Observation on the growth behavior of small surface cracks using remote measurement system

A new experimental system which uses a remote measurement system (RMS) constructed by means of an image processing technique was applied to the observation of small surface fatigue crack behavior in 1Cr-1Mo-0.25V steel and type 304 stainless steel at room temperature as well as at elevated temperature. This system consists of a long distance focusing microscope, a CCD camera, a light source, a 3-axis controller, a personal computer and a data translation card. The resolution of this system is 1.1 mu m. This system allows one to observe the surface crack length down to 30 mu m. Using this system, the growth rates of small surface cracks on smooth specimens were studied in terms of stress intensity factor range and compared with those of long cracks.