Published: Jan 1975
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Two previously developed failure criteria for predicting the uniaxial tensile strength of a laminated composite containing through-the-thickness material discontinuities (notches) are subjected to further experimental scrutinization. In particular, the two-parameter (unnotched tensile strength of the laminate and a characteristic length) models, which are capable of predicting observed discontinuity size effects without resorting to the concepts of linear elastic fracture mechanics, are based on limited experimental verification.
In the present paper, and experimental program is presented which examines the effect of changes in the material system, the laminate fiber orientations, and the notch shape and size (stress gradient), on the model predictions. This is accomplished by obtaining experimental data on two material systems, glass/epoxy and graphite/epoxy, in conjunction with two orientations of fiber-dominated laminates containing through-the-thickness circular holes and sharp tipped cracks of several sizes.
In addition to the test results, two observations based on the models are presented. First, the statistical failure distribution for a composite containing a circular hole is predicted using the models and shown to agree well with experimental observations. Second, an Irwin type correction factor applied to the stress intensity factor is shown to result in nearly constant values of the critical stress intensity factor for all values of crack length. The correction factor is shown to be related to the characteristic length of the present models.
fracture properties, composite materials, stresses, laminates, fracture strength, failure, notch strength
Assistant professor, University of Utah, Salt Lake City, Utah
Materials research engineer, Mechanics and Surface Interactions BranchAir Force Materials Laboratory, Wright-Patterson AFB, Ohio