P-11 Effects of single overload on crack propagation of specimens with sharp notch in low carbon steel

Abstract

The purpose of the present study is to evaluate fatigue crack propagation in tensile overloaded specimen with sharp notch. A 6 mm long u-shaped notch was cut in the center section of the specimen. Notch root radii of 0.1 mm, 1 mm and 2 mm were chosen for testing. These specimens were regarded as center notched specimens. The crack propagation behavior of these specimens was compared with a center cracked specimen. Push-pull fatigue tests were carried out under stress ratios R=0, -1, and -1.5. The stress intensity factors of notched specimen were calculated using the body force method. A special investigation was made into the results for ρ=1 mm. After overload, retardation of crack growth was observed under R=0 and -1, for the notched specimens and center cracked specimens. However, where R=-1.5, crack growth acceleration was observed after overload in both types of specimens. Thus, acceleration and deceleration of crack propagation were observed depending on the applied stress conditions. Even though crack growth was accelerated or decelerated, the rate was able to be evaluated by effective stress intensity factor range after 0.1 mm crack growth from notch root in the present experimental cases. This behavior is related that the stress intensity factors of the present notched specimens are almost same as that of the center cracked specimen after 0.1 mm crack growth.