Abstract
The approaches used to calculate the fatigue life of components must inevitably consider multiaxial stresses. Compared to proportional loading, the calculation of nonproportional loading is particularly challenging, especially since different materials exhibit the effects of nonproportional hardening and shifts in fatigue life. In this paper, the critical plane approach of scaled normal stresses, first proposed by Gaier and Dannbauer and later published in a modified version by Riess et al., is investigated in detail. It is shown that, on the one hand, compatibilities exist or can be established with known proportional strength criteria that can account for the varying ductility of different materials. Furthermore, it is demonstrated that the scaled normal stress approach can be formulated in such a way that different strength criteria can be used therein. As an example, the generally formulated approach for scaled normal stresses is applied to test results from ductile cast iron material EN-GJS-500-14. Different correction factors accounting for nonproportional loading are investigated. Through appropriate parameterization of one of the studied corrections, proportional and nonproportional test results were observed to fall within one common scatter band.
Highlights
The purpose of this paper is to show that compatibility can be established between the scaled normal stress approach and different multiaxial fatigue criteria, which are well accepted but applicable only for proportional loading
From the results of cyclic testing of either material specimens and components or component-like specimens under both proportional and nonproportional loading, two phenomena are known to occur that shall be discussed in more detail below, namely (1) nonproportional hardening of the material (Section 2.4.1) and (2) shifts in fatigue life to either higher or lower number of cycles compared to proportional loadings (Section 2.4.2)
The effect of shifts in fatigue life under nonproportional loading may be connected atondth, ethsaums,etomnecohnapnrisompos rdteioscnraiblecdycinlicSehcatirodne2n.i4n.1g, a(cnodmthpeaaruetwhoirtshsSeeecotnioenin2c.o4n.1s)is[t1e4n]c.y in the explanation solely for nonproportional hardening: a significant difference between the local stress–strain states between proportional and nonproportional loading should only result if the loading is in a range that leads to noteworthy plastic strain components
Summary
Fatigue assessments for components relevant to safety are conducted either on an experimental basis or by using calculation approaches. Assessments of analytical fatigue strength need to be able to handle multiaxial nonproportional loads while producing reliable results. This objective contrasts with the fatigue strength data commonly available in practice: 1. As an alternative to experimental determination, these properties can be estimated using statistical dependencies (see, for example, [3,4]). This does not change the range of validity of the properties
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