NTRS - NASA Technical Reports Server

Back to Results
Thermoviscoelastic characterization and prediction of Kevlar/epoxy composite laminatesThe thermoviscoelastic characterization of Kevlar 49/Fiberite 7714A epoxy composite lamina and the development of a numerical procedure to predict the viscoelastic response of any general laminate constructed from the same material were studied. The four orthotropic material properties, S sub 11, S sub 12, S sub 22, and S sub 66, were characterized by 20 minute static creep tests on unidirectional (0) sub 8, (10) sub 8, and (90) sub 16 lamina specimens. The Time-Temperature Superposition-Principle (TTSP) was used successfully to accelerate the characterization process. A nonlinear constitutive model was developed to describe the stress dependent viscoelastic response for each of the material properties. A numerical procedure to predict long term laminate properties from lamina properties (obtained experimentally) was developed. Numerical instabilities and time constraints associated with viscoelastic numerical techniques were discussed and solved. The numerical procedure was incorporated into a user friendly microcomputer program called Viscoelastic Composite Analysis Program (VCAP), which is available for IBM PC type computers. The program was designed for ease of use. The final phase involved testing actual laminates constructed from the characterized material, Kevlar/epoxy, at various temperatures and load level for 4 to 5 weeks. These results were compared with the VCAP program predictions to verify the testing procedure and to check the numerical procedure used in the program. The actual tests and predictions agreed for all test cases which included 1, 2, 3, and 4 fiber direction laminates.
Document ID
Document Type
Conference Paper
Gramoll, K. C. (Memphis State University TN, United States)
Dillard, D. A. (Virginia Polytechnic Institute, and State University Blacksburg, United States)
Brinson, H. F. (Texas, University San Antonio, United States)
Date Acquired
August 14, 2013
Publication Date
January 1, 1990
Subject Category
Meeting Information
Symposium on Composite Materials: Testing and Design(Sparks, NV)
Funding Number(s)
Distribution Limits