Fiber Microstructure and Fatigue

Strong fibers can fail at low stresses under cyclic loading. This phenomenon, which is called cyclic fatigue, occurs to an unexplained extent only when part (or all) of the fiber is compressed or twisted for some fraction of the strain cycle. Industrial yarns used in rubber, a 2 MMM lb. annual market in which USA fiber producers are highly competitive, must retain a maximum fraction of their initial strength after long term fatigue. The general problem encountered is that as fiber strength or stiffness is increased, resistance to fatigue decreases. Although intrinsic properties of single-ply radial tires temporarily reduced the need for improved fiber fatigue properties, gradual increases in fiber stiffness over the years are once again focussing attention on fatigue.