Effects of 1.0% Superimposed Mean Strain on the Bending Fatigue Strength of Zircaloy-4

The superposition of 1.0% mean strain on constant - deflection cycled bending-fatigue specimens of Zircaloy-4 plate reduces the fatigue strength^a at both room temperature and 600°F. The implications of these test results on recommended fatigue design procedures are examined. Limited studies of crack propagation in Zircaloy plate indicated conformance with the hypotheses of Frost and Dugdale. It was also found that an oxide film formed by exposure to 680°F water for 72 hours is detrimental to fatigue strength at room temperature.