This paper describes the results of a numerical and experimental study of the behavior of comer crack located at a hole. The comer crack growth shape depends on stress concentration factor, initial crack shape condition, and load condition such as load ratio R and load interaction.
Fatigue crack growth tests are conducted with 7075-T6 aluminum alloy specimens by measuring the crack closure using Laser Interferometry Strain / Displacement Gage(ISDG). This measuring device has been used due to the following features such as a very short gage length, no electrical or mechanical contact, no temperature sensitivity, ability of measuring the displacement near the crack tip. In paticular, the single tensile overload test is performed to investigate the load interaction effect.
On the other hand, because the crack opening load has significantly an effects on fatigue crack growth rate, it is important to find exact crack opening load. Even though the crack opening load is determined from Load and Reduced Displacement signal, there is no generally accepted way to measure the exact crack opening load. A new method to determine crack opening load from displacement difference signal of the photo-diode of the ISDG is suggested. And because the opening load is sensitive to measurement location, proper the measurement location was also suggested through crack opening simulation and experiments using ISDG.
The corner crack front shape and the growth behavior were obtained through numerical simulation. The experiments performed with 7075-T6 aluminum specimen confirmed the simulated crack front shape and the growth of the corner crack.
