Loss of entanglement density during crazing |
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Authors: | Chris S Henkee Edward J Kramer |
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Affiliation: | (1) Department of Materials Science and Engineering and Materials Science Center, Cornell University, 14853 Ithaca, New York, USA;(2) Present address: Central Research, Mobil Chemical Company, PO Box 240, 08818 Edison, NJ, USA |
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Abstract: | The formation of fibril surface area during craze growth requires a loss of entangled strand density in the fibrils themselves. To demonstrate the decrease in entangled chain density, thin films of polystyrene are bonded to soft copper grids and strained in tension. This procedure produces crazed specimens in which the craze fibrils can be characterized by a well-defined draw ratio,
0. The films are then exposed to electron irradiation. This produces chemical crosslinks between the molecules, thus forming a crosslinked network. Subsequent heating of the film aboveT
g results in the entanglement network trying to retract to =1. The crosslink network, however, tries to maintain the . of the craze fibrils at
0. The craze fibrils thus retract to Ferry's state of ease ,
S, where the tension of the entanglement network is balanced by the compression of the crosslink network. Measurements of
s in crazes crosslinked and then healed confirm that a 25 to 50% loss of entanglement density in craze fibrils occurs, in agreement with theoretical predictions. |
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Keywords: | |
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