Multiple Crack Extension and Temperature Effect of Perforated Plate in Elevated Temperature Fatigue Test

The present paper presents the experimental results for fatigue crack propagation of SUS304 steel perforated plate at an elevated temperature of 550°C. (1) The specimens have two holes placed at an angle of 30°, 60° and 90°. Crack initiation cycle is determined from the pictures showing crack propagation process, which are measured with a CCD camera at a regular interval cycle. The stress concentration is larger in the order of 60°, 90° and 30°, the number of cycles to failure N_f follows this order. By using the inelastic strain amplitude, cycles to crack initiation for each specimen can be predicted. Hereafter, multiple cracks at different sites propagate according to the strain concentration contours. (2) The effect of high temperature on fatigue strength is also investigated for temperature from 500°C to 700°C. Cracks occurring at hole sides are measured by a CCD camera and the crack growth is calculated from photographs. Some specimens show the multiple small cracks at hole-side. (3) This paper also discusses fatigue evaluation of the circular notched plate under the inter-laminar shear loading at elevated temperature. FEM analysis of a specimen shows the distribution of stress under inter-laminar shear loading. Fatigue tests were conducted, and compared with results of analysis. The stress distribution under the inter-laminar shear loading shows unique distributions compared with those under the tensile loading, which is consistent with experimental results.