Tarek M. A. A. EL-Bagory

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

Plastic Load of Precracked Polyethylene Miter Pipe Bends Subjected to In-Plane Bending Moment

The main purpose of the present paper is to investigate the effect of crack depth on the limit load of miter pipe bends (MPB) under in-plane bending moment. The experimental work is conducted to investigate multi miter pipe bends, with a bend angle 90 o , pipe bend factor h=0.844, standard dimension ratio SDR=11,and three junctions under a crosshead speed 500 mm/min. The material of the investigated pipe is a high-density polyethylene (HDPE), which is used in natural gas piping systems. The welds in the miter pipe bends are produced by butt-fusion method. The crack depth varies from intrados to extrados location according to the in-plane opening/closing bending moment respectively. For each in-plane bending moment the limit load is obtained by the tangent intersection (TI) method from the load deflection curves produced by the testing machine specially designed and constructed in the laboratory 1 . The study reveals that increasing the crack depth leads to a decrease in the stiffness and limit load of (MPB) for both inplane closing and opening bending moment. Higher values of the limit load are reached in case of opening bending moment. This behavior is true for all investigated crack depths.

Crack Growth Behavior of Pipes Made From Polyvinyl Chloride Pipe Material

The behavior of crack growth of polymeric materials is affected by several operating conditions such as, crosshead speed, specimen thickness, load line, and specimen configurations which reverse the behavior of crack from stable to unstable crack growth behavior. The main objective of the present paper is the determination of plane strain fracture toughness (KIC) for polyvinyl chloride (PVC) used in piping water transmission systems. The dimensions of the PVC pipe are outside diameter, Do=315 mm, standard dimensions ratio, SDR=13.23, ratio between outside to inside radii Ro/Ri =1.179 and pipe thickness, t =24 mm. Curved specimens are prepared from a pipe by cutting 12 mm thickness ring segments. The curved specimens are divided into two specimen configurations, namely curved three point bend, CTPB and C-shaped tension, CST specimens. All specimens are provided artificially with a pre-crack. CTPB specimen is further cut into five 72O sectors with each being centrally notched to a depth approximately a = 0.479 of the wall thickness. CST specimen configuration is characterized by the eccentricity X =0, and 0.5W, of the loading holes from the bore surface. Linear elastic fracture mechanics theory (LEFM) is used to predict the plane strain fracture. The tests are carried out at room temperature, Ta equal 20 oC and different crosshead speeds of (10- 500 mm/min). The fracture test results reveal that, the crosshead speed has been proven to affect the mode of failure and mode of fracture. At lower crosshead speeds the mode of failure is ductile, while at higher crosshead speeds it is brittle. The specimen configuration affects also on the fracture toughness. C-shaped tension specimens show higher fracture toughness in case of pin loading location X =0.5W than X = 0 by about (12%). Transitional crosshead speed is affected by specimen geometry. C-shaped tension specimens (CST) at x= 0 and 0.5W have higher transitional crosshead speed compared with CTPB specimen configuration.

Evaluation of Fracture Toughness Behavior of Polyethylene Pipe Materials

The main purpose of the present paper is to investigate the effect of crosshead speed, specimen thickness, and welding on the fracture toughness. The material of the investigated pipe is a high density polyethylene (HDPE), which is commonly used in natural gas piping systems. The welding technique used in this study is butt-fusion (BF) welding technique. The crosshead speed ranged from 5 to 500 mm/min and specimen thickness ranged from 9 to 45 mm for both welded and unwelded specimens at room temperature, Ta = 20 °C. Curved three point bend (CTPB) specimens were used to determine KQ. Furthermore, the results of fracture toughness, KQ, will be compared with the plane–strain fracture toughness, JIC, for welded and unwelded specimens. The experimental results revealed that KQ increases with increasing the crosshead speed, while KQ decreases as the specimen thickness increases. The investigation reveals that the apparent fracture toughness, KQ, for HDPE pipe of unwelded specimen is greater than that of corresponding value for welded specimen. The same trend was observed for the plane-strain fracture toughness, JIC. At lower crosshead speeds there is a minimum deviation in KQ between welded and unwelded specimens, while the deviation becomes larger with increasing crosshead speed.

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.Copyright