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Research Papers

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

[+] Author and Article Information
Gang Deng, Tsutomu Nakanishi

Department of Mechanical Systems Engineering, Faculty of Engineering, University of Miyazaki, Miyazaki 889-2192, Japan

Yoshihiko Sakanashi

Mechanical Systems Engineering Course, Graduate School of Engineering, University of Miyazaki, Miyazaki 889-2192, Japan

J. Eng. Mater. Technol 131(1), 011007 (Dec 17, 2008) (6 pages) doi:10.1115/1.3026549 History: Received February 14, 2008; Revised August 06, 2008; Published December 17, 2008

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.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Change in the electric resistance of ion-sputtered film due to crack initiation and crack growth

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Figure 2

Test piece for crack initiation detection test

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Figure 3

System used to measure the electric resistance of the film

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Figure 4

A view of the test piece with an ion-sputtered film on the test

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Figure 5

Electric resistance of an ion-sputtered film during the test without crack initiation on a steel test piece

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Figure 6

Change in the electric resistance of the ion-sputtered film during fatigue crack initiation on an acrylic test piece

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Figure 7

A view of the microcrack initiated on the notch surface

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Figure 8

Shape of the crack initiated in an acrylic test piece

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Figure 9

Electric resistance increase rate for different shapes of films

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Figure 10

Section view of the crack initiation detection spot of a steel test piece

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Figure 11

Change in the electric resistance of the ion-sputtered film during crack initiation on a steel test piece

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Figure 12

Views of a microcrack initiated as observed from the notch surface direction and the depth direction of a steel test piece

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Figure 13

Shape of the crack initiated in a steel test piece

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