The effect of rotating-bending fatigue on high-density polyethylene

Abstract

External factors, such as main stresses, frequency of the loading, shape and history of loading (hysteresis) have an important effect on the fatigue behavior of high-density polyethylene. HDPE pipes, used in the transport and distribution of water and are required for oscillating loads caused by internal pressure or external loads. These cyclic loads cause the pipe's failure due to fatigue. In a polymer fatigue occurs at stress levels that are low relative to the yield strength [1]. This paper presents results from the assessment of the mechanical behavior of specimen test taken from PE 100 pipe in the case of variable stresses. Thus, compressive and tensile stresses are induced on the specimen test as it is simultaneously bent and rotated. The rotating-bending fatigue test is performed when the specimen test is placed with the extremities on two supports and supports a load applied in four-points placed symmetrically with respect to the supports, at 1/3 of the distance between the supports, according to [2]. The effect of the values of the number of cycles until failure in the case of rotating-bending fatigue stress on mechanical properties of HDPE is also compared with the same factor in the case of axial fatigue stress. The polyethylene pipe may be subjected to random variable stresses. In practice, variable loading patterns as strain rate, temperature, hydrostatic pressure, pressure from to the vehicle wheels, the movement and the variable weights supported by the surrounding soil are causes that could lead to the bending of PE pipe. These loads generate oscillating axial stresses. The bending of the pipe is cause of the cross-section modification (roundness modification) of it.