Biaxial Failure Analysis of Graphite Reinforced Polyimide and Epoxy Fabric Composites
Final rept. 1 Jun 1997-31 May 2001
DENVER UNIV CO
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Comprehensive analyses of residual stresses in unidirectional and fabric graphitepolyimide composites were conducted in this study. In the experimental part of this research, numerous XRD measurements were made to determine residual strains and stresses in embedded Al and Ag inclusions placed in four ply 8 harness satin 8HS woven and 6 ply unidirectional graphitePMR-15 composites. In the modeling part of this research, the residual thermal stresses in the unidirectional and woven composites were evaluated by performing linear and visco-elastic computations. In addition, analytical approaches were used to predict the magnitudes of the residual thermal stresses in the composites as a function of temperature, time, composite architecture and external loads. The numerically and analytically determined residual stresses in the composites were subsequently compared to the residual stresses determined from the X-ray analysis in conjunction with the application of the linear elastic and visco-elastic Eshelby models for multiple ellipsoidal inclusions. The effect of external bending loads on the residual strains and stresses in the embedded particles was also experimentally and numerically investigated. A new methodology was proposed for the evaluation of interfaminar residual thermal stresses in unidirectional and woven polymer matrix composites based on XRD measurements of residual stresses in embedded crystalline inclusions in conjunction with the application of the visco-elastic Eshelby method for multiple inclusions.
- Laminates and Composite Materials