• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.42-50
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• 2005

This paper presents an ultra precision machining system using a high sensitive force sensing module to measure machining forces and penetration displacement in a tip-based nanopatterning. The force sensing module utilizes a leaf spring mechanism and a capacitive displacement sensor and it has been designed to provide a measuring range from 80 ${\mu}N$ to 8 N. This force sensing module is mounted on a PZT driven in-feed motion stage with 1 nm resolution. The sample can be moved by X-Y scanning motion stage with 5 nm resolution. In nano indentation experiments and patterning experiments, the machining forces were controlled and monitored by the force sensing module. Then, the patterned samples were measured by AFM. Experimental results demonstrated that the developed system can be used as an effective device in nano indentation and nanopatterning operation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.168-174
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• 1998

In the present study, a method for measuring the relative density by the hardness measurement was proposed for sintered metal powder compacts. It is based on the indentation force equation, by which the relative density is related with the hardness, that was obtained by the finite element analysis of rigid-ball indentation on sintered metal powder compacts. For verifying the method, it was applied to prediction of density distributions in sintered and sintered-and-forged Fe-0.5%C-2%Cu powder compacts.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.06a
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• pp.743-744
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• 2007

• Journal of Welding and Joining
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• v.23 no.3
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• pp.40-46
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• 2005

Air gun has been one of the good tools to press two sheet metals. However, it is not easy to control the acting force precisely. A Servo-gun is a good tool to control the acting force on the workpiece comparing with the air gun. Servo-gun has a higher tensile shear strength and lower indentation depth as well as smaller spatter. Dynamic resistance was obtained according to the acting force and welding current. As the acting force was changed during welding, the welding quality was increased.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.5
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• pp.273-278
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• 2019

In this study, a new simple method for the estimation of hyperelastic material properties by indentation tests is proposed. Among hyperelastic material models, the Yeoh model with three material properties ($C_{10}$, $C_{20}$, $C_{30}$) is adopted to describe the strain energy density in terms of strain invariants. Finite element simulations of the spherical indentation of hyperelastic materials of the Yeoh model with different material properties are performed to establish a database of indentation force-displacement curves. The indentation force-displacement curves are fitted by cubic polynomials, which are approximated as a product of third-order polynomials of ($C_{10}$, $C_{20}$, $C_{30}$). A regression analysis is conducted to determine the coefficients of the equations for the indentation force-displacement curve approximations. A regression equation is used to estimate the hyperelastic material properties. The present method is verified by comparing the estimated material properties with true values.

• Journal of the Korean Ceramic Society
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• v.39 no.12
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• pp.1149-1152
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• 2002

Indentation was used to analyze high pressure phases of silicon. Phase transformations on both loading time and loading rate were studied. Micro-raman spectroscopy was used to observe the indentation-induced transformations. As the loading time increased, Si-III and Si-XII disappeared and only a-Si was observed in (111) samples. As the loading time increased, the residual stress was removed by creation of cracks or dislocations. At 0.1 mm/min loading rate, pop-in . At 5 mm/min loading rate pop-in was observed in force/displacement curve of (111) sample, but pop-in was not observed in force/displacement curve of (100) sample. This result indicates that the loading rate affects the volume of phase transformation in silicon.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.154-157
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• 2002

A cyto-indentation technique was used to obtain the biomechanical compressive compliance property of an chondrocyte cell attached to glass surface, which was tried to generate joint cartilage by tissue engineering. Piezo-transducer system and dual photo-diode system were used to conduct mechanical indentation through displacement-controlled testing and the measurement of corresponding cell reaction force. The Poisson's ratio of 0.37 was quoted from other report. The compressive compliance of chondrocyte, that was determined by elastic contact theory, was 1.38${\pm}$0.057 kPa. This value is 30% higher than that of MG63 osteoblast-like cell. The cyto-indentation technique employed in this study is so precise that it can quantify the biomechanical property of single cell.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.777-781
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• 2004

This paper presents a force/displacement sensing system to measure penetration depths and machining forces during pattering operation. This sensing system consists of a leaf spring mechanism and a capacitive sensor, which is mounted on a PZT driven in-feed motion stage with 1nm resolution. The sample is moved by a xy scanning motion stage with 5nm resolution. The constructed system was applied to nano indentation experiments, and the load-displacement curves of silicon(111) and aluminum were obtained. Then, the indentation samples were measured by AFM. Experimental results demonstrated that the developed system has the ability of preforming force/depth sensing indentations

• Tribology and Lubricants
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• v.39 no.6
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• pp.273-277
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• 2023

This paper presents a molecular dynamics simulation-based numerical investigation of the influence of surface energy on water lubrication. Models composed of a crystalline substrate, half cylindrical tip, and cluster of water molecules are prepared for a tribological-characteristic evaluation. To determine the effect of surface energy on lubrication, the surface energy between the substrate and water molecules as well as that between the tip and water molecules are controlled by changing the interatomic potential parameters. Simulations are conducted to investigate the indentation and sliding processes. Three different normal forces are applied to the system by controlling the indentation depth to examine the influence of normal force on the lubrication of the system. The simulation results reveal that the solid surface's surface energy and normal force significantly affect the behavior of the water molecules and lubrication characteristics. The lubrication characteristics of the water molecules deteriorate with the increasing magnitude of the normal force. At a low surface energy, the water molecules are readily squeezed out of the interface under a load, thus increasing the frictional force. Contrarily, a moderate surface energy prevents expulsion of the water molecules due to squeezing, resulting in a low frictional force. At a high surface energy, although squeezing of the water molecules is restricted, similar to the case of moderate surface energy, dragging occurs at the soil surface-water molecule interface, and the frictional force increases.

• Steel and Composite Structures
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• v.27 no.4
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• pp.427-438
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• 2018

In this paper, the single and multi-objective optimization of thin-walled conical tubes with different types of indentations under axial impact has been investigated using surrogate models called metamodels. The geometry of tapered thin-walled tubes has been studied in order to achieve maximum specific energy absorption (SEA) and minimum peak crushing force (PCF). The height, radius, thickness, tapered angle of the tube, and the radius of indentation have been considered as design variables. Based on the design of experiments (DOE) method, the generated sample points are computed using the explicit finite element code. Different surrogate models including Kriging, Feed Forward Neural Network (FNN), Radial Basis Neural Network (RNN), and Response Surface Modelling (RSM) comprised to evaluate the appropriation of such models. The comparison study between surrogate models and the exploration of indentation shapes have been provided. The obtained results show that the RNN method has the minimum mean squared error (MSE) in training points compared to the other methods. Meanwhile, optimization based on surrogate models with lower values of MSE does not provide optimum results. The RNN method demonstrates a lower crashworthiness performance (with a lower value of 125.7% for SEA and a higher value of 56.8% for PCF) in comparison to RSM with an error order of $10^{-3}$. The SEA values can be increased by 17.6% and PCF values can be decreased by 24.63% by different types of indentation. In a specific geometry, higher SEA and lower PCF require triangular and circular shapes of indentation, respectively.