A Practical Method for Fatigue Crack Initiation Detection Using an Ion-Sputtered Film

Abstract

The development of fatigue in a machine element can be divided into the fatigue crack initiation stage and the crack growth stage. The effects of the surface conditions, such as roughness and surface qualities, on the fatigue strength are considered to be restricted to the fatigue crack initiation stage. Thus, these effects can be evaluated exactly by the investigation on the fatigue crack initiation life. In this research a practical method is presented for detecting fatigue crack initiation during fatigue tests using an ion-sputtered film. Ion-sputtered films were formed on acrylic and steel test pieces having a specially designed round notch. Three-point bending fatigue tests were performed and the instants of fatigue crack initiation on the notched surface of both acrylic and steel test pieces during the tests were identified clearly; thus the fatigue crack initiation life can also be determined experimentally using the presented method. In addition, since the system used to measure the electric resistance of the film, which indicates the crack initiation, is extremely simple, that is, it consists of a variable resistor, a DC power source, and a data recorder, this method is considered very practical for monitoring crack initiation.