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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Nanoindentation ： ウィキペディア英語版 Nanoindentation Nanoindentation is a variety of indentation hardness tests applied to small volumes. Indentation is perhaps the most commonly applied means of testing the mechanical properties of materials. The nanoindentation technique was developed in the mid-1970s to measure the hardness of small volumes of material. ==Background== In a traditional indentation test (macro or micro indentation), a hard tip whose mechanical properties are known (frequently made of a very hard material like diamond) is pressed into a sample whose properties are unknown. The load placed on the indenter tip is increased as the tip penetrates further into the specimen and soon reaches a user-defined value. At this point, the load may be held constant for a period or removed. The area of the residual indentation in the sample is measured and the hardness, $H$, is defined as the maximum load, $P\_$, divided by the residual indentation area, $A\_r$: :$H=\backslash frac\}.$ For most techniques, the projected area may be measured directly using light microscopy. As can be seen from this equation, a given load will make a smaller indent in a "hard" material than a "soft" one. This technique is limited due to large and varied tip shapes, with indenter rigs which do not have very good spatial resolution (the location of the area to be indented is very hard to specify accurately). Comparison across experiments, typically done in different laboratories, is difficult and often meaningless. Nanoindentation improves on these macro- and micro-indentation tests by indenting on the nanoscale with a very precise tip shape, high spatial resolutions to place the indents, and by providing real-time load-displacement (into the surface) data while the indentation is in progress. In nanoindentation small loads and tip sizes are used, so the indentation area may only be a few square micrometres or even nanometres. This presents problems in determining the hardness, as the contact area is not easily found. Atomic force microscopy or scanning electron microscopy techniques may be utilized to image the indentation, but can be quite cumbersome. Instead, an indenter with a geometry known to high precision (usually a Berkovich tip, which has a three-sided pyramid geometry) is employed. During the course of the instrumented indentation process, a record of the ''depth'' of penetration is made, and then the area of the indent is determined using the known geometry of the indentation tip. While indenting, various parameters such as load and depth of penetration can be measured. A record of these values can be plotted on a graph to create a ''load-displacement curve'' (such as the one shown in Figure 1). These curves can be used to extract mechanical properties of the material. *Young's modulus: The slope of the curve, $dP/dh$, upon unloading is indicative of the stiffness $S$ of the contact. This value generally includes a contribution from both the material being tested and the response of the test device itself. The stiffness of the contact can be used to calculate the reduced Young's modulus $E\_r$: $E\_r=\backslash frac\backslash frac\backslash frac+C\_3h\_c^+\backslash ldots+C\_8h\_c^$ Where $C\_0$ for a Berkovich tip is 24.5 while for a cube corner (90°) tip is 2.598. The reduced modulus $E\_r$ is related to Young's modulus $E\_s$ of the test specimen through the following relationship from contact mechanics: $1/E\_r=(1-\backslash nu\_i^2)/E\_i+(1-\backslash nu\_s^2)/E\_s.$ Here, the subscript $i$ indicates a property of the indenter material and $\backslash nu$ is Poisson's ratio. For a diamond indenter tip, $E\_i$ is 1140 GPa and $\backslash nu\_i$ is 0.07. Poisson’s ratio of the specimen, $\backslash nu\_s$, generally varies between 0 and 0.5 for most materials (though it can be negative) and is typically around 0.3. *Hardness: There are two different types of hardness that can be obtained from a nano indenter: one is as in traditional macroindentation tests where one attains a single hardness value per experiment; the other is based on the hardness as the material is being indented resulting in hardness as a function of depth. $H=\backslash frac\}.$ The hardness is given by the equation above, relating the maximum load to the indentation area. The area can be measured after the indentation by in-situ atomic force microscopy, or by 'after-the event' optical (or electron) microscopy. An example indentation image, from which the area may be determined, is shown at right. Some nanoindenters use an ''area function'' based on the geometry of the tip, compensating for elastic load during the test. Use of this area function provides a method of gaining real-time nanohardness values from a load-displacement graph. However, there is some controversy over the use of ''area functions'' to estimate the residual areas versus direct measurement. An area function $A\_p(h\_c)$ typically describes the projected area of an indent as a 2nd-order polynomial function of the indenter depth $h$. When too many coefficients are used, the function will begin to fit to the noise in the data, and inflection points will develop. If the curve can fit well with only two coefficients, this is the best. However, if many data points are used, sometimes all 6 coefficients will need to be used to get a good area function. Typically, 3 or 4 coefficients works well.〔Hysitron; Service Document Probe Calibration; CSV-T-003 v3.0; http://www.hysitron.com/media/1683/t-003-v30-probe-calibration.pdf〕 Exclusive application of an area function in the absence of adequate knowledge of material response can lead to misinterpretation of resulting data. Cross-checking of areas microscopically is to be encouraged. *Strain-rate sensitivity: The strain-rate sensitivity of the flow stress $m$ is defined as $m=\backslash frac\}\},$ where $\backslash sigma=\backslash sigma(\backslash dot)$ is the flow stress and $\backslash dot$ is the strain rate produced under the indenter. For nanoindentation experiments which include a holding period at constant load (i.e. the flat, top area of the load-displacement curve), $m$ can be determined from $d\backslash ln=m\; d\backslash ln.$ The subscripts $p$ indicate these values are to be determined from the plastic components ''only''. *Activation volume: Interpreted loosely as the volume swept out by dislocations during thermal activation, the activation volume $V^$ * is $V^$ *=9 k_B T \frac, where $T$ is the temperature and ''kB'' is Boltzmann's constant. From the definition of $m$, it is easy to see that $V^$ *\propto (H m)^. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nanoindentation」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.