scholarly journals Taking into account the non-proportional loading effect on high cycle fatigue life predictions obtained by invariant-based approaches

2019 ◽  
Vol 300 ◽  
pp. 12003
Author(s):  
Lorenzo Bercelli ◽  
Cédric Doudard ◽  
Sylvain Moyne
Keyword(s):  
High Cycle Fatigue ◽  
Equivalent Stress ◽  
Multiaxial Fatigue ◽  
Proportional Loading ◽  
Industrial Structures ◽  
Complete Chain ◽  
Stress Signals ◽  
Definition Of ◽  
Life Predictions ◽  
Fatigue Criterion

Industrial structures are often subjected to multiaxial fatigue loadings. If the multiple stress signals are not synced the loading is said to be non-proportional. Most of the multiaxial fatigue criteria give highly inaccurate lifetime predictions when used in the case of such loadings. The scalar equivalent stress defined by the criteria does not take into account the non-proportional nature of the multiaxial loading and leads to non-conservative predictions. Moreover a multiaxial fatigue criterion can only be applied on a stress cycle which has no clear definition when multiple unsynced signals are to be considered. This study addresses these issues by proposing a correction of an invariant based multiaxial fatigue criterion through the definition of a non-proportional degree indicator. A definition of multiaxial cycle is also given based on the Wang-Brown method. Finally a complete chain of invariant based lifetime prediction for non-proportional multiaxial fatigue is validated.

scholarly journals New research findings on non-proportional low cycle fatigue

2019 ◽  
Vol 300 ◽  
pp. 08003
Author(s):  
Anghel Cernescu ◽  
Rhys Pullin
Keyword(s):  
Low Cycle Fatigue ◽  
Strain Range ◽  
Material Constant ◽  
Multiaxial Fatigue ◽  
Shear Strain Rate ◽  
Proportional Loading ◽  
New Research ◽  
Life Predictions ◽  
Multiaxial Loadings ◽  
Additional Hardening

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.

In-Phase and Out-of-Phase Multiaxial Fatigue

1991 ◽  
Vol 113 (1) ◽  
pp. 112-118 ◽  
Author(s):  
F. Ellyin ◽  
K. Golos ◽  
Z. Xia
Keyword(s):  
External Pressure ◽  
Damage Parameter ◽  
Multiaxial Fatigue ◽  
Pressure Vessel Steel ◽  
Proportional Loading ◽  
Vessel Steel ◽  
Total Strain Energy Density ◽  
Number Of Cycles ◽  
Life Predictions ◽  
Cycles To Failure

In this investigation, thin-walled circular cylindrical specimens fabricated from a low alloy pressure vessel steel (ASTM A-516 Gr. 70) were subjected to various multiaxial loading conditions. The tests were conducted under strain-controlled condition, and loading was provided through an axial actuator and internal and external pressure across the specimen wall. Four in-plane strain ratios (ρ = Δεt/Δεa) were tested, and the most damaging case was the equi-biaxial in-plane straining, ρ = 1. For the latter condition, 90 deg out-of-phase loading was also investigated. These tests indicated a dramatic decrease in the number of cycles to failure, Nf, as a result of out-of-phase loading. The influence of the plastic strain path on life is thus clearly demonstrated. It is shown that the total strain energy density, ΔWt = ΔWe+ + ΔWp, correlates with both the in-phase and out-of-phase cyclic tests, and therefore is a proper damage parameter to be used for life predictions. A brief description of how ΔWt can be calculated is given for the case of proportional loading. The predicted results are compared with the experimental data, and the agreement is found to be very good indeed.

Evaluation of Multiaxial Fatigue Life Prediction Methodologies for Ti-6Al-4V

2002 ◽  
Vol 124 (2) ◽  
pp. 229-237 ◽  
Author(s):  
Alan R. Kallmeyer ◽  
Ahmo Krgo ◽  
Peter Kurath
Keyword(s):  
Fatigue Damage ◽  
Life Prediction ◽  
Equivalent Stress ◽  
Multiaxial Fatigue ◽  
Critical Plane ◽  
Proportional Loading ◽  
Biaxial Fatigue ◽  
Fatigue Data ◽  
Stress States ◽  
Mean Stresses

Many critical engineering components are routinely subjected to cyclic multiaxial stress states, which may include non-proportional loading and multidimensional mean stresses. Existing multiaxial fatigue models are examined to determine their suitability at estimating fatigue damage in Ti-6Al-4V under complex, multiaxial loading, with an emphasis on long-life conditions. Both proportional and non-proportional strain-controlled tension/torsion experiments were conducted on solid specimens. Several multiaxial fatigue damage parameters are evaluated based on their ability to correlate the biaxial fatigue data and uniaxial fatigue data with tensile mean stresses (R>−1) to a fully-reversed (R=−1) uniaxial baseline. Both equivalent stress-based models and critical plane approaches are evaluated. Only one equivalent stress model and two critical plane models showed promise for the range of loadings and material considered.

The Influence of Multiaxial Superimposed Static Mean Stress on High-Cycle Fatigue Life of Cu-ETP Copper

2016 ◽  
Vol 250 ◽  
pp. 157-162
Author(s):  
Lukasz Pejkowski ◽  
Dariusz Skibicki ◽  
Mateusz Wirwicki
Keyword(s):  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Fatigue Tests ◽  
Multiaxial Fatigue ◽  
Mean Stress ◽  
Loading Conditions ◽  
Cycle Fatigue ◽  
Proportional Loading ◽  
Mean Stresses

High–cycle multiaxial fatigue tests under proportional and non-proportional loading conditions with various combinations of superimposed static mean stresses was carried out on Cu-ETP copper. The results show differences in fatigue life between various ratios of mean stresses. These results are similar to others described in the literature.

Multiaxial high-cycle fatigue life prediction model based on the critical plane approach considering mean stress effects

2016 ◽  
Vol 27 (1) ◽  
pp. 32-46 ◽  
Author(s):  
Jia-Liang Zhang ◽  
De-Guang Shang ◽  
Yu-Juan Sun ◽  
Xiao-Wei Wang
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Multiaxial Fatigue ◽  
Cycle Fatigue ◽  
Critical Plane ◽  
Stress Effects ◽  
Critical Plane Approach ◽  
Fatigue Criterion

The aim of this paper is to propose a modified multiaxial high-cycle fatigue criterion based on the critical plane approach. The proposed criterion contains three parameters, that is, shear stress amplitude, normal stress amplitude and mean normal stress. In order to take into account the mean shear stress effects, the critical plane is determined by the maximum shear stress. In the proposed multiaxial fatigue criterion, the influence of mean normal stress on fatigue damage is also considered. Based on the proposed criterion, the multiaxial fatigue life is predicted, and the results showed a good agreement with experimental data obtained from some literatures.

The Effect of Stress Amplitude on Multi-Axial High-Cycle Fatigue Failure under Constant Amplitude Loading

2009 ◽  
Vol 417-418 ◽  
pp. 877-880
Author(s):  
Xin Hong Shi ◽  
Jian Yu Zhang ◽  
Rui Bao ◽  
Bin Jun Fei
Keyword(s):  
Fatigue Life ◽  
Fatigue Failure ◽  
Inflection Point ◽  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Equivalent Stress ◽  
Maximum Principal Stress ◽  
Cycle Fatigue ◽  
Pure Torsion ◽  
Proportional Loading

Studies about the effect of stress characteristics on multi-axial high-cycle fatigue of metals are still insufficient. Up to now, little work about the effect of different ratio of stress amplitude has been done on multi-axial fatigue under the same equivalent stress. In this paper, the effect of ratio of stress amplitude, under the same Von-Mises equivalent stress is studied from theory and experiment. The results show that the main factor of multi-axial high-cycle fatigue failure is the maximum principal stress. For proportional loading, fatigue life raises when ratio of stress amplitude increase. The variety of fatigue life is not obvious when is larger than a certain value and its value closes to that of pure torsion. For non-proportional loading, when ratio of stress amplitude increases, fatigue life raise at first, then has an inflection point. The value of at the inflection point changes with phase difference and its value is 0.5 while phase angle is 90º. Fatigue life of uniaxial tension was lower than that of pure torsion.

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