The Aerospace industry is interested in reducing the weight of launch vehicles by using carbon fiber reinforced polymer (CFRP) composite materials for storage of cryogenic propellents. However, micro-cracks have been reported to develop at cryogenic temperatures (1-5), which can result in leak paths for the propellents. One source of micro-cracks is a mismatch between the coefficients of thermal expansion (CTE) of the fiber and the polymer matrix (1). The difference in the rate of contraction and expansion between the fiber and the matrix results in thermal strains, that if sufficiently large can initiate micro-cracks. A reduction in these strains can be obtained by reducing the CTE difference between the fiber and the matrix. Additionally, clay platelets or small tactoids, which have high aspect ratios, can raise the resin's modulus thus reinforcing the resin rich zones. The addition of nano-modifiers to the matrix resin and its effects on CTE is currently being studied. Chemically pillared montmorillonite clays are being nano-dispersed into epoxy resin by direct mechanical mixing and into low viscosity resin/solvent solutions using sonication. After removing the solvent, the resulting nano-modified epoxies are converted into CFRP composites. An analytical model to predict the CTE change due to platelet-shaped nano-modifiers has been developed and compared with experimental results.
Performance of modified epoxies in composites at cryogenic temperatures
2004
9 Seiten, 16 Quellen
Aufsatz (Konferenz)
Englisch
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