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Brittle to ductile: Fracture toughness mapping on controlled epoxy networks
Author(s) -
Crawford Emmett D.,
Lesser Alan J.
Publication year - 1999
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.11425
Subject(s) - materials science , fracture toughness , brittleness , composite material , fracture mechanics , epoxy , fracture (geology) , yield (engineering) , toughness , strain energy release rate , flexural strength
Abstract A series of epoxy networks with controlled molecular weight between crosslinks (M c ) was constructed with a difunctional epoxy resin and a mixture of aliphatic amines. The glass transition and yield strengths decreased as M c increased, while the elastic properties were independent of M c . In determining the effect of M c on fracture toughness, the fracture behavior changed from a brittle fracture to a ductile fracture as M c increased. The tests and analyses used to evaluate the fracture energy changed from a linear elastic fracture mechanics approach for brittle failures to an elastic‐plastic fracture mechanics approach for ductile failures. The ductile responses also showed an increasing fracture resistance with crack extension. Two popular models were used to describe the fracture energy as a function of yield strength. The analysis showed that a change in fracture energy by a thermally induced change in yield strength was equivalent to a change in fracture energy by a chemically induced change in yield strength. In addition, comparisons between the two models allowed insightful relationships to be drawn.