• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.145-148
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• 2006

Cold gas dynamic spray is a relatively new coating process by which coatings can be produced without significant heating during the process. Cold gas dynamic spray is conducted by powder sprayed by supersonic gas jet, and generally called the kinetic spray or cold-spray. Cold-spray was developed in Russia in the early 1980s to overcome the defect of thermal spray method. Its low process temperature can minimize thermal stress and also reduce the deformation of the substrate. Most researches on cold-spray have focused on micro scale coating, but our research team tried to apply this method to macro scale deposition. The macro scale deposition causes deformation of a thin substrate which is usually convex to the deposited side. In this research, the main cause of the deformation was investigated using 6061-T6 aluminum alloy and properties of deposited aluminum layer such as coefficient of thermal expansion, Elastic modulus, hardness, electric conductivity were measured. From the result of the analysis, it was concluded that compressive residual stress was the main reason of substrate deformation while CTE had little effect.

• Korean Journal of Computational Design and Engineering
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• v.15 no.6
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• pp.411-417
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• 2010

In this paper, the boom of a floating crane is modeled as a 3-dimensional elastic beam in order to analyze the dynamic response of the crane and its cargo. The boom is divided into more than two elements based on finite element formulation, and deformation of each element is expressed in terms of shape matrix and nodal coordinates. The equations of motion for the elastic boom consist of a mass matrix, a stiffness matrix, and a quadratic velocity vector that contains the gyroscopic and Coriolis forces. The size and complicity of the matrices increase in proportion with the number of elements. Therefore, it is not possible to derive the equations of motion explicitly for different number of elements. To overcome this difficulty, matrices for one 3-dimensional element are expressed with elementary sub-matrices. In particular, the quadratic velocity vector is derived as a product of a shape matrix and a 3-dimensional rotation matrix. By using the derived matrices, the equations of motion for the multi-element boom are automatically constructed. To verify the implementation of the elastic boom based on finite element formulation, we simulated a simple vibration of the elastic boom and compared the average deformation with the analytic solution. Finally, heave motion of the floating crane and surge motion of the cargo are presented as application examples of the elastic boom.

• Tribology and Lubricants
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• v.32 no.1
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• pp.1-8
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• 2016

This paper focuses on the thermal deformation induced preload change in the tilting pad journal bearing, using a three-dimensional (3D) thermo-hydro-dynamic (THD) approach. Preload is considered as a critical factor in designing the tilting pad journal bearing. The initial preload measured under nil external load and nil thermal gradient is influenced by two factors, namely, the thermal deformation and elastic deformation. Thermal deformation is due to a temperature distribution in the bearing pads, whereas the elastic deformation is due to fluid forces acting on the pads. This study focuses on the changes induced in preload and film clearance due to thermal deformation. The generalized Reynolds equation is used to evaluate the force of the fluid and the 3D energy equation is used to calculate the temperature of the lubricant. The abovementioned equations are combined by establishing a relationship between viscosity and temperature. The heat transfer within the bearing pads, the lubricant, and the spinning journal is calculated using the heat flux boundary condition. The 3D Finite Element Method (FEM) is used in modeling the (1) heat conduction in the spinning journal and bearing pads, (2) thermal gradient induced thermal distortion of the spinning journal and pads, and (3) viscous shearing, and heat conduction and convection in a thin film. This evaluation method has an increased fidelity, and it can prove to be a cost-effective tool that can be used by designers to predict the dynamic behavior of a bearing.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.2
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• pp.63-71
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• 2001

This paper introduces a method for calculation of dynamic stress occurring in flexible bodies of a moving multibody system by using commercial softwares DADS for dynamic analysis and MSC/NASTRAN for finite element analysis. Three methods for model transient response analysis of a flexible body are summarized. Elastic deformation of a flexible body can be described with normal modes and static modes composed of constraint modes and residual attachment modes. The deformation modes divided into fixed-interface modes and free-interface modes can be determined by using MSC/NASTRAN and selected for dynamic analysis. The dynamic results obtained from DADS are utilized to calculate dynamic stress by using mode-displacement method or mode-acceleration method of MSC/NASTRAN. As a numerical example of the analysis, we used a three dimensional slider-crank model with a flexible connecting rod.

• Structural Engineering and Mechanics
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• v.14 no.4
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• pp.455-472
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• 2002

The paper involves the study on the elastic and elasto-plastic stress wave propagation in the 1-D and 2-D solid media. The Smooth Particle Hydrodynamics equations governing the elastic and elasto-plastic large deformation dynamic response of solid structures are presented. The proposed additional stress points are introduced in the formulation to mitigate the tensile instability inherent in the SPH approach. Both incremental rate approach and leap-frog algorithm for time integration are introduced and the new solution algorithm is developed and implemented. Two examples on stress wave propagation in aluminium bar and 2-D elasto-plastic steel plate are included. Results from the proposed SPH approach are compared with available analytical values and finite element solutions. The comparison illustrates that the stress wave propagation problems can be effectively solved by the proposed SPH method. The study shows that the SPH simulation is a reliable and robust tool and can be used with confidence to treat transient dynamics such as linear and non-linear transient stress wave propagation problems.

• Advances in aircraft and spacecraft science
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• v.3 no.4
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• pp.471-502
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• 2016

This paper presents the dynamic instability analysis of un-damped elastically supported piezoelectric functionally graded (FG) beams subjected to in-plane static and dynamic periodic thermomechanical loadings with uncertain system properties. The elastic foundation model is assumed as one parameter Pasternak foundation with Winkler cubic nonlinearity. The piezoelectric FG beam is subjected to non-uniform temperature distribution with temperature dependent material properties. The Young's modulus and Poison's ratio of ceramic, metal and piezoelectric, density of respective ceramic and metal, volume fraction exponent and foundation parameters are taken as uncertain system properties. The basic nonlinear formulation of the beam is based on higher order shear deformation theory (HSDT) with von-Karman strain kinematics. The governing deterministic static and dynamic random instability equation and regions is solved by Bolotin's approach with Newmark's time integration method combined with first order perturbation technique (FOPT). Typical numerical results in terms of the mean and standard deviation of dynamic instability analysis are presented to examine the effect of slenderness ratios, volume fraction exponents, foundation parameters, amplitude ratios, temperature increments and position of piezoelectric layers by changing the random system properties. The correctness of the present stochastic model is examined by comparing the results with direct Monte Caro simulation (MCS).

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.369-377
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• 2018

In this article, buckling and free vibration of functionally graded (FG) nanobeams resting on elastic foundation are investigated by developing various higher order beam theories which capture shear deformation influences through the thickness of the beam without the need for shear correction factors. The elastic foundation is modeled as linear Winkler springs as well as Pasternak shear layer. The material properties of FG nanobeam are supposed to change gradually along the thickness through the Mori-Tanaka model. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. From Hamilton's principle, the nonlocal governing equations of motion are derived and then solved applying analytical solution. To verify the validity of the developed theories, the results of the present work are compared with those available in literature. The effects of shear deformation, elastic foundation, gradient index, nonlocal parameter and slenderness ratio on the buckling and free vibration behavior of FG nanobeams are studied.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.4
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• pp.271-277
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• 2017

In this paper, the amplitude and frequency dependent dynamic characteristics of the equivalent stiffness of a rubber bushing are investigated. A new mathematical model is proposed to explain the large deformation and size effect of a rubber bushing. The proposed model consists of elastic, viscous, and frictional stress components and the equivalent strain. The proposed model is verified using experimental results. The comparison shows that the proposed model can accurately predict the equivalent stiffness values of a rubber bushing under various magnitudes and frequencies. The developed model could be used to predict the dynamic equivalent stiffness of a rubber bushing in automotive engineering.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.5
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• pp.114-121
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• 2004

Recently, the finite element absolute nodal coordinate formulation (ANCF) was developed for the large deformation analysis of flexible bodies in multi-body dynamics. This formulation is based on the finite element procedures and the general continuum mechanics theory to represent the elastic forces. In this paper, a computation method of dynamic stress in flexible multi-body dynamics using absolute nodal coordinate formulation is proposed. Numerical examples, based on an Euler-Bernoulli beam theory, are shown to verify the efficiency of the proposed method. This method can be applied for predicting the fatigue life of a mechanical system. Moreover, this study demonstrates that structural and multi-body dynamic models can be unified in one numerical system.

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.179-181
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• 2003

The present study focuses on the effect of geometrical discontinuity, strength mismatch, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on the ductile crack initiation using two-parameter criterion. Fracture initiation testing has been conducted under static and dynamic loading using circumferentially notched round-bar specimens. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal elastic-plastic dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out.