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Microvoids are trapped in the resin between individual filaments in glass-resin composites to the extent of 10 to 109 voids per cubic inch. These air voids result from slow and unequal capillary penetration of resin into spaces between filaments during the impregnation process. The poor resin wettability of commercially finished filaments aggravates the situation. Reducing the contact angle to zero and/or causing the tension to oscillate as the strand passed through the resin markedly reduced the number of voids. Composite test rings having void contents of 0.2 volume % or less had interlaminar shear strengths 40 to 100% greater than the conventional rings with high void contents (5%).Qlass-resin composite materials have attracted increasing interest wherever there is a need for materials having high strength-to-weight ratios. Usually, these composites are fabricated by the resin impregnation of glass fiber mat, glass cloth, or continuous glass filaments.

In a continuing study of flame extinguishment, ~, 2, 3, 4 we report on scaling studies for dry chemicals on larger heptane diffusion flames (0.29 m 2 and 2.32 m 2 pans). We demonstrate again that small particle sizes extinguish most effectively. Extinguishment is related to heat absorption by decomposing or vaporizing particles. We show that the limiting particle size for each dry chemical--that is, the maximum size which completely decomposes or vaporizes in the flame--is independent of flame size for the systems studied. We broaden and apply the concept of latent or maximum effectiveness 2,3 to pan fires of all sizes. Finally, we describe and characterize an aerodynamic effect in the transport of powders, where large particles with their higher momenturn entrain and drag smaller, more effective particles into the flame.We also show that extinction curves, involving the ratio of real-to-latent extinction weight and the proportion of small to large particles, have predictable shapes and predictable quantitative levels for most dry chemicals. We have developed the real-to-latent concept along with scaling equations for agent mixtures and for a wide spectrum of agents and particle sizes.

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