Size distribution of surface cracks and crack pattern in austenitic SUS316 steel plates fatigued by cyclic bending

Abstract

The size distribution of surface cracks and the crack pattern were examined on the specimens of the SUS316 steel plates fatigued by cyclic bending. The size distribution of the cracks could be approximated to a logarithmic normal distribution, irrespective of the maximum total strain range or the number of fatigue cycles. The number of the cracks (Nu) of the length (x′) equal to or larger than a given size (X) could be approximated to a power law, Nu∝ X−a, with a scaling exponent a at the larger crack sizes in the fatigued specimens of the SUS316 steel. The value of a decreased with increasing the number of fatigue cycles because of the increase in the number and size of fatigue cracks, and was larger in the specimens tested at the smaller total strain range. Effects of experimental variables on the scaling exponent (a) were also shown in this study. The fractal dimension of spatial crack distribution (the fractal dimension of crack pattern) (D) increased in the range from about 0.9 to about 1.2 with increasing the number of fatigue cycles, and was larger in the specimens fatigued at the larger total strain range. There was a negative correlation between the value of a and the value of D on fatigue cracks, although there was no unique relationship between these two values.