Fracture characterization of recycled high density polyethylene/nanoclay composites using the essential work of fracture concept

Abstract

The effect of nanoclay on the plane-strain fracture behavior of pristine High density polyethylene (HDPE) and recycled HDPE blends was studied using the essential work of fracture (EWF) concept. The failure mode of EWF tested specimens was found to be associated with the specific non-EWF (b B w p,B ). Adding 6-wt% of nanoclay to pristine HDPE and 2-wt% to recycle-blends greatly decreased the b B w p,B values and led to a transition from ductile to brittle failure mode. A fractographic study revealed that the difference in failure modes was caused by the changes in micro and macro morphologies, which could be related with the specific EWF (w e,B ). In the ductile failure, w e,B is governed by the fibril size; adding nanoclay and recycled HDPE to pristine HDPE decreased the fibril size and subsequently lowered the w e,B value. In the brittle failure, the w e,B value was enhanced by creating a rough fracture surface. Adding nanoclay to pristine HDPE, a steadily decrease in w e,B was measured until 4-wt% after which the change was insignificant. Conversely, nanoclay content more than 2-wt% in recycle-blends greatly decreased the w e,B value. A transition map was constructed to illustrate the potential failure mode and the associated fracture morphology based on the tested material compositions. POLYM. ENG. SCI., 56:222-232, 2016.

Effects of recycled HDPE and nanoclay on stress cracking of HDPE by correlatingJcwith slow crack growth

“…The test data are separated according to the testing temperatures at 30 and 70°C. The SCR test data were extrapolated to generate a single failure curve at 23°C using Popelar's shift method and rate process method in order to correlate with data obtained from the uniaxial tensile test and the essential work of fracture (EWF) test .…”

“…Equation implies that the plane‐strain fracture toughness ( J ) can be also calculated once the corresponding failure time is known. In our previous study, the critical J values ( J c ) for tested materials were determined using the EWF test together with energy partitioning method . The load‐displacement curves obtained from the EWF tests are now converted to load‐time curves based on the tensile testing strain rate of 5 mm/min, as illustrated in Fig.…”

“…The tensile strain was measured using an extensometer with a gauge length of 25 mm. The secant modulus at 1.5% of strain and corresponding stress were used to represent the elastic modulus and yield stress based on the elastic‐plastic model .…”

“…This article discusses a new approach to correlate SCG to the fracture toughness based on elastic‐plastic fracture mechanics (EPFM). The SCG behavior was evaluated using the notched constant ligament stress (NCLS) test, while the fracture toughness was determined in our previous papers using the essential work of fracture (EWF) concept . The correlation concept was studied on recycled HDPE materials .…”

Effects of ethylene‐octene copolymer (POE) on the brittle to ductile transition of high‐density polyethylene/POE blends

“…In viewpoint of the work of fracture, the essential work of fracture before necking is the surface-related fracture energy while the subsequent nonessential plastic work is the volumerelated energy dissipated under a plastic deformation. [30] PE-HD is semicrystalline, whose plastic behavior is greatly affected by the state of their amorphous phase. [31] More importantly, POE is elastomeric.…”