• Journal of the Korean Society for Precision Engineering
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• v.24 no.2 s.191
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• pp.118-126
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• 2007

Most of materials receive forces in use so that the characteristics of materials must be considered in system design to prevent deformation or destruction. Mechanical properties of materials can be expressed as responsible level of material itself under the exterior operation. Main mechanical properties are strength, hardness, ductility and stiffness. Currently, among major measure facilities to measure the mechanical properties, advanced indentation technique has important use in industrial areas due to nondestructive and easy applications for mechanical tensile properties and evaluation of residual stress of materials. This study is to find the optimum experimental condition about residual stress advanced indentation technique for accurate analysis of the welded joint of steel materials through indentation load-depth curve obtained from cruciform specimen experiment. Optimum selection was applied to the welded joint of real steel materials to find out non-equi-biaxial stress state and the results were compared with general residual stress analyzing method fur verification.

• Advanced Composite Materials
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• v.18 no.1
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• pp.1-20
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• 2009

This paper describes the results of experiments and numerical simulation studies on the impact and indentation damage created by low-velocity impact subjected onto honeycomb sandwich panels for application to the BIMODAL tram. The test panels were subjected to low-velocity impact loading using an instrumented testing machine at six energy levels. Contact force histories as a function of time were evaluated and compared. The extent of the damage and depth of the permanent indentation was measured quantitatively using a 3-dimensional scanner. An explicit finite element analysis based on LS-DYNA3D was focused on the introduction of a material damage model and numerical simulation of low-velocity impact responses on honeycomb sandwich panels. Extensive material testing was conducted to determine the input parameters for the metallic and composite face-sheet materials and the effective equivalent damage model for the orthotropic honeycomb core material. Good agreement was obtained between numerical and experimental results; in particular, the numerical simulation was able to predict impact damage area and the depth of indentation of honeycomb sandwich composite panels created by the impact loading.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.237-242
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• 2001

Residual stress is a dominant obstacle to efficient production and safe usage of products by reducing the mechanical strength and failure properties. Especially, it causes interfacial failure and substrate deflection in the case of thin film. So, the exact evaluation and optimum control of thin film residual stress is indispensable. However, hole drilling or X-ray diffraction techniques have some limits in application to thin film. And, curvature technique for thin film materials cannot give the information about local stress variation. Therefore, we applied the nanoindentation technique in evaluating the thin film residual stress. In this study, we modeled the change of indentation loading curve for residually stressed and stress-free thin films during stress relaxation. The value of residual stress was directly related to the indentation depth change by relaxation. The residual stress from nanoindentation analysis was consistent with the result from curvature technique.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.306-314
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• 2006

Instrumented indentation technique is a new way to evaluate nondestructive such mechanical properties as flow properties, residual stress and fracture toughness by analyzing indentation load-depth curves. This study evaluated quantitatively the flow properties of steels and residual stress of weldments. First, flow properties can be evaluated by defining a representative stress and strain from analysis of deformation behavior beneath the rigid spherical indenter and the parameters obtained from instrumented indentation tests. For estimating residual stress, the deviatoric-stress part of the residual stress affects the indentation load-depth curve, so that by analyzing the difference between the residual-stress-induced indentation curve and residual-stress-free curve, the quantitative residual stress of the target region can be evaluated. The algorithm for flow property evaluation was verified by comparison with uniaxial tensile test and the residual stress evaluation model was compared to mechanical cutting and ED-XRD results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.64-72
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• 2014

In the past, prism patterns have been linear triangular shapeswith a $90^{\circ}$ angle; however, new micro prism patterns having acute angles or obtuse angles have recently been the subject of demandin the display, lighting and photovoltaic industries. Micro-cutting experiments for micro-prism patterns having $60^{\circ}$, $90^{\circ}$, and $120^{\circ}$ angles on an electroplated Ni mold were performed and it was found in this study that the specific cutting resistance increased with a decrease in the tool angles (prism pattern angles). The cause of this variation had been thought to be the increase of the ploughing force due to tip rounding and the friction force due to the edge effect. However, the depth of the cut was large enough that it was possible to neglect these effects. Therefore, this study introduced the concept of representative stress of indentation. The measured stress was varied according to the indentation depth eventhoughthetestedspecimenswereidentical ; the varied stress was termed the representative stress. According to indentation theory, the strain that the Ni mold experienced increased with a decrease in the tool angle. Based on the stress-strain relationship, higher strain means higher stress and higher specific cutting resistance. Therefore, the specific cutting resistance was higher at smaller tool angles that had higher strain and stress.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.339-346
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• 2003

Molecular dynamic simulations of nano indentation on single-crystal silicon (100) surface were performed using diamond indentor. Silicon substrate and diamond indentor were modeled diamond structure with Tersoff potential model. Phase transformation of silicon, incipient plastic deformation, change of incident temperature distribution are investigated through the change of potential energy distribution, displacement-load diagram, the change of kinetic energy distribution and displacements of silicon atoms. Phase transformation is highly localized and consists of a high-density region surrounding the tip. Axial load linearly increased according to the indenting depth. Number of atoms with high kinetic energy increased at the interface between substrate and indentor tip.

• Tribology and Lubricants
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• v.15 no.1
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• pp.52-58
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• 1999

Nano-indentation and nano-scratch tests were peformed to assess the mechanical and tribological properties of the coating on a commercially available thin-film magnetic recording disk. Surface topography and roughness of the disk was studied using atomic force microscopy. The hardness and elastic modulus data show a peak at an indentation depth equivalent to the thickness of carbon overcoat, indicating strong influence of the coatin $g_strate interaction and the coating surface roughness on the measurements. The variations of surface roughness data were analysed statistically based on the normal probability distribution theories and Weibull cumulative probability theories.es.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2002.05a
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• pp.38-38
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• 2002

Kinetic indentation technique was studied and a method to evaluate wear and fatigue behaviors of irradiated small specimen was suggested. The method is based on both the proportion of elastic and plastic deformation and values obtained by micro-hardness test. The parameters obtained from the diagram of load-indentation depth-time are required to evaluates wear and fatigue properties. Considering the irradiated test specimen, it is one of possible and useful methods to estimate the irradiated wear and fatigue behaviors of the small size specimen. This article briefly describes the status of irradiated material study in domestic research reactor.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.288-290
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• 2005

Apparent mechanical properties in structural components can be different from the initially designed values due to the formation of the residual stress in metal forming and welding. Therefore, the evaluation of residual stress has great importance in the reliability diagnosis of structural components. A nondestructive continuous indentation technique has been proposed to evaluate various strength concerning mechanical properties from the analysis of load-depth curve. In this study, quantitative residual stress estimation on API X65 welded joints for natural gas pipeline was performed by analyzing the variation of indentation loading curve by residual stress through a new proposed theoretical model.

• Journal of the Korean institute of surface engineering
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• v.54 no.4
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• pp.171-177
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• 2021

This paper is concerned with the surface hardness measurement of NiP-coated AA7050 using different loads from 10 to 100 g. The surface hardness was observed to increase from 180 to 600 H_v with increasing NiP layer thickness, depending on the load applied for indentation. When NiP coating thickness is thinner than 2 ㎛, the surface hardness of NiP-coated AA7050 was mainly determined by AA7050 substrate, while it was significantly increased by NiP coating layer when NiP coating thickness is thicker than 2 ㎛. Hardness of AA7050 substrate itself was not dependent on the applied load but the hardness of NiP-coated AA7050 was largely influenced by the load applied for indentation. The largest difference of hardness between 10 g and 100g of applied loads, was obtained at the NiP thickness of about 8 ㎛ above which the measured hardness at 10 g reached a maximum value of about 600 H_v. It was also observed that indentation-induced plastic deformation next to the indented zone occurs when NiP layer is 5.64 times thicker than the depth of impression formed by indentation.