New Method of Electric Measurement of Crack Length.

This paper concerns improvements on devices used for determining the existence or propagation of a crack on an electrically conducting material. The procedure consists in ensuring a pulsed electric supply, which reduces the response time of the measurement, and, more important still, makes it free of noise and of the dc amplifier zero drift. In the case of cyclic loadings, the pulse may be synchronized with these loadings. After a description of a new type of instrument, the paper emphasizes, in specific applications, its great flexibility of use and the performance obtained.