Abstract
This paper discusses the phase shift effect occurring between two and more load channels of multiaxially loaded specimens. The discussion concludes that there is an extreme shortage of good experimental data that would prove the existence and the trend of the phase shift effect in the high-cycle fatigue region. It is no wonder that there are so many fatigue strength estimation criteria that use quite different computational concepts, because the response to the phase shift effect in the experimental base is often hidden in a conglomeration of other interacting effects. The paper presents results of a sensitivity study that compares the fatigue strength estimation results for various such criteria for the same stress amplitudes, but for different phase shifts between the push-pull and torsion load channels. These results show that, with the exception of criteria, that assume a zero phase shift effect, the phase shift affects the results of each studied fatigue strength estimation criterion in a different way. If well-organized experiments were available, experiments corresponding to the described comparison between in-phase and out-of-phase loading would show the right trends, and the optimum criterion could be selected. A proposal for such an experimental setup is provided in the paper.
Highlights
The paper presents results of a sensitivity study that compares the fatigue strength estimation results for various such criteria for the same stress amplitudes, but for different phase shifts between the push-pull and torsion load channels. These results show that, with the exception of criteria that assume a zero phase shift effect, the phase shift affects the results of each studied fatigue strength estimation criterion in a different way
What basic conditions must be met before any multiaxial fatigue strength criterion can be classified as good enough? The use of multiaxial criteria is a response to any loading that causes stress/strain tensors to have more than one dominant component
With the exception of the FF experiments, which are expected to be affected by the use of inadequate fatigue strength in pure torsion loading, the equivalent stress ratios MMP,90/ MMP,0 span from 0.94 to 0.97, and the out-of-phase loading would lead to lower fatigue strengths
Summary
What basic conditions must be met before any multiaxial fatigue strength criterion can be classified as good enough? The use of multiaxial criteria is a response to any loading that causes stress/strain tensors to have more than one dominant component. One of the most explicit summaries of the findings of previous researchers, in stress-based and strain-based fatigue life prediction was provided by Sonsino [3], and [4] His conclusions are that the switch from in-phase loading to out-of-phase loading while keeping the same stress amplitudes on individual load channels causes: different materials. Another weak point of typical benchmark test sets is that they are often evaluated overall, and not in parts (e.g. in-phase (IP) and out-of-phase (OP) loadings separately). The non-zero phase shift effect could be traced, if the data could be rated as credible, which they are not [15] as noted above
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