scholarly journals Fatigue Life Monitoring Program of RMAF MiG-29

2008 ◽  
Vol 5 (1) ◽  
pp. 27
Author(s):  
Wahyu Kuntjoro ◽  
Ibrahim Bahari ◽  
Abdul Ghani Ujang ◽  
Assanah Mohd Mydin
Keyword(s):  
Fatigue Life ◽  
Stress Level ◽  
Structural Integrity ◽  
Low Cycle Fatigue ◽  
Monitoring Program ◽  
Stress Effect ◽  
Counting Procedure ◽  
Fatigue Damage Accumulation ◽  
Rainflow Cycle Counting ◽  
Lug Joints

The Royal Malaysian Airforce (RMAF) operates one squadron of MiG-29 which were designed on Safe Life principle. RMAF conducts a fatigue life monitoring program to these airplanes. This activity is conducted based on the experience of having the fatigue life monitoring program to the RMAF F/A-18D. The fatigue life of RMAF MiG-29 is based on the wing-fuselage lug joint structure, and Low Cycle Fatigue (LCF) approach is adopted. The stress spectra of this component, is derived through mapping of g-spectra to the 1-g stress level of the lug. The g-history is obtained from the accelerator installed in the airplane, while the 1-g stress level is obtained by finite element modeling of the wing structure and lug joints. Rainflow cycle counting procedure was then applied. The fatigue characteristics (strain-life) of the lug material was obtained from the laboratory test, using the lug material sample, combined with the empirical formula of strain-life diagram. Notched effect is taken into account using Neuber theory. Mean stress effect is dealt with using Smith-Watson-Topper formula. Miner’s rule is used to calculate the fatigue damage accumulation. A fatigue life prediction software for RMAF MiG-29 which incorporates the above concepts had been developed. Currently, this software is operational with the RMAF MiG-29, and is being used as part of its Aircraft Structural Integrity Program (ASIP). This paper reports on the development of the fatigue life monitoring strategy and software for the RMAF MiG-29.

scholarly journals Multiaxial fatigue life estimation in low-cycle fatigue regime including the mean stress effect

2018 ◽  
Vol 165 ◽  
pp. 16002
Author(s):  
Daniela Scorza ◽  
Andrea Carpinteri ◽  
Giovanni Fortese ◽  
Camilla Ronchei ◽  
Sabrina Vantadori ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Equivalent Strain ◽  
Mean Value ◽  
Multiaxial Fatigue ◽  
Stress Effect ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Structural Components ◽  
Mean Stress Effect

The goal of the present paper is to discuss the reliability of a strain-based multiaxial Low-Cycle Fatigue (LCF) criterion in estimating the fatigue lifetime of metallic structural components subjected to multiaxial sinusoidal loading with zero and non-zero mean value. Since it is well-known that a tensile mean normal stress reduces the fatigue life of structural components, three different models available in the literature are implemented in the present criterion in order to take into account the above mean stress effect. In particular, such a criterion is formulated in terms of strains by employing the displacement components acting on the critical plane and, then, by defining an equivalent strain related to such a plane. The Morrow model, the Smith-Watson-Topper model and the Manson-Halford model are applied to define such an equivalent strain. The effectiveness of the new formulations is evaluated through comparison with some experimental data reported in the literature, related to biaxial fatigue tests performed on metallic specimens under in-and out-of-phase loadings characterised by non-zero mean stress values.

scholarly journals Fatigue Damage Accumulation Modeling of Metals Alloys under High Amplitude Loading at Elevated Temperatures

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1030 ◽  
Author(s):  
Jarosław Szusta ◽  
Andrzej Seweryn
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Damage Accumulation ◽  
Elevated Temperatures ◽  
Low Cycle Fatigue ◽  
High Amplitude ◽  
Metal Alloys ◽  
Damage State ◽  
State Variable ◽  
Fatigue Damage Accumulation

This article presents an approach related to the modeling of the fatigue life of constructional metal alloys working under elevated temperature conditions and in the high-amplitude load range. The article reviews the fatigue damage accumulation criteria that makes it possible to determine the number of loading cycles until damage occurs. Results of experimental tests conducted on various technical metal alloys made it possible to develop a fatigue damage accumulation model for the LCF (Low Cycle Fatigue) range. In modeling, the material’s damage state variable was defined, and the damage accumulation law was formulated incrementally so as to enable the analysis of the influence of loading history on the material’s fatigue life. In the proposed model, the increment of the damage state variable was made dependent on the increment of plastic strain, on the tensile stress value in the sample, and also on the actual value of the damage state variable. The model was verified on the basis of data obtained from experiments in the field of uniaxial and multiaxial loads. Samples made of EN AW 2024T3 aluminum alloy were used for this purpose.

A Kt-Based Method for Calculating LCF Life of Notched Specimens

1994 ◽  
Vol 116 (4) ◽  
pp. 403-408 ◽  
Author(s):  
N. Merah ◽  
T. Bui-Quoc ◽  
M. Bernard
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Stress Level ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Cycle Fatigue ◽  
Unnotched Specimen ◽  
Stress Raisers

Under cyclic loading, the effect of stress raisers on the fatigue life depends upon several parameters, the most important being the stress concentration factor, the stress level, and the material notch sensitivity. In particular, in the low-cycle fatigue region, a number of procedures are currently used, but additional developments are required for improvement of the life prediction capabilities. In this paper, a method is proposed for calculating notched specimen low-cycle fatigue life from unnotched specimen data using as the main parameter the stress concentration factor combined with the applied stress level and the cyclic-hardening properties of the material. The proposed method is then applied to several materials with a variety of notch geometries to obtain the predicted lives. The correlation between the calculated lives and the experimental data is discussed in connection with the predictions obtained from Neuber’s and Zwicky’s relations.

Effect of Temperature Changes on the Waveform of Fatigue Damage Accumulation

2014 ◽  
Vol 598 ◽  
pp. 160-167 ◽  
Author(s):  
Stanisław Mroziński ◽  
Michał Piotrowski
Keyword(s):  
Fatigue Life ◽  
Temperature Change ◽  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Effect Of Temperature ◽  
Cycle Fatigue ◽  
Temperature Changes ◽  
Fatigue Damage Accumulation ◽  
Two Temperatures

In this paper there have been presented the results of low-cycle fatigue tests of steel P91 samples in the conditions of isothermal fixed amplitude loads as well as loads with a temperature change. Fixed amplitude isothermal loads were conducted on five levels of full strain and in two temperatures T1=20°C and T2=600°C. In the paper there has been found a significant influence of the sequence of temperature changes on the cyclic properties after the temperature change and on the fatigue life. The conducted experimental verification of the Palmgren-Miner hypothesis proved its influence on the temperature changes during the tests.

scholarly journals The influence of exposed to corrosion length of rebars on fatigue life of RC elements

2021 ◽  
Vol 349 ◽  
pp. 02013
Author(s):  
Konstantinos Koulouris ◽  
Maria Basdeki ◽  
Charis Apostolopoulos
Keyword(s):  
Fatigue Life ◽  
Mass Loss ◽  
Structural Integrity ◽  
Low Cycle Fatigue ◽  
Corrosion Damage ◽  
Mechanical Tests ◽  
Fatigue Lifetime ◽  
Accelerated Corrosion ◽  
Corrosion Of Steel ◽  
Main Factor

Deterioration of reinforced concrete is a main factor on estimation of structures' service lifetime. As it is well known, both corrosion of steel reinforcement and earthquake events, have detrimental effects on structural integrity of RC elements. In this study, the fatigue life of corroded reinforcement is investigated. Bare and embedded (in concrete) specimens of rebars are tested in low cycle fatigue conditions after accelerated corrosion experiments using impressed current technique. Corrosion damage, in terms of mass loss, and the mechanical tests of fatigue are taken account in function of the exposed to corrosion length of reinforcement. The outcomes attained from the experimental study indicate higher mass loss values of specimens with short exposed to corrosion length than the corresponding mass loss values of specimens with long exposed to corrosion length at the same tested corrosion time; subsequently resulting in their reduced fatigue lifetime. Extrapolating the abovementioned results on RC elements in marine environment located in seismic prone areas, issues are raised concerning the assessment of structural integrity and the parameters which are taken into account on monitoring of high importance structures.

Fatigue Life Simulation of a High Pressure Breech System

2006 ◽  
Vol 326-328 ◽  
pp. 1027-1030 ◽  
Author(s):  
Seung Kee Koh ◽  
Eui Gyun Na ◽  
Tae Hyun Baek ◽  
K.J. Kang ◽  
S.T. Ahn ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Stress Analysis ◽  
Structural Integrity ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Local Strain ◽  
Fatigue Tests ◽  
Ring Groove

In order to evaluate the structural integrity of the breech system used for a thick-walled cylinder subjected to pulsating high internal pressure, fatigue life simulation of a breech system was performed. A stress analysis of the breech was performed to locate the critical region vulnerable to crack initiation. Low-cycle fatigue behavior of the breech material was investigated to obtain the fatigue crack initiation properties. Elastic-plastic finite element stress analysis resulted in a stress concentration at the breech ring groove root. Strains at the breech ring and block were experimentally measured using strain gages and resulted in similar values compared to the calculated strains. Local strain approach was employed to estimate the fatigue life of the breech system for crack initiation at the groove root of the breech ring. Fatigue tests using simulation specimens were performed and an averaged fatigue life was obtained, showing a very good agreement with the calculated fatigue life within a factor of two.

scholarly journals Prediction of Strain Fatigue Life of HRB400 Steel Based on Meso-Deformation Inhomogeneity

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1464
Author(s):  
Lili Jin ◽  
Bin Zeng ◽  
Damin Lu ◽  
Yingjun Gao ◽  
Keshi Zhang
Keyword(s):  
Fatigue Life ◽  
Standard Deviation ◽  
Longitudinal Strain ◽  
Low Cycle Fatigue ◽  
Peak Stress ◽  
Cyclic Process ◽  
Stress Effect ◽  
Statistical Parameters ◽  
Statistical Characterization ◽  
Deformation Inhomogeneity

The relationship between strain fatigue life and evolution of meso-deformation inhomogeneity was studied, through the cyclic process of numerical simulation of crystal plasticity compared with the fatigue test of steel hot-rolled ribbed-steel bar 400 (HRB400). The statistical characterization parameters at grain level, including the standard deviation of the dot product of longitudinal stress and strain, the product of the macro stress and the standard deviation of the longitudinal strain, and the product of the macro stress ratio and the standard deviation of the longitudinal strain, were proposed and respectively applied to measure the meso-deformation inhomogeneity of materials. These parameters take the effect of peak stress into account, distinct from the pure strain statistical parameters. The numerical results demonstrate that the low-cycle fatigue life curves of materials are predictable using the new parameters as FIPs (fatigue indicator parameters), and the predictions are more rational than by utilizing the FIPs without considering the peak stress effect.

scholarly journals Experimental Investigation of Second-Harmonic Lamb Wave Generation in Additively Manufactured Aluminum

2018 ◽  
Vol 1 (4) ◽  
Author(s):  
Benjamin Steven Vien ◽  
Wing Kong Chiu ◽  
L. R. Francis Rose
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Second Harmonic ◽  
Low Cycle Fatigue ◽  
Propagation Distance ◽  
Nonlinearity Parameter ◽  
Harmonic Amplitude ◽  
Cycle Fatigue ◽  
Fatigue Damage Accumulation

The correlation between the nonlinear acousto-ultrasonic response and the progressive accumulation of fatigue damage is investigated for an additively manufactured aluminum alloy AlSi7Mg and compared with the behavior of a conventional wrought aluminum alloy 6060-T5. A dual transducer and wedge setup is employed to excite a 30-cycle Hann-windowed tone burst at a center frequency of 500 kHz in plate-like specimens that are 7.2 mm thick. This choice of frequency-thickness is designed to excite the symmetric Lamb mode s1, which, in turn, generates a second-harmonic s2 mode in the presence of distributed material nonlinearity. This s1-s2 mode pair satisfies the conditions for internal resonance, thereby leading to a cumulative build-up of amplitude for the second-harmonic s2 mode with increasing propagation distance. Measurements of a nonlinearity parameter β derived from the second-harmonic amplitude are plotted against propagation distance at various fractions of fatigue life under constant amplitude loading, for three different stress levels corresponding to low-cycle fatigue (LCF), high-cycle fatigue (HCF), and an intermediate case. The results show both qualitative and quantitative differences between LCF and HCF, and between the additively manufactured specimens and the wrought alloy. The potential use of this nonlinearity parameter for monitoring the early stages of fatigue damage accumulation, and hence for predicting the residual fatigue life, is discussed, as well as the potential for quality control of the additive manufacturing (AM) process.

Continuum damage mechanics application in low-cycle thermal fatigue

2012 ◽  
Vol 22 (2) ◽  
pp. 285-300 ◽  
Author(s):  
M Mashayekhi ◽  
A Taghipour ◽  
A Askari ◽  
M Farzin
Keyword(s):  
Fatigue Life ◽  
Thermal Fatigue ◽  
Damage Evolution ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Isothermal Condition ◽  
Continuum Damage Mechanics ◽  
Life Assessment ◽  
Continuum Damage ◽  
Fatigue Damage Accumulation

In this article, a fatigue model for low-cycle thermal fatigue formulated in a continuum damage mechanics framework is presented. The model is based on a unified damage law presented by Lemaitre for low-cycle fatigue, which has been extended to low-cycle thermal fatigue. The temperature dependencies of material parameters are considered in the damage evolution integration to take the non-isothermal condition of loading into account. This model considers the stress triaxiality and non-linearity of damage evolution, and it is developed to a fatigue damage accumulation rule in which the load sequence effect is also included. The stabilized structural response under thermomechanical loading motivates the use of uncoupled analysis approach making the model a fast tool suitable for design purposes in the costly and time-consuming field of thermomechanical fatigue life assessment. To demonstrate the capability and ease of use of this model for real industrial applications, the low-cycle thermal fatigue life of a stainless steel engine exhaust manifold which is in an early stage of design is assessed.

Low-Cycle Fatigue Life Prediction by a New Critical-Plane Method

2008 ◽  
Vol 385-387 ◽  
pp. 209-212
Author(s):  
Dan Jin ◽  
Jian Hua Wu ◽  
Yang Zhang
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Weight Function ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
304 Stainless Steel ◽  
Cycle Fatigue ◽  
Critical Plane ◽  
Plane Method ◽  
Rainflow Cycle Counting

A series of low-cycle fatigue experiments of axial-torsional loading of variable amplitudes were performed on the tubular specimens of 304 stainless steel. Two models of multiaxial low-cycle fatigue life, KBM and FS method, are evaluated based on the fatigue life data of 304 stainless steel. Rainflow cycle counting and the Liner Damage Rule are used to calculate fatigue damage. It was shown that the part prediction results are nonconservative for the two models. The life prediction is done again based on the weight function critical plane method for the two models. The prediction results are better by using the weight function critical plane method than the previous results for KBM model. But the prediction results are improved little for FS model in spite of the weight function critical plane method being used.

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