scholarly journals Influence of the Elastoplastic Strain on Fatigue Durability Determined with the Use of the Spectral Method

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 423 ◽  
Author(s):  
Michał Böhm ◽  
Mateusz Kowalski ◽  
Adam Niesłony
Keyword(s):  
Fatigue Life ◽  
Probability Density ◽  
Spectral Method ◽  
Fatigue Tests ◽  
Life Assessment ◽  
Loading Conditions ◽  
Random Loading ◽  
Elastoplastic Deformations ◽  
Fatigue Life Assessment ◽  
Safe Side

The paper presents experimental static and fatigue tests results under random loading conditions for the bending of 0H18N9 steel. The experimental results were used in performing calculations, according to the theoretical assumptions of the spectral method of fatigue life assessment, including elastoplastic deformations. The presented solution extends the use of the spectral method for material fatigue life assessment, in terms of loading conditions, above Hooke’s law theorem. The work includes computational verification of the proposal to extend the applicability of the spectral method of determining fatigue life for the range of elastoplastic deformations. One of the aims of the proposed modification was to supplement the stress amplitudes used to calculate the probability density function of the power spectral density of the signal with correction, due to the plastic deformation and its use for notched elements. The authors have tested the method using four of the most popular probability density functions used in commercial software. The obtained results of comparisons between the experimental and calculation results show that the proposed algorithm, tested using the Dirlik, Benasciutti–Tovo, Lalanne, and Zhao–Baker models, does not overestimate fatigue life, which means that the calculations are on the safe side. The obtained results prove that the elastoplastic deformations can be applied within the frequency domain for fatigue life calculations.

Determination of Fatigue Life with the Use of Spectral Method on the Basis of Fatigue Strain Characteristics

2014 ◽  
Vol 224 ◽  
pp. 112-117 ◽  
Author(s):  
Michał Böhm ◽  
Adam Niesłony
Keyword(s):  
Fatigue Life ◽  
Spectral Method ◽  
Analytical Formula ◽  
Life Assessment ◽  
Engineering Practice ◽  
Strain Characteristic ◽  
Fatigue Life Assessment ◽  
Theoretical Assumptions ◽  
New Formula

The paper presents a new formula for fatigue life determination with the use of the spectral method for fatigue life assessment on the basis of fatigue strain characteristics. The spectral method is widely used together with the stress characteristics, but the literature does not contain a case where it is used together with strain characteristics. The paper shows the theoretical assumptions as well as the derived analytical formula for fatigue life determination. The presented formula is using constants gained from the Manson-Coffin-Basquin strain characteristic. Due to the popularity of strain characteristics, the formula may be widely used in the engineering practice.

scholarly journals Unified Principal S–N Equation for Friction Stir Welding of 5083 and 6061 Aluminum Alloys

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Xiangwei Li ◽  
Ji Fang ◽  
Xiaoli Guan
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Friction Stir Welding ◽  
Test Data ◽  
Fatigue Tests ◽  
Life Assessment ◽  
Test Results ◽  
Friction Stir ◽  
Fatigue Life Assessment ◽  
Curve Equation

AbstractWith the popularization of friction stir welding (FSW), 5083-H321 and 6061-T6 aluminum alloy materials are widely used during the FSW process. In this study, the fatigue life of friction stir welding with two materials, i.e., 5083-H321 and 6061-T6 aluminum alloy, are studied. Fatigue tests were carried out on the base metal of these two materials as well as on the butt joints and overlapping FSW samples. The principle of the equivalent structural stress method is used to analyze the FSW test data of these two materials. The fatigue resistances of these two materials were compared and a unified principal S–N curve equation was fitted. Two key parameters of the unified principal S–N curve obtained by fitting, Cd is 4222.5, and h is 0.2693. A new method for an FSW fatigue life assessment was developed in this study and can be used to calculate the fatigue life of different welding forms with a single S–N curve. Two main fatigue tests of bending and tension were used to verify the unified principal S–N curve equation. The results show that the fatigue life calculated by the unified mean 50% master S–N curve parameters are the closest to the fatigue test results. The reliability, practicability, and generality of the master S–N curve fitting parameters were verified using the test data. The unified principal S–N curve acquired in this study can not only be used in aluminum alloy materials but can also be applied to other materials.

Development of a Fatigue Life Assessment and Prediction Framework for a Bimetallic-Welded Thick-Wall Component of a Steam Turbine

2016 ◽  
Author(s):  
M.-H. Herman Shen ◽  
Sajedur Akanda ◽  
Xia Liu ◽  
Peng Wang
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Steam Turbine ◽  
Room Temperature ◽  
Analytical Framework ◽  
Fatigue Tests ◽  
Life Assessment ◽  
Thick Wall ◽  
Fatigue Life Assessment ◽  
Control Constant

In this investigation, we have applied an integrated experimental-analytical framework for fatigue life assessment and prediction of a thick-wall component of a high-pressure (HP) steam turbine. Emphasis is placed on the development of an effective experimental and analytical procedure for life characterization on the basis of low cycle and high cycle fatigue (LCF/HCF) in order to improve the safety, reliability, and affordability of real world steam turbine operations. Stress-control constant amplitude fully reversed fatigue tests were performed in room temperature and 500°C to serve two purposes: (a) to obtain experimental stress-life (S-N) curves and (b) to assess the values of the parameters of the energy-based framework to predict the fatigue life. The experimental and the predicted S-N curves are compared with each other in case of both the room and the elevated temperature to examine the soundness of the present energy-based model to predict fatigue life. The present lifing model was found to be able to predict both the room and elevated temperature LCF/HCF life of the thick-wall component with excellent accuracy. Furthermore, the elevated temperature fatigue life is found to be lower than the room temperature fatigue life due to the lower fatigue toughness at elevated temperature.

Multi-Axial Cycle Counting and Fatigue Life Assessment Based on Nominal and Battelle Structural Stresses

2010 ◽  
Author(s):  
Zhigang Wei ◽  
Pingsha Dong ◽  
Jeong K. Hong ◽  
Thomas P. Forte
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Life Assessment ◽  
Nominal Stress ◽  
Loading Path ◽  
Crack Plane ◽  
Structural Stress ◽  
Loading Conditions ◽  
Welded Structures ◽  
Fatigue Life Assessment

In this paper, a path-dependent maximum range (PDMR) multi-axial cycle counting method is presented for performing fatigue life assessment of engineering components under general variable-amplitude multi-axial loading conditions. The PDMR method has two distinct features: (a) multi-axial cycle counting, in which the cycle counting is conducted in an equivalent stress or strain space, and (b) explicit loading path dependency. For uniaxial loading data, the PDMR and the ASTM standard Rainflow methods both generate the same counting results. The path-length, a function of both normal and shear stress components on a critical crack plane, is proposed as a fatigue damage parameter for ductile materials. PDMR can be applied to welded structures, in which the crack plane is usually known in advance, as well as to non-welded structures, in which the critical plane approach can be implemented into PDMR to determine both the fatigue crack orientation and the associated fatigue damage. The effectiveness and robustness of the PDMR method have been validated by its ability to correlate nominal stress and Battelle structural stress fatigue data including pure-bending, pure-torsion, in-phase, and out-of-phase loading conditions for welded tube-to-flange steel structures. The relationship between the data correlations based on nominal stress and Battelle structural stress for these loading conditions is illustrated. Finally, one-parameter and two-parameter equivalency approaches for PDMR operation are also introduced and discussed.

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