The role of crack morphology on the failure behavior of laminated composites Page: 1 of 9
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THE ROLE OF CRACK MORHOLGY ON THE FAILURE BEHAVIOR OF LAMINATED
Ames Laboratory, Iowa State University
Ames, IA 50010
In this study, the failure of the ductile layers from collinear and delaminating cracks that occur
in laminated composite systems was studied using a constitutive relationship that accounts for
strength degradation resulting from the nucleation and growth of voids. The results indicate that
in laminated composites, void nucleation and growth ahead of the cracks occur at a much faster
rate due to evolution of much higher stress values at the interface region. For delaminating crack
cases, the fracture behavior is strongly influenced by the delamination length. The resistance of
the ductile layers to crack extension can be significantly reduced by short delamination lengths.
Laminated composites containing ductile layers are currently under development not only to
improve the fracture toughness of inherently brittle intermetallics and ceramics [1-9], but also to
increase the relatively low fracture toughness of metal matrix composite systems[10,11 ]. The
recent reviews treating the contribution of the ductile phase to the composite toughening have
indicated that this contribution depends on the strength, volume fraction and failure characteristics
of the ductile reinforcing phase. It is also apparent that the failure of the ductile layers is strongly
affected by the degree of the constraint that is largely controlled by the interfacial behavior of the
As schematically illustrated in Fig. 1, several failure modes of the brittle layers such as only
formation of collinear cracks, with multiple cracking and with delamination in various lengths are
usually seen in most of the experimental studies[ 1-l1]. In this study, the growth of such cracks
into the ductile layers are studied by using a constitutive relation that accounts for strength
degradation resulting from the nucleation and growth of micro-voids in the ductile layers. The
results obtained for the laminated composite cases are compared with the growth behavior of the
cracks in the same ductile material as a homogenous isotropic case.
The basis for the constitutive model for the ductile layers is a flow potential introduced by
Gurson[18,19), in which voids are represented in terms of a single internal variable, f, the void
4 =- + 2fqcosh -1-q 2=f (1)
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Biner, S.B. The role of crack morphology on the failure behavior of laminated composites, article, July 1, 1997; Iowa. (digital.library.unt.edu/ark:/67531/metadc691228/m1/1/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.