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Use of unbalanced laminates as a screening method for microcrackingState-of-the-art, high temperature polyimide matrix composites, reinforced with continuous graphite fibers are known to be susceptible to intraply cracking when thermally cycled over their useful service temperature range. It is believed that the transply cracking, in part, results from residual stresses caused by differences in coefficients of thermal expansion (CTE) between the polymer matrix and the reinforcement. Thermal cycling tests to investigate this phenomenon involve expensive time and energy consuming programs which are not economically feasible for use as a part of a materials screening process. As an alternative to thermal cycling studies, a study of unbalanced crossply graphite fiber reinforcement composites was conducted to assess the effect of the composite ply layup and surface condition on the residual stresses that remain after the processing of these materials. The residual stresses were assessed by measuring the radii of curvature of the types of laminates that were studied. The temperature at which stress-free conditions existed were determined and a dye penetrant method was used to observe surface damage resulting from excessive residual stress buildup. These results are compared with some published results of thermal cycling tests that were previously conducted on balanced polyimide composites.
Document ID
Document Type
Conference Paper
Papadopoulos, Demetrios S.
(Case Western Reserve Univ. Cleveland, OH., United States)
Bowles, Kenneth J.
(NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1990
Subject Category
Composite Materials
Report/Patent Number
NAS 1.15:102517
Meeting Information
International SAMPE Symposium(Anaheim, CA)
Accession Number
Funding Number(s)
Distribution Limits
Work of the US Gov. Public Use Permitted.
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