A New Test Setup for Testing Polyethylene Tubes Under Constant and Cyclic Internal Pressures

A test system was designed to evaluate the failure behavior of a thin-wall small-diameter polyethylene tube under internal pressure. The test setup was capable of delivering constant (static) and cyclic (dynamic) pressure patterns as well as maintaining an elevated testing temperature to accelerate the failure. Desired pressure patterns were obtained by controlling the opening/closing duration of the solenoid valves accordingly. A water-sensing system was used to detect the failure time, particularly for small brittle failure. A data acquisition system based on LabView[TM] was used to control and record the applied pressures and the failure times. The constant pressure tests were performed at 65 and 75[degrees]C and the cyclic pressure tests were performed at 75[degrees]C. The test data obtained from the constant pressure tests exhibited two distinguishable linear regions in a log-log plot of hoop stress versus failure time. Slope values of -0.034 and -0.113 were obtained for ductile and brittle regions, respectively. A brittle failure curve with slope of -0.039 was obtained under the cyclic pressure testing condition. The slow crack growth (SCG) failure was considerably accelerated by the cyclic loading.