Gel Electrode Evaluation of Fatigue Performance of Aluminum Components

The gel electrode produces clearly visible images of fatigue cracks in aluminum alloys. The only preparation required is the formation of a thin (1.4 × 10⁻⁵ mm) anodic oxide film on the surface. After fatigue cycling a gel electrolyte is pressed against the surface and a voltage pulse applied. As the current flows preferentially to the fatigue cracks an image is formed in the surface of the gel. The technique is extremely sensitive -- fatigue cracks as short as 10⁻² mm have been detected -- and provides a more rapid and more complete evaluation of the fatigue performance of automotive components than has been possible hitherto. This initial application at the Chevrolet Engineering Center demonstrates the following advantages. (i) Primary fatigue sites are detected very early in a test so that designs can be rapidly evaluated and compared. (ii) Sites of secondary fatigue damage are also detected so that several design changes can be incorporated simultaneously.