ENVIRONMENTAL-EFFECTS ON STITCHED RTM TEXTILE COMPOSITES

The effects of temperature and humidity cycling on mechanical properti es of A54/3501-6 quasi-isotropic textile composites were determined. T he composites were resin transfer molded from unstitched, Kevlar 29 st itched, and S-2 glass stitched uniweave fabric preforms. Data presente d include photomicrographs, compression strengths and compression-comp ression fatigue results for environmentally cycled and uncycled compos ites. After manufacture, microcracks developed around the glass and Ke vlar stitching. These microcracks did not grow after environmental cyc ling. The unstitched material developed microcracks only after cycling . Temperature and humidity cycling reduced the static compression stre ngth of the unstitched and Kevlar stitched uniweave materials nearly 1 0 percent. Under the same conditions the glass stitched uniweave mater ial lost 3 percent of its baseline strength. Combined temperature and humidity cycling did not affect the fatigue properties of the uniweave materials when the test specimens were dried to their original weight s before testing. Temperature cycling at constant 40 percent humidity, resulted in a 5 percent decrease in static compression strength for t he unstitched and Kevlar stitched material. Unstitched, glass stitched and Kevlar stitched materials exposed to constant 60 degrees C and 95 percent relative humidity for 80 days and then saturated in 70 degree s C water, lost 17, 7 and 19 percent of their baseline compression str ength, respectively. These conditions lowered the fatigue strengths on ly after saturation. Braided composites including, a stitched 2-D brai d, an unstitched 2-D braid and a 3-D braid were also exposed to enviro nmental cycling. The moisture absorption in the AS4/E905L system was l ower than the AS4/3501-6 system. Consequently environmental cycling ha d little effect on the static or fatigue strengths of braided material s.