Time dependent crack growth in polyethylene: characterizing the da/dt = AKn dependence and the effects of Igepal
Abstract
Testing of newly developed high density polyethylene (HDPE) resins is both time consuming and costly. This thesis presents a fracture mechanics approach to ranking polymers and predicting lifetimes for long-term, brittle-like failures by studying slow crack growth (SCG) rate as a function of stress intensity. Constant load single-edge-notch bend (SENB) tests commonly know as ''three point bend'' tests have been performed on deeply notched specimens. The load-line displacement as a function of time was measured. The material compliance was calculated and used to determine the crack growth rate (da/dt) as a function of stress intensity (K₁). Very good repeatability was demonstrated and da/dt was found to be a unique function of K₁ giving the some crack growth rate at a particular K₁ for very different combinations of load and initial crack length (a[]). It was demonstrated that da/dt vs. K₁ curve comparisons can be used to rank a material's resistance to slow crack growth. A set of da/dt =AK[] data was combined with a single Stage II hydrostatic rupture test point to predict the entire Stage II failure curve. This research also characterized the effects of Igepal on the total times to failure, crack initiation times, crack growth times, and da/dt vs. K₁ curves of two HDPE materials. SENB failure times were compared to PENT failure times to conclude that the SENB test is more accurate in determining failure times and is a superior measure of a materials resistance to SCG.
Description
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Includes bibliographical references (leaves 113-114).
Issued also on microfiche from Lange Micrographics.
Includes bibliographical references (leaves 113-114).
Issued also on microfiche from Lange Micrographics.
Keywords
mechanical engineering., Major mechanical engineering.