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

Abstract

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.

A new algorithm for estimating fatigue life under mean value of stress

“…This reduction can be achieved by the so-called fatigue criteria. 6,[9][10][11][12][13][14][15][16][17] Although there are several approaches to an assessment of the fatigue of metallic materials referred in the literature, those that are related to the conception of critical plane received a wide range of applications. [18][19][20] The main difference between them consists in defining the orientation of the critical plane where maximum damage occurs.…”

“…whereas the values of shear mean stresses in direction s τ ns;m ¼ À0; 5σ m;k sin 2α þ τ m;k cos 2α: (12) Defining the orientation of critical plane and calculating the amplitude of equivalent cycle σ eq, a in critical plane…”

“…In the case of multiaxial state, which is most commonly present in the real designs and elements of devices, it is necessary to reduce it to an equivalent uniaxial state. This reduction can be achieved by the so‐called fatigue criteria . Although there are several approaches to an assessment of the fatigue of metallic materials referred in the literature, those that are related to the conception of critical plane received a wide range of applications .…”

A comparison of multiple step and single step methods for determining cyclic stress-strain relationship for two non-masing materials

“…The complexity of the phenomenon of fatigue degradation of materials results in many models used in various design situations. For example, a different approach is necessary in case of random loading (Kurek et al, 2017), block loading (Skibicki et al, 2014) or non-proportional loading (Pejkowski, 2017). Most of models require determination of specific material parameters (Pejkowski and Skibicki, 2015;Skibicki, 2007;.…”

Finite Element Analysis of Ventilation System Fire Damper Dynamic Time-History

“…Correct operation of this kind of installation depends on taking into account different general types of loadings at the design stage, such as fatigue loadings for instance [3,4]. Especially for offshore drilling tower construction types, the following types of loadings are listed in the NORSOK standard: impact loads caused by explosion or ship collision, and loads caused by extreme weather or earthquake [5].…”