• Proceedings of the KSME Conference
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• 2004.11a
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• pp.308-313
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• 2004

SP test has been confirmed the availability, however the application of SP test is hampered because the relation of stress-strain and load-displacement is not determined definitely. This study suggested an evaluation technique of plastic flow characteristic for X20CrMoV121 steel weldment through inverse analysis using SP test and finite element analysis(FEA). From the result, good agreement was found in load-displacement curves obtained from SP test and FEA. Also, The behavior of load-displacement curve from FEA show a rule that load is increase with increasing K(strength coefficient) and displacement is increase with increasing n(work hardening index). From the inverse analysis, true stress-strain curve could be obtained for each local structure of weldment. And the CGHAZ and WM, which showed lower load- displacement behavior, have smaller work hardening index, while FGHAZ have the largest index.

• Structural Engineering and Mechanics
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• v.45 no.4
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• pp.471-494
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• 2013

In this paper, identification of isotropic and orthotropic linear elastic material constitutive parameters has been demonstrated by a FEA-free energy-based inverse analysis method. An important feature of the proposed method is that it requires no finite element (FE) simulation of the tested material. Full-field displacements calculated using digital image correlation (DIC) are used to compute DIC stress fields enforcing the equilibrium condition and DIC strain fields using interpolation functions. Boundary tractions and displacements are implicitly recast into an objective function that measures the energy residual of external work and internal elastic strain energy. The energy conservation principle states that the residual should be zero, and so minimizing this objective function inversely identifies the constitutive parameters. Synthetic data from simulated testing of isotropic materials and orthotropic composite materials under 2D plane stress conditions are used for verification of the proposed method. When identifying the constitutive parameters, it is beneficial to apply loadings in multiple directions, and in ways that create non-uniform stress distributions. The sensitivity of the parameter identification method to noise in both the measured full-field DIC displacements and loadings has been investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.4
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• pp.393-400
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• 2011

In this study, a procedure for the inverse estimation of the fatigue life parameters of springs which utilize the field fatigue life test data is proposed to replace real test with the FEA on fatigue life prediction. The Bayesian approach is employed, in which the posterior distributions of the parameters are determined conditional on the accumulated life data that are routinely obtained from the regular tests. In order to obtain the accurate samples from the distributions, the Markov chain Monte Carlo (MCMC) technique is employed. The distributions of the parameters are used in the FEA for predicting the fatigue life in the form of a predictive interval. The results show that the actual fatigue life data are found well within the posterior predictive distributions.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.9
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• pp.972-981
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• 2008

The blower which is installed in a FCEV(fuel cell electric vehicle) may cause noise due to misalignment and unbalance of mechanical components that rotate at high speed. One of the key points in efforts to minimize the noise radiation from a blower is the knowledge of the main radiating component and the relation between the surface vibration of a blower and the sound pressure. In this research, the blower model is developed based on FEM(finite element method). FE(finite element) model is reliable by correlation of frequencies and MAC(modal assurance criterion) values between EMA(experimental modal analysis) and FEA(finite element analysis). This model is applied to predict the vibration of a blower by using inverse force identification method and predict the radiating noise by using BEM(boundary element method). Comparing the frequencies of resonance and those mode shapes between EMA and FEA, a structural modification of the FE model is evaluated for reducing the parameters of the blower noise.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1377-1384
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• 2010

The objective of this study is to determine the best material model that represents the deformation behavior of the Sn37Pb solder alloy accurately. First, a specimen is fabricated and subjected to a thermal cycle with temperatures ranging from the room temperature to $125^{\circ}C$. An experiment is conducted to examine deformation by Moire interferometry. Three different constitutive equation models are used in the finite element analysis (FEA) of the thermal cycle. In order to minimize the difference between the FEA results and the experimental results, the material parameters of the solder alloy are considered to be unknown and are determined by conducting optimization. As a result of the study, the Anand model is found to represent the deformation behavior of the solder most accurately.

• Structural Engineering and Mechanics
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• v.32 no.5
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• pp.667-683
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• 2009

FE model-based dynamic analysis has been widely used to predict the dynamic characteristics of civil structures. In a physical point of view, an FE model is unavoidably different from the actual structure as being formulated based on extremely idealized engineering drawings and design data. The conventional model updating methods such as direct method and sensitivity-based parameter estimation are not flexible for model updating of complex and large structures. Thus, it is needed to develop a model updating method applicable to complex structures without restriction. The main objective of this paper is to present the model updating method based on the hybrid genetic algorithm (HGA) by combining the genetic algorithm as global optimization method and modified Nelder-Mead's Simplex method as local optimization method. This FE model updating method using HGA does not need the derivation of derivative function related to parameters and without application of complicated inverse analysis methods. In order to allow its application on diversified and complex structures, a commercial FEA tool is adopted to exploit previously developed element library and analysis algorithms. Moreover, an output-level objective function making use of measurement and analytical results is also presented to update simultaneously the stiffness and mass of the analysis model. The numerical examples demonstrated that the proposed method based on HGA is effective for the updating of the FE model of bridge structures.