Crack Growth Behavior of Pipes Made From Polyvinyl Chloride Pipe Material1

Abstract

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 precrack. CTPB specimen is further cut into five 72 deg 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 0.5 W, of the loading holes from the bore surface. The 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 °C, and different crosshead speeds of (10–500 mm/min). The numerical analysis carried out within the frame of the present work is done using the finite element program Cosmos 2.6. Finite element method (FEM) is used to compute the stress intensity factor KQ surrounding the crack tip. The computed stress intensity factor can then be compared with that obtained by theoretical equation. The experimental 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 also affects the fracture toughness. CST specimens show higher fracture toughness in the case of pin loading location X = 0.5W than X = 0 by about (12%). The transitional crosshead speed is affected by specimen geometry. CST specimens (CST) at X = 0 and 0.5W have higher transitional crosshead speed compared with the CTPB specimen configuration.

Application of fracture mechanics for the characterization of PVC pipes. I. Evaluation of the applicability of the EWF technique in specimens produced directly from pipes

“…In a similar approach, stress intensity factor at plastic collapse ( K C ) values were determined by regression using the same load vs displacement data obtained for EWF, assuming that for SENB and CTPB specimens Equation (3a) and (3b), respectively, apply [ 27,28 ] : where P C is the load at failure (plastic collapse or tear onset) and Y is a geometrical energy correction factor depending on the specimen type and testing condition. For SENB and CTPB specimens values of Y were determined using Equation (4a) and (4b), respectively [ 27,28 ] : …”

“…In a similar approach, stress intensity factor at plastic collapse (K C ) values were determined by regression using the same load vs displacement data obtained for EWF, assuming that for SENB and CTPB specimens Equation (3a) and (3b), respectively, apply [27,28] :…”

“…where P C is the load at failure (plastic collapse or tear onset) and Y is a geometrical energy correction factor depending on the specimen type and testing condition. For SENB and CTPB specimens values of Y were determined using Equation (4a) and (4b), respectively [27,28] :…”

Application of fracture mechanics for the characterization of poly(vinyl chloride) pipes. II. Evaluation of a ring‐type specimen for fracture mechanics testing

“…where the partial derivative expresses the change in deformational energy U as a function of the crack length a, for a given constant displacement u, using the same load versus displacement data obtained for EWF. Also, in a similar approach as presented previously, [20,21] stress intensity factor at plastic collapse (K C ) values were determined by regression using the same data, assuming that Equation (6a) [27] and (6b) [28] apply for, respectively, CTPB-and SNRT-type specimens:…”

“…where P C is the load at failure (plastic collapse or tear onset), Y is a geometrical energy correction factor depending on the specimen type and testing condition, and θ is the half angle between the center of the original pipe and the support roller in the three-point bending assembly. For CTPB-type specimens values of Y were determined using Equation ( 7) [27] :…”