Presenter Information

William J. Baxter, General Motors

Location

La Jolla, CA

Start Date

1-1-1989 12:00 AM

Description

The fatigue testing of prototype components is very time consuming. A basic limitation is that conventional techniques cannot detect fatigue cracks until they have grown to several millimeters in length. For aluminum alloys this problem was overcome by the development of the gel electrode method of imaging very small (10-2 mm) cracks. This technique has now been modified for applications to steel. A primary requirement is that prior to fatigue testing, the surface is coated with a thin (30 nm) insulating dual-layer oxide/organic film by a two step anodization process. During testing, the film is ruptured if a fatigue crack forms in the steel. When the surface is contacted with a gel electrode, a 4V, 200 ms pulse causes current to flow preferentially to the crack. This current forms an image which is retained in the surface of the gel. This paper is illustrated by images of fatigue cracks in a dual phase steel and a high strength low alloy (HSLA) steel. The images are well defined and can be repeated many times, as required for periodic in situ inspection during component testing. Features of the image are correlated with crack segments only 10-2 mm long.

Volume

8B

Chapter

Chapter 9: Characterization of Materials

Section

Ferrous Materials and Methods

Pages

2127-2132

DOI

10.1007/978-1-4613-0817-1_270

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Imaging Fatigue Cracks in Low Carbon Steels with the Gel Electrode

La Jolla, CA

The fatigue testing of prototype components is very time consuming. A basic limitation is that conventional techniques cannot detect fatigue cracks until they have grown to several millimeters in length. For aluminum alloys this problem was overcome by the development of the gel electrode method of imaging very small (10-2 mm) cracks. This technique has now been modified for applications to steel. A primary requirement is that prior to fatigue testing, the surface is coated with a thin (30 nm) insulating dual-layer oxide/organic film by a two step anodization process. During testing, the film is ruptured if a fatigue crack forms in the steel. When the surface is contacted with a gel electrode, a 4V, 200 ms pulse causes current to flow preferentially to the crack. This current forms an image which is retained in the surface of the gel. This paper is illustrated by images of fatigue cracks in a dual phase steel and a high strength low alloy (HSLA) steel. The images are well defined and can be repeated many times, as required for periodic in situ inspection during component testing. Features of the image are correlated with crack segments only 10-2 mm long.