A study on observation and growth behavior of small surface cracks by remote measurement system

Abstract

A new experimental system using remote measurement system (RMS) and image processing technique was applied for studying the growth behavior of small surface fatigue cracks in 1Cr −1Mo−0.25V steel at room temperature. The system includes a long distance focusing microscope, a CCD camera, a light source, a 3-axis controller a monitor, a personal computer 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 μm of surface fatigue crack length. The length of surface fatigue crack could be successfully measured by the RMS during testing as well as after the test. The growth rate of small cracks on smooth specimens was represented in terms of stress intensity factor and J-integral. At equivalent elastic stress intensity factor levels, the growth rate of small surface cracks was not consistent and faster than that of long crack of CT specimen.