MICROVOIDS IN GLASS-FILAMENT-WOUND STRUCTURES: THEIR MEASUREMENT, MINIMIZATION, AND CORRELATION WITH INTERLAMINAR SHEAR STRENGTH

A statistical point-count method adapted from petrographic modal analysis was studied as a quantitative means of measuring void content in filament wound composites and tentatively appears to be a more precise, rapid, and versatile method than other techniques presently being used, especially at low-void-content levels 1 vol-. Low-void-content 1 vol- filament-wound NOL rings were fabricated by a continuous single-strand-winding process and resin impregnation at reduced pressure with the vacuum applied only to the resin bath. Working of the strand during the resin impregnation step by various configurations of guide rolls and strand vibrating devices either at atmospheric or reduced pressure was relatively ineffective in decreasing void content as compared with vacuum resin impregnation alone. Regression correlation analysis studies have shown that a linear inverse relationship exists between the interlaminar shear strength and the void content of NOL rings and that void content is the primary factor influencing interlaminar shear strength. The high degree of correlation between interlaminar shear strength and void content derived from the statistical regression correlation analysis is indirect supporting evidence that the point-count method for the quantitative measurement of the void content of composite structures has a relatively high degree of precision.