• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1560-1565
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• 2003

Tapping mode atomic force microscopy (TM-AFM) utilizes the dynamic response of a resonating probe tip as it approaches and retracts from a sample to measure the topography and material properties of a nanostructure. We present recent results based on nonlinear dynamical systems theory, computational continuation techniques and detailed experiments that yield new perspectives and insight into AFM. A dynamic model including van der Waals and Derjaguin-Muller-Toporov (DMT) contact forces demonstrates that periodic solutions can be represented with respect to the approach distance and excitation frequency. Turning points on the surface lead to hysteretic amplitude jumps as the tip nears/retracts from the sample. Experiments are performed using a tapping mode tip on a graphite sample to verify the predictions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.393-398
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• 2002

Rubber isolator has properties that can adjust easily stiffness and can be formed various shape. Also, it has high damping and is effective about structure-borne noise at high frequency range, So, rubber mount has widely used to isolate vibration at industrial equipment and construction field. However, rubber material is nonlinear and require enough consideration about shape factor whenever it is designed. The purpose of this paper is to develop conical rubber mount using compression and shear elasticity. The first, the dimension of mount is calculated by theoretical analysis considering design condition and static characteristics have been analyzed by FEM method. In addition, the fatigue test of rubber mount is performed to get reliability for product life and dynamic stiffness test is executed to get dynamic magnification factor. Finally, transmissibility test of vibration isolator has been carried out to suggest normal quantity data about vibration isolation.

• Design & Manufacturing
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• v.2 no.2
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• pp.1-5
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• 2008

Mechanical properties of the materials used for mold and industrial machinery under high strain rate loading conditions such as high impact loading are required to provide appropriate safety assessment to varying dynamically loaded mechanical structures. The Split Hopkinson Pressure Bar(SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, the dynamic deformation behavior of a brass under high strain rate compressive loading conditions has been determined using the SHPB technique.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.6
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• pp.83-89
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• 2002

The purpose of this study is to obtain the basic data for the development of construction material products using non-active Hwangto and stone dust. The test result shows that the unit weight is in the range of 2,050~2,135 kg/m$^3$, the compressive strength is in the range of 107~451 kgf/cm$^2$, the bending strength is in the range of 23~81 kgf/cm$^2$ and the dynamic modulus is in the range of 137$\times$10$^3$~318$\times$10$^3$ kgf/cm$^2$. Also, it is decreased with increase using the non-active Hwangto and stone dust, respectively. The incorporation of non-active Hwangto for cement is possible to 40% in strength.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.525-527
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• 2008

N-Type $SbI_3$-doped $95%{Bi_2}{Te_3}-5%{Bi_2}{Se_3}$ compounds were prepared by a gas atomization and Magnetic Pulsed Compaction process. The dynamic recrystallization and thermoelectric properties of the MPCed bulks with consolidation temperatures and times were investigated by a combination of microscopy, XRD and thermoelectric property testing. The microstructure of MPCed bulk shows homogeneous and fine distribution through consolidated bulks due to dynamic recrystallization during hot MPC. This research presented the challenges toward the successful consolidation of thermoelectric powder using magnetic pulsed compaction (MPC).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.852-855
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• 2005

Structural Dynamic Modification(SDM) is a technique to improve structure's dynamic characteristics by adding and removing substructures or changing material properties and shape of structures. This paper describes SDM techniques applied to a large structure with too many DOFs. The goal of this SDM technique is to modify a targe structure efficiently for its natural frequencies to avoid excitation frequencies. In this case, models reduced by Component Mode Synthesis(CMS) method that is a coupling technique are used to analyze a large structure efficiently. This paper considers a helicopter deck model with 55,000 DOFs as an application.

• Structural Engineering and Mechanics
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• v.3 no.3
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• pp.273-287
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• 1995

Stochastic response of systems to random excitation can be estimated by direct integration methods in the time domain such as the stochastic central difference method (SCDM). In this paper, the SCDM is applied to compute the variance and covariance in response of linear and nonlinear structures subjected to random excitation. The accuracy of the SCDM is assessed using two-DOF systems with both deterministic and random material properties excited by white noise. For the former case, closed-form solutions can be obtained. Numerical results also are presented for a simply supported geometrically nonlinear beam. The stiffness of this beam is modeled as a random field, and the beam is idealized by the stochastic finite element method. A perturbation technique is applied to formulate the equations of motion of the system, and the dynamic structural response statistics are obtained in a time domain analysis. The effect of variations in structural parameters and the numerical stability of the SCDM also are examined.

• Advances in nano research
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• v.13 no.1
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• pp.47-61
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• 2022

The present research investigates the dynamic behavior of a rotating functionally graded (FG) nonlocal cylindrical beam. The cylindrical beam is mathematically modeled via third-order beam theory linked with nonlocal strain gradient theory. The tube structure is made of functionally graded materials composed of Aluminum oxide coated on the Nickel, which the mechanical properties vary in the tube radius direction according to the power law. The bending harmonic force is applied in the tube length middle. The nonlocal spinning equations of the tube are derived via the energy method of the Hamilton principle, and they are solved via a robust numerical procedure for different boundary conditions. The main application of the rotating nanostructures is for the production of small-scale motors and devices and the drug-delivery application, the presented results can help the researcher have a better view regarding the different conditions.

• Structural Engineering and Mechanics
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• v.89 no.5
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• pp.437-452
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• 2024

Functionally graded materials (FGMs) have gained substantial attention from researchers due to their exceptional strength and thermal resistance. Their utilization in the aviation and automobile industries has significantly improved the efficiency of various structural components. Moreover, stiffened panels find wide applications in aerospace and automobile structures and these panels are frequently exposed to extreme environments. It is from this perspective that our research is focused on analysing the vibroacoustic response of stiffened functionally graded panels subjected to external dynamic excitations in a thermal environment. In the present research work, a finite element model is developed to conduct the dynamic analysis of functionally graded stiffened panels using the first-order shear deformation theory. Subsequently, a boundary element based model is also developed and coupled with the finite element model to investigate the sound radiation behaviour of those panels in a thermal environment. The material properties of FG stiffened panels are considered as temperature dependent, while the thermal environment is assumed to be acting as linearly varying through the panel's thickness. The present investigation aim to compare the vibroacoustic responses of different panels due to stiffener orientations, material compositions, power law indices and plate thicknesses at various temperatures. The research findings highlight the significant impact of addition of stiffeners, its orientation and material compositions on the sound radiation characteristics of these panels under thermal environments. The present numerical model can easily be employed for analysing the sound radiation behaviour of other types of flat or curved stiffened panels having arbitrary geometry and boundary conditions.

• Journal of the Korean Society for Railway
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• v.17 no.1
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• pp.43-51
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• 2014

In the earth structures of railways, large coarse granular materials are widely used as fill materials. However, experimental studies that consider the dynamic properties of these coarse granular materials have rarely been carried out in Korea due to the lack of a large scale test apparatus in this country. In this study, large scale cyclic triaxial tests were carried out for materials such as reinforced roadbed (subballast, graded crushed stone), transition zone gravel, and the upper subgrade of a railway. These specimens were prepared according to certain conditions (dry unit weight, grain size distribution, and so on) specified in the Korea railroad design standard. Based on these large triaxial test results, normalized shear modulus and damping ratio curves according to small strain level are suggested. A model and coefficients for each material are also proposed.