Abstract
rack opening displacement of the mode I surface crack was measured using digital image correlation. Pulsating tension tests were carried out with the stress ratio R=0.2 and 0.5 using A7075 aluminum alloy. The crack tip opening stress was determined to various crack length based on the crack opening displacement. Crack tip opening stress was the almost same value as the minimum stress when 7M).5. On the other hand, crack tip opening stress was close to the half of the maximum stress when R=0.2. The stress ratio dependence did not disappear, even if the crack propagation rate was arranged with the effective stress intensity factor range. The relationship between the crack propagation rate and crack opening displacement near the crack tip was hardly dependent on the stress ratio.
