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The fracture behavior of surface embrittled polymers
Author(s) -
So Paul K.,
Broutman L. J.
Publication year - 1986
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760261702
Subject(s) - crazing , materials science , embrittlement , composite material , brittleness , ductility (earth science) , natural rubber , polymer , deformation (meteorology) , fracture (geology) , surface energy , cracking , fracture mechanics , coating , elastomer , creep
Normally ductile polymers may exhibit unexpected brittle fractures because of a phenomenon termed surface embrittlement. The problem may arise whenever a thin brittle layer is present on the surface, which may result from the application of brittle paint or, more commonly, from surface degradation caused by exposure to elevated temperatures, ultra‐violet radiation, and stress‐cracking agents. In rubber‐modified polymers such as acrylonitrile‐butadiene‐styrene and high‐impact polystyrene, exposure to the outdoor environment inevitably results in the formation of a thin surface layer containing cross‐linked rubber particles in a matrix of reduced molecular weight. Although the depth of material adversely affected is typically small compared to the bulk, a drastic reduction in ductility nonetheless has been observed. To better understand the mechanism of embrittlement, this paper examines the criterion for embrittlement by considering the mechanism for enhanced energy absorption of rubber‐toughened plastics and elementary concepts of fracture mechanics. It has been shown that a critical coating thickness exists when multiple crazing is essentially inoperative and the deformation is localized, to the tip of a fast moving sharp crack restricting strain energy dissipation to a relatively small region.