Fatigue life calculation of notched specimens by modified Wöhler curve method and theory of critical distance under multiaxial random loading

2021 ◽  
Author(s):  
Zhengbo Luo ◽  
Huaihai Chen ◽  
Jie Wang ◽  
Ronghui Zheng
Keyword(s):  
Fatigue Life ◽  
Critical Distance ◽  
Random Loading ◽  
Notched Specimens ◽  
Curve Method

scholarly journals Evaluation of notch effects in low cycle fatigue of alloy 718 using critical distances

2018 ◽  
Vol 165 ◽  
pp. 15001 ◽  
Author(s):  
Robert Eriksson ◽  
Kjell Simonsson ◽  
Daniel Leidermark ◽  
Johan Moverare
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Notch Root ◽  
Stress Gradient ◽  
Critical Distance ◽  
Fatigue Tests ◽  
Alloy 718 ◽  
Notched Specimens ◽  
Turbine Disks ◽  
As Stress

Gas turbine disks contain many notch-like features acting as stress raisers. The fatigue life based on the notch root stress may be overly conservative as the steep stress gradient in front of the notch may give rise to so-called notch support. In the current work, the theory of critical distances was applied to the prediction of the total fatigue life of low cycle fatigued, notched specimens made from alloy 718. The fatigue tests were performed at 450 °C and 550 °C. It was found that, for lives shorter than 5000–10000 cycles, the notched specimens had longer lives than would have been expected based on the notch root strain. For lives longer than 5000–10000 cycles, there were no notch support. The life prediction for notched specimens could be significantly improved by basing the prediction on the strain chosen some distance from the notch (the critical distance). An expression for calculating the critical distance based on the notch root strain was suggested.

Effect of Loading Sequence on the Fatigue Life of Notched Specimens Made From Steel and Aluminium Alloys

1991 ◽  
Vol 44 (1) ◽  
pp. 27-35 ◽  
Author(s):  
Otto Buxbaum ◽  
Hartmut Kla¨tschke ◽  
Helge Oppermann
Keyword(s):  
Fatigue Life ◽  
Aluminium Alloys ◽  
General Relation ◽  
Statistical Parameter ◽  
Axial Loading ◽  
Fatigue Tests ◽  
Test Results ◽  
Random Loading ◽  
Test Load ◽  
Notched Specimens

A statistical parameter which can be derived from the Markov matrix has been defined in order to characterize the intermixture of random loading fluctuations. By means of this intermixture parameter, load sequences for fatigue tests can be generated closer to reality, and thus more reliable effects as well as effects resulting from loading sequences can be taken into account quantitatively in life calculations. The intermixture parameter has been calculated for 17 test load sequences. The corresponding fatigue test results obtained for notched specimens (Ki = 1.4–3.6) made from steels or aluminium alloys, either under bending or axial loading, led to a general relation between intermixture and fatigue life, being primarily influenced by the stress ratio.

A Method for Fatigue Analysis of Pipelines on Topsides of FPSO Systems

2005 ◽  
Author(s):  
Pol Spanos ◽  
Alba Sofi ◽  
Juan Wang ◽  
Berry Peng
Keyword(s):  
Fatigue Life ◽  
Random Vibration ◽  
Equations Of Motion ◽  
Plug Flow ◽  
Fatigue Curve ◽  
Sea Waves ◽  
Random Loading ◽  
Euler Beam ◽  
Stress Spectrum ◽  
The Galerkin Method

Pipelines located on the decks of FPSO systems are exposed to damage due to sea waves induced random loading. In this context, a methodology for estimating the fatigue life of conveying-fluid pipelines is presented. The pipeline is subjected to a random support motion which simulates the effect of the FPSO heaving. The equation of motion of the fluid-carrying pipeline is derived by assuming small amplitude displacements, modeling the empty pipeline as a Bernoulli-Euler beam, and adopting the so-called “plug-flow” approximation for the fluid (Pai¨doussis, 1998). Random vibration analysis is carried out by the Galerkin method selecting as basis functions the natural modes of a beam with the same boundary conditions as the pipeline. The discretized equations of motion are used in conjunction with linear random vibration theory to compute the stress spectrum for a generic section of the pipeline. For this purpose, the power spectrum of the acceleration at the deck level is determined by using the Response Amplitude Operator of the FPSO hull. Finally, the computed stress spectrum is used to estimate the pipeline fatigue life employing an appropriate S-N fatigue curve of the material. An illustrative example concerning a pipeline simply-supported at both ends is included in the paper.

scholarly journals Fatigue Life Analysis of Aluminum Alloy Notched Specimens under Non-Gaussian Excitation based on Fatigue Damage Spectrum

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Kuanyu Chen ◽  
Guangwu Yang ◽  
Jianjun Zhang ◽  
Shoune Xiao ◽  
Yang Xu
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Relative Error ◽  
Gaussian Distribution ◽  
Calculation Method ◽  
Shaking Table ◽  
Notched Specimens ◽  
Acceleration Method ◽  
Non Gaussian

In this study, a non-Gaussian excitation acceleration method is proposed, using aluminum alloy notched specimens as a research object and measured acceleration signal of a certain airborne bracket, during aircraft flight as input excitations, based on the fatigue damage spectrum (FDS) theory. The kurtosis and skewness of the input signal are calculated and the non-Gaussian characteristics and amplitude distribution are evaluated. Five task segments obey a non-Gaussian distribution, while one task segment obeys a Gaussian distribution. The fatigue damage spectrum calculation method of non-Gaussian excitation is derived. The appropriate FDS calculation method is selected for each task segment and the acceleration parameters are set to construct the acceleration power spectral density, which is equivalent to the pseudo-acceleration damage. A finite-element model is established, the notch stress concentration factor of the specimen is calculated, the large mass point method is used to simulate the shaking table excitation, and a random vibration analysis is carried out to calculate the accelerated fatigue life. The simulation results show that the relative error between the original cumulative damage and test original fatigue life is 15.7%. The shaking table test results show that the relative error of fatigue life before and after acceleration is less than 16.95%, and the relative error of test and simulation is 24.27%. The failure time of the specimen is accelerated from approximately 12 h to 1 h, the acceleration ratio reaches 12, and the average acceleration ideal factor is 1.125, which verifies the effectiveness of the acceleration method. It provides a reference for the compilation of the load spectrum and vibration endurance acceleration test of other airborne aircraft equipment.

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