Improving the fatigue strength of a multiple hole specimen by applying additional holes or notches

Abstract A series of tests were conducted in aluminum alloy 2024-T3 to investigate the effect of additional holes and notches on the fatigue behavior of double hole specimens. Also, circular pins were inserted into the additional holes, but not removed before testing in some cases. Basic specimen has dual holes and their cracks interacted with the specimen edge. Within the present study conditions, the longest fatigue life was observed where dual holes had a shorter distance between their edges and a longer distance from specimen edge to holes. The shortest fatigue life was observed where there was a longer distance between the hole edges. This paper describes how the improvement of fatigue life in the shorter life case of a basic specimen was examined by applying additional holes or notches. The crack initiation and growth behavior was observed and the mechanism of the extension of the fatigue life was investigated. The finite element method (FEM) was used to analyze the stress concentration around the basic dual holes, additional holes and notches in the present specimens. Then it was discussed how the reduction of stress concentration around the basic dual holes affected the fatigue life of the double holed specimens. A method of enhancement of fatigue life of notched material is discussed in the present study.