Plane strain fracture toughness of polyethylene pipe materials

Abstract

The plane strain fracture toughness of medium density polyethylene pipe materials has been investigated over a range of test temperatures and rates. Conditions are defined under which valid fracture toughness values can be obtained; at higher temperatures the material is notch‐insensitive. Fracture surface morphology is described, and features are compared with predictions from the Dugdale model. The toughness derives from a band of fibrillar, drawn morphology associated with crack initiation or slow growth. The plane strain fracture toughness correlates with percent crystallinity according to the same relationship whether the crystallinity is varied by thermal treatment, comonomer content, or molecular weight.

A study of brittle‐ductile transition in polyethylene

“…However, studies of the effect of material morphology, such as crystallinity, on BDTT are limited. It has been shown that annealing or slow cooling resulted in a higher value of BDTT for low density polyethylene (LDPE) (61, and that annealing also resulted in a decrease in the toughness at -60 to -90°C for medium density polyethylene (MDPEI (8). For high density polyethylene (HDPE), annealing increased the toughness at ambient temperature by about three times (10).…”

Effect of strain rate, thickness, welding on the J–R curve for polyethylene pipe materials

“…In their study the stress intensity factor and crack mouth opening displacement coefficient have been derived as a function of angular span of ring segment h 1 . For pipe made from MDPE, Mandell et al [22,23] have studied the effect of specimen thickness, B on the plane strain fracture toughness, K IC . The specimen thickness is varied within the range 3-23 mm.…”

“…At lower temperatures K IC is greater due to greater stiffness whereas that, J IC has lower energy absorption as the fracture mode becomes less ductile and unstable. Mandell et al [22,23] have investigated the plane strain fracture toughness, K IC , for pipe made from MDPE pipe material over a large range of test temperatures and strain rates. The fracture test specimens are fabricated both as directly cut from pipe walls as well as from flat plates.…”

Polymer applications

“…A method for inducing brittle failure for testing was developed as a plane strain fracture toughness test [282,283]. The test involved notehing the specimen and using a razor !…”