ABSTRACT
This chapter deals with the effects of resin toughness, fiber sizing, environmental moisture, and operating temperature on the durability of composites. It discusses the strong and expected positive influence of the resin toughness, as well as the small roles of the environmental moisture and operating temperatures. The failure thresholds are short-term ply strengths measured at room temperature in a dry atmosphere. The increased temperature and high water intake have the same effect on the ply, since both expand the resin. Increments in resin toughness or in the operating temperature delay the pipe cracking and produce higher weep thresholds. This improvement is expected for both tougher resins and at higher temperatures. Experimental evidence—backed by careful reasoning—indicates that brittle plies develop many short cracks, as opposed to the few long cracks observed in tough plies. The weep times of sanitation pipes with weep barriers of different resins are similar to those of oil pipes with unidirectional plies.
