• Structural Engineering and Mechanics
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• v.52 no.3
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• pp.469-483
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• 2014

In an indentation approach, the smooth rigid spherical ball penetrated into a deformable flat is considered for the study based on contact mechanics approach. The elastic-plastic frictionless spherical indentation analysis has been under taken in the finite element analysis using "ABAQUS" and experimental study. The spherical indentation has been studied for the materials like steel, aluminium, copper and brass with an identical spherical indenter for diverse indentation depths. The springback analysis is executed for studying the actual indentation depth after the indenter is unloaded. In the springback simulation, the material recovers its elastic deformation after the indenter is unloaded. The residual diameter and depth of an indentation for various materials are measured and compared with simulation results. It shows a good agreement between the simulation and an experimental studies.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.9
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• pp.943-951
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• 2014

The tip geometries of the pyramidal and conical indenters used for micro/nano-indentation tests are not sharp. They are inevitably rounded because of their manufacturability and wear. In many indentation studies, the tip geometries of the pyramidal indenters are simply assumed to be spherical, and the theoretical solution for spherical indentation is simply applied to the geometry at a shallow indentation depth. This assumption, however, has two problems. First, the accuracy of the theoretical solution depends on the material properties and indenter shape. Second, the actual shapes of pyramidal indenter tips are not perfectly spherical. Hence, we consider the effects of these two problems on indentation tests via finite element analysis. We first show the relationship between the Poisson's ratio and load-displacement curve for spherical indentation, and suggest improved solutions. Then, using a possible geometry for a Berkovich indenter tip, we analyze the characteristics of the load-displacement curve with respect to the indentation depth.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.12
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• pp.1357-1365
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• 2009

In this study, we enhance the numerical approach of Lee et al.$^{(1)}$ to spherical indentation technique for property evaluation of hyper-elastic rubber. We first determine the friction coefficient between rubber and indenter in a practical viewpoint. We perform finite element numerical simulations for deeper indentation depth. An optimal data acquisition spot is selected, which features sufficiently large strain energy density and negligible frictional effect. We then improve two normalized functions mapping an indentation load vs. deflection curve into a strain energy density vs. first invariant curve, the latter of which in turn gives the Yeoh-model constants. The enhanced spherical indentation approach produces the rubber material properties with an average error of less than 3%.

• Structural Engineering and Mechanics
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• v.53 no.3
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• pp.429-442
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• 2015

The measurement from the indentation process depends on the amount of pile-up or sink-in around the contact impressions. In this paper, finite element concept is utilized to study the pile-up and sink-in behaviour for the wide range of materials with different young's modulus, yield stresses, strain-hardening exponents and coefficient of friction values. The exact indentation model is created by using the two dimensional axisymmetrical model for simulating the spherical indentation process on the lines of Taljat and Pharr (2004) work. The result shows that during spherical indentation process the amount of pile-up is greatly influenced by the strain hardening exponents in addition to other material properties and depth of penetration. The numerical results from the finite element analysis are also validated using the exact multilinear material properties obtained from the tensile testing for the materials like mild steel, brass and aluminium.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.266-271
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• 2001

Spherical indentation technique was developed to evaluate the flow properties of metallic materials in carbon steel, stainless steel and alloys, etc. Through the spherical indentation test, differently degraded 1Cr-1Mo-0.25V steel's mechanical properties were observed and compared with conventional standard test data. The flow properties of 1Cr-1Mo-0.25V steels were estimated by analyzing the indentation load-depth curve. To characterize the flow property, we used material yield slope and constraint factor index rather than strain-hardening exponent because the variation of strain-hardening exponent was very little and the data showed irregularly. And the constraint factor's effect was small when the material yield slope was taken into account.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.268-271
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• 2010

In this paper, forward and reverse analysis is introduced in order to estimate the elastic-plastic properties from a power-law hardening bulk specimen materials with one simple spherical indentation impression test. In order to verify the reliability of the reverse analysis, we have simulated about a large range of materials that essentially cover all engineering materials, using ABAQUS(6.91) program. Then, we could obtained the fitting functions and plastic parameters from the numerical analysis results. Next, through the procedure of reverse analysis we can obtain the yield stress and power-law exponent. Finally, obtain good agreement between the result from reverse analysis and initial input data from experiment.

• 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 Biomedical Engineering Research
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• v.26 no.2
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• pp.117-122
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• 2005

The elastic modulus and the apparent density of the trabecular bone were evaluated from spherical indentation tests and Computed Tomography (CT) and their relationship was quantified. The femurs were prepared for trabecular bone analysis. Embedded with respect to their anatomical orientation, the transverse planes of the trabecular bone specimens were scanned at 1㎜ intervals using a CT scanner. The metaphyseal regions of femurs were sectioned with a diamond-blade saw, producing 8㎜ cubes. Using a specially made spherical indentation tester, the cubes were mechanically tested in the anterior-posterior (AP), medial-lateral (ML), and inferior-superior (IS) directions. After determination of modulus from the mechanical testing, the apparent densities of the specimens were measured. The results showed that the IS modulus was significantly greater than both the AP and ML moduli with the AP modulus greater than the ML modulus. This demonstrated that orthogonality was a structural characteristic of the trabecular bone. The power relationship between the modulus and the apparent density was also found to be statistically significant.

• 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.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.4
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• pp.353-360
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• 2010

In this paper, an efficient algorithm is established in order to estimate the plastic properties of power-law hardening bulk specimen materials with one simple spherical indentation impression test. This work is based on a new formulation of representative strain and, therefore, compare to the preceding approaches the fitting parameters are significantly reduced. Moreover, the new definition of representative strain endowed more physical meaning to the representative strain. In order to verify the reliability of the reverse analysis, we have studied a broad set of materials whose property ranges cover essentially all engineering metals and alloys. Based on the indentation force-displacement P-${\delta}$ curves obtained from numerical simulations, the characteristics of the indentation response and material elastoplastic properties are bridged via explicit functions. Next, through the procedure of reverse analysis the yield stress and power-law hardening exponent of bulk specimen materials can be determined. Finally, good agreement between the result from reverse analysis and initial input data from experiment can be observed.