Prediction of the Cyclic Life of Pieces with Macrocracks by Thermographic Method

摘要

To improve the accuracy for prediction of cyclic life of pieces with macrocracks we propose to use a new thermographic method. Traditionally this question is solved on the basis Paris formula which connects the speed of crack growth (SCG) with Stress intensity factor K. However parameter K is not identical to the SCG because K doesn’t consider non-linear processes at the top of crack (TC). That is why the using K gives the considerable error. For overcoming this problem we proposed instead of K to connect SCG with another diagnostic parameter, such as ΔS(1c)—increment of specific entropy for cycle (ISE) at the TC, which can be calculated with sufficient accuracy through passive temperature field on the surface of tested object. Parameter ISE can be obtained both simultaneously with building of a kinetic fatigue diagram and on the basis of measuring of temperature under exploitation of piece. In both cases the prediction of cyclic lifetime is much higher than with the help parameter K. Besides parameter ISE allows to follow the crack development inside tested object. This means that suggested parameter ISE is more universal and convenient than traditional parameter K.