DETECTION OF CRACKS IN TEST PIECES

摘要

PURPOSE:To enable direct reading of the length of cracks from detected values while eliminating the calibration of the quality and shape of a test piece or the atmospheric temperature by measuring the length from a linear division ratio based on a crack detection distance and an energization distance separately arranged. CONSTITUTION:An energization lead wire and a crack potential difference detection lead wire 7 are arranged above and below a test piece 4 through a notch 3 in such a manner a specified energization distance and a specified crack detection distance are separately provided therefor. A power source 6 is connected to the lead wire 5 and an amplifier 8 to the lead wire 7 separately. An amplifier 11 is connected to the lead wire 5 and outputs thereof are inputted into a divider 12 with outputs from the amplifier 8 to compute the ratio between both voltages, which is directly read with an indicator 9. In this case, the resistance due to cracks of the test piece 4 and changes in the resistance of the test piece with the development of cracks are expressed by a function only between the crack detection distance and the energization distance. The proper setting of these distances permits the linearization of the length of the cracks with respect to the resistance ratio within a specified range.