Relationship between fatigue striation height and stress ratio

In order to obtain stress ratio as well as stress intensity factor range which was applied on the material before failure from the fracture surface observation, the effect of stress ratio on fatigue striation height has been investigated on two different alloys (an Fe-3% Si single crystalline alloy and a 7075 polycrystalline aluminium alloy). Striation height has been measured both microscopically using a scanning tunnelling microscope and macroscopically using a scanning electron microscope. Striation height increased with decreasing stress ratio on both the materials at a given crack growth rate. This tendency was found by all the measuring methods used. This suggests that not only stress amplitude but also stress ratio which were applied on the material before the failure could be obtained by post-failure analysis.