Model of non-proportional fatigue load in the form of block load spectrum

Service load is often a non-proportional multi-axial load. The result of operation of such type of load on constructional elements is the decrease of fatigue lives in relation to proportional load of the same equivalent value. There are many damage models for non-proportional fatigue, however, none of them obtained general acceptance. The key issue for creation of correct damage model is the selection of appropriate load parameters. The article presents methodology of obtaining cumulative exceeding histogram (load spectrum) containing key parameters of non-proportional load. The hereby work includes: proposal of method of forming of block load spectrum for non-proportional load, example block load programs for various types of multi-axial load and results of experimental tests of fatigue lives obtained on the basis of formulated programs.