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.

Novel and Applicable Method to Determine Equivalent Strain Range and Equivalent Strain Direction Under Multiaxial Non-Proportional Loading

2019 ◽  
Author(s):  
Charles R. Krouse ◽  
Grant O. Musgrove ◽  
Taewoan Kim ◽  
Seungmin Lee ◽  
Muhyoung Lee
Keyword(s):  
Fatigue Life ◽  
Turbine Blade ◽  
Low Cycle Fatigue ◽  
Dimensional Space ◽  
Strain Range ◽  
Element Model ◽  
Equivalent Strain ◽  
Loading Conditions ◽  
Proportional Loading ◽  
Strain Direction

Abstract When considering mechanical components that are subjected to complex loading conditions, it is difficult to achieve accurate predictions of low-cycle fatigue life. For multiaxial and non-proportional loads, the principal strain directions vary in three-dimensional space with time. The commonly accepted methods to determine fatigue life under such loading conditions are based on a critical plane approach, and they rely heavily on accurate strain range estimates. However, there is no singly accepted method to determine the critical plane, equivalent strain magnitude, or equivalent strain direction. Furthermore, current suggestions are computationally intensive and challenging to implement. This paper offers a novel and concise method to accurately determine equivalent strain range and equivalent strain direction under multiaxial, non-proportional loading in three-dimensional space. A practical approach is provided for implementing the method, and an example of an application using a finite element model of a first stage turbine blade is discussed. To demonstrate the approach, ANSYS Mechanical was used to simulate a turbine blade under transient loading conditions and to determine the resulting strains. Equivalent strain range results were applied to a Coffin-Manson relation to determine the low-cycle fatigue life of every node within the finite element model of the first stage turbine blade. The post-processing of the strain predictions, which yielded the equivalent strain range and equivalent strain direction, is discussed in detail.

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.

Multiaxial Low Cycle Fatigue Life Prediction at 300 °C Using Equivalent Strain Appoach

2011 ◽  
Vol 361-363 ◽  
pp. 1669-1672
Author(s):  
Wen Xiao Zhang ◽  
Guo Dong Gao ◽  
Guang Yu Mu
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Strain Range ◽  
Cyclic Fatigue ◽  
Equivalent Strain ◽  
Multiaxial Fatigue ◽  
Fatigue Life Prediction ◽  
Cycle Fatigue

The low cycle fatigue behavior was experimentally studied with the 3-dimension notched LD8 aluminum alloy specimens at 300°C. The 3- dimension stress-strain responses of specimens were calculated by means of the program ADINA. The multiaxial fatigue life prediction was carried out according to von Mises’s equivalent theory. The results from the prediction showed that the equivalent strain range can be served as the valid mechanics for predicting multiaxial high temperature and low cyclic fatigue life.

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.

scholarly journals Mean stress effects on Low-Cycle Fatigue behaviour of Inconel 718 alloy

2019 ◽  
Vol 300 ◽  
pp. 15004
Author(s):  
Sabrina Vantadori ◽  
Andrea Carpinteri ◽  
Camilla Ronchei ◽  
Daniela Scorza ◽  
Andrea Zanichelli
Keyword(s):  
Inconel 718 ◽  
Low Cycle Fatigue ◽  
Strain Ratio ◽  
Fatigue Behaviour ◽  
Multiaxial Fatigue ◽  
Test Results ◽  
Proportional Loading ◽  
Inconel 718 Alloy ◽  
Stress Effects ◽  
Biaxial Fatigue

Uniaxial and biaxial fatigue test results related to Inconel 718 specimens are analysed by using the critical plane-based multiaxial fatigue criterion by Carpinteri et al., formulated in terms of strain, in conjunction with a model similar to that by Smith-Watson-Topper (SWT). More precisely, both smooth solid specimens and thin-walled tubular specimens subjected to proportional and non-proportional loading consisting of tension, torsion, and combined tension and torsion loading under strain control are examined, for strain ratio equal to 0 or -1. Fatigue life is then analytically computed through the above procedure and compared with the experimental one, in terms of number of loading cycles needed to form a surface crack whose length is equal to 1 mm.

Multiaxial Fatigue Damage Models

1987 ◽  
Vol 109 (4) ◽  
pp. 293-298 ◽  
Author(s):  
D. Socie
Keyword(s):  
Crack Growth ◽  
Fatigue Damage ◽  
Hydrostatic Stress ◽  
Damage Model ◽  
Strain Range ◽  
Multiaxial Fatigue ◽  
304 Stainless Steel ◽  
Proportional Loading ◽  
Damage Models ◽  
Strain Model

Two multiaxial fatigue damage models are proposed: a shear strain model for failures that are primarily mode II crack growth and a tensile strain model for failures that are primarily mode I crack growth. The failure mode is shown to be dependent on material, strain range and hydrostatic stress state. Tests to support these models were conducted with Inconel 718, SAE 1045, and AISI Type 304 stainless steel tubular specimens in strain control. Both proportional and non-proportional loading histories were considered. It is shown that the additional cyclic hardening that accompanies out of phase loading cannot be neglected in the fatigue damage model.

Comparative Study of the Additional Hardening Effects of Three Structural Steels

2006 ◽  
Vol 514-516 ◽  
pp. 534-538
Author(s):  
Luís G. Reis ◽  
Bin Li ◽  
Manuel de Freitas
Keyword(s):  
Low Cycle Fatigue ◽  
Testing Machine ◽  
Great Influence ◽  
Structural Steels ◽  
Loading Path ◽  
Multiaxial Loading ◽  
Cycle Fatigue ◽  
Proportional Loading ◽  
Loading Paths ◽  
Additional Hardening

For a safe and reliable design of components, it is needed to study the effects of multiaxial loading and particularly the non-proportional loadings on the fatigue damage. The objective of this paper is to evaluate and compare the additional hardening effects of proportional and non-proportional loading paths. Low-cycle fatigue behaviour of three structural steels: CK45 (ferritic-perlitic microstructure) normalized steel, 42CrMo4 (bainitic microstructure) quenched and tempered steel and stainless steel (austenitic microstructure) X10CrNiS 18 9 are studied under different proportional and non-proportional loading paths and different levels. A series of tests of biaxial low-cycle fatigue composed of tension/compression with static or cyclic torsion were carried out on a biaxial servo-hydraulic testing machine Instron 8088. The experiments showed that the three materials studied have very different additional hardening behaviour, under multiaxial cyclic loading paths. The local cyclic stress/strain states are influenced by the multiaxial loading paths due to interactions between the normal stress and shear stress during cyclic plastic deformation. The microstructure is an important key and has a great influence on the additional hardening. The additional hardening effect is dependent of the loading path and also the intensity of the loading.

scholarly journals A Novel Energy-Critical Multiaxial Fatigue Life Prediction for Low Cycle Fatigue under Mixed-Mode Loading

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1066 ◽  
Author(s):  
Jie Zhou ◽  
Hong-Zhong Huang ◽  
He Li
Keyword(s):  
Mixed Mode ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Multiaxial Fatigue ◽  
Cycle Fatigue ◽  
Modified Model ◽  
Proposed Model ◽  
Failure Evolution ◽  
Practical Design ◽  
Multiaxial Loadings

Fatigue failure evolution is a process of damage accumulation under continued stresses and forces. The mechanical component is always subjected to various loadings and the lifespan is mainly governed by fatigue. The low cycle fatigue (LCF) is a key failure mode of many components. In order to estimate the LCF life under multiaxial loadings in practical design, a modified model is proposed, based on the Fatemi-Socie (FS) and Smith-Watson-Topper (SWT) models, which considers the effects of shear and tensile behaviours. Then a novel judgment criterion is presented to distinguish the mixed-mode loadings and the procedures to employ the proposed model are also presented. Furthermore, two types of materials (TC4 and GH4169) and comparisons with the FS, Wang-Brown (WB) and redefined SWT (Re-SWT) models are employed to verify the accuracy and effectiveness of the proposed model, which has shown more reasonable predictions than the other models.

scholarly journals A new multiaxial fatigue life prediction model considering additional hardening effect

2020 ◽  
Vol 12 (6) ◽  
pp. 168781402093533
Author(s):  
Li Bin ◽  
Liu Jianhui ◽  
Wang Xiuli
Keyword(s):  
Fatigue Life ◽  
Prediction Model ◽  
Life Prediction ◽  
Multiaxial Fatigue ◽  
Fatigue Life Prediction ◽  
Proportional Loading ◽  
Hardening Effect ◽  
Proposed Model ◽  
Additional Hardening ◽  
Life Prediction Model

The established linear fatigue life prediction model based on the Miner rule has been widely applied to fatigue life prediction under constant amplitude uniaxial and multiaxial loading. Considering the physical significance of crack formation and propagation, a multiaxial equivalent linear fatigue life prediction model is put forward based on Miner rule and critical plane method under constant amplitude loading. The essence of this approach is that the equivalent strain, which consists of the shear strain and normal strain on the critical plane, replaces the relevant parameter of uniaxial nonlinear fatigue damage model. The principal axes of stress/strain rotate under non-proportional loading. Meanwhile, the microstructure of material and slip systems change, which lead to additional hardening effect. The ratio of cyclic yield stress to static yield stress is used to represent the cyclic hardening capacity of material, and the influence of phase difference and loading condition on the non-proportional hardening effect is considered. The multiaxial fatigue life is predicted using equivalent stain approach, maximum shear stain amplitude model, CXH model, and equivalent multiaxial liner model under proportional and/or non-proportional loading. The smooth and notched fatigue specimens of four kinds of materials (Q235B steel, titanium alloy TC4, Haynes 188, and Mod.9Cr-1Mo steel) are used in the multiaxial fatigue experiments to verify the proposed model. The predicted results of these materials are compared with the test results, and the results show that these four models can achieve good effect under proportional loading, but the proposed model performs better than the other three models under non-proportional loading. Meanwhile, it also verifies that the proposed enhancement factor can reflect the influence of phase difference and material properties on additional hardening.

An Experimental Evaluation for Four Multiaxial Fatigue Approaches

2014 ◽  
Vol 627 ◽  
pp. 425-428
Author(s):  
Dan Jin ◽  
Da Jiang Tian ◽  
Qi Zhou Wu ◽  
Wei Lin
Keyword(s):  
Low Cycle Fatigue ◽  
Multiaxial Fatigue ◽  
304 Stainless Steel ◽  
Normal Strain ◽  
Cycle Fatigue ◽  
Critical Plane ◽  
Maximum Shear Strain ◽  
Rainflow Cycle Counting ◽  
Tubular Specimens ◽  
Damage Rule

A series of tests for low cycle fatigue were conducted on the tubular specimens for 304 stainless steel under variable amplitude and irregular axial-torsional loading. Rainflow cycle counting and linear damage rule are used to calculate fatigue damage and four approaches, e.g. SWT(Smith-Watson-Topper), KBM(Kandil-Brown-Miller), FS(Fatemi-Socie), and LKN(Lee-Kim-Nam) approach are employed to predict the fatigue life. The maximum shear strain plane, the maximum normal strain plane, and the maximum damage plane are considered as the critical plane, respectively. The effects of the choice of the critical plane on previous approaches are discussed. It is shown that comparing with the maximum shear/normal strain approach, the predictions are improved by using the maximum damage plane approach, part nonproportional paths for SWT, AV and part nonproportional paths for KBM, TV paths for FS. But for LKN, the prediction results are nonconservative for some paths than that of the maximum shear/normal strain approach.

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