Fractal dimension evolution of thermal shock micro-crack net in gray cast iron

Gray cast iron specimen was heated to a fixed temperature with high frequency, then was cooled to room temperature by spraying water to the heated surface. This process was repeated until a crack whose length exceeded 3 mm appeared. The surface was taken pictures every fixed number of cycles, then the surface micro-crack pattern change was obtained. The pictures were processed only keeping cracks, then were analyzed with box-counting fractal method. The relationship between the fractal dimension of the micro-crack net and the thermal shock cycles was obtained. The result indicates the fractal dimension of the surface micro-crack would converge to a fixed value.