Simple method and instrument for recording the development of cracks

A method is proposed for measuring the length of a crack in an electrically conducting material based on the use of a resistance bridge circuit. The accuracy in measuring the crack length with the proposed instrument is determined by the accuracy of the relative change in the resistance of the portion with a crack and is of the order of 1 to 3%. The instrument is free of errors caused by temperature changes. With a sufficient current through the sample an instability in the line voltage of plus or minus 10% causes a change in the position of the measuring slide of not more than 0.5%.