Development of ΔK-decreasing test method of the metal film by displacement constraint along the elliptical through hole-edge

Abstract

A new ΔK-decreasing test method of the metal film was developed. The film was adhered to a through elliptical hole in a base plate and was fatigued in accordance with the displacement constraint along the hole-circumference in the base plate subjected to a cyclic stress. Commonly, a stress intensity factor range was increased with a crack propagation under a constant stress amplitude but was decreased toward the hole-edge because of the difference in thickness between the film and the base plate in this ΔK-decreasing test method. The decrease in a stress intensity factor with a crack propagation was calculated by FEM analysis and the optimum aspect ratio of an elliptical hole was determined. Using the ΔK-decreasing test method, the crack propagation test was conducted for metal films. As a result, the fatigue crack propagation rate was decreased and was arrested near the hole-edge under the constant stress amplitude to the base plate. The threshold stress intensity factor ranges were obtained for some kinds of metal film and the accuracy of the testing method was discussed.

Keywords

• metal film
• δk-decreasing test
• threshold stress intensity factor range
• crack opening displacement
• finite element method