• Journal of the Korean Society for Precision Engineering
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• v.20 no.12
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• pp.142-147
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• 2003

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions such as high impact loading are required to provide appropriate safety assessment to varying dynamically leaded 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 ]ending conditions. In this paper, the dynamic deformation behavior of a brass under both high strain rate compressive loading conditions has been determined using the SHPB technique.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.347-350
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• 2005

A ship collision analysis by finite element method is performed considering the effects of mass and speed of ship and material and shape of structures to analyze the dynamic characteristics by ship collision. From this analysis, collision load-time history and inelastic deformation of ship and structures are obtained. Dynamic characteristics are different from each other according to interaction. between ship and structures. It seems that there are lots of factor to have effects on the ship-structures interaction. But because little information is available on the behavior of the inelastic deformation of materials and structures during the type of dynamic impacts associated with vessel impact, assumptions based on experience and sound engineering practice should be substituted. Therefore more researches on the interaction between ship and structures are required.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.42-47
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• 2004

Metallic glasses are amorphous meta-stable solids and are now being processed in bulk form suitable for structural applications including impact. Bulk metallic glasses have many unique mechanical properties such as high yield strength and fracture toughness, good corrosion and wear resistance that distinguish them from crystalline metals and alloys. However, only a few studies could be found mentioning the dynamic response and damage of metallic glasses under impact or shock loading. In this study, we employed a small explosive detonator for the dynamic indentation on a Zr-based bulk amorphous metal in order to evaluate the damage behavior of bulk amorphous metal under impact loading. These results were compared with those of spherical indentation under quasi-static and impact loading. The interface bonded specimens were adopted to observe the appearances of subsurface damage induced during indentation under different loading conditions.

• Earthquakes and Structures
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• v.9 no.5
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• pp.1045-1067
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• 2015

A performance-based design (PBD) procedure, initially proposed for the seismic design of buildings, is tailored herein to the structural configurations commonly adopted in bridges. It aims at the efficient design of bridges for multiple performance levels (PLs), achieving control over a broad range of design parameters (i.e., strains, deformations, ductility factors) most of which are directly estimated at the design stage using advanced analysis tools (a special type of inelastic dynamic analysis). To evaluate the efficiency of the proposed design methodology, it is applied to an actual bridge that was previously designed using a different PBD method, namely displacement-based design accounting for higher mode effects, thus enabling comparison of the alternative PBD approaches. Assessment of the proposed method using nonlinear dynamic analysis for a set of spectrum-compatible motions, indicate that it results in satisfactory performance of the bridge. Comparison with the displacement-based method reveals significant cost reduction, albeit at the expense of increased computational effort.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.5
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• pp.46-54
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• 2004

A cutting force model predicting the dynamic force induced by the axial vibration of it plate in face milling is introduced. When a plate face is milled, deformation in tool axial direction is considerable. Therefore, cutting forces are affected by not only inner-outer modulation in feed direction but also by axial deformation. A PTP (peak-to-peak) diagram made by the simulated dynamic force model is evaluated. The stability of the face milling process such as the chatter outset, and the stable cutting region can be simply estimated. Simulation results are compared with that of experiment.

• Steel and Composite Structures
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• v.50 no.2
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• pp.135-148
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• 2024

This paper analytically investigates the free vibration analysis of functionally graded-carbon nanotube reinforced composite (FG-CNTRC) plates by dynamic stiffness method (DSM). The properties of CNTRC are determined with the extended rule of mixture. The governing differential equations of motion based on the first-order shear deformation theory of CNTRC plate are derived using Hamilton's principle. The FG-CNTRC plates are studied for a uniform and two different distributions of carbon nanotubes (CNTs). The accuracy and performance of the DSM are compared with the results obtained from closed closed-form and semi-analytical solution methods in previous studies. In this study, the effects of boundary condition, distribution type of CNTs, plate aspect ratio, plate length to thickness ratio, and different values of CNTs volume fraction on the natural frequencies of the FG-CNTRC plates are investigated. Finally, various natural frequencies of the plates in different conditions are provided as a benchmark for comparing the accuracy and precision of the other analytical and numerical methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.175-181
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• 2010

This paper presents the dynamic analysis method for estimating the performance of flat-type blades in wiper systems. The blade has nonlinear characteristics since the rubber is a hyper-elastic material. Thus, modal coordinate and absolute nodal coordinate formulations were used to describe the dynamic characteristic of the blade. The blade was structurally analyzed to find the bending characteristics of the cross section of the blade. According to the analysis results, the blade section is divided into three deformation bodies: rigid, small, and large. For the small deformation body, the modal coordinate formulation is used, while the absolute nodal coordinate formulation is used for the large deformation body. To verify the dynamic analysis result, an experiment was performed. The simulation and experiment results were compared to verify the flexible multi-body dynamic model.

• Transactions of Materials Processing
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• v.33 no.5
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• pp.348-353
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• 2024

The S355NL steel has garnered attention as a structural material for applications in extremely challenging environments owing to its excellent mechanical properties. This study investigated the hot deformation behavior of S355NL steel through compression tests conducted in a temperature range of 900-1200℃ and a strain rate range of 10^-3-1 s^-1 to explore the optimal processing parameters. The flow behaviors consisted of an initial rapid increase and subsequent plateau with a marginal decrease in stress. This phenomenon was interpreted in terms of microstructural evolution, such as dislocation density and dynamic recrystallization. The efficiency of power dissipation and instability domains were derived using the dynamic material model based on the compression test dataset, providing a series of processing maps. In contrast to conventional processing maps plotted for a single strain value, this study has established ten maps at a strain interval of 0.1. This approach allowed for the consideration of continuously variable strain parameters, which is inherent to an actual metal-forming process. The efficiency of power dissipation was strongly governed by the high temperatures (≥ 1100℃). The strain rates barely affected the efficiency, but it primarily contributed to the instability domains. The application of high strain rates (≥ 10^-1s^-1) generated a region of negative instability due to the absence of dynamic recrystallization and the presence of cracks at grain boundaries.

• Transactions of Materials Processing
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• v.10 no.3
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• pp.206-213
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• 2001

Dynamic deformation of metallic materials mostly accompanies substantial amounts of deformation heat. Since the flow stress of deformation is sensitive to temperature, implication of heat due to plastic work is essential to the evaluation of constitutive relations. In this study, a series of compression tests were conducted for SAF 2507 super duplex stainless steel at various temperatures and strain rates. The accumulation of plastic work was calculated through numerical integration and converted into the elevation of temperature. Subsequent logarithmic interpolation deduced isothermal flow surfaces, which were primary input data of finite element analysis. Simple closed die forging process was analyzed and optimized with commercial FEM code applying both raw and calibrated material database. The effect of accounting deformation heat was more noticeable in high-speed forming process.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.195-198
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• 2000

It can be acquired the high effective productivity through of high speed, precision of machine tools, and then, machine tools will be got a competitive power. Industrially advanced countries already developed that the high speed feed is 60m/min using the high speed ball screw. Also, a lot of problems have happened the feed drive system. It is necessary to study about the characteristics of thermal deformation played a more critical role than static stiffness and dynamic rigidity in controlling the level of machining accuracy. In spite of the improving the thermal deformation characteristics of machine tools at the design stage, there are always some residual errors that have to be compensated for during machining. In this study, thermal deformation error automated compensation device with multiple linear regression is proposed that thermal deformation error can be eliminated at the machining stage. The developed device has been practically applied to the feed drive unit.