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Abstract

A closed loop feedback control system has been developed to obtain cure cycles which reduce the cure-induced stresses in single fiber/matrix model composites. In this feedback system, thermal expansion and stress relaxation are used to counteract the stresses resulting from the chemical shrinkage. The feedback system is applied to two different fibers (carbon and glass) in four different resins [3501-6, 934, and 977-3 epoxies and 5250-4 bismaleimide (BMI)]. The completeness of the cure is verified by comparing glass transition temperature (T_g) for polymers cured using the standard cure cycles (cycles recommended by the prepreg manufactures) and the feedback cure cycles. The durations of the feedback cure cycles are within that of the standard cycles. Test results indicate that feedback cure cycles reduce the curvature of unsymmetrical laminates as a measure of residual stresses.

Keywords

cure cycle optimization feedback control residual stresses stress relaxation thermosets volume changes

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References

1. J.D. Russell and A. Lee ,. 1977. "Effect of Cure Cycle on the Specific Volume of 3501-6 Epoxy," Proceedings of 29th International SAMPE Conference, Orlando, Florida, 29, 289-301.

2. S.R. White and H.T. Hahn , 1995. "Cure Cycle Optimization for the Reduction of Processing-Induced Residual Stresses in Composite Materials," J. of Composite Materials 27(14): 1352-1378.

3. H. Sarrazin , B. Kim , S-H. Ahn , and G.S. Springer , 1995. "Effect of Processing Temperature and Layup on Springback," J. of Composite Materials, 29(10): 1278-1294.

4. M.S. Madhukar , M.S. Genidy , and J.D. Russell , 2000. "A New Method to Reduce Cure-Induced Stresses in Thermoset Polymer Composites, Part I: Test Method," this issue of J. of Composite Materials.

5. M.S. Genidy , M.S. Madhukar , and J.D. Russell , 1997. "Optimized Cure Cycle to Minimize Fiber Stresses in Polymer Matrix Composites," Proceedings of the Eleventh International Conference on Composite Materials, Gold Coast, Queensland, Australia, Volume IV: 171-180.

6. M.S. Genidy , M.S. Madhukar , and J.D. Russell , 1997. "A Feedback System to Obtain an Optimum Cure Cycle to Thermoset Matrix Composites," Proceedings of 29th International SAMPE Conference, Orlando, Florida, 29: 302-316.

7. J.D. Russell, 1991. "Analysis of Viscoelastic Properties of High-Temperature Polymer Using a Thermodynamic Equation of State," M.S. Thesis, University of Dayton, Ohio, USA.

8. J.D. Russell , 1993. "Cure Shrinkage of Thermoset Composites," SAMPE Quarterly, 24(2): 28-33.

9. J.D. Russell , M.S. Madhukar , M.S. Genidy and A.Y. Lee , 2000. "A New Method to Reduce Cure-Induced Stresses in Thermoset Polymer Composites, Part III: Correlating Stress History to Viscosity, Degree of Cure, and Cure Shrinkage," this issue of J. of Composite Materials.

A New Method to Reduce Cure-Induced Stresses in Thermoset Polymer Composites,Part II: Closed Loop Feedback Control System

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