Effects of R-ratio on the off-axis fatigue behavior of unidirectional hybrid GFRP AI laminates at room temperature

摘要

Effects of stress ratio on the off-axis fatigue behavior of the unidirectional fiber-metal hybrid GFRP A1 laminate (GLARE-2) at room temperature are studied. Constant amplitude fatigue tests at three kinds of stress ratios R = 0.4, 0.1 and -0.2 are performed on coupon specimens with different fiber orientations theta = 0 deg, 5 deg , 10 deg , 15 deg , 20 deg , 30 deg , 45 deg , 60 deg and 90 deg in the GFRP layers. It is observed that the fatigue life of GLARE-2 is extended by the increase in stress ratio for every fiber orientation. A linear relationship of the Goodman type can approximately be fitted to the constant fatigue life data for GLARE-2, regardless of the fiber orientations. The fatigue fracture of GLARE-2 is characterized by the fatigue failure of the GFRP layers for theta = 0-15 deg, while it is brought about by the fatigue failure of the aluminum-alloy layers for theta = 30-90 deg. For each of the two groups, a master S-N relationship can be identified by means of a modified fatigue strength ratio. A fatigue damage mechanics model that considers the effect of stress ratio is developed using a modified theoretical fatigue strength ratio based on the Tsai-Hill static failure criterion. It is demonstrated that the fatigue model can successfully be used for description of the off-axis fatigue behavior of GLARE-2 over a range of stress ratios.