formation of nodular structures observed on the fracture surface. The presence of the nodular structures (at regions close to the threshold) has retarded the fibrillation of crazes, which then blunted the crack propagation.

Improvements to C-ring fracture toughness test for poly(vinyl chloride) pipes

Abstract Examination of the published procedure for performing calculations on data obtained from the C-ring fracture toughness test for unplasticised poly(vinyl chloride) reveals a major flaw. The dimensions of the specimens do not satisfy the ASTM criteria for plane strain conditions and correction factors are therefore introduced. However, there is an error in the calculation procedure, which results in variations in the severity of the test with pipe wall thickness. An improved approach is proposed and recommendations are made for changing the ISO/DIS 11673·2 test standard, to allow for variations in the yield strength of unplasticised poly(vinyl chloride) and to identify the calculated data as K c rather than K 1c.