Abstract
Keywords:
Hole expansion, Edge margin, Residual stress, Fatigue strength, Crack growth behavior
Abstract
Joint holes for the fasteners have an especially significant effect on fatigue strength because stress is concentrated on the holes. Currently, hole expansion is the most widely used mechanical method to enhance the fatigue strength in the hole region. The method introduces an efficient compressive residual stress in the region around the hole. The objective of this research evaluated the optimum hole expansion ratio, residual stress and the fatigue strength properties after hole expansion with edge margin changes of 2024-T351 aluminum alloy by using the primary member of industry structures. Residual stress was measured along the width from the hole edge to the free edge of the specimen in regular distances along the radial and tangential direction and fatigue tests were conducted by using hydraulic material-testing machine. The hole expansion ratio was 3.7 ~ 4.6 % due to hole expansion with various edge margins and the maximum residual stress was about 1.6 times of yield stress after hole expansion. The total fatigue life improved by 2 ~ 54 times due to hole expansion, by retarding crack initiation and propagation. The research results also show that in order to have effective hole expansion, a hole expansion between 3.7 ~ 4.0 % and an edge margin over 1.25 were needed. The most effective hole expansion is accomplished with an edge margin of 1.5.