The paper presents the results of tests on fatigue crack growth under bending in an elastic-plastic material. Specimens with rectangular sections and stress concentrator in the form of external one-sided sharp notch were used. The tests were performed under the stress ratios R = - I, - 0.5, O. The test results were described by the /'i ]-integral range and compared with the /'i K stress intensity factor range. It has been found that there is a good agreement between the test results and the empirical formula of fatigue crack growth rate, which includes the /'i ]-integral range.

The paper presents kinetic fatigue crack growth curve for IOHNAP steel, which is verified experimentally. An energy approach based on the M-integral range is shown. The tests have been carried out on plane specimens With notches under tension-compression for three values of stress ratio R. The J-integral is calculated analytically and by the finite element method. A relationship for the description of the whole kinetic crack growth curve including J-integral is presented. It is shown that at the constant loading and the change of stress ratio R from - 1 to O the fatigue crack growth rate increases. A relationship is proposed in the paper for description of the kinetic crack growth curve. It gives results that are consistent with experimental ones and those obtained with the use of the finite element method (FEM).