Correlation of the crack initiation stress with epoxy network topology

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Much controversy surrounds the dependence of stress intensity factor of glassy thermosets, epoxies in particular, with crosslink density. One could scan the literature and find references that claim K{sub Ic} increases with crosslink density, decreases with crosslink density, or is independent of crosslink density. The authors feel that two factors contribute to this confusion. First, a typical method for assessing this dependence relies on modifying the crosslink density by changing the precursor epoxy molecular weight. On the other hand, one could change stoichiometry or quench the reaction at intermediate extents of reaction to obtain large changes in crosslink density. However, ... continued below

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3 p.

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Adolf, D.; Weeks, T. & McCoy, J. March 1, 1997.

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  • Adolf, D. Sandia National Labs., Albuquerque, NM (United States)
  • Weeks, T.
  • McCoy, J. New Mexico Inst. of Mining and Technology, Socorro, NM (United States)

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  • Sandia National Laboratories
    Publisher Info: Sandia National Labs., Albuquerque, NM (United States)
    Place of Publication: Albuquerque, New Mexico

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Description

Much controversy surrounds the dependence of stress intensity factor of glassy thermosets, epoxies in particular, with crosslink density. One could scan the literature and find references that claim K{sub Ic} increases with crosslink density, decreases with crosslink density, or is independent of crosslink density. The authors feel that two factors contribute to this confusion. First, a typical method for assessing this dependence relies on modifying the crosslink density by changing the precursor epoxy molecular weight. On the other hand, one could change stoichiometry or quench the reaction at intermediate extents of reaction to obtain large changes in crosslink density. However, most studies have not measured the resulting stress intensity factor of these partially cured systems at constant T-T{sub g}, where T{sub g} is the glass transition temperature of the epoxy. Since T{sub g} can change significantly with cure and since fracture processes at the crack tip are dissipative, they must work at constant T-T{sub g} to ensure that the nonlinear viscoelastic mechanisms are fairly compared. In this study, they quenched the reaction of the diglycidyl ether of bisphenol A (DGEBA) and diethanolamine (DEA) at various stages past the gel point and measured the three-point-bend stress intensity factor at a constant T-T{sub g} = {minus}50 C. The trend is clear and significant; increasing crosslink density directly increases the load-to-fail.

Physical Description

3 p.

Notes

OSTI as DE97003837

Source

  • 4. international conference on composites engineering, Kona, HI (United States), 6-12 Jul 1997

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  • Other: DE97003837
  • Report No.: SAND--97-0490C
  • Report No.: CONF-970741--1
  • Grant Number: AC04-94AL85000
  • Office of Scientific & Technical Information Report Number: 486156
  • Archival Resource Key: ark:/67531/metadc681338

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  • March 1, 1997

Added to The UNT Digital Library

  • July 25, 2015, 2:21 a.m.

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  • April 13, 2016, 1:17 p.m.

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Adolf, D.; Weeks, T. & McCoy, J. Correlation of the crack initiation stress with epoxy network topology, article, March 1, 1997; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc681338/: accessed December 11, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.