Effect of specimen geometry on the predicted mechanical behavior of polyethylene pipe material

The primary objective of the present paper is to depict the mechanical behavior of high density polyethylene, (HDPE), pipes under different loading conditions with different specimen geometries to provide the designer with reliable design data relevant to practical applications. Therefore, it is necessary to study the effect of strain rate, ring configuration, and grip or fixture type on the mechanical behavior of dumb-bell-shaped, (DBS), and ring specimens made from HDPE pipe material. DBS and ring specimens are cut from the pipe in longitudinally, and circumferential (transverse) direction respectively. On the other hand, the ring specimen configuration is classified into two types; full ring, (FR), and notched ring, (NR) (equal double notch from two sides of notched ring specimen) specimens according to ASTM D 2290-12 standard. Tensile tests are conducted on specimens cut out from the pipe with thickness 10 mm at different crosshead speeds (10–1000 mm/min), and ambient temperature, Ta = 20 °C to investigate the mechanical properties of DBS, and ring specimens. In the case of test specimens taken from longitudinal direction from the pipe a necking phenomenon before failure appears at different locations along the gauge section. On the other hand, the fracture of NR specimens occurs at one notched side. The results demonstrated that the NR specimen has higher yield stress than DBS, and FR specimens at all crosshead speeds. The present experimental work reveals that the crosshead speed has a significant effect on the mechanical behavior of both DBS, and ring specimens. The fixture type plays an important role in the mechanical behavior for both FR and NR specimens at all crosshead speeds.</jats:p

Effect of loading rate and pipe wall thickness on the strength and toughness of welded and unwelded polyethylene pipes

The primary objective of this paper is to depict the mechanical behavior of welded and unwelded high-density polyethylene (HDPE), pipes to provide the designer with reliable design data relevant to practical applications. Therefore, it is necessary to study the effect of strain rate and specimen configuration on the mechanical behavior of welded and unwelded pipes made from HDPE. Tensile tests are conducted on specimens longitudinally cut from the pipe with thickness (10 and 30 mm), at different crosshead speeds (5-500 mm/min), and different gauge lengths (20, 25, and 50 mm) to investigate the mechanical properties of welded and unwelded specimens. All tests are performed at room temperature (Ta=23 °C). Butt fusion, BF, welding method is used to join the different parts of HDPE pipes. The present results showed that the mechanical characteristics of welded specimens are lower than those of unwelded specimens. In the case of test specimens taken from unwelded pipe, the results of mechanical characteristics revealed that a necking phenomenon before failure appears at different locations along the gauge section. On the other hand, the fracture of welded specimens almost occurs at the fusion zone. It is found that the crosshead speed and specimen configurations have a significant effect on the mechanical behavior of both welded and unwelded specimens

Validation of linear elastic fracture mechanics in predicting the fracture toughness of polyethylene pipe materials

The main purpose of the present paper is to compare between the fracture toughness based on linear elastic fracture mechanics (GIC), and that based on nonlinear fracture mechanics (JIC). The material of the investigated pipe is a high-density polyethylene (HDPE), which is commonly used in natural gas piping systems. The welds at the pipe junction are produced by butt-fusion (BF), welding. Curved three-point bend (CTPB), fracture specimens are used. The crosshead speed ranged from 5 to 500 mm/min and specimen thickness ranged from 9 to 45mm for both welded and unwelded specimens at room temperature Ta, equal 23°C. The study reveals that the crosshead speed has a significant effect on the fracture toughness of both welded and unwelded specimens. The results of GIC for different specimen thickness and crosshead speed found previously by the authors [1] have been compared with JIC under the same operating conditions [2]. The comparison between welded and unwelded specimens revealed that in the welded specimens there is a marginal difference between fracture toughness measured using linear elastic fracture mechanics LEFM and elastic plastic fracture mechanics EPFM, for both crosshead speeds.</jats:p

Mechanical behavior of welded and un-welded polyethylene pipe materials

The primary objective of the present paper is to depict the mechanical behavior of high density polyethylene, HDPE, pipes to provide the designer with reliable design data relevant to practical applications. Therefore, it is necessary to study the effect of strain rate and specimen configuration on the mechanical behavior of welded and un-welded pipes made from HDPE. Tensile tests are conducted on specimens longitudinally cut from the pipe with thickness (10, and 30 mm), at different crosshead speeds (5-500 mm/min), and different gauge lengths (20, 25, and 50 mm) to investigate the mechanical properties of welded and un-welded specimens. Butt-fusion, BF, welding method is used to join the different parts of HDPE pipes. In the case of test specimens taken from un-welded pipe a necking phenomenon before failure appears at different locations along the gauge section. On the other hand, the fracture of welded specimens almost occurs at the fusion zone. At lower crosshead speeds the fracture of welded specimen occurs in all specimen configurations at the fusion zone. The present experimental work reveals that the crosshead speed has a significant effect on the mechanical behavior of both welded and un-welded specimens. Copyright © 2013 by ASME