Abstract
One of the challenges regarding multiaxial fatigue damage predictions is non-proportional loading. Relevant studies have shown that these multiaxial loadings cause significant additional hardening and reduction in durability due to non-proportionality. Fatigue life predictions due to non-proportional loadings are based on an equivalent non-proportional strain range that considers a material constant related to additional hardening and a non-proportionality factor. In this paper an analysis of the non-proportional factor for three multiaxial loadings forming a square in γ/√3 – ε coordinates is carried out. One of the observations revealed by this analysis is the sensitivity of the non-proportional factor to variable shear strain rate.
Highlights
The stress or strain state in a material point is defined as a multiaxial state
Based on an experimental study of low-cycle fatigue tests under combined axial and torsional strains with different phase angles, Kanazawa, Brown and Miller, [1-3], highlighted a number of significant issues. These can be summarized as: a) during out-of-phase biaxial tests, fatigue cracks initiate on the plane of maximum shear strain; b) the fatigue life is governed by the shear strain range and the amplitude of normal strain on the plane of maximum shear strain; c) the out-of-phase loading condition with phase angle of 90° and strain ratio λ = γa/εa = 1.5 gave the lowest lifetime
An equivalent non-proportional strain range is defined which correlates the non-proportional experimental data. This strain range includes a material constant that describes the additional cyclic hardening under 90° out-ofphase and a factor that expresses the severity of non-proportional loading obtained directly from the strain history
Summary
The stress or strain state in a material point is defined as a multiaxial state. This multiaxiality is influenced by the external load, geometry, residual stress, etc. Multiaxial loadings are non-proportional if the principal directions and the corresponding principal stresses/strains change over a loading cycle Such loadings are very common in the operation of mechanical components, can be complex as a variation over time and it is difficult to quantify their effect on the fatigue life. Considering this phenomenon quantified through a parameter, it was possible to correlate out-of-phase data in a single stress-strain curve. This factor can vary from zero for proportional load to 1 for a semi-circular load These studies are focused on the overall correlation of non-proportional experimental data through an equivalent parameter that includes a factor corresponding to additional cyclic hardening and respectively a factor corresponding to the loading path. For these loadings the non-proportional load factor and implicitly their effect on fatigue damage has been analysed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
