Measurement of Small Crack Lengths under Creep-Fatigue Condition by means of Image Processing

Abstract

In relation to the evaluation of remaining life of high-temperature components based on statistics of extremes, this paper is concerned with application of image processing to measurement of small crack lengths. Creep-fatigue tests were carried out on SUS 316 L. Smooth specimens were subjected to slow-fast cyclic strain of a total strain range of 1% at 65O°C in air with ε^^.=2x1O^-5/s in tension and ε^^.=2x1O^-3/s in compression. Taking replicas of the specimen surface, the images of the replicas were put into the image processing unit. Using some new algorithms and conventional algorithms, individual crack lengths were measured. The crack length measured by means of image processing was compared with that determined by manual measurement with a microscope. The distribution of the small crack length was also studied. Furthermore, propagation and coalescence behavior of cracks was investigated by means of image processing.