FATIGUE BEHAVIOR OF E-GLASS FIBER-REINFORCED PHENOLIC COMPOSITES - EFFECT OF TEMPERATURE, MEAN STRESS AND FIBER SURFACE-TREATMENT

Phenolic matrix is reinforced by unidirectional E-glass fibers with vo lume fractions of 0.30 and 0.45. Three different surface treatments ar e applied to the E-glass fibers. The composite specimens are tested at ambient condition and temperatures of 100-degrees, 150-degrees and 20 0-degrees-C with stress levels of R(sigma(min)/sigma(max)) equal to 0 and 0.4 for load frequencies of 1.5, 10 and 25 Hz. Data are presented in terms of SIN curves and assessed by degradation of modulus based on compliance. For a particular fiber glass surface treatment and volume fraction, the composite specimen is notched and tested at room temper ature and 200-degrees-C. A fatigue strength reduction factor K(f) is d efined and obtained such that the results could be compared with those of the unnotched specimens. Notch effect is small if the hole diamete r is equal to the specimen thickness; it would be important for larger hole sizes. Fractured surfaces are examined by the scanning electron microscope.