• Steel and Composite Structures
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• v.30 no.1
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• pp.1-12
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• 2019

In this research, an efficient mixed mode I/II fracture criterion is developed for fracture investigation of orthotropic materials wherein crack is placed along the fibers. This criterion is developed based on extension of well-known Maximum Tensile Stress (MTS) criterion in conjunction with a novel material model titled as Equivalent Reinforced Isotropic Model (ERIM). In this model, orthotropic material is replaced with an isotropic matrix reinforced with fibers. A comparison between available experimental observations and theoretical estimation implies on capability of developed criterion for predicting both crack propagation direction and fracture instance, wherein the achieved fracture limit curves are also compatible with fracture mechanism of orthotic materials. It is also shown that unlike isotropic materials, fracture toughness of orthotic materials in mode $I(K)_{IC}{\mid})$ cannot be introduced as the maximum load bearing capacity and thus new fracture mechanics property, named here as maximum orthotropic fracture toughness in mode $I(K_{IC}{\mid}^{ortho}_{max})$ is defined. Optimum angle between crack and fiber direction for maximum load bearing in orthotropic materials is also defined.

• Earthquakes and Structures
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• v.27 no.2
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• pp.97-111
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• 2024

In this paper, buckling conditions and retrofitting of cylindrical steel water storage tanks with different roof types and wall thicknesses were investigated by using finite element method. Four roof types of cylindrical steel tanks which are open-top, flat-closed, conical-closed and torispherical-closed and three wall thicknesses of 4, 6 and 8 mm were considered in FE modeling of cylindrical steel tanks. The roof shapes significantly affect load distribution on the tank shell under the seismic action. Composite FRP materials are widely used for winding thin-walled cylindrical steel structures. The retrofitting efficiency of cylindrical steel water tank is tested under the seismic loading with the externally bonded CFRP laminates. In retrofitting of cylindrical steel tank, the CFRP composite material coating method was used to improve of seismic performance of cylindrical steel tanks. ANSYS software was used to analyze the cylindrical steel tanks and maximum equivalent (von-Mises) and directional deformation were obtained. Equivalent (von-Mises) stresses significantly decreased due to the coating of the tank shell with FRP composite material. In thin-walled steel structures, excessive stress causes buckling and deformations. Therefore, retrofitting led to decrease in stress, reductions in directional and buckling deformation of the open-top, flat-closed, conical-closed and torispherical-closed tanks.

• Fire Science and Engineering
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• v.31 no.1
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• pp.42-49
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• 2017

The present article reports the tracking characteristics of phenolic resin insulation material due to accelerated degradation. For assessing insulation degradation of the phenolic resin insulation material, experiment samples with equivalent years of 0, 10, 20, 30, and 40 years were produced by conducting accelerated degradation experiments using Arrhenius equation. Subsequently, tracking experiments according to KS C IEC 60112 standard were conducted for the experiment samples that were previously subjected to accelerated degradation. According to the measured results for tracking characteristics of phenolic resin subjected to accelerated degradation, upon dropping of 0.1% ammonium chloride, the risks were shown to increase by 1.38 times for the equivalent life of 10 years; 1.45 times for 20 years; 1.62 times for 30 years; and 1.94 times for 40 years based on the equivalent life of 0 year. Upon dropping of 0.01% ammonium chloride, the risks were shown to increase by 1.39 times for the equivalent life of 10 years; 1.52 times for 20 years; 1.99 times for 30 years; and 5.30 times for 40 years. According to the experimental results, the tracking risk was shown to be higher for longer-duration insulation degradation due to aging. In particular, the risk was observed to be greatly increased in the case of the equivalent life of 40 years. Therefore, it is proposed that the occurrence possibility and the risk of electric fires could be minimized through institutional preparation of recommended replacement period by considering risks such as insulation degradation, etc. due to aging.

• Transactions on Electrical and Electronic Materials
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• v.17 no.6
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• pp.311-316
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• 2016

Batteries are critical components of electric vehicles and energy storage systems. The connection of a battery to the power grid for charge and discharge greatly affects energy storage. Therefore, an accurate and easy-to-observe battery model should be established to achieve systematic design, simulation, and SOC (state of charge) estimations. In this review, several equivalent circuit models of representative significance are explained, and their respective advantages and disadvantages are compared to determine and outline their reasonable applications to Li-ion batteries. Numerous commonly used model parameter identification principles are summarized as well, and basic model verification methods are briefly introduced for the convenient use of such models.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.844-847
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• 2006

In this paper, the forced vibration of damped composite beam with I-type section was analyzed. The damping material was assumed to have complex Young's modulus. Damped composite beam structure could be modeled using equivalent beam elements with less D.O.F. rather than solid elements. Finite element method for 6 D.O.F. equivalent beam element was formulated and programmed using complex values. The results of frequency responses revealed good agreement with those of NASTRAN in both Euler beam model and Timoshenko beam model.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1061-1069
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• 2005

In part I of this papter Nonlinear Response Optimization using Equivalent Static Loads (NROESL) method/algorithm is developed to conduct optimization for nonlinear behavior structures. The method/algorithm is also verified to show its convergency and optimality. In this present paper, the NROESL algorithm is applied to several structural problems with geometric and/or material nonlinearity. Conventional optimization with sensitivity analysis using the finite difference method is also applied to the same examples. The results of the optimizations are compared. The proposed method is very efficient and derives good solutions.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.735-739
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• 2011

In this study, a chair with 5 or 6 legs was designed using the commercial program CATIA V5 in order to efficiently design considering the load conditions. In addition, the stress analysis and shape optimization were carried out using ANSYS Workbench for the chair consisting of stainless steel, aluminum alloys, magnesium alloys and structural steel. As a result, a chair with five legs showed the maximum equivalent stress at the end of the edge of the wheel parts and on the other hand, a chair with six legs showed the maximum equivalent stress at the corner of the connecting parts of the pillar and leg. In addition, the material and the weight was reduced by shape optimization for the chair model with 5 legs and maximum equivalent stress for stainless steel was found that greatly relaxed, compared with that of before shape optimization model.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.964-968
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• 2001

The refractory-lined pipe is used to protect the system from high-temperature of the internal flow. The property of the refractory has an effect upon the stress analysis for fluid catalyst cracking(FCC) unit piping design. The equivalent elastic modulus and density considering steel and refractory must be applied in the stress analysis of the system. In the research, the theoretical method to obtain the value of the equivalent property is introduced and then the parametric analysis is carried out to understand the characteristic of the material properties.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.1
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• pp.157-173
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• 2015

In the present study, the existing equivalent stain method is improved to make up for its weaknesses. The improved inherent strain model is built considering more sophisticated three dimensional constraints which are embodied by six cubic elements attached on three sides of a core cubic element. From a few case studies, it is found that the inherent strain is mainly affected by the changes in restraints induced by changes of temperature-dependent material properties of the restraining elements. On the other hand, the degree of restraints is identified to be little influential to the inherent strain. Thus, the effect of temperature gradients over plate thickness and plate transverse direction normal to welding is reflected in the calculation of the inherent strain chart. The welding deformation can be calculated by an elastic FE analysis using the inherent strain values taken from the inherent strain chart.

• Proceedings of the KIEE Conference
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• 2005.04a
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• pp.120-122
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• 2005

Magnetic field analysis of claw-pole type generator using equivalent circuit is presented in this paper. On the basis of 3D geometry and flux paths, equivalent magnetic circuit is designed and field analysis is performed by solving the circuit. Non-linear characteristic of material is considered for precise analysis results. 3D FEA is performed to verify analysis results, and flux densities in rotor and stator regions are compared. Calculated no-load back emf for field input voltage and speed are verified by experiment. Comparing to 3D FEA, presented method provides precise results with instant calculation time.