RESEARCH ON USING INFRARED IMAGING TECHNIQUES TO MEASURE MODE-I CRACK STRESS INTENSITY FACTORS

Mode-I cracks are the primary type of engineering crack shapes at present. Stress intensity factors of cracks in most engineering structural parts are not suitable for contact measurement. Modeling calculations are also very time-consuming and difficult due to complicated stress conditions. Infrared thermal image technology of non-contact measurement is presented for fracture problems of materials and structures as a new experimental method. The quantitative relationship between the volumetric strain and temperature variation was acquired by thermal and mechanical response research of 304 stainless steel specimens, in which the surface temperature changes under different cyclic tensile frequency conditions were measured. By subjecting the compact tension specimens to cyclic loading while synchronously measuring the temperature field of its crack tip, the mode-I stress intensity factor of nearby crack tip was obtained. Experimental results show that the relationship between the temperature variation and volumetric strain of the material is linear under approximate adiabatic condition. The experimental errors of stress intensity factors under different loading cases are within 2% by comparing with theoretical values. It illustrates that the method of using infrared thermal image to directly measure stress intensity factors under cyclic load cases in practical engineering is feasible and reliable.