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An energy analysis of crack-initiation and arrest in epoxyThe objective of this work is to study fracture processes such as crack initiation and arrest in epoxy. A compact tension specimen with displacement-controlled loading is employed to observe multiple crack initiations and arrests. The energy release rate at crack initiation is significantly higher than that at crack arrest, as has been observed elsewhere. In this study, the difference between these energy release rates is found to depend on specimen size (scale effect), and is quantitatively related to the fracture surface morphology. The scale effect, similar to that in strength theory, is conventionally attributed to the statistics of defects which control the fracture process. Triangular shaped ripples, deltoids, are formed on the fracture surface of the epoxy during the slow sub-critical crack growth, prior to the smooth mirrorlike surface characteristic of fast cracks. The deltoids are complimentary on the two crack faces which excludes any inelastic deformation from consideration. The deltoids are analogous to the ripples created on a river surface downstream from a small obstacle. However, in spite of the expectation based on this analogy and the observed scale effect, there are no 'defects' at the apex of the deltoids detectable down to the 0.1 micron level. This suggests that the formation of deltoids during the slow process of subcritical crack growth is an intrinsic feature of the fracture process itself, triggered by inhomogeneity of material on a submicron scale. This inhomogeneity may be related to a fluctuation in the cross-link density of the epoxy.
Document ID
19920067153
Document Type
Reprint (Version printed in journal)
Authors
Chudnovsky, A. (NASA Lewis Research Center Cleveland, OH, United States)
Kim, A. (Illinois, University Chicago, United States)
Bosnyak, C. P. (Dow Chemical Co. Freeport, TX, United States)
Date Acquired
August 15, 2013
Publication Date
June 1, 1992
Publication Information
Publication: International Journal of Fracture
Volume: 55
Issue: 3 Ju
ISSN: 0376-9429
Subject Category
STRUCTURAL MECHANICS
Funding Number(s)
CONTRACT_GRANT: NAG3-1034
Distribution Limits
Public
Copyright
Other