SYMPOSIA PAPER Published: 01 January 1976
STP28656S

Fracture Toughness Testing of Glassy Plastics

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Despite widespread use of linear elastic fracture mechanics to describe brittle fracture in glassy plastics, prior work has not established a valid fracture toughness criterion based on the unique aspects of polymer mechanical behavior. In this study, fracture toughness tests on poly(methyl methacrylate) (PMMA) were correlated with crack-tip crazing and fracture surface morphology in order to assess the influence of dissipative processes and crack growth modes on standard toughness test variables. Various Kc criteria were examined for their relevance to PMMA, a material with a velocity dependence of fracture typical of glassy plastics. Since crack-tip crazing is restricted in this material, crack extension is essentially elastic for all normal specimen dimensions and precrack conditions. The load instability at the maximum of the load-displacement record is distinguished from the point of intrinsic instability, which is indicated by the K versus ˙a relationship. The load instability leads to a geometry-dependent Kc criterion which can be described analytically, and procedures for measuring a Kc based on intrinsic instability are defined for a standard fracture test. Measured values are in reasonable agreement with estimates derived from K versus ˙a in the literature. The implications of the geometric effects on instability are discussed for other materials and specimen geometries.

Author Information

Margolis, RD
GRTL Company, Birmingham, Mich.
Dunlap, RW
Carnegie-Mellon University, Pittsburgh, Pa.
Markovitz, H
Carnegie-Mellon University, Pittsburgh, Pa.
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Details
Developed by Committee: E08
Pages: 391–408
DOI: 10.1520/STP28656S
ISBN-EB: 978-0-8031-4676-1
ISBN-13: 978-0-8031-0318-4