• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.185-192
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• 1988

Computation of the elasto-plastic solution of ball indentation was carried out by the quadratic programming method. The problem was formulated as an elasto-plastic contact problem under the assumption of small displacement and small deformation and then transformed into a minimization problem. Finite element approximation resulted in a quadratic programming problem. Numerical and experimental study were done with aluminium Al 2024-T351 and commercially pure copper. The computed load-displacement curves were in good agrement with those obtained from experiments. Tabor's relationship for representative strains was also examined. Stress distributions were found to resemble closely those results available in the literature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.98-106
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• 2016

Measurements of the elastic modulus and hardness using a nano indentation machine rely on the equation for the fitted contact area, which is valid for only sink-in materials. For most soft engineering materials that involve pile-up behavior rather than sink-in, the contact area equation underestimates the contact area and thus overestimates the elastic modulus and hardness. This study proposes a correction method to amend erroneous hardness measurements in pile-up situations. The method is a supplemental derivation to the original hardness measurement with the known value of the elastic modulus. The method was examined for soft engineering metals, Al 6061 T6 and C 12200, via tensile tests, nano indentation tests, impression observations, and finite element analysis. The proposed technique shows reasonable agreement with the analytical results accounting for strain gradient plasticity from a previous study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.10
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• pp.5974-5979
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• 2014

Lightweight parts with very uniform precision are manufactured by an indent method and the press technique has been improved. Upon assembly with an indent method, a deformation force due to the compressive force occurs between the pin and hole and the contact surface is affected by damage. Therefore, a 3 dimensional model was made using the CATIA program and the damage on the surface contacted with indent was estimated through the ANSYS program in this study. In the analysis result, the maximum load applied at the PCB plate was 21.3 N when the pin goes through the PCB plate. When PCB plate came out of the pin, the maximum load was 19.24 N. As the structural analysis result, the maximum equivalent stress of Pin 1 was 192.96MPa because the maximum stress occurs at Pin 1 among all parts of this study model. By examining the damage property of the contacted indent and applying this study result to the design of real indentation, the damage can be prevented and the durability can be estimated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.21-26
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• 2016

This study evaluates the magnitudes and distributions of contact tangential forces with the swaging depth of punch acting at the contact surfaces between a rotor core slot and a Cu bar during a sequential rotor core swaging process. The effects of the core slot shape on the magnitudes and distributions of the total contact forces were investigated to improve the productivity of the rotor core swaging process. Parametric elastic-plastic numerical analyses were performed using simplified two-dimensional cyclic symmetric plane strain models to evaluate the contact force distributions at the contact surfaces. The numerical analysis results show that the total contact tangential forces increased by about 55% with the adjacent Cu bar swaging process. The length of the core slot is a dominant factor in the core slot design as result of the increased total contact tangential forces during the swaging process of the rotor core.

• Elastomers and Composites
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• v.39 no.1
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• pp.23-35
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• 2004

In this work, effects of hyper-elastic rubber material properties on the indentation load-deflection curve and subindenter deformation are first examined via finite element (FE) analyses. An optimal data acquisition spot is selected, which features maximum strain energy density and negligible frictional effect. We then contrive two normalized functions, which map an indentation load vs. deflection curve into a strain energy density vs. first invariant curve. From the strain energy density vs. first invariant curve, we can extract the rubber material properties. This new spherical indentation approach produces the rubber material properties in a manner more effective than the common uniaxial tensile/compression tests. The indentation approach successfully measures the rubber material properties and the corresponding nominal stress-strain curve.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.5
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• pp.529-535
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• 2012

This paper deals with the determination of mechanical properties of various galvanized steel sheets that are used for fabricating automobile bodies; the instrumented indentation technique and finite element analysis were used for the determination. First, tensile tests were conducted to obtain the true stress-true strain curves of galvanized steel sheets with various thicknesses. Load-deformation curves were then obtained by using the instrumented indentation testing machine, and they were compared with load-deformation curves obtained by finite element analysis. Further, true stress-true strain curves were obtained at the optimal observation point by finite element analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1079-1089
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• 2015

In this paper, we propose a method to evaluate the material properties of high-yield strength materials exceeding 10GPa from spherical indentation. Using a regression equation considering four indentation variables, we map the load displacement relation into a stress-strain relation. To calculate the properties of high-strength materials, we then write a program that produces material properties using the loading / unloading data from the indentation test. The errors in material properties computed by the program are within 0.3, 0.8, and 6.4 for the elastic modulus, yield strength, and hardening coefficient, respectively.

• Journal of the Korean Institute of Gas
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• v.2 no.1
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• pp.40-46
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• 1998

Mathematical modeling on the corrosion of the steel casing and main pipe due to the protection current resulting from a cathodic protection system was carried out using boundary element method. The model is consisted of Laplace's equation with non-linear boundary conditions(Tafel equations) and the iterative technique to determine the miexed potential of the steel casing. The model is applied to the normal steel casing section as well as abnormal one with defects such as metal touch and insulation defects. From the modeling procedure, we can calculate the potential distributions and current density distributions of the system. The theoretical results of the qualitatiive corrosion aspect along the steel casing and main pipe agree well with the experimental results within the experimental conditions studied.

• Journal of the KSME
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• v.44 no.3
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• pp.46-54
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• 2004

이 글에서는 독자의 이해를 돕기 위해, 비교적 쉽게 전산모사 할 수 있는 균열진동해석, 나노압입 해석, 나노리소그래피 해석 등 세 가지에 대한 분자동역학 해석 결과를 소개한다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.38-38
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• 2003

최근 나노기술의 발달과 더불어 나노재료에 대한 특성평가 요구가 높아지고 있고, 따라서 나노스케일로 재료의 기계적 거동을 분석할 수 있는 나노인덴테이션 기법이 심도있게 연구되고 있다. 본 연구에서는 나노인덴테이션을 이용하여 여러 가지 재료의 탄성 소성 변형 거동을 관찰 조사하고 이를 다시 유한요소법(FEM)으로 모사하여 해석하였다. 나노인덴테이션으로 재료 표면에 압입하여 탄소성 변형을 일으켰으며 이때의 가하중과 변형깊이를 측정하여 하중-변형 곡선을 얻었다. 매우 작은 접촉응력 조건하에서는 탄성변형의 비율이 매우 높았는데 하중-변형 곡선으로부터 재료의 나노 경도와 탄성 계수값을 얻을 수 있었다. 실험적으로 얻은 하중-변형 곡선을 3 차원의 유한요소법(FEM)을 이용하여 모사하였는데 상호간에 매우 근접한 결과를 얻을 수 있었다. 이 때 압자의 모양, 압입 깊이, 재료의 종류, 둥을 변수로 하여 여러 가지 조건하에서 압입실험을 하였으며 그 결과를 유한요소법으로 모사하였다.