Abstract
This paper contains a proposition of a new method of determining the fatigue life of elements subjected to non-stationary loads. The model was based on the determination of the time-variable equivalent weighted amplitude. This amplitude is derived on a continuous basis as the arithmetic mean of nth root of the amplitudes that occur up to a given time. The analysis of the proposed model was carried out on the basis of selected literature insights based on specimens made of P91 and P92 steels. The experimental tests were performed under block loading with a zero mean value in the conditions of tension-compression with a small number of cycles.
Highlights
For many years, a hypothesis of fatigue damage accumulation has been sought, which could be used for fatigue damage accumulation in the case of other cases than loads with constant amplitude
On the basis of such loads, another hypothesis named after Marko-Starkey [6] was formulated, in which a distinction is made between loading blocks, number of cycles and the material constant characteristic for a given material
The monograph by Szala [7] contains a discussion including the description of the fatigue damage accumulation hypothesis in terms of the stress, energy and strain model, and offers a summary of the scientific achievements in the area of research concerned with fatigue damage accumulation
Summary
A hypothesis of fatigue damage accumulation has been sought, which could be used for fatigue damage accumulation in the case of other cases than loads with constant amplitude. Where: φ – material constant, N – current number of cycles, Nf – cumulative number of cycles to failure, Nfi – total number of cycles to failure corresponding to a given load amplitude; Subsequently, it has been demonstrated that both models describe the results of experimental studies relatively well. These models cannot be utilized for fatigue life assessment without gaining prior information regarding this fatigue life, as the calculations require the total number of cycles to failure (Nf). The aim of this study is to develop such a model and its verification on the basis of on fatigue tests available in the literature, performed on specimens made of P91 and P92 steel in the range of a small number of cycles
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