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Ultra-Low Expansion Metal Matrix Composites.
Final rept. 4 Aug 78-30 Sep 80,
MASSACHUSETTS INST OF TECH CAMBRIDGE LAB FOR MFG AND PRODUCTIVITY
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The satisfactory performance of mirror substrates of High Energy Large Optics HALO and High Energy Laser Optics HELO requires that the distortion of these substrates due to temperature variations be less than 0.1 um per meter ideally zero thermal expansion in the temperature range 150-300L. In addition they should have high thermal conductivity, high microyield strength and low density. Moreover, they should be extremely resistant to outgasing. A thermoelastic analysis has been carried out to compute the coefficient of thermal expansion CTE. Exact equations for stresses, strains and CTE have been derived for a two phase composite. The results indicate that the thermal expansion coefficient of the composite is a sensitive function of the CTEs of the constituent phases and insensitive to the elastic moduli of Poissons ratios. It is shown that to produce ultra low to zero CTE materials two phases, one with low positive CTE and the other with large negative CTE, are required. Further, the amount of the matrix and dispersed phases should be controlled to within a few percent.
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