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Effect of contact stresses in four-point bend testing of graphite/epoxy and graphite/PMR-15 composite beamsThe results of in-plane four-point bend experiments on unidirectionally reinforced composite beams are presented for graphite/epoxy (T300/934) and graphite/polyimide (G30-500/PMR-15) composites. The maximum load and the location of cracks formed during failure were measured for testpieces with fibers oriented at various angles to the beam axis. Since most of the beams failed near one or more of the load points, the strength of the beams was evaluated in terms of a proposed model for the local stress distribution. In this model, an exact solution to the problem of a localized contact force acting on a unidirectionally reinforced half plane is used to describe the local stress field. The stress singularity at the load points is treated in a manner similar to the stress singularity at a crack tip in fracture mechanisms problems. Using this approach, the effect of fiber angle and elastic material properties on the strength of the beam is described in terms of a load intensity factor. For fiber angles less than 45 deg from the beam axis, a single crack is initiated near one of the load points at a critical value of the load intensity factor. The critical load intensity factor decreases with increasing fiber angle. For larger fiber angles, multiple cracks occur at locations both near and away from the load points, and the load intensity factor at failure increases sharply with increasing fiber angle.
Document ID
19920050965
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Binienda, W. K.
(Akron, University OH, United States)
Roberts, G. D.
(NASA Lewis Research Center Cleveland, OH, United States)
Papadopoulos, D. S.
(Case Western Reserve University Cleveland, OH, United States)
Date Acquired
August 15, 2013
Publication Date
April 1, 1992
Publication Information
Publication: SAMPE Quarterly
Volume: 23
ISSN: 0036-0821
Subject Category
Structural Mechanics
Accession Number
92A33589
Distribution Limits
Public
Copyright
Other

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