• Title/Summary/Keyword: Indentation load-depth curve

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Enhanced Spherical Indentation Techniques for Property Evaluation (향상된 구형 압입 물성평가법)

  • Lee, Hyung-Yil;Lee, Jin-Haeng
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.4
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    • pp.461-471
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    • 2007
  • In this work, indentation theory of Lee $et al.^{(1)}$ for 6% indentation of indenter diameter is extended to an indentation theory for 20% indentation. For shallow indentation, the effect of friction on load-depth curve is negligible, but different materials can show nearly identical load-depth curves. On the basis of this observation, a new numerical approach to deep indentation techniques is proposed by examining the finite element solutions. With this new approach, from the load-depth curve, we obtain stress-strain curve and the values of Young's modulus, yield strength and strain-hardening exponent with an average error of less than 3%.

Evaluation of Thin Film Residual Stress through the Theoretical Analysis of Nanoindentation Curve (나노 압입곡선의 이론적 분석을 통한 박막의 잔류응력 평가)

  • Lee, Yun-Hee;Jang, Jae-Il;Kwon, Dong-Il
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.7
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    • pp.1270-1279
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    • 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.

Prediction of State of Cutting Surfaces of Polymers by Analysis of Indentation Load-depth Curve (압입하중-변위곡선 분석을 통한 폴리머 소재의 절삭표면상태 예측에 관한 연구)

  • Jeon, Eun-Chae;Kim, Jae-Hyun;Je, Tae-Jin
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.10 no.4
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    • pp.76-81
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    • 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.

Evaluation of Flow Stress using Geometric Conditions of Ball Indentation Test (압입 시험의 기하학적 조건과 유동 응력 선도와의 관계에 관한 연구)

  • 이병섭;이호진;이봉상
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.05a
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    • pp.291-294
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    • 2003
  • Ball indentation tests have been used to estimate the mechanical properties of materials by some investigators. In this study, load-depth curves from ball indentation tests have been analysed using the geometric conditions of ball indentation. Series of numerical calculations and experimental results showed that those curves could be simplified by linear functions. After linearizing the indentation curves, the estimation process of the flow properties became straight forward and the scatter of results could be drastically reduced.

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Evaluation of Flow Stress using Geometric Conditions of Ball Indentation Tests (볼 압입 시험의 기하학적 조건과 유동 응력 곡선의 관계에 관한 연구)

  • 이병섭;이호진;이봉상
    • Transactions of Materials Processing
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    • v.12 no.4
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    • pp.328-333
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    • 2003
  • Ball indentation tests have been used to estimate the mechanical properties of materials by several investigators. In this study, load-depth curves from ball indentation tests were analyzed using the geometric conditions of the contact between ball and specimen. A series of numerical calculations and experimental results showed that the contact load-depth curves could be simplified by linear functions. Once we obtained the contact indentation depth from linearizing the experimental indentation curves, the estimation process of the flow properties became straight-forward and the scatter of results could be drastically reduced.

Enhanced Spherical Indentation Techniques for Rubber Property Evaluation (향상된 구형압입 고무 물성평가법)

  • Hwang, Kyu-Min;Oh, Jopng-Soo;Lee, Hyung-Yil
    • 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%.

A Berkovich Indentation Technique Based on 3D FEA solutions for Material Property Evaluation (3차원 유한요소해에 기초한 Berkovich 압입 물성평가법)

  • Kim, Min-Soo;Hyun, Hong-Chul;Lee, Kyoung-Yoon;Lee, Hyung-Yil
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.1-6
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    • 2008
  • Due to the self-similarity of Berkovich and conical indenters, different materials may show the same loaddepth curve for single indentation. In this study, we first compare the load-depth characteristics of conical and Berkovich indenters via finite element method. We also analyze the variation of load-depth curves with angle of Berkovich indenter, indentation parameters, and material properties. With numerical regressions of obtained data, we then propose dual-Berkovich indentation formulae for material property evaluation. The proposed approach provides the values of elastic modulus, yield strength and strain-hardening exponent and corresponding stress-strain curve with an average error of less than 3%. The method is valid for any elastic indenters made of tungsten carbide and diamond for instance.

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Influence of Indenter Tip Geometry and Poisson's Ratio on Load-Displacement Curve in Instrumented Indentation Test (계장화 압입시험의 하중-변위 곡선에 미치는 선단 형상 및 푸아송비의 영향)

  • Lee, Jin Haeng
    • 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.

Calibration of Contact Depth for Evaluating Residual Stress using Instrumented Indentation Testing (연속압입시험법을 이용한 원전구조물의 잔류응력 평가를 위한 접촉깊이의 보정)

  • Kim, Young-Cheon;Kang, Seung-Kyun;Ahn, Hee-Jun;Kim, Kwang-Ho;Kwon, Dongil
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.7 no.1
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    • pp.41-47
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    • 2011
  • Residual stress is the key parameter for reliability and lifetime assessment because it can reduce the fatigue strength and fracture properties of industrial structures. Recently, instrumented indentation testing (IIT) has been widely used for evaluating it, since it does not need specific specimen and time-consuming procedure. However, conventional Oliver-Pharr method, which is used for calibrating contact depth to analyze indentation load-depth curve, cannot estimate plastic pile-up between indenter and surface of specimen. Here, we introduce f parameter which is the ratio of contact depth and maximum depth, to consider pile-up height. And, its application for evaluating residual stress of weldment is introduced.

A Study of Non-destructive Indentation and Small Punch Tests for Monitoring Materials Reliability (소재의 안전전단을 위한 비파괴 압입 및 소형펀치 시험법 연구)

  • Ok Myoung-Ryul;Ju Jang-Bog;Lee Jeong-Hwan;Ahn Jeong-Hoon;Nahm Seung Hoon;Lee Hae-Moo;Kwon Dongil
    • 한국가스학회:학술대회논문집
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    • 1997.09a
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    • pp.78-85
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    • 1997
  • Indentation and small punch tests are very powerful methods to monitor the materials reliability since they are very simple, easy and almost non-destructive. First, recently-developed continuous indentation test can provide the more material properties such as hardness, elastic modulus, yield strength, work-hardening exponent, etc., than the conventional hardness test. In our study, the true stress-strain curve was derived from the indentation load-depth curve for spherical indentation. In detail, the strain was able to be obtained from plastic depth/contact radius ratio, and the flow stress was from mean contact pressure through the analysis of elastic-plastic indentation stress field. Secondly, the small punch test was studied to evaluate the fracture toughness and defomation properties such as elastic modulus and yield strength. Like the indentation test, this test can be applied without severe damage of the target structure.

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