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Crazing, yielding, and fracture of polymers. I. Ductile brittle transition in polycarbonate
Author(s) -
Legrand D. G.
Publication year - 1969
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1969.070131010
Subject(s) - crazing , materials science , brittleness , polycarbonate , composite material , glass transition , polymer , stress (linguistics) , fracture toughness , yield (engineering) , philosophy , linguistics
Most thermoplastics far below their glass transition give a brittle fracture when de‐formed in uniaxial tension. Bisphenol‐A polycarbonates are an exception and deform in a ductile manner. However, it has been observed in Izod impact studies of notched samples that the mode of failure changes from a ductile to a brittle fracture on annealing samples below T g . It has been found that, when notched samples are stressed, a Griffith type flaw is formed under the notch. The criterion for the ductile brittle transition is evaluated in terms of σG (the stress required to propagate the Griffith flaw), and σ y , the yield stress for the polymer. It has been found that the density and yield stress for the samples annealed at various temperatures are dependent upon previous thermal history and in particular on the molecular weíAght. On the basis of these measurements, it is concluded that many of the so‐called anomalous effects observed with polycarbonate can be explained.