Abstract
An investigation has been carried out concerning the influence of stress waveform and wet environment on the fatigue fracture behavior of aramid single fiber. The aramid fiber used in this study was Kevlar 49 manufactured by Du Pont. Tension-tension fatigue tests were conducted under inusoidal, negative pulse and positive pulse waveforms for the fiber preconditioned in laboratory air and in wet air (RH 98±2%, 20±2℃). The fatigue strength of Kevlar 49 tested in wet air was lower than that in laboratory air, and the fatigue strength in air under negative pulse waveform was higher than those under other two waveforms. The fiber broke with fiber splitting for the quasistatic tensile tests and the fatigue tests under sinusoidal and positive pulse waveforms in air. In contrast with these, the fiber broke with transverse crack when the specimen was subjected to the negative pulse waveform, with longer fatigue life. This final fracture morphology under negative pulse waveform corresponded to the transverse undulations that were observed by atomic force microscope(AFM).
