• 대한기계학회논문집A
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• 제36권1호
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• pp.81-90
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• 2012

재료시험기법 중 하나인 압입시험은 크리프 특성 분석에 이용될 수 있다. 그러나 많은 기존 연구들이 정상상태의 크리프 특성만을 이용하고 있기 때문에, 단축시험과 압입시험 사이에는 상당한 차이가 발생한다. 따라서 정확한 크리프 평가를 위해서는 천이 크리프 특성을 고려하여야 한다. 본 연구에서는 Ogbonna 등(14)의 구형 압입자를 이용한 천이 크리프 해석을 확장, 자기 유사성을 갖는 원뿔형 압입자에 적용했다. 천이 크리프 특성을 유한요소해석을 통해 분석하여 정리하였으며, 구형 및 원뿔형 압입시험의 천이 특성을 비교했다. 또한 재료의 탄성변형률, 압입자 형상, 압입접촉면적, 대표 변형률 등 기존 평가법들에서 정량적으로 잘 고려되지 못하고 있는 부분들을 살펴보고 그 해결방안을 제시했다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.256-261
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• 2000

In this study, we derived work-hardening exponent using continuous indentation test technique. Continuous indentation test technique is a powerful method to evaluate mechanical properties, such as hardness, modulus, ${\sigma}-{\varepsilon}$ curves and etc. It has many merits conventional indentation test has. The relationship between true stress and mean contact pressure and between strain and indentation depth were derived. While the indenter pushes the materials, the region around the indenter is deflected elastically. It is called elastic deflection. And pile-up phenomenon related to plastic deformation around the indenter increased the contact depth, and sink-in phenomenon decreases. So we calibrated contact depth change by considering elastic deflection and pile-up/sink-in. Using calibrated contact depth we redefined the relationship between true stress and mean contact pressure and between strain and contact depth. Through these relationship we could derive work-hardening exponent by analyzing load-depth curves. And it showed good agreement with tensile test results.

• 한국군사과학기술학회지
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• 제6권4호
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• pp.73-79
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• 2003

Fatigue test is conducted to see the effect of pre-indentation on the fatigue crack retardation of Al5052-H18 plate. Metallographic observation is introduced to deduce the relationship between fatigue crack retardation and fracture appearance with indentation. The grain size of the specimen becomes smaller with the increase of indentation force and the plastic zone is formed with the decrease of grain size. The fatigue striations are appeared densely as the Indentation force becomes higher. Metallographic observation and fatigue test results show that the indentation force has the limited value in improving fatigue crack retardation. Important point to retard the fatigue crack growth is that the crack growth path should pass through the indented area.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 춘계학술대회 논문집
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• pp.191-194
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• 2002

The tensile properties of materials can be obtained just in accordance with conventional tensile testing methods which are described in several standards. However, the standard testing methods cannot be applicable due to the destructive testing procedure and specimen size requirement for some cases including on-service facility materials. Therefore, simple, non-destructive and advanced indentation technique was proposed. This test measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation and fracture. In this paper, the research trend of non-destructive evaluation of tensile properties using advanced indentation system and its application fields are reviewed and discussed.

• 한국철도학회논문집
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• 제7권2호
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• pp.142-148
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• 2004

When material properties depend much on positions in a material or it is difficult to make test specimens from a material or component, an instrumented indentation test described in ISO 14577-1, 14577-2 or KS B 0950 can be used to measure material properties and damage. In this study, first of all, the principals of the instrumented indentation test, KS B 0950 are introduced and yield strengths, tensile strengths and work hardening exponents of base materials, heat affected zones and weld materials are measured. In addition, the influence of post-weld heat treatment on the material properties is investigated. Finally the fatigue lift of butt welded specimens are evaluated by the local strain approach. To calculate local strains and stresses, elasto-plastic finite element analysis is conducted using the measured properties.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.503-504
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• 2006

Determination of elastic properties of nano-scale materials using nano-indentation tests is well established, but that of plastic properties is not yet clear. This paper presents a method to extract plastic properties from nano-indentation test, together with results from detailed elastic-plastic FE analysis. It shows that the plastic properties determined from this method are not unique, in the sense that a number of different plastic properties can give the same load-displacement response from nano-indentation test. possible ways to overcome such problems are discussed.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 춘계학술대회 논문집
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• pp.1607-1612
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• 2007

To assure safe usage of railway rolling stock, it is important to evaluate the strength of the wheel which is core part in bogies. However, conventional standard testing methods using destructive technique could not evaluate mechanical properties of degraded wheels during rolling stock maintenance work. Instrumented indentation test is a new way to evaluate nondestructively the strength of mechanical components by analyzing indentation load-depth curves. In this study, to evaluate tensile strength of the wheel, instrumented indentation test is performed nondestructively according to KS B 0950. Furthermore, test results are examined by tensile test in accordance with KS R 9221.

• 한국정밀공학회지
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• 제22권10호
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• pp.186-194
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• 2005

This study was designed to investigate the mechanical properties of the coating layer on electronic galvanized sheet steel as a part of the ongoing research on the coated steel. Those properties were determined using nano-indentation, the finite element method, and artificial neural networks. First and foremost, the load-displacement curve (the loading-unloading curve) of coatings was derived from a nano-indentation test by CSM (continuous stiffness measurement) and was used to measure the elastic modulus and hardness of the coating layer. The properties derived were applied in FE simulations of a nano-indentation test, and the analytical results were compared with the experimental result. A numerical model for FE simulations was established for the coating layer and the substrate separately. Finally, to determine the mechanical properties of the coating, such as the stress-strain curve, functional equations of loading and unloading curves were introduced and computed using the neural networks method. The results show errors within $5\%$ in comparison with the load-displacement measured by a nano-indentation test.

• 대한기계학회논문집A
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• 제28권5호
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• pp.578-585
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• 2004

Hardness test is performed for determination of the other properties, such as strength, wear resistance and deformation resistance, as well as hardness itself. And it is performed for prediction of residual lifetime by analysis of hardness reduction or hardness ratio. However, hardness test has limitation that observation of residual indent is needed for determination of hardness value, and that is the reason for not to be widely used in industrial field. Therefore, in this study, we performed researches to obtain Brinell hardness value from quantitative numerical formula by analysing relationship between indentation depths from indentation load-depth curve and mechanical properties such as work hardening exponent, yield strength and elastic modulus.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2089-2095
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• 2002

Ceramic/metal composites have many attractive properties and great potential fur applications. Interfacial fracture properties of different layered composites are important in material integrity. Therefore, evaluation of fracture toughness at interface is required in essence. In this study, the mechanical characteristics for interface of ceramic/metal composites were investigated by indentation test of micro-hardness method. Apparent interfacial toughness of TBC system could be determined with a relation between the applied load and the length of the crack formed at the interface by indentation test.