Tensile properties of flow-formed polypropylene pipe

Abstract

The effects of varying the percentage reduction on the tensile properties of flow-formed polypropylene pipes were investigated. Flow-forming, which is a single-point cold rolling process, was performed by using two rollers in a single pass on a conventional lathe machine. Specimens were cut at different orientation angles to the pipe direction. The load-extension behaviour of the flow-formed material showed that the phenomena of yielding and cold drawing gradually become less prominent above 30% reduction. These phenomena were also functions of the orientation angle. From the variations of tensile properties with orientation angle, it was concluded that flow-forming can produce high anisotropy, especially above 30% reduction. Improvements in yield and tensile strength were achieved after about 35 to 45% reduction. The tensile modulus increased significantly after 50% reduction. The yield strain reaches a maximum at about 50 to 60% reduction. Elongation at break decreases with increased reduction. It was noted that 80% reduction appeared to be the maximum reduction, after which the material will exhibit extremely low ductility. © 1991 Chapman and Hall Ltd.