Application of the potential-difference method to register cracks during creep

The kinetics of crack propagation is an important problem of study when evaluating the long-term strength of structural elements in power-engineering equipment. A study is made of the possibilities of the potential difference method for registering the onset and the stable-growth process of cracks during creep. Tests were made on specimens of 09Kh16N15M3B steel under constant loading conditions and temperatures (873 and 923 K). An electrical machining method was used to produce a stress concentrator having a radius 100 μm at the apex. The tests were performed on a modified AIMA-5-2 machine. During stops in the testing the length of the crack was measured with a type MBS-1 microscope. Calibration curves are presented for specimens having one and two notches. The potential-difference method can be successfully used to check for the presence and development of cracks at any sites on structural elements where creep conditions exist