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A B S T R A C TThe authors analysed influence of a component of the torsional moment M as under the complex loading state, that is under bending with torsion, on fatigue life during initiation and propagation of fatigue cracks. Simulation of specimen life was performed according to the relationships describing the crack propagation rate and including the equivalent stress intensity factor range K eq . Under complex loading, increase of amplitude of the torsional moment M as for a given initial value of the resultant moment M aw0 caused a higher fatigue life of specimens made of 10HNAP and 18G2A steels. This fatigue life increase was described by a nonlinear equation, the parameters of which had been determined from the experimental results. The fatigue lives estimated according to the assumed models were compared with those obtained from tests.Keywords bending with torsion; equivalent stress intensity factor range; fatigue life; mixed mode loading. N O M E N C L A T U R Ea = crack length a e xpi = crack length obtained while tests a max e xpi = maximum crack length a k = the critical crack length a p = the initial length of crack a o bli = calculated crack length b = width of the specimen d i = minimal length of the interval E = Young's modulus G = strain energy release rate G eq = equivalent strain energy release rate G I = strain energy release rate for mode I G III = strain energy release rate for mode III h = height of the specimen k 2 and k 3 = coefficients dependent on side ratios b/h K eq = equivalent stress intensity factor K I = stress intensity factor for mode I K III = stress intensity factor for mode III M ag and M as = amplitudes of the bending and torsional moments M g = bending moment M K I , M K I I I = shape correction coefficients for modes I and III M mg and M ms = mean values of the bending and torsional moments (constant) M s = torsional moment

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The article discusses the problem related to estimating fatigue life of elements containing stress concentrators. The algorithm for estimating fatigue life presented in this work uses a fictitious ray based on the Neuber method. The proposed algorithm takes into account the variability of microstructural length, which depends on the number of failure cycles. The function thus obtained can be used to select the appropriate value for this length, which simplifies the calculation procedure needed to estimate fatigue life. In addition, this work includes an analysis of the impact of variable cutout geometry on the value of the support coefficient. As a result, it was possible to extend the application of this concept to lower fatigue life values and to structural elements with different notch geometries. The method was verified by performing experiments using elements made of three steel grades. A good correlation between calculation and experimental results was obtained.

The main aim of the paper is determination of residual stresses in explosively welded steel-titanium bimetal. The analysis considers two bimetallic specimens: before and after the heat treatment. In residual stress determination the hole drilling method along with finite element analysis were applied. The results show different residual stress states depending on the heat treatment. The obtained results are confirmed by thermal stress calculation.