Abstract
In this paper, an experimental analysis for determining the fatigue strength of PE-100, one of the most used High Density Polyethylene (HDPE) materials for pipes, under cyclic axial loadings is presented. HDPE is a thermoplastic material used for piping systems, such as natural gas distribution systems, sewer systems and cold water systems, which provides a good alternative to metals such as cast iron or carbon steel. One of the causes for failures of HDPE pipes is fatigue which is the result of pipes being subjected to cyclic loading, such as internal pressure, weight loads or external loadings on buried pipes, which generate stress in different directions: circumferential, longitudinal and radial. HDPE pipes are fabricated using an extrusion process, which generates anisotropic properties. By testing in the Laboratory a series of identical specimens obtained directly from PE-100 HDPE pipes in longitudinal directions, the relationships between amplitude stress and number of cycles (S-N curve) test frequency 2 Hz and stress ratio R = 0.0 are established.
Highlights
The behavior of polymers gains more and more relevance in the study of materials, due to the growing utilization of polymers in complex applications, as a consequence of their technical advantages and lower cost [1]
An experimental fatigue study was carried out that showed that the fatigue strength of High Density Polyethylene (HDPE) grade PE-100 pipes depends on the pipe stress
Fatigue lives of HDPE are widely stochastic and a scatter in the number of cycles to rupture is observed for the same stress level
Summary
The behavior of polymers gains more and more relevance in the study of materials, due to the growing utilization of polymers in complex applications, as a consequence of their technical advantages and lower cost [1]. The High Density Polyethylene (HDPE) is one of the most used polymers in the industry due to the diversity of its applications and to the multiple advantages that it has over more conventional materials. A piping system is subjected to internal pressure or external loads varying in magnitude and frequency, generating different responses from the material [2]. Such cyclic loads cause cumulative damage and cracking that could produce a piping system failure [3]. It is important to emphasize that this presents a problem that should be especially considered, since a stress value lower than yield strength can produce a pipe failure in a relative short period of operation if the pressure is cyclic [4]
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