Volume 16, Issue 3 (May 1988)
Strain Gage Analysis of Residual Stress in Plastic Pipes
Residual stress distribution in medium density polyethylene (MDPE) 102 mm (4 in.) pipe with 11.1 mm wall thickness is evaluated using three different procedures. A modified layer removal procedure is employed to evaluate the residual stress component in the longitudinal direction as a function of the pipe wall thickness. On the other hand, the residual stress distribution in the circumferential direction is estimated using the conventional ring slitting method. A strain gage technique for direct residual strain measurements is described. The results obtained from the three procedures in a given direction are in qualitative agreements. A tensile residual stress dominates about 24% of the inner section of the pipe wall. The residual stress then becomes compressive reaching its maximum value at the outermost layer.
The stress values obtained from the first two techniques appear unrealistically excessive. On the other hand, those obtained from direct strain measurements appear reasonable as indicated by recent crack propagation studies in the specimens prepared from the same pipe sample.