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A ring bending test was devised to evaluate the behavior of plastic pipes that have been held under constant deformation and then subjected to intermittent loads. The apparatus consists of a frame capable of locking the test pipe at a fixed level of deflection in ring bending. A load cell monitors the change in force with passing time required to hold the deflection level. At preselected time intervals an additional deflection increment is briefly applied to the pipe and then released. The load required to produce this deflection increment is recorded. The pipe is then returned to the original level of deformation. Test results show that the long term decrease in load, or stress relaxation, is unaffected by the short term load increments. The short term modulus is much greater than the long term relaxation modulus and does not decrease with time. Test results also show that short term load increments may be treated as a new load on the pipe, with a stiffness response governed by the short term modulus.
long-term modulus, parallel plate, plastic pipe, relaxation, short-term modulus, viscoelastic, Young's modulus
Senior AssociateDoctoral Student, Simpson, Gumpertz and Heger, Inc.University of Massachusetts, ArlingtonAmherst, MAMA
Professor of Civil Engineering, University of Massachusetts, Amherst, MA
Graduate Student, University of Massachusetts, Amherst, MA