• 마이크로전자및패키징학회지
• /
• 제26권4호
• /
• pp.95-100
• /
• 2019

연속압입시험법은 기존의 잔류응력 측정기법에 대한 대체기법으로 많은 분야에서 연구되고 있다. Knoop 압입자는 이러한 압입시험에서 잔류응력의 방향성을 결정하기 위해 이용되어 왔다. 기존 연구에 의하면 Knoop 압입자의 두 가지 응력환산계수의 비는 실험적으로 0.34로 고정되어 있는 것으로 알려져 있으나 이에 대하여 정량적인 분석이 부족하고, 깊이에 따른 실험결과는 미비하여 산업현장에 적용하기에 장벽이 존재한다. 본 연구에서는 연속압입시험법을 이용한 잔류응력의 방향성 측정을 위하여 응력환산계수의 비를 유한요소해석을 이용하여 측정하였다. 본 연구에서는 유한요소해석을 이용하여 압입깊이에 따른 응력환산계수의 비를 분석하고자 하였다. 이론적인 Knoop 압입자와 시편을 모델링하여 일축 잔류응력 상태에서 각각의 응력환산계수를 산출하였다. 압입자 장축 및 단축 방향의 응력환산계수를 주어진 깊이에 따라 예측할 수 있는 모델을 제시하였고, 그 원인을 분석하였다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2005년도 춘계학술대회 논문집
• /
• pp.1774-1779
• /
• 2005

Most of materials receive force in using, therefore, the characteristics of materials must be considered in system design not to occur deformation or destruction. Mechanical properties about materials can be expressed as responsible level of material itself under the exterior operation. Main mechanical properties is strength, hardness, ductility and stiffness etc. Currently, among major measure facilities to measure such mechanical properties, advanced indentation technique has focused in industrial areas as reason of 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 give non-equi-biaxial stress state and compared with general residual stress analyzing method for verification.

• 한국기계가공학회지
• /
• 제10권4호
• /
• pp.76-81
• /
• 2011

UV imprinting process can manufacture high-functional optical components with low cost. If hard polymers can be used as transparent molds at this process, the cost will be much lower. However, there are limited researches to predict the machinability and the burr of hard polymers. Therefore, a new method to predict them by analyzing load-depth curves which can be obtained by the instrumented indentation test was developed in this study. The load-depth curve contains elastic deformation and plastic deformation simultaneously. The ratio of the plastic deformation over the sum of the two deformation is proportional to the ductility of materials which is one of the parameters of the machinability and the burr. The instrumented indentation tests were performed on the transparent molds of the hard polymers and the values of ratio were calculated. The machinability and the burr of three kinds of hard polymers were predicted by the ratio, and the prediction was in agreement with the experimental results from the machined surfaces of the three kinds of hard polymers.

• 한국정밀공학회지
• /
• 제24권2호
• /
• pp.118-126
• /
• 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.

• 한국세라믹학회지
• /
• 제41권1호
• /
• pp.19-23
• /
• 2004

The Hertzian indentation contact damage behavior of porous alumina with controlled pore shape was investigated by experiments. Porous alumina ceramics containing well-defined pore shape, size and distribution were prepared by incorporation of fugitive spherical starch. Porous alumina with isolated pore structure was prepared with porosity range up to 30%. The indentation stress-strain curves of porous alumina were constructed. Elastic modulus and yield stress can be obtained from the stress-strain relationship. Impulse excitation method for the measurement of elastic modulus was also conducted as well as Hertzian indentation and was confirmed as a useful tool to evaluate the elasticity of highly porous ceramics. Elastic modulus of the inter-connected pore structure is more sensitive to porosity than that of the isolated pore structure. When the specimen had isolated pore structure, higher yield point was obtained than it had inter-connected pore structure. This study proposed that the elastic modiulus of porous ceramics is strongly related to not only porosity, but also the structure of pore.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2004년도 추계학술대회 논문집
• /
• pp.343-346
• /
• 2004

In recent years, various forms of indentation testing have been increasingly used to determine the material properties of specimens. This technique, particularly the nano-indentation method , has been extended to the testing of coating systems in order to calculate the individual properties of the thin coatings and the substrates. However, the interpretation of the test data to achieve this is complex and continues to be a widely studied subject. Based on the finite element method of coated surfaces indented by a Berkovich diamond tip, this paper describes methods for combining FEM and experimental indentation testing to determine coating modulus and hardness independent of substrate effects. Using this proposed methodology, testing and FEM to measure coefficients of friction of sheet steel for outer panel were studied.

• 대한기계학회논문집A
• /
• 제26권7호
• /
• pp.1270-1279
• /
• 2002

Residual stress is a dominant obstacle to efficient production and safe usage of device by deteriorating the mechanical strength and failure properties. Therefore, we proposed a new thin film stress-analyzing technique using a nanoindentation method. For this aim, the shape change in the indentation load-depth curve during the stress-relief in film was theoretically modeled. The change in indentation depth by load-controlled stress relaxation process was related to the increase or decrease in the applied load using the elastic flat punch theory. Finally, the residual stress in thin film was calculated from the changed applied load based on the equivalent stress interaction model. The evaluated stresses for diamond-like carbon films from this nanoindentation analysis were consistent with the results from the conventional curvature method.

• Journal of Mechanical Science and Technology
• /
• 제18권10호
• /
• pp.1730-1737
• /
• 2004

The BI (Ball Indentation) method has the potential to assess the mechanical properties and to replace conventional fracture tests. In this study, the effect of aging on mechanical behavior of 1Cr-1Mo-0.25V steels procured by isothermal aging heat-treatment at four different aging times in the range of 0～1820 hours at 630$^{\circ}C$, were investigated using BI system.

• 한국해양공학회지
• /
• 제15권2호
• /
• pp.61-65
• /
• 2001

The fracture toughness of ceramics can be measure by such various methods as DT (double torsion), CN (chevron notch) etc. But, the application of these methods to the engineering ceramics is very difficult because of its very high hardness. So, IF (indentation fracture) method is generally used for the evaluation of fracture toughness of ceramics. The Median crack induced by the sharp Vickers indenter was compared with the detected AE (acoustic emission) signal. On the silicon nitride ceramics, the AE test results agree fairly well with the median crack occurance and growth process. But, on the alumina, very many complicated crack signals were detected besides median crack. It can be considered that the IF methods must be used in limited engineering ceramics materials.

• 소성∙가공
• /
• 제29권6호
• /
• pp.316-322
• /
• 2020

The flow stress curve is usually determined via uniaxial tensile or simple compression test. However, the flow stress curve up to high strain cannot be obtained using these two tests. This study presents a simple method for obtaining the flow stress curve up to high strain via FE analysis, a simple compression test, and an indentation test. In order to draw the flow stress curve up to high strain, the indentation test was carried out with the pre-stained specimen using the simple compression test. The flow stress curve of Al6110 was evaluated up to high strain using the proposed method, and the result was compared with the flow stress curve of the uniaxial tensile test of the initial material.