Accession Number : ADA302327

Title :   Accelerated Viscoelastic Characterization of T3OO/5208 Graphite-Epoxy Laminates.

Descriptive Note : Contractor rept.,

Corporate Author : VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF ENGINEERING SCIEN CE AND MECHANICS

Personal Author(s) : Tuttle, M. E. ; Brinson, H. F.

PDF Url : ADA302327

Report Date : MAR 1985

Pagination or Media Count : 235

Abstract : The viscoelastic response of polymer-based composite laminates, which may take years to develop in service, must be anticipated and accommodated at the design stage. Accelerated testing is therefore required to allow long-term compliance predictions for composite laminates of arbitrary layup, based solely upon short-term tests. In this study, an accelerated viscoelastic characterization scheme is applied to T3OO/52O8 graphite-epoxy laminates. The viscoelastic response of unidirectional specimens is modeled using the theory developed by Schapery. The transient component of the viscoelastic creep compliance is assumed to follow a power law approximation. A recursive relationship is developed, based upon the Schapery single-integral equation, which allows approximation of a continuous time-varying uniaxialload using discrete steps in stress. The viscoelastic response of T3OO/S2O8 graphite-epoxy at 1490 to transverse normal and shear stresses is determined using 90-deg and lO-deg off-axis tensile specimens, respectively. In each case the seven viscoelastic material parameters required in the analysis are determined experimentally, using a short-term creep/creep recovery testing cycle. A sensitivity analysis is used to select the appropriate short-term test cycle. It is shown that an accurate measure of the power law exponent is crucial for accurate long-term predictions, and that the calculated value of the power law exponent is very sensitive to slight experimental error in recovery data. (MM)

Descriptors :   *LAMINATES, *VISCOELASTICITY, *GRAPHITE EPOXY COMPOSITES, STRESS STRAIN RELATIONS, COMPUTER PROGRAMS, POLYMERS, COMPOSITE MATERIALS, STIFFNESS, ELASTIC PROPERTIES, STRAIN(MECHANICS), SHEAR STRESSES, RECURSIVE FUNCTIONS, CREEP, RELAXATION, FAILURE(MECHANICS), STRENGTH WEIGHT RATIO, ACCELERATED TESTING, AXIAL LOADS.

Subject Categories : Laminates and Composite Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE