Abstract
The paper presents results of calculation for modelling of the stressstrain relationship in the case of block loads with mean load value. A model, based on the stable hysteresis loops, was assumed and modified to use for block loading analysis. For stress history calculation, the proposed model and two other constitutive models were used. Results of fatigue test of specimens made of S355J0 steel subjected to bending block loading with mean load value are presented and used to verify the proposed model. In the tests, the mean load was increased and decreased in subsequent blocks. The changes of strain recorded during the tests shown in the paper indicate a different behavior of the material. Damage accumulation degree for block sequence was used to compare the results of calculations. It was shown, that stress history parameters (stress amplitude and mean stress value in this case) are similar for all investigated models.
Highlights
O bservation of the relation between strains of the structural materials and loading applied to the structure allow assessing the phenomena which occurs during fatigue of materials [1, 2]
The tests presented by Chiou and Yip [8] shows the effect of the mean load based on the example of research on AISI 316 alloy steel subjected to uniaxial loads of constant amplitude and the saw-toothed waveform
The aim of performed calculations is to establish a parameters of the stress history for each sequence of the applied block loads respecting both paths of changes of the mean load using proposed model, Garud-Mroz proposal and Chu
Summary
O bservation of the relation between strains of the structural materials and loading applied to the structure allow assessing the phenomena which occurs during fatigue of materials [1, 2]. The area of the stress-strain hysteresis loop is identified with the plastic strain energy density This energy parameter is widely used in so called energy based criteria to describe and predict the fatigue life of material, eg. In the case of complex load, during operation of the structures, some changes of the shape and location of the hysteresis loop are observed It has to be considered in the algorithm of the fatigue life calculation, where the influence of the different load parameters on the strain-stress relationship is important. Studying papers on that problem, we can find that there is no standard procedure for fatigue life calculation and some researchers obtained completely opposite results [6] Most of those considerations were based on experimental results which were obtained for different materials, loading conditions, applied stress levels. The authors Memon at al. [9] shows the results of fatigue tests under conditions of two-stage block loads in Lo-Hi and Hi-Lo sequences (Fig. 1) for different sequences of amplitude and the mean stressess
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