Accelerated testing method to estimate the long‐term hydrostatic strength of semi‐crystalline plastic pipes

Abstract

The ability to quickly develop predictions of the service lifetime of plastic pipes at different load levels allows designers to choose the best plastic material and design pipe for a specific application. Additionally, it helps material producers to rapidly design, manufacture, test, screen, and modify the base polymeric material. The aim of this study is to introduce a combined experimental and analytical framework to develop accelerated lifetime estimates for semicrystalline plastic pipes which is sensitive to the structure, orientation, and morphology changes introduced by changing processing conditions. To accomplish this task, high density polyethylene (HDPE) is chosen as the exemplary base material and custom fixtures are developed to admit tensile and hoop burst tests on the as-manufactured HDPE pipes. A pressure-modified Eyring flow equation is employed to predict the rupture lifetime of HDPE pipes using the measured mechanical properties under uniaxial tensile and compression loading in different temperatures and strain rates. The method allows the prediction of pipe service lifetimes in excess of 50 years using experiments conducted over approximately 10 days instead of the traditional 13 months. POLYM. ENG. SCI., 60:879-888, 2020.POLYMER ENGINEERING AND SCIENCE-2020 FIG. 7. The compression stress-strain results under different strain rates and elevated temperature of 60 C. Solid lines are the tangent lines and circles are the yield points. a) Model predictions of time-to-failure and biaxial creep tests results at room temperature and (b) the model predictions at three different temperature compared with experimental data for a PE100 grade pipe.

Revisiting creep test on polyethylene pipe—Data analysis and deformation mechanisms

“…The phenomenon of two trend lines in Figure 5 was also reported in the literature, for compression‐molded PE sheet [ 20 ] and PE pipe, [ 9,10 ] but the two trend lines were regarded as one bi‐linear trend line. The main difference in the bi‐linear trend lines between PE sheet and PE pipe is the temperature dependence of the slope for the trend line.…”

“…Two Eyring's processes connected in parallel have been suggested to be adequate to describe PE's viscous behavior, and verified using data from monotonic tests. [ 10, 13 ] Analysis conducted in this study uses one of the two Eyring's processes to represent deformation in the amorphous ( am ) phase. Since the amorphous phase is believed to dominate the deformation process in the low stress regime, the applied stress is denoted by σ am and the activation energy for deformation by ∆H am .…”

“…In view that these standard tests take more than 13 months to complete, many research groups are actively searching for alternative methods to shorten the test time so that the tests are applicable to product development at an early stage or after a major pipe repair during the service. [ 8–10 ]…”

“…With the assumption that the DB transition does not occur, Taherzadehboroujeni et al [ 10 ] followed the work by Govaert's group [ 9, 11 ] and proposed the combination of results from short‐term tensile and compressive tests to determine values for constants in a pressure‐modified Eyring's model so that the model can be used to predict long‐term performance of PE pipe. These works report the change of the trend line between applied stress and failure time under creep loading, but the trend line change does not represent the DB transition because failure mode after the trend line change remains ductile and direction of the trend line change is opposite to that by the DB transition.…”

The Synergic Effects of FDM 3D Printing Parameters on Mechanical Behaviors of Bronze Poly Lactic Acid Composites

“…They used the FDM method for fabricating CFRP composites, and the carbon fiber was added to composites filaments. In most traditional manufacturing methods, such as plastic molding [25][26][27], the tensile strength is acceptable due to the cohesion of materials. However, as one of the major disadvantages of additive manufacturing, they may result in weaker mechanical properties (electrical and thermal conductivity, optical transparency, and strength of printed parts).…”