• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.6
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• pp.64-73
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• 2004

A fatigue damage accumulation model based on the continuum damage mechanics theory was developed where modulus decay ratios in tension and shear were used as indicators for damage variables D. In the model, the damage variables are considered to be second-order tensors. Then, the maximum principal damage variable, $D^*$ is introduced. According to the similarity to the principal stress, $D^*$ is obtained as the maximum eigen value of damage tensor [D]. Under proportional tension and torsion loadings, fatigue lives were satisfactorily predicted at any combined stress ratios using the present model in which the Fatigue characteristics only under uniaxial tension and pure torsion loadings were needed. Fatigue life prediction under uniaxial tension and pure torsion loadings, was performed based on the damage mechanics using boundary element method.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.04a
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• pp.352-361
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• 2003

A fatigue damage accumulation model based on the continuum damage mechanics theory was develope(1 where modules decay ratios in tension and shear on used as indicators for damage variables D . In the model, the damage variables are considered to be second-order tensors. Then the maximum principal damage variable, $D^*$ is introduced According to the similarity to the Principal stress, $D^*$ is obtained as the maximum eigen value of damage tensor [D']. Under proportional tension and torsion loadings, fatigue lives were satisfactorily predicted at any combined stress ratios using the present model in which the fatigue characteristics only under uniaxial tension and pure torsion loadings on needed. Fatigue life prediction under uniaxial tension and pure torsion loadings, was performed based on the damage mechanics using boundary element method.

• Structural Engineering and Mechanics
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• v.17 no.5
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• pp.655-670
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• 2004

This paper aims to evaluate the effect of typhoons on fatigue damage accumulation in steel decks of long-span suspension bridges. The strain-time histories at critical locations of deck sections of long-span bridges during different typhoons passing the bridge area are investigated by using on-line strain data acquired from the structural health monitoring system installed on the bridge. The fatigue damage models based on Miner's Law and Continuum Damage Mechanics (CDM) are applied to calculate the increment of fatigue damage due to the action of a typhoon. Accumulated fatigue damage during the typhoon is also calculated and compared between Miner's Law and the CDM method. It is found that for the Tsing Ma Bridge case, the stress spectrum generated by a typhoon is significantly different than that generated by normal traffic and its histogram shapes can be described approximately as a Rayleigh distribution. The influence of typhoon loading on accumulative fatigue damage is more significant than that due to normal traffic loading. The increment of fatigue damage generated by hourly stress spectrum for the maximum typhoon loading may be much greater than those for normal traffic loading. It is, therefore, concluded that it is necessary to evaluate typhoon induced fatigue damage for the purpose of accurately evaluating accumulative fatigue damage for long-span bridges located within typhoon prone regions.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.193-198
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• 2001

The feasibility of the acoustic emission technique in predicting the residual fatigue life of STS304 stainless steel is presented. Acoustic emission was continuously monitored during the fatigue tests. Considerable acoustic emission occurred during the first few cycles. Acoustic Emission increased rapidly at about 90% of the fatigue life, clear and ample warning of impending fatigue failure was observed. Fatigue damage accumulation was evaluated in terms of an AE cumulative counts. The AE cumulative counts may be taken as an indicator of fatigue cumulative damage. Fatigue damages corresponding to 20, 40, 60 and 80% of the total life were induced at a cyclic stress amplitude. The specimens with and without fatigue damage were subjected to tensile tests. In tensile tests, the total cumulative counts were reduced with increasing fatigue damage. It was observed that the residual tensile strength of material did not change significantly with prior cyclic loading damages.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.79-84
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• 2003

A fictitious crack model was used to analyze fatigue crack growth under the influence of residual stress. In the fictitious crack model, crack is represented in terms of the separation of two adjacent interfaces and the constitutive equation between the separation and traction is assumed. The effect of fatigue loading was included in the constitutive equation by considering damage accumulation in the cohesive zone. To investigate the effect of the residual stress on the fatigue crack growth, we calculated the residual stress distribution due to transient heat flux to the specimen by finite element method. Fatigue crack growth was simulated by the fictitious crack model with repeated loading. The mode-I crack growth rates were compared for the cases with and without the compressive residual stress around the crack tip. It was observed that the mode-I crack growth can be suppressed by compressive residual stress.

• Structural Engineering and Mechanics
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• v.44 no.4
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• pp.417-429
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• 2012

Taking the superficial temperature increment as the major fatigue damage indicator, the infrared thermography was used to predict fatigue parameters (fatigue strength and S-N curve) of welded joints subjected to fatigue loading with a high mean stress, showing good predictions. The fatigue damage status, related to safety evaluation, was tightly correlated with the temperature field evolution of the hot-spot zone on the specimen surface. An energetic damage model, based on the energy accumulation, was developed to evaluate the residual fatigue life of the welded specimens undergoing cyclic loading, and a good agreement was presented. It is concluded that the infrared thermography can not only well predict the fatigue behavior of welded joints, but also can play an important role in health detection of structures subjected to mechanical loading.

• Journal of Aerospace System Engineering
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• v.3 no.4
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• pp.27-34
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• 2009

This paper deals with the lifetime prediction of Aircraft Flaperon Joint made of AISI 4130 steel. Reviews are performed on the published damage models at first. And three different damage models are used for predicting the fatigue life of the structure subjected to variable amplitude fatigue loading. These models require no increase in complexity of use, nor do they require additional material property or mission loading information to achieve the improved accuracy. Finally a comparison among the fatigue results is performed. It is observed that the Miner's rule could predict longer life than other cumulative damage models which take into account loads below the endurance limit.

• Progress in Superconductivity and Cryogenics
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• v.3 no.1
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• pp.1-5
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• 2001

In order to investigate the effect of fatigue damage on the properties of RRR in this study. fatigue tests at room temperature and residual resistivity measurement tests at 12K were carried out using annealed 9 strand Cu-Ni/NbTi/Cu composite cables Through fatigue tests of NbTi composite cables. a conventional S-N curve could be obtained even though there existed a possibility of fretting among strands, From the resistivity measurement of a NbTi strand after fatigue test, it was found that the RRR of xii·gin strand for annealed cables was 3 times more than that for as-received one. With increasing of fatigue cycles at a sress amplitude level. the RRR decreased. which was resulted from the accumulation of damage such as lattice defects and dislocation within the Cu stabilizer.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.3
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• pp.248-254
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• 2015

The strength and fatigue life of Satin and Twill-woven CF/epoxy composite(CFRP) have been investigated. Damage mechanism fatigue method has been used to assess fatigue damage accumulation. It is based on measured residual stiffness and residual strength of carbon-fiber reinforced plastic(CFRP) laminates under cyclic loading. Fatigue damage evolution in composite laminates and predict fatigue life of the laminates were simulated by finite element analysis(FEA) method. The stress analysis was carried out in MSC patran/Nastran. A modified Hashin's failure criterion di rmfjapplied to predict the failure of the experimental data of fatigue life but a Ye-delamination criterion was ignored because of 2D modeling. Almost linear stiffness and strength degradation were observed during most of the fatigue process. These stress distribution data were adopted in the simulation to simulate fatigue behavior and estimate life of the laminates. From the results, the predicted fatigue life is more conservatively estimated than the experimental results.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2000.02a
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• pp.104-108
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• 2000

In this study, the fatigue test at room temperature and residual resistivity measurement test at 12K were carried out, respectively, using a 0 strand Cu-Ni/NbTi/Cu composite cable, in order to investigate how the annealing treatment effects on critical properties due to fatigue damage. Through a fatigue test of a 0 strand Cu-Ni/NbTi/Cu composite cables, a conventional S-N curve was obtained even though there existed a possibility of fretting among strands. From the resistivity measurement of a NbTi strand after fatigue tests, it was found that the RRR for annealed cables was 3 times more than that for as-received one, but with increase of the repeated number the RRR decreased which was resulted from the accumulation of damage such as lattice defects dislocation within the Cu stabilizer.