• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.911-914
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• 2005

Soft tissue characterization and modeling based on living tissues has been investigated in order to provide a more realistic behavior in a virtual reality based surgical simulation. In this paper, we characterize the nonlinear viscoelastic properties of intra-abdominal organs using the data from in vivo animal experiments and inverse FE parameter estimation algorithm. In the assumptions of quasi-linear-viscoelastic theory, we estimated the nonlinear material parameters to provide a physically based simulation of tissue deformations. To calibrate the parameters to the experimental results, we developed a three dimensional FE model to simulate the forces at the indenter and an optimization program that updates new parameters and runs the simulation iteratively. The comparison between simulation and experimental behavior of pig intra abdominal soft tissue are presented to provide a validness of the tissue model using our approach.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.116-119
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• 2003

In this study, to achieve the optimal conditions for mechanical hyper-fine pattern fabrication process, deformation behavior of the materials during indentation was studied with numerical method by ABAQUS S/W. Brittle materials (Si, Pyrex glass) were used as specimens, and forming conditions to reduce the elastic restoration and pile-up was proposed. The indenter was modeled a rigid surface. Minimum mesh sizes of specimens are 1-10nm Comparison between the experimental data and numerical result demonstrated that the finite element approach is capable of reproducing the loading-unloading behavior of a nanoindentation test. The result of the investigation will be applied to the fabrication of the hyper-fine pattern.

• Korean Journal of Materials Research
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• v.13 no.1
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• pp.53-58
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• 2003

For the rib materials in PDP(plasma display panel), an effective method to improve the mechanical properties is to form a composite material by reinforcing a glass matrix with rigid fillers, such as alumina and titania powders. In this study, two types of ribs with different volume percent of fillers and with different glass matrix were tested for hardness, Young's modulus with the Berkovich indentation. As a result, cracks appeared around at the load of 1345 mN for the dense type of rib, while porous one endured until 2427 mN without any crack formation. Young's modulus and hardness decreased at the range: 90∼65 GPa, 9∼4 GPa, respectively as a function of indent load. Thus, a new method with nanoindenter represents a possible evaluation method for mechanical properties of barrier ribs.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.4
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• pp.26-33
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• 2002

One characteristic of Fine-Blanking is that the size and the direction of stress and strain are very complex in the plastic flow according to the condition of blanking. Especially, they are affected by the clearance of punch and die, by the force of blanking holder and by the force of counter punch. The purpose of this research is to how the deformation behavior in shear zone more clearly, based on Green & Cauch's large deformation theory. The deformation behavior and cracks were investigated in each step of shear, according to punch penetration increase, the use of V-indenter ring and the hardness of materials. This research found that the transforming behavior was the same as pure discretion and the cracks could be prevented when hardness is low.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.333-338
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• 1998

Mechanical properties of polycrystalline{{{{ {Ti }_{3 }{SiC}_{2 } }} were investigated. Hertzian indentation test using a spher-ical indenter was used to study elastic and plastic behavior in{{{{ {Ti }_{3 }{SiC}_{2 } }} A high ratio of hardness to elastic mo-dulus indicated that mechanical properties of{{{{ {Ti }_{3 }{SiC}_{2 } }} are somehow similar to those of metals. Indentation stress-strain curve deviated from an ideal elastic limit indicating exceptional plasticity in this material. De-formation zones were formed below the contact as well as around the contact area. Intragrain slip would ac-count for high plasticity.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.3
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• pp.122-128
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• 2000

세라믹, 다이야몬드등과 같은 고경질재료에 대한 미소형상의 가공은 대단히 어렵고 일반적인 방법으로는 상당한 시간을 요구한다. 이러한 재료의 고능률 가공을 실현하기 위하여, 메탈본드 다이야몬드휠에 전해 인프로세스 드레싱(Electrolytic In-Process Dressing)을 적용한 연삭을 머시닝센타에서 시도하였다 본 연구에서, 메탈본드 다이야몬드휠은 전기방전에 의하여 고능률로 트루잉(truing)되었다. 알루미나 세라믹의 핀선단($\phi$50$\mu\textrm{m}$)과 로커웰 경도측정기의 다이야몬드 압입자(indenter)($\phi$40$\mu\textrm{m}$)를 ELID연삭에 의하여 창성하였다. 그 결과를 본 논문에서 보고한다.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.5
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• pp.210-217
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• 2003

In this study, to achieve the optimal conditions for mechanical hyper-fine pattern fabrication process, deformation behavior of the materials during indentation was studied with numerical method by ABAQUS S/W. Polymer (PMMA) and brittle materials (Si, Pyrex glass) were used as specimens, and forming conditions to reduce the elastic restoration and pile-up was proposed. The indenter was modeled a rigid surface. Minimum mesh sizes of specimens are 1-l0mm. The result of the investigation will be applied to the fabrication of the hyper-fine pattern and mold.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.4
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• pp.294-302
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• 1999

Evaluation of Brinell standard hardness tester was carried out to secure its application as a national standard for Brinell hardness. Accuracies and reliabilities in load application, indenter diameter and indentation measurement were tested through evaluation of these components. The accuracies of load application for various loading conditions were within the limit of ISO and KS specifications. Errors in the indentation measurement due to the difference in personnel characters were successfully removed by utilising automatic indentation measurement system. In overall, the tester and the indentation measuring system were found to be eligible as a national standard of Brinell hardness.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.148-151
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• 2004

Mechanical properties such as Young's modulus and hardness of thin film in coated steel are difficult to determine by nano-indentation from the conventional analysis using the load-displacement curve. Therefore, an analysis of the nano-indentation loading curve was used to determine the Young's modulus, hardness and strain hardening exponent. A new method is recently being developed for plasticity properties of materials from nano-indentation. Elastic modulus of the thin films shows relatively small influence whereas yield strength and strain hardening are found to have significant effect on measured data. The load-displacement behavior of material tested with a Berkovich indenter and nano-indentation continuous stiffness method is used to measure the modulus and hardness through thin films.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1685-1696
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• 2001

A novel indentation theory is proposed by examining the data from the incremental plasticity theory based finite element analyses. First the optimal data acquisition location is selected, where the strain gradient is the least and the effect of friction is negligible. This data acquisition point increases the strain range by a factor of five. Numerical regressions of obtained data exhibit that strain hardening exponent and yield strain are the two main parameters which govern the subindenter deformation characteristics. The new indentation theory successfully provides the stress-strain curve with an average error less than 5%.