• 대한기계학회논문집
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• 제17권10호
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• pp.2483-2490
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• 1993

This paper presents a systematic formulation for the kinematic and dynamic analysis of flexible multibody systems. The system equations of motion are derived in terms of relative and elastic coordinates using velocity transformation technique. The position transformation equations that relate the relative and elastic coordinates to the Cartesian coordinates for the two contiguous flexible bodies are derived. The velocity transformation matrix is derived systematically corresponding to the type of kinematic joints connecting the bodies and system path matrix. This matrix is employed to represent the equations of motion in relative coordinate space. Two examples are taken to test the method developed here.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1154-1158
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• 2003

Finite element analysis of welding processes, which entail phase evolution, heat transfer and deformations, is considered in this paper. Attention focuses on numerical implementation of the thermo-elastic-plastic constitutive equation proposed by Leblond in consideration of the transformation plasticity. Based upon the multiplicative decomposition of deformation gradient, hyperelastic formulation is employed for efficient numerical integration, and the algorithmic consistent moduli for elastic-plastic deformations including transformation plasticity are obtained in the closed form. The convergence behavior of the present implementation is demonstrated via a couple of numerical examples.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.334-336
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• 2009

An elastic-plasticity model during the austenitic decomposition was derived and implemented to incorporate the two important deformation behaviors observed during the phase transformations: the volumetric strain and transformation induced plasticity due to the temperature change and phase transformation. To obtain transformed phase volume fractions during cooling, the fourth order Runge-Kutta method was used to solve the Kirkaldy's phase kinetics model which is function of temperature, austenitic grain size and chemical composition. The volumetric strain was calculated by considering the densities of constituent phases, while the transformation induced plasticity was based on the micro-plasticity due to the volume mismatch between soft austenitic phase and other harder phases. The constitutive equations were implemented into the implicit finite element software and a simple boundary value problem was chosen as a model problem to validate the effect of transformation plasticity on the deformation behavior of steel under cooling from high temperature. It was preliminary concluded that the transformation plasticity plays a critical role in relaxing the developed stress during forming and thus reducing the magnitude of springback.

• 한국산업융합학회 논문집
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• 제25권6_2호
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• pp.1055-1062
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• 2022

In this study, the mechanical properties of 80% cold-rolled austenitic 316L stainless steel were evaluated using specimens subjected to reverse transformation at 500-750℃ for 20 minutes and reverse transformation at 700℃ for 2-60 minutes. Also, for the elastic wave obtained from the tensile test, the dominant frequency according to the reverse transformation condition was investigated by time-frequency analysis. The SEM image of the 80% cold-rolled material was transformed into martensite and showed line and cross shapes. The TEM image showed that line shapes were shown at the grain, and grain boundary of martensite. The higher the heat treatment temperature and the longer time, the larger the grain. Tensile strength decreased as the heat treatment temperature and time increased, but elongation increased. Hardness was proportional to tensile strength. This is because the grain with different directions showed the same direction due to reverse transformation. The dominant frequency was decreased and then increased as the temperature and time increased. This is because the direction of the grain is different at a low temperature and the same direction is shown at a high temperature.

• 대한의용생체공학회:의공학회지
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• 제28권2호
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• pp.169-173
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• 2007

During laser irradiation, mechanically deformed cartilage undergoes a temperature dependent phase transformation resulting in accelerated stress relaxation. Clinically, laser-assisted cartilage reshaping may be used to recreate the underlying cartilaginous framework in structures such as ear, larynx, trachea, and nose. Therefore, research and identification of the biophysical transformations in cartilage accompanying laser heating are valuable to identify critical laser dosimetry and phase transformation of cartilage for many clinical applications. quasi-elastic light scattering was investigated using Ho : YAG laser $(\lambda=2.12{\mu}m\;;\;t_p\sim450{\mu}s)$ and Nd:YAG Laser $(\lambda=1.32{\mu}m\;;\;t_p\sim700{\mu}s)$ for heating sources and He : Ne $(\lambda=632.8nm)$ laser, high-power diode pumped laser $(\lambda=532nm)$, and Ti : $Al_2O_3$ femtosecond laser $(\lambda=850nm)$ for light scattering sources. A spectrometer and infrared radiometric sensor were used to monitor the backscattered light spectrum and transient temperature changes from cartilage following laser irradiation. Analysis of the optical, thermal, and quasi-elastic light scattering properties may indicate internal dynamics of proteoglycan movement within the cartilage framework during laser irradiation.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.151-154
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• 2001

Shape memory alloy (SMA) has demonstrated its potentials for various smart structure applications. SMA wires undergo a reversible phase transformation from martensite to austenite as temperature increases. This transformation leads to shape recovery and associated recovery strains. If SMA actuators are embedded off the neutral surface and are oriented in arbitrary angles with respect to a beam axis, then the beam bends and twists due to the coupling effects of recovery strains activated. In this study, the bending and twisting of a SMA/Composite beam were controlled by both electric resistive heating and passive elastic tailoring. 3-dimensional finite element formulations were derived and validated to analyze the responses of the SMA/Composite beam. Numerical results show that the shape of the SMA/Composite beam can be controlled by judicious choices of control temperatures, SMA angles, and elastic tailoring.

• Structural Engineering and Mechanics
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• 제44권3호
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• pp.267-288
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• 2012

Free vibration analysis of arbitrary quadrilateral thick plates with internal columns and elastic edge supports is presented by using the powerful pb-2 Ritz method and Reddy's third order shear deformation plate theory. The computing domain of arbitrary quadrilateral planform is mapped onto a standard square form by coordinate transformation. The versatile pb-2 Ritz functions defined by the product of a two-dimensional polynomial and a basic function are taken to be the admissible functions. Substituting these displacement functions into the energy functional and minimizing the total energy by differentiation, leads to a typical eigenvalue problem, which is solved by a standard eigenvalue solver. Stiffness and mass matrices are numerically integrated over the plate by using Gaussian quadrature. The accuracy and efficiency of the proposed method are demonstrated through several numerical examples by comparison and convergency studies. A lot of numerical results for reasonable natural frequency parameters of quadrilateral plates with different combinations of elastic boundary conditions and column supports at any locations are presented, which can be used as a benchmark for future studies in this area.

• 소성∙가공
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• 제20권5호
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• pp.350-356
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• 2011

Shape memory alloys(SMAs) exhibit pseudoelastic behavior, characterized by the recovery of an original shape even after severe deformation, during loading and unloading within appropriate temperature regimes. The distinctive mechanical behavior is associated with stress-induced transformation of austenite to martensite during loading and reverse transformation to austenite upon unloading. To develop a material model for SMAs, it is imperative to consider the difference in moduli of active phases. For example, the Young’s modulus of the martensite is one-third to one half of that of the austenite. The model proposed herein is a modification of the one proposed recently by Ho[17]. The prediction of the behavior of SMAs during unloading before the onset of reverse transformation was improved by introducing a new internal state variable incorporating the variation of the elastic modulus.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.604-607
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• 2005

The free vibration of solid circular plates has been studied using the differential transformation method(DTM). The effects such as mass at edge and elastic restraints have been considered. In order to avoid the singularity problem at the solid circular center two regularity conditions were applied with respect to the number of circumferential nodal line. The non-dimensional natural frequencies of the general circular plates were obtained for various boundary conditions. The results obtained by this method were compared with previous works. DTM showed fast convergency, accuracy, efficiency and validity in solving vibration problem of general circular plates.

• Structural Engineering and Mechanics
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• 제87권2호
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• pp.165-172
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• 2023

This paper presents a novel method for modeling elastic wave propagation in long beams. The proposed method derives a solution for the transient transverse displacement of the beam's neutral axis without assuming the separation of variables (SV). By mapping the governing equation from the space domain to the frequency domain using Fourier transformation (FT), the transverse displacement function is determined as a convolution integral of external loading functions and a combination of trigonometric and Fresnel functions. This method determines the beam's response to general loading conditions as a linear combination of the analytical response of a beam subjected to an abrupt localized loading. The proposed solution method is verified through finite element analysis (FEA) and wave propagation patterns are derived for tone burst loading with specific frequency contents. The results demonstrate that the proposed solution method accurately models wave dispersion, reduces computational cost, and yields accurate results even for high-frequency loading.