A STUDY ON OBSERVATION AND GROWTH-BEHAVIOR OF SMALL SURFACE CRACKS BYREMOTE MEASUREMENT SYSTEM

A new experimental system using remote measurement system(RMS) and ima ge processing technique was applied for studying the growth behavior o f small surface fatigue cracks in 1Cr -1Mo-0.25V steel at room tempera ture. The system includes a long distance focusing microscope, a CCD c amera, a light source, a 3-axis controller, a monitor, a personal comp uter and a data translation card. The measurement error of the system appeared to be 0.8%. It is possible for this system to measure down to 30 mu m of surface fatigue crack length. The length of surface fatigu e crack could be successfully measured by the RMS during testing as we ll as after the test. The growth rate of small cracks on smooth specim ens was represented in terms of stress intensity factor and J-integral . At equivalent elastic stress intensity factor levels, the growth rat e of small surface cracks was not consistent and faster than that of l ong crack of CT specimen.