JP2015004535A - Fracture toughness measuring method of test piece, and mixed solution for fracture toughness measurement of test piece - Google Patents
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Abstract
Description
本発明は、セラミックス材料や超硬材料、金属間化合物などの脆性物質の破壊靭性を測定する方法に関し、特に圧子圧入法（Indentation Fracture法、IF法）による破壊靭性の測定方法に関する。 The present invention relates to a method for measuring the fracture toughness of a brittle substance such as a ceramic material, a super hard material, or an intermetallic compound, and more particularly to a method for measuring the fracture toughness by an indentation press-fitting method (Indentation Fracture method, IF method).
セラミックス等の脆性材料の破壊靭性の測定法として、圧子圧入法（以下「IF法」と記載する）があり、材料の研究開発や製造現場での品質管理、商取引における製品品質のクラス分けなど、多方面で世界的に用いられている。 As a method of measuring fracture toughness of brittle materials such as ceramics, there is an indenter press-in method (hereinafter referred to as “IF method”), such as material research and development, quality control at the manufacturing site, and product quality classification in commerce, etc. Used worldwide in many ways.
IF法は、図５、図６に例示したように、鏡面に仕上げた試験片（脆性材料）１の表面にビッカース圧子２を所定の荷重で押し込み、圧痕３の周りに半円形もしくは半楕円形の垂直亀裂４を発生させ、この圧痕３の対角線長さ2a1,2a2、亀裂長さ2C１,2C２、押込荷重、弾性率をもとに、破壊靭性を評価する方法である。その測定操作の簡便性と実用性から、この方法は、JIS R1607「ファインセラミックスの室温破壊じん（靱）性試験方法」においては、予亀裂導入破壊試験法（SEPB法：Single−Edge−Precracked−Beam Method）に準じる測定方法として採用されている。 In the IF method, as illustrated in FIGS. 5 and 6, the Vickers indenter 2 is pushed into the surface of the mirror-finished test piece (brittle material) 1 with a predetermined load, and a semicircular or semielliptical shape around the indentation 3. The vertical crack 4 is generated, and the fracture toughness is evaluated based on the diagonal lengths 2a 1 and 2a 2 , crack lengths 2C 1 and 2C 2 , indentation load, and elastic modulus of the indent 3. Because of the simplicity and practicality of the measurement operation, this method is based on the precracking fracture test method (SEPB method: Single-Edge-Precracked-) in JIS R1607 "Testing method for room temperature fracture toughness of fine ceramics". It is used as a measurement method according to Beam Method.
このJIS R1607においては試験回数を５回以上として、個々の圧痕３の測定値から、次の式によって破壊靭性が算出される。 In this JIS R1607, the number of tests is 5 or more, and the fracture toughness is calculated from the measured value of each indentation 3 by the following formula.
ここで、Ｋｃは破壊靭性値（ＭＰａ・m1/2）、Ｅは弾性率（Ｐａ）でJIS R 1602によって測定された値を用いる。ＨＶはビッカース硬さ（Ｐａ）、Ｐは押込荷重（Ｎ）でビッカース圧子の押込荷重として硬さ試験機に設定した押込荷重（Ｎ）を用いる。Ｃは亀裂長さの平均の半分（ｍ）であり、ａは圧痕の対角線長さの平均の半分（ｍ）である。図５に示した圧痕の対角線長さ2a1,2a2と亀裂長さ2C１,2C２は、多くの場合、硬度計に付属の光学顕微鏡と測定ゲージ(オクラと呼ぶ)、または、金属顕微鏡などを用いて測定されることが一般的である。また、光学顕微鏡の対物レンズの倍率は10倍から20倍であり、接眼レンズの倍率は5〜10倍であることが多い。JIS R1607においてはこのように個々の圧痕に対して破壊靭性が計算され、その平均値を破壊靭性値として報告することになっている。 Here, K c is a fracture toughness value (MPa · m 1/2 ), and E is an elastic modulus (Pa) measured by JIS R 1602. HV is Vickers hardness (Pa), P is indentation load (N), and the indentation load (N) set in the hardness tester is used as the indentation load of the Vickers indenter. C is half of the average crack length (m), and a is half the average diagonal length of the indentation (m). In most cases, the indentation diagonal lengths 2a 1 and 2a 2 and crack lengths 2C 1 and 2C 2 shown in FIG. 5 are an optical microscope and a measurement gauge (called okra) attached to the hardness meter, or a metal microscope. It is common to measure using, for example. Moreover, the magnification of the objective lens of the optical microscope is 10 to 20 times, and the magnification of the eyepiece is often 5 to 10 times. In JIS R1607, fracture toughness is calculated for each indentation in this way, and the average value is reported as the fracture toughness value.
ファインセラミックスを対象とした破壊靭性の測定においては、JISに採用されている上記の三好の式（化１）が用いられることが国内では一般的である（JIS R1607、2010年 解説ｐ.20−23参照）。一方で、IF法の算出式は、経験的な式であることから、同じ測定パラメータを用いるものの係数や指数が若干異なるだけの算出式が多く提案されており、国外においては新原の式が多用されている（ISO14627，ASTM F2094など）。また、超硬材料や金属間化合物などでは、これらとはまた異なる算出式が用いられることもある。 In the measurement of fracture toughness for fine ceramics, it is common in Japan that the above Miyoshi formula (Formula 1) adopted in JIS is used (JIS R1607, 2010, p.20-). 23). On the other hand, since the calculation formula of the IF method is an empirical formula, many calculation formulas that use the same measurement parameters but with slightly different coefficients and indices have been proposed. (ISO14627, ASTM F2094, etc.). In addition, different calculation formulas may be used for superhard materials and intermetallic compounds.
また、ベアリングボールを始め切削工具などのセラミックス製の比較的小型製品の破壊靭性の評価には、3×4×40mm程度の試験片を必要とする破壊靭性測定方法を利用することができない。一方、IF法は圧痕を打つことができる平らな面があれば測定できるために、小試験片に対応できるというメリットを有している。さらに、IF法は、試験方法が簡単であり試験環境の制御も比較的容易という長所も有している。このような理由から、IF法は、国内では標準的な破壊靭性の測定手法として主に工業界において多用されている。 In addition, the fracture toughness measurement method that requires a test piece of about 3 × 4 × 40 mm cannot be used to evaluate the fracture toughness of relatively small products made of ceramics such as bearing balls and cutting tools. On the other hand, the IF method has an advantage that it can be applied to a small test piece because it can be measured if there is a flat surface on which an indentation can be made. Further, the IF method has the advantage that the test method is simple and the control of the test environment is relatively easy. For these reasons, the IF method is frequently used in the industry mainly as a standard fracture toughness measurement method in Japan.
しかしながら、国外においては、共通試験片を用いた国際的なラウンドロビン試験において著しく再現性に劣るなどの理由から、国際標準化が見送られ、標準的な試験手法としてみなされてこなかった。 However, international standardization has been postponed overseas and has not been regarded as a standard test method because of remarkably poor reproducibility in an international round robin test using a common test piece.
測定値の再現性が劣る主な理由の一つに、従来の光学顕微鏡による観察においては、例えば、一般的な硬さ試験機に付属の光学顕微鏡と測定ゲージ（オクラ）を用いた場合では、亀裂４先端の識別が困難で、測定者の主観や経験、視力に依存して亀裂長さの測定精度が大きく低下するといったことが挙げられる。特に、白色のセラミックスなどでは亀裂先端が不明瞭であることが多く、測定精度の低下が避けられない。 One of the main reasons why the reproducibility of measured values is inferior is that in observation with a conventional optical microscope, for example, when using an optical microscope and measurement gauge (Okra) attached to a general hardness tester, For example, it is difficult to identify the tip of the crack 4, and the measurement accuracy of the crack length greatly decreases depending on the subjectivity, experience, and visual acuity of the measurer. In particular, in white ceramics, the crack tip is often unclear, and a reduction in measurement accuracy is inevitable.
そして、このような問題を解決するための方法についての検討がなされている。具体的には、例えば、特許文献１では、IF法による試験に先立ち、セラミックス試験片の表面に予め、不透明かつ有色な揮発性の塗料を薄く塗布し乾燥させて被膜を形成する方法が提案されている。 And the examination about the method for solving such a problem is made. Specifically, for example, Patent Document 1 proposes a method in which an opaque and colored volatile paint is thinly applied in advance to the surface of a ceramic test piece and dried to form a film prior to the test by the IF method. ing.
さらに、特許文献２では、IF法による試験に先立ち、金属薄膜を蒸着させ、その後にビッカース圧子を圧入し、生成する亀裂を光学顕微鏡で観察する方法が提案されている。この方法によれば、試験片自体の亀裂観察は困難でも、薄膜に生じた亀裂の観察は容易であることから、試験片の亀裂の識別が容易にでき、破壊靭性測定が容易かつ正確にできるとされている。 Further, Patent Document 2 proposes a method in which a metal thin film is vapor-deposited prior to a test by the IF method, and then a Vickers indenter is press-fitted and a generated crack is observed with an optical microscope. According to this method, even though it is difficult to observe the crack of the test piece itself, it is easy to observe the crack generated in the thin film. Therefore, the crack of the test piece can be easily identified, and the fracture toughness can be easily and accurately measured. It is said that.
さらに別の方法として、倍率が40〜50倍以上の対物レンズ採用し、顕微鏡観察の分解能を向上させて亀裂先端の位置決めを容易にし、亀裂先端間の長さを試料ステージの移動量から求めるという方法も提案されている(非特許文献１)。 As another method, an objective lens with a magnification of 40 to 50 times or more is adopted to improve the resolution of microscopic observation to facilitate the positioning of the crack tip, and the length between the crack tips is obtained from the amount of movement of the sample stage. A method has also been proposed (Non-Patent Document 1).
しかしながら、特許文献１、２の方法では、インクの被膜や金属薄膜が試験片に確実に密着して、試験片表面に生じた亀裂がそのまま被膜にも正確に伝わっているかどうかを保証することができない。すなわち、図７に例示したように、例えば、セラミックスなどの試験片では脆性であるために微小な変位でも亀裂が生じるが、これら薄膜は延性を有するから、下にあるセラミックス試験片に亀裂が生じていても微小な変位では膜が伸びるだけで亀裂が生じない可能性がある。さらには、試験片表面から膜が剥離している可能性もある。このために試験片に生じた亀裂長さを正確に測定できなくなってしまう恐れがある。 However, in the methods of Patent Documents 1 and 2, it is possible to ensure that the ink film or the metal thin film is in close contact with the test piece and that the crack generated on the surface of the test piece is directly transmitted to the film as it is. Can not. That is, as illustrated in FIG. 7, for example, a test piece such as ceramics is brittle and thus cracks occur even with a minute displacement. However, since these thin films have ductility, cracks occur in the underlying ceramic test pieces. However, if the displacement is small, the film may be stretched and cracks may not occur. Furthermore, the film may be peeled off from the surface of the test piece. For this reason, there is a fear that the crack length generated in the test piece cannot be measured accurately.
また、特許文献１、２のような被膜が試験片表面に存在すると、ビッカース圧子の圧入時に生じる圧子と試験片との摩擦が、膜を付けずに試験片に直に圧入した時の摩擦と異なるため、測定される破壊靭性の値に影響すると考えられる。さらに、膜に用いるインクや金属の種類及び膜厚によって試験片の圧入時の摩擦の大きさが異なると考えられるため、インクの成分や金属の種類及び膜の作製条件や膜厚を厳密に統一しなければ、再現性ある測定値は期待できない。このように、特許文献１、２の方法は、IF法による試験に先立って試験片に予め被膜を形成するため、測定値のばらつきを抑えることが難しく、広く普及するには至っていない。 In addition, when a coating as in Patent Documents 1 and 2 is present on the surface of the test piece, the friction between the indenter and the test piece generated when the Vickers indenter is pressed is the friction when the test piece is directly pressed into the test piece without attaching a film. Due to the difference, it is considered that the measured fracture toughness value is affected. In addition, since the magnitude of friction when press-fitting a test piece varies depending on the type of ink and metal used for the film and the film thickness, the ink components, metal type, film preparation conditions and film thickness are strictly unified. Otherwise, reproducible measurements cannot be expected. As described above, the methods of Patent Documents 1 and 2 form a film in advance on the test piece prior to the test by the IF method, so that it is difficult to suppress variations in measured values and have not been widely used.
さらに、非特許文献１の方法では、高倍率の対物レンズが必要であるため、低倍率での測定に対応し難く、また、移動量が正確に測定できる試料ステージを利用するため、汎用性に欠けるという問題がある。 Furthermore, since the method of Non-Patent Document 1 requires a high-magnification objective lens, it is difficult to support measurement at a low magnification, and since a sample stage that can accurately measure the amount of movement is used, it is versatile. There is a problem of lacking.
本発明は、以上のとおりの事情に鑑みてなされたものであり、IF法において、試験片に生じた亀裂長さを高精度かつ再現性高く測定することができ、低倍率での測定にも対応可能な汎用性に優れた試験片の破壊靭性測定方法を提供することを課題としている。また、この試験片の破壊靭性測定方法に利用される破壊靭性測定用混合溶液を提供することを課題としている。 The present invention has been made in view of the circumstances as described above, and in the IF method, the crack length generated in the test piece can be measured with high accuracy and high reproducibility, and can be measured at a low magnification. It is an object to provide a fracture toughness measuring method of a test piece excellent in versatility that can be handled. Another object of the present invention is to provide a mixed solution for measuring fracture toughness used in this method for measuring fracture toughness of test pieces.
上記の課題を解決するために、本発明の破壊靭性測定方法は、試験片の破壊靭性測定方法であって、以下の工程、（１）試験片の表面にビッカース圧子を圧入して圧痕および亀裂を生じさせる工程、（２）試験片の表面に樹脂と溶媒を含む混合溶液を塗布し、圧痕および亀裂を覆う透明被膜を形成する工程、（３）前記透明被膜が形成された試験片表面の圧痕の対角線長さおよび亀裂長さを顕微鏡で計測する工程、を含むことを特徴としている。 In order to solve the above-mentioned problems, the fracture toughness measurement method of the present invention is a test method for fracture toughness of a test piece, which includes the following steps: (1) Indentation and cracking by pressing a Vickers indenter into the surface of the test piece (2) A step of applying a mixed solution containing a resin and a solvent to the surface of the test piece to form a transparent film covering the indentations and cracks, and (3) a surface of the test piece on which the transparent film is formed. A step of measuring the diagonal length and crack length of the indentation with a microscope.
この破壊靭性測定方法では、前記工程（２）で形成される透明被膜の厚みが、４０ｎｍ〜３００ｎｍの範囲であることが好ましい。 In this fracture toughness measurement method, it is preferable that the thickness of the transparent film formed in the step (2) is in the range of 40 nm to 300 nm.
この破壊靭性測定方法では、前記工程（２）における混合溶液の溶媒は、非極性溶媒であることがより好ましい。 In this fracture toughness measurement method, the solvent of the mixed solution in the step (2) is more preferably a nonpolar solvent.
この破壊靭性測定方法では、前記工程（２）における混合溶液における樹脂の濃度は、１％〜２５％であることがさらに好ましい。 In this fracture toughness measuring method, the resin concentration in the mixed solution in the step (2) is more preferably 1% to 25%.
本発明の試験片の破壊靭性測定用混合溶液は、樹脂と非極性溶媒とを含み、試験片の表面にビッカース圧子を押し込んで生じた圧痕および亀裂を覆って透明被膜を形成するものであることを特徴としている。 The mixed solution for fracture toughness measurement of the test piece of the present invention contains a resin and a nonpolar solvent, and forms a transparent film covering the indentation and cracks generated by pressing a Vickers indenter on the surface of the test piece. It is characterized by.
この試験片の破壊靭性測定用混合溶液では、樹脂の濃度は、１％〜２５％であることが好ましい。 In the mixed solution for measuring fracture toughness of the test piece, the concentration of the resin is preferably 1% to 25%.
本発明の破壊靭性測定方法によれば、IF法において、試験片に生じた亀裂長さを高精度かつ再現性高く測定することができ、低倍率での測定にも対応可能であるため汎用性に優れている。また、本発明の試験片の破壊靭性測定用混合溶液によれば、上記効果を確実に実現することができる。 According to the fracture toughness measurement method of the present invention, in the IF method, the crack length generated in the specimen can be measured with high accuracy and high reproducibility, and it can be used for measurement at a low magnification. Is excellent. In addition, according to the mixed solution for measuring fracture toughness of the test piece of the present invention, the above-described effect can be reliably realized.
本発明者らは、上記従来技術の問題点を解決するため、測定する試験片の亀裂の識別、長さ計測を容易かつ正確に行うことが可能な新しい測定方法を開発することを目標として鋭意研究を積み重ねた。 In order to solve the above-mentioned problems of the prior art, the present inventors diligently aiming to develop a new measurement method capable of easily and accurately performing crack identification and length measurement of a specimen to be measured. Accumulated research.
その結果、非常に細く、かつコントラストが弱い試験片の亀裂先端の観察を困難にしている要因は、例えば図１に例示したように、試料表面上の微細な凹凸による光の乱反射であり、この光の乱反射がノイズとなり、亀裂先端からの光の反射を識別し難くしていると推察された。 As a result, the factor that makes it difficult to observe the crack tip of a specimen that is very thin and has low contrast is, for example, irregular reflection of light due to fine irregularities on the sample surface, as illustrated in FIG. It was inferred that the diffuse reflection of light became noise, making it difficult to distinguish the reflection of light from the crack tip.
このような推察に基づいて、本発明者らは、試験片へのビッカース圧子の圧入後に圧痕および亀裂を樹脂と溶媒を含む混合溶液で被覆して透明被膜を形成することにより、光の乱反射を抑制し、亀裂の識別を容易かつ正確に行うことができるのではないかと着想し、本発明を完成させるに至った。 Based on such inferences, the present inventors made irregular reflection of light by forming a transparent film by coating indentations and cracks with a mixed solution containing a resin and a solvent after injecting a Vickers indenter into a test piece. It was conceived that cracks could be easily and accurately identified, and the present invention was completed.
以下、本発明の試験片の破壊靭性測定方法およびこれに利用される破壊靭性測定混合溶液の一実施形態について詳しく説明する。 Hereinafter, an embodiment of a fracture toughness measurement method for a test piece of the present invention and a fracture toughness measurement mixed solution used therefor will be described in detail.
本発明の試験片の破壊靭性測定方法は、JIS R1607（2010年）に示されるＩＦ法に沿って行うことができる。そして、本発明の試験片の破壊靭性測定方法は、以下の工程、
（１）試験片の表面にビッカース圧子を圧入して圧痕および亀裂を生じさせる工程、
（２）試験片の表面に樹脂と溶媒を含む混合溶液を塗布し、圧痕および亀裂を覆う透明被膜を形成する工程、
（３）前記透明被膜が形成された試験片表面の圧痕の対角線長さおよび亀裂長さを顕微鏡で計測する工程、
を含む。
The method for measuring the fracture toughness of the test piece of the present invention can be carried out according to the IF method shown in JIS R1607 (2010). And the fracture toughness measuring method of the test piece of the present invention includes the following steps:
(1) a step of pressing a Vickers indenter into the surface of the test piece to generate indentations and cracks;
(2) A step of applying a mixed solution containing a resin and a solvent to the surface of the test piece to form a transparent film covering the indentations and cracks,
(3) a step of measuring the diagonal length and crack length of the indentation on the surface of the test piece on which the transparent film is formed with a microscope,
including.
工程（１）では、試験片の表面にビッカース圧子を圧入して圧痕および亀裂を生じさせる。 In step (1), a Vickers indenter is pressed into the surface of the test piece to generate indentations and cracks.
試験片は、破壊靭性を測定すべき試料を３×４×４０ｍｍ程度の大きさに切り出したものであり、材料としては、ＩＦ法の測定対象とされる各種セラミックス 、超硬材料、金属間化合物などを適宜選択することができる。 The test piece is obtained by cutting a sample whose fracture toughness is to be measured into a size of about 3 × 4 × 40 mm, and includes, as materials, various ceramics, super hard materials, and intermetallic compounds that are measured by the IF method. Etc. can be appropriately selected.
ビッカース圧子の圧入の際の押込荷重や荷重保持時間などの条件は適宜設定することができ、例えば、押込荷重は４．９〜４９０Ｎ、荷重保持時間は、１０〜３０秒程度の範囲を例示することができる。 Conditions such as indentation load and load holding time when the Vickers indenter is press-fitted can be appropriately set. For example, the indentation load is 4.9 to 490 N, and the load holding time is in the range of about 10 to 30 seconds. be able to.
工程（２）では、試験片の表面に樹脂と溶媒を含む混合溶液を塗布し、圧痕および亀裂を覆う透明被膜を形成する。 In step (2), a mixed solution containing a resin and a solvent is applied to the surface of the test piece to form a transparent film that covers the indentations and cracks.
混合溶液に含まれる樹脂は、例えば、ロジン、ギルソナイトなどの天然樹脂や、ポリエチレン、ポリプロピレン、ポリ塩化ビニル、ポリスチレン、フタル酸樹脂などの合成樹脂などを例示することができる。また、樹脂には、合成樹脂に添加されるパラフィンやステアリン酸などの公知の滑剤、安定剤、可塑剤などが含まれていてもよい。 Examples of the resin contained in the mixed solution include natural resins such as rosin and gilsonite, and synthetic resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, and phthalic acid resin. The resin may also contain known lubricants such as paraffin and stearic acid, stabilizers, plasticizers and the like added to the synthetic resin.
溶媒は、樹脂を溶解できるものであれば特に限定されないが、水分の混入を避けるために、非極性溶媒であることが望ましい。溶媒に水分が含まれると、セラミックスにおいては低速亀裂成長が生じ、本来の亀裂長さよりも長い亀裂が測定される恐れがある。したがって、溶媒が非極性溶媒であることで、試験片の亀裂を正確に測定することができる。 The solvent is not particularly limited as long as it can dissolve the resin, but is preferably a nonpolar solvent in order to avoid mixing of moisture. When moisture is contained in the solvent, slow crack growth occurs in the ceramic, and there is a possibility that a crack longer than the original crack length is measured. Therefore, the crack of a test piece can be correctly measured because a solvent is a nonpolar solvent.
また、溶媒は、混合溶液を試験片に塗布した後速やかに乾燥する高い揮発性を有していることが好ましい。 Moreover, it is preferable that the solvent has high volatility which dries quickly after apply | coating a mixed solution to a test piece.
具体的には、溶媒としては、例えば、市販のペイント薄め液やシンナー（例えば、ロックペイント株式会社製など）、リグロインなどの高沸点石油系溶剤、メチルシクロヘキサンや、ノルマルヘキサン、ノルマルヘプタンなどの脂肪族炭化水素などを例示することができる。 Specifically, examples of the solvent include commercially available paint thinning solutions and thinners (for example, manufactured by Rock Paint Co., Ltd.), high-boiling petroleum solvents such as ligroin, fats such as methylcyclohexane, normal hexane, and normal heptane. A group hydrocarbon etc. can be illustrated.
そして、上記のような樹脂と溶媒を含む混合溶液としては、例えば、非極性溶媒を用いている市販のフタル酸樹脂ワニスを好適に例示することができる。 And as a mixed solution containing the above resin and a solvent, the commercially available phthalic-acid resin varnish which uses a nonpolar solvent can be illustrated suitably, for example.
これらの樹脂と溶媒を含む混合溶液の濃度としては、例えば、市販のワニス（樹脂成分５０重量％）を薄め液で希釈する場合では、樹脂成分の濃度が1〜25重量％の範囲であることが好ましく、さらに、樹脂成分が4〜12重量％であることがより好ましい。混合溶液中の樹脂濃度が１重量％未満であると、１回の塗布で十分な厚みの透明被膜を形成することが難しく、4回以上の重ね塗りする場合には被膜の表面の平滑性が損なわれる恐れがあるためである。一方、樹脂濃度が25重量％を超えると、１回の塗布で好適な被膜厚さよりも厚い透明被膜が形成されてしまうといった問題や、混合溶液の粘性が高いと試験片表面に亀裂全体を覆うように液を押し広げて塗布する際に、場所によって厚みのむらが生じやすく、試料表面に均一に塗布が難しくなるという問題が生じる。したがって、樹脂成分の濃度が1〜25重量％、好ましくは4〜12重量％であることによって、1、2回の塗布で好適な厚みで、かつ表面が平滑な透明被膜を形成することができるため、試験片の表面の凹凸からの乱反射光を著しく低減することができる。 As the concentration of the mixed solution containing these resins and solvents, for example, when a commercially available varnish (resin component 50 wt%) is diluted with a dilute solution, the concentration of the resin component is in the range of 1 to 25 wt%. Further, the resin component is more preferably 4 to 12% by weight. When the resin concentration in the mixed solution is less than 1% by weight, it is difficult to form a transparent film having a sufficient thickness by one application. This is because it may be damaged. On the other hand, if the resin concentration exceeds 25% by weight, a transparent coating thicker than a suitable film thickness is formed by a single application, and if the viscosity of the mixed solution is high, the entire crack surface is covered on the surface of the test piece. Thus, when the liquid is spread and applied, there is a problem in that unevenness in thickness is likely to occur depending on the location, and it becomes difficult to apply uniformly to the sample surface. Therefore, when the concentration of the resin component is 1 to 25% by weight, preferably 4 to 12% by weight, a transparent film having a suitable thickness and a smooth surface can be formed by one or two coatings. Therefore, irregularly reflected light from the irregularities on the surface of the test piece can be significantly reduced.
透明被膜の厚みとしては、40〜300ｎｍの範囲にあることが好ましく、90〜110ｎｍの範囲であることがより好ましい。混合溶液の濃度及び塗布量を適宜選択することにより、好ましい透明被膜の厚さに形成することができる。透明被膜の厚みが40ｎｍ未満であると、試験片の表面凹凸からの乱反射光を十分に除去できなくなるためである。一方、透明被膜の厚みが300ｎｍを超えると、亀裂からのかすかな光の反射さえも弱めてしまい、亀裂自体が見えにくくなる恐れがあるためである。したがって、透明被膜の厚みを40〜300ｎｍ、好ましくは90〜110ｎｍの範囲とすることで、試験片の表面凹凸からの乱反射光を抑制し、亀裂を正確に識別することができる。なお、本発明における「透明被膜の厚み」は、試験片表面の平坦な面から透明被膜の表面までの距離をいう。 The thickness of the transparent coating is preferably in the range of 40 to 300 nm, and more preferably in the range of 90 to 110 nm. By suitably selecting the concentration and the coating amount of the mixed solution, it can be formed to a preferred transparent film thickness. This is because if the thickness of the transparent coating is less than 40 nm, irregularly reflected light from the surface irregularities of the test piece cannot be sufficiently removed. On the other hand, if the thickness of the transparent coating exceeds 300 nm, even faint light reflection from the crack is weakened, and the crack itself may be difficult to see. Therefore, by setting the thickness of the transparent coating in the range of 40 to 300 nm, preferably 90 to 110 nm, it is possible to suppress irregular reflection light from the surface irregularities of the test piece and accurately identify cracks. The “thickness of the transparent coating” in the present invention refers to the distance from the flat surface of the test piece surface to the surface of the transparent coating.
また、試験片への混合溶液の塗布法も特に限定されないが、簡便な方法しては、例えば、フェルトや、綿棒などに混合溶液を含浸させて、圧痕と亀裂全体を覆うように軽く塗る方法などを例示することができる。混合溶液の樹脂濃度が低い場合（樹脂成分10重量％未満）は、所定の厚みの透明被膜を形成するために、圧痕と亀裂の周辺全体をフェルトの先もしくは綿棒などで2〜3回なぞるようにして、均一に混合液を塗布することができる。一方、混合溶液の樹脂濃度が高い場合（樹脂成分10重量％以上）では、樹脂濃度が低い場合に比べて少なくてよいので、なぞる回数は１回でも好適な厚みの透明被膜を形成することができる。 In addition, the method of applying the mixed solution to the test piece is not particularly limited, but as a simple method, for example, a method of impregnating the mixed solution into a felt, a cotton swab, etc., and applying lightly so as to cover the indentation and the entire crack Etc. can be illustrated. If the resin concentration of the mixed solution is low (less than 10% by weight of the resin component), trace the entire periphery of the indentation and crack with a felt tip or cotton swab 2 to 3 times to form a transparent film with the specified thickness. Thus, the mixed solution can be uniformly applied. On the other hand, when the resin concentration of the mixed solution is high (resin component: 10% by weight or more), it may be less than when the resin concentration is low, so that a transparent film having a suitable thickness can be formed even if the number of times of tracing is one. it can.
そして、混合溶液において揮発性の高い非極性溶媒を使用する場合、混合溶液中の樹脂濃度が低い場合は、塗布した混合溶液の揮発成分（非極性溶媒）が多いので、溶液塗布後に３０秒程度で乾燥し、混合溶液中の樹脂濃度が高い場合は数秒で乾燥が完了する。これにより、試験片表面に薄く平滑な透明被膜を均一に形成することができる。 And when using a highly volatile nonpolar solvent in the mixed solution, if the resin concentration in the mixed solution is low, there are many volatile components (nonpolar solvent) in the applied mixed solution, so about 30 seconds after applying the solution. When the resin concentration in the mixed solution is high, the drying is completed within a few seconds. Thereby, a thin and smooth transparent film can be uniformly formed on the surface of the test piece.
工程（３）では、前記透明被膜が形成された試験片表面の圧痕の対角線長さおよび亀裂長さを顕微鏡で計測する。 In step (3), the diagonal length and crack length of the indentation on the surface of the test piece on which the transparent film is formed are measured with a microscope.
図５に例示したように、本発明における「圧痕の対角線長さ」は、長さ2a1,2a2で表され、「亀裂長さ」は、対向する亀裂の先端の間の長さ2C1,2C2で表される。この圧痕の対角線長さおよび亀裂長さを適宜な光学顕微鏡を用いて計測し、押込荷重、弾性率とともに、現在提案されている算出式（JIS R 1607の式（化１）、ISO14627，ASTM F2094など）に基づいて試験片の破壊靭性を評価することができる。 As illustrated in FIG. 5, the “diagonal diagonal length” in the present invention is represented by the lengths 2a 1 and 2a 2 , and the “crack length” is the length 2C 1 between the tips of the opposing cracks. , represented by 2C 2. The diagonal length and crack length of this indentation are measured using an appropriate optical microscope, and together with the indentation load and elastic modulus, the currently proposed calculation formula (JIS R 1607 formula (Chemical formula 1), ISO14627, ASTM F2094 Etc.), the fracture toughness of the specimen can be evaluated.
本発明の試験片の破壊靭性測定方法は、工程（２）において、試験片の表面に樹脂と溶媒を含む混合溶液を塗布し、圧痕および亀裂を覆う透明被膜を形成する。このため、透明被膜が試験片表面の凹凸を埋めて平滑な表面を形成し、試験片表面の凹凸からの乱反射光を著しく低減することができる（図２）。これにより、ノイズの減少、つまりＳ／Ｎ比の増大により、亀裂からのかすかな反射でも比較的容易にとらえることができるので、亀裂先端の位置を容易かつ正確に識別して計測することが可能となる。 In the method for measuring fracture toughness of a test piece of the present invention, in step (2), a mixed solution containing a resin and a solvent is applied to the surface of the test piece to form a transparent film covering the indentations and cracks. For this reason, the transparent coating fills the unevenness on the surface of the test piece to form a smooth surface, and the irregularly reflected light from the unevenness on the surface of the test piece can be significantly reduced (FIG. 2). As a result, it is possible to easily detect the position of the crack tip easily and accurately because it is possible to catch even a slight reflection from the crack by reducing noise, that is, increasing the S / N ratio. It becomes.
本発明の試験片の破壊靭性測定方法では、試験片に亀裂を形成した後に透明被膜を形成するため、従来技術（特許文献１、２）のように試験片に生じた亀裂が被膜に正確に転写されない可能性や、試験片表面からの被膜の剥離の可能性を考慮する必要が全くない。また、ビッカース圧子の圧入時は、透明被膜を形成する前であるから、特許文献１、２のようにビッカース圧子と被膜との摩擦が測定値に影響することもない。 In the method for measuring fracture toughness of a test piece according to the present invention, since a transparent film is formed after forming a crack in the test piece, the crack generated in the test piece is accurately formed in the film as in the prior art (Patent Documents 1 and 2). There is no need to consider the possibility of transfer or the possibility of peeling of the coating from the surface of the test piece. Further, since the Vickers indenter is pressed before the transparent film is formed, the friction between the Vickers indenter and the film does not affect the measured value as in Patent Documents 1 and 2.
さらに、高倍率（例えば倍率が40〜50倍以上）の対物レンズなどを必ずしも必要とせず、汎用の試験装置や、比較的低倍率の光学顕微鏡によって、試験片に生じた亀裂長さを高精度かつ再現性高く測定することができる。このため、本発明の試験片の破壊靭性測定方法は、汎用性に優れ、新たに特別な器具を必要としないため、コストの負担も少ない。 In addition, it does not necessarily require an objective lens with a high magnification (for example, a magnification of 40 to 50 times or more), and a high-precision crack length generated on a test piece can be detected with a general-purpose test device or a relatively low magnification optical microscope. And it can measure with high reproducibility. For this reason, the fracture toughness measuring method for a test piece according to the present invention is excellent in versatility and does not require a new special instrument, so the cost burden is small.
より詳しくは、本発明の試験片の破壊靭性測定方法により、次のような効果が奏される。（１）圧痕対角線長さと亀裂長さの測定に用いる光学顕微鏡の対物レンズの倍率が１０〜２０倍で接眼レンズの倍率が５〜１０倍のような低倍率での測定においては、透明被膜の形成により、精確かつ迅速な破壊靭性の測定方法を提供することができる。
（２）圧痕対角線長さと亀裂長さの測定に用いる光学顕微鏡の対物レンズの倍率が４０〜５０倍で接眼レンズの倍率が１０倍以上のような高倍率での測定においては、透明被膜の形成により、迅速な破壊靭性の測定方法を提供することができる。
（３）試験片表面に、亀裂の識別を容易にすることのできる薄く均一な透明被膜を作成するために用いる破壊靭性測定用混合溶液を提供することができる。
（４）新たな装置を必要とせず、汎用の設備で十分に対応できることから、万人の破壊靭性の測定誤差を低減し、測定値の再現性を向上させることができる。
（５）測定誤差の低減により再現性が向上するため、異なる測定機関において測定された値であっても、信頼してそのデータを用いることができる。
（６）試験片上面に平滑かつ均一な透明被膜を形成するので、研磨途中の粒の破砕や脱落による表面の凹凸や研磨傷がほとんどないようなきわめて平滑な鏡面状態に試験片表面を加工せずとも、十分に信頼できる測定が可能である。このため、試験片表面の鏡面仕上げの条件を緩和することができ、ひいては、研磨工程の簡略化、低コスト化、短時間化に寄与できる。
（７）試験片表面の透明被膜が亀裂先端への水分の侵入を遮ることから、低速亀裂成長を抑制でき、低速亀裂成長の影響による測定誤差を低減することができる。
More specifically, the following effects are exhibited by the method for measuring fracture toughness of a test piece of the present invention. (1) In the measurement at a low magnification such as the magnification of the objective lens of the optical microscope used for the measurement of the indentation diagonal length and the crack length is 10 to 20 times and the magnification of the eyepiece is 5 to 10 times, Formation can provide an accurate and rapid method of measuring fracture toughness.
(2) In measurement at a high magnification such as the magnification of the objective lens of the optical microscope used for measurement of the indentation diagonal length and crack length is 40 to 50 times and the magnification of the eyepiece is 10 times or more, formation of a transparent film Thus, it is possible to provide a quick method for measuring fracture toughness.
(3) It is possible to provide a mixed solution for fracture toughness measurement used to create a thin and uniform transparent film capable of easily identifying cracks on the surface of a test piece.
(4) Since a new apparatus is not required and a general-purpose facility can sufficiently cope with it, it is possible to reduce the measurement error of everyone's fracture toughness and improve the reproducibility of measured values.
(5) Since the reproducibility is improved by reducing the measurement error, even if it is a value measured in a different measuring organization, the data can be used with confidence.
(6) Since a smooth and uniform transparent film is formed on the upper surface of the test piece, the surface of the test piece should be processed into a very smooth mirror surface so that there are almost no surface irregularities or polishing scratches caused by crushing or dropping of grains during polishing. At the very least, a sufficiently reliable measurement is possible. For this reason, the condition of mirror finishing on the surface of the test piece can be relaxed, and as a result, the polishing process can be simplified, the cost can be reduced, and the time can be shortened.
(7) Since the transparent coating on the surface of the test piece blocks moisture from entering the crack tip, slow crack growth can be suppressed, and measurement errors due to the influence of slow crack growth can be reduced.
本発明の試験片の破壊靭性測定方法は、以上の実施形態に限定されることはない。例えば、破壊靭性の算出には、公知の算出式を使用することができ、弾性率と押込荷重と亀裂長さ、圧痕の対角線長さに基づいて算出することができる。 The method for measuring the fracture toughness of the test piece of the present invention is not limited to the above embodiment. For example, a known calculation formula can be used for calculation of fracture toughness, and it can be calculated based on elastic modulus, indentation load, crack length, and diagonal length of indentation.
次に、実施例により本発明の試験片の破壊靭性測定方法について具体的に説明するが、以下の実施例によってなんら限定されるものではない。 Next, the method for measuring the fracture toughness of the test piece of the present invention will be specifically described by way of examples, but is not limited by the following examples.
＜実施例１＞対物レンズを10倍とし接眼レンズを10倍とした低倍率観察での測定精度及び作業効率の向上
焼結助剤に炭素とホウ素を用いて焼結した炭化ケイ素焼結体（イビセラム SC―850）から切り出した3×4×40ｍｍの試験片の表面を鏡面研磨し試験片として用いた。この試験片は、非特許文献１に報告されているIF法の国内ラウンドロビン試験に用いられた試験片と同様のもので、同じ表面仕上げとなっている。このために、報告された値と以下の実施例で測定された値を比較することにより、その測定精度を評価することができるという利点を有する。以下に試験手順を詳述する。
<Example 1> Improvement of measurement accuracy and work efficiency in low-magnification observation with objective lens 10 times and eyepiece lens 10 times Sintered silicon carbide sintered using carbon and boron as sintering aid ( The surface of a 3 × 4 × 40 mm test piece cut out from Ibizerum SC-850) was mirror-polished and used as a test piece. This test piece is the same as the test piece used in the IF round domestic round robin test reported in Non-Patent Document 1, and has the same surface finish. For this reason, it has the advantage that the measurement accuracy can be evaluated by comparing the reported values with the values measured in the following examples. The test procedure is described in detail below.
試験片表面にビッカース圧子を荷重196N（20kgf）にて圧入して押し込み、圧痕およびその周囲に亀裂を形成した（工程（１））。その各圧痕部分について、図５に例示した圧痕の縦と横の２方向の対角線長さ2a１及び2a２、そして、亀裂長さ2C１と2C２を、10倍の対物レンズと10倍の接眼レンズを装着した硬度計付属の顕微鏡により、オクラを用いた一般的な測定を行った。 A Vickers indenter was pressed into the surface of the test piece with a load of 196 N (20 kgf) and pressed to form an indentation and a crack around the indentation (step (1)). For each indentation portion, the diagonal lengths 2a 1 and 2a 2 in the vertical and horizontal directions of the indentation illustrated in FIG. 5 and the crack lengths 2C 1 and 2C 2 are set to 10 times the objective lens and 10 times as large. General measurements using okra were performed with a microscope attached to a hardness meter equipped with an eyepiece.
ここで、押込荷重を196Nとしたのは、JIS R1607の解説において、押込荷重としては196N又は294N程度が望ましいとされており、炭化ケイ素のような低靱性材料の場合は、剥離が発生しないように荷重を選ぶ必要があるとされていることから、剥離を避けるために196Nを選択した。 Here, the indentation load was set to 196N. According to the explanation of JIS R1607, the indentation load is preferably about 196N or 294N. In the case of a low toughness material such as silicon carbide, no peeling occurs. In order to avoid peeling, 196N was selected.
まず、圧痕導入後に、通常の測定手法に従い圧痕の対角線長さと亀裂長さを測定した。次に、非極性溶媒として塗料用シンナー（ロックペイント株式会社製 ペイント薄め液）を用いて市販のワニス（ロックペイント株式会社製、フタル酸樹脂ワニス、樹脂成分48重量%）を希釈した混合溶液（破壊靭性測定用混合溶液）を作製した（樹脂成分4.2重量％）。そして、この混合溶液を染み込ませた綿棒を用いて、圧痕及び亀裂を覆うように試験片表面に混合溶液を薄く均一に塗布し、約１分ほど放置して乾燥させ、厚みが約100ｎｍの透明被膜を形成させた（工程（２））。対物レンズを10倍とし接眼レンズを10倍とした硬度計付属の顕微鏡を用いて同一測定者が圧痕の対角線長さおよび亀裂長さを測定し、透明被膜の測定精度に及ぼす効果を調べた（工程（３））。 First, after the indentation was introduced, the diagonal length and crack length of the indentation were measured according to a normal measurement method. Next, using a paint thinner (a paint thinning solution manufactured by Rock Paint Co., Ltd.) as a non-polar solvent, a mixed solution obtained by diluting a commercially available varnish (manufactured by Rock Paint Co., Ltd., phthalic resin varnish, resin component 48% by weight) ( A mixed solution for fracture toughness measurement) was prepared (resin component 4.2 wt%). Then, using a cotton swab soaked with this mixed solution, apply the mixed solution thinly and uniformly on the surface of the test piece so as to cover the indentations and cracks, leave it to dry for about 1 minute, and have a thickness of about 100 nm. A film was formed (step (2)). The same measurer measured the diagonal length and crack length of the indentation using the microscope attached to the hardness scale with the objective lens 10 times and the eyepiece 10 times, and investigated the effect on the measurement accuracy of the transparent coating ( Step (3)).
試験片表面に透明被膜を形成しない場合と透明被膜を形成した場合での、各圧痕の縦と横の対角線長さの平均と亀裂長さの平均を表１に示す（測定値の単位：μｍ）。 Table 1 shows the average of the vertical and horizontal diagonal lengths and the average of the crack lengths when the transparent film is not formed on the surface of the test piece and when the transparent film is formed (unit of measurement value: μm). ).
表１に示したように、透明被膜の有無にかかわらず、圧痕の対角線長さはほぼ等しかった。一方、亀裂の長さ２Ｃは、「透明被膜あり」の方が〜30μmほど「被膜なし」の場合よりも長くなった。このことから、試験片の表面に透明被膜を形成することにより乱反射光が抑制され、透明被膜を形成しない場合には識別困難であった亀裂の先端までしっかりと観察ができ、亀裂長さを正確に長く測定できたことがわかる。透明被膜を形成した場合の6個の亀裂長さ２Ｃの平均値は、694.2±8.5μmであり、非特許文献１において報告されている、対物レンズの倍率を40〜50倍として接眼レンズの倍率を10倍以上とした高倍率観察と移動ステージを用いた手法により同一試験片における亀裂長さを高精度で測定した値、697.8±12.7μmに極めてよく一致しているといえる。このことから、透明被膜ありの場合は、高倍率観察による測定と同程度の高精度の測定が出来たことが明らかである。 As shown in Table 1, the diagonal length of the indentation was almost equal regardless of the presence or absence of the transparent coating. On the other hand, the crack length 2C was about 30 μm longer with “with transparent coating” than with “without coating”. As a result, by forming a transparent film on the surface of the test piece, irregular reflection light is suppressed, and it is possible to firmly observe the crack tip, which was difficult to identify without forming a transparent film, and to accurately determine the crack length. It can be seen that it was possible to measure for a long time. The average value of 6 crack lengths 2C when a transparent coating is formed is 694.2 ± 8.5 μm, and the magnification of the eyepiece lens reported in Non-Patent Document 1 is 40 to 50 times. It is very close to the value of 697.8 ± 12.7μm, which is a highly accurate measurement of the crack length in the same specimen by high magnification observation with a magnification of 10 times or more and a method using a moving stage. From this, it is clear that in the case of the transparent film, the measurement with the same high accuracy as that by the high magnification observation could be performed.
さらに、6個の圧痕の測定に要する時間も、「透明被膜なし」では30分ほど要したが、「透明被膜あり」の場合、容易に亀裂を識別できるので、測定に要する時間はわずか15分であり、「透明被膜なし」の場合の半分の時間しか必要とせず、著しい作業効率の向上が見られた。
＜実施例２＞対物レンズを50倍とし接眼レンズを10倍とした高倍率観察での作業効率の向上
次に、非特許文献1に記載の高精度の測定手法を用いて、すなわち、50倍の対物レンズと10倍の接眼レンズで亀裂先端を観察してその位置を精確に求め、試料ステージを移動することにより亀裂先端間の距離を精確に測定した。この手法で、試験片の圧痕と亀裂に透明被膜を形成しない場合と、透明被膜を形成した場合で測定を行い、高倍率観察における本発明の方法の有効性を調査した。その結果として得られた各圧痕の対角線長さ２aの平均値と、亀裂長さ2Ｃの平均値を表２に示す（測定値の単位：μｍ）。
In addition, the time required to measure the six indentations was about 30 minutes with “without transparent coating”, but with “with transparent coating”, cracks can be easily identified, so the measurement takes only 15 minutes. Only half of the time required for “without transparent coating” was required, and a significant improvement in work efficiency was observed.
<Example 2> Improvement of working efficiency in high-magnification observation in which the objective lens is 50 times and the eyepiece lens is 10 times Next, using the high-precision measurement method described in Non-Patent Document 1, that is, 50 times The tip of the crack was observed with an objective lens and a 10x eyepiece, and the position was accurately determined. The distance between the crack tips was accurately measured by moving the sample stage. By this method, measurement was performed when a transparent film was not formed on the indentation and crack of the test piece and when a transparent film was formed, and the effectiveness of the method of the present invention in high magnification observation was investigated. The average value of the diagonal length 2a and the average value of the crack length 2C of each indentation obtained as a result are shown in Table 2 (unit of measurement value: μm).
表２に示したように、透明被膜の有無にかかわらず、圧痕の対角線長さはほぼ等しく、６個の平均値もほぼ同じ値となった。また、亀裂の長さ２Ｃも、透明被膜の有無にかかわらず、ほぼ同一であった。この亀裂長さの値は、非特許文献１において報告されている、同一試料を高倍率観察により高精度で測定した値、697.8±12.7μｍによく一致しており、高倍率観察においては、透明被膜の有無は測定精度にほとんど影響を与えなかった。 As shown in Table 2, the diagonal lengths of the indentations were almost the same regardless of the presence or absence of the transparent coating, and the average value of the six was almost the same value. Also, the crack length 2C was almost the same regardless of the presence or absence of the transparent coating. This crack length value is in good agreement with 697.8 ± 12.7μm, which is reported in Non-Patent Document 1 and measured with high precision by high magnification observation, and is transparent in high magnification observation. The presence or absence of the coating hardly affected the measurement accuracy.
しかしながら、6個の圧痕の測定に要する時間は、「透明被膜なし」では26分ほど要したが、「透明被膜あり」の場合、乱反射光が抑制され、容易に亀裂を識別できるので測定に要する時間はわずか12分と半分以下の時間しか必要とせず、著しい作業効率の向上が見られた。
＜実施例３＞異なる測定者による低倍率観察での測定における再現性の向上
次に、測定者による測定値のばらつきを調べることを目的として、６個の圧痕を形成後に、３人の測定者が間隔を開けずに連続して、通常の低倍率観察による上記の方法で亀裂長さを測定した。そして、測定後に、非極性溶媒と樹脂からなる混合溶液を綿棒を用いて薄く均一に圧痕及び亀裂を覆うように試験片表面に塗布し、同じ顕微鏡を用いて、引き続いて、３人の測定者が同じ亀裂を測定した。その結果として得られた各圧痕ごとの縦と横の亀裂長さ２Ｃの平均を表３に示す（測定単位：μｍ）。
However, the time required to measure the six indentations was about 26 minutes in the case of “without transparent coating”, but in the case of “with transparent coating”, diffuse reflection is suppressed and cracks can be easily identified, so measurement is required. The time required was only 12 minutes and less than half, and a significant improvement in work efficiency was seen.
<Example 3> Improvement of reproducibility in measurement by low-magnification observation by different measurers Next, three measurers are formed after forming six indentations for the purpose of examining variations in measured values by measurers. However, the crack length was measured by the above-mentioned method by usual low-magnification observation without gaps. After the measurement, a mixed solution composed of a nonpolar solvent and a resin was applied to the surface of the test piece so as to cover the indentations and cracks thinly and uniformly using a cotton swab, and subsequently, using the same microscope, three measurers Measured the same crack. The average of the vertical and horizontal crack lengths 2C for each indentation obtained as a result is shown in Table 3 (measurement unit: μm).
表３に示したように、同じ圧痕において、透明被膜ありの場合には測定者間のばらつきが低下することが明らかになった。各測定者の平均値を比較しても、透明被膜なしでは、亀裂の長さが654μｍから664まで10μｍほどの相違があるが、透明被膜ありでは693.6μｍから695.5μｍまで、わずか2μｍほどの相違しかなく、極めて高い一致を示した。非特許文献1において報告されている、同一試料を高倍率観察により高精度で測定した値は、697.8±12.7μｍであることから、圧痕形成後に透明被膜を形成する本発明の方法によれば、乱反射光が抑制され、測定者の主観や経験、視力に関わりなく、低倍率観察でも高倍率観察による測定と同程度の高精度の測定が出来たことが明らかであり、このことが、高い再現性をもたらした主因といえる。また、各測定者による６個の圧痕の標準偏差は、透明被膜なしでは、14μｍから24μｍと大きくばらついているが、透明被膜ありの場合は全体的に小さく、かつ、8.5μｍから10.8μｍとなっており、同一測定者の測定においても、安定してばらつきの小さな測定ができることがわかる。 As shown in Table 3, it has been clarified that, in the same indentation, when there is a transparent film, the variation between the measurers decreases. Even if the average value of each measurer is compared, there is a difference of 10 μm from 654 μm to 664 in the crack length without the transparent film, but a difference of only 2 μm from 693.6 μm to 695.5 μm with the transparent film. However, it showed very high agreement. The value of the same sample reported in Non-Patent Document 1 measured with high precision by high-magnification observation is 697.8 ± 12.7 μm, so according to the method of the present invention for forming a transparent film after indentation formation, It is clear that diffuse reflection was suppressed, and high-precision measurements were possible even with low-magnification observations, regardless of the subject's subjectivity, experience, and visual acuity. It can be said that this is the main cause of sex. In addition, the standard deviation of the six indentations by each measurer varies widely from 14 μm to 24 μm without the transparent coating, but is small overall with the transparent coating and from 8.5 μm to 10.8 μm. It can be seen that even the measurement by the same measurer can stably measure with little variation.
さらに、6個の圧痕の測定に要する時間も、「透明被膜なし」では平均30分ほど要したが、「透明被膜あり」の場合、乱反射光が抑制されることで容易に亀裂を識別できるので、測定に要する時間はわずか15分であり、「透明被膜なし」の場合の半分の時間しか必要とせず、著しい作業効率の向上が見られた。 Furthermore, the time required to measure the six indentations took about 30 minutes on average with “without transparent coating”, but with “with transparent coating”, cracks can be easily identified by suppressing irregular reflection light. The time required for the measurement was only 15 minutes, and only half the time required for “without transparent coating” was required, and a significant improvement in work efficiency was observed.
以上の亀裂長さの読取り値からJIS R1607に定める算出式により、破壊靭性を計算した。ここで、弾性率Ｅは超音波パルスエコー法により測定し、Ｅ＝３６５ＧＰａを代入した。また、圧痕の対角線長さ２ａは以下の表４に示した実測値を用いた（測定単位：μｍ）。このようにして算出された破壊靭性を表５に示す（単位：ＭＰａ・ｍ1/2）。 Fracture toughness was calculated from the above crack length readings using the formula defined in JIS R1607. Here, the elastic modulus E was measured by an ultrasonic pulse echo method, and E = 365 GPa was substituted. Moreover, the diagonal value 2a of the indentation used the measured value shown in the following Table 4 (measurement unit: μm). The fracture toughness calculated in this way is shown in Table 5 (unit: MPa · m 1/2 ).
表５に示したように、「透明被膜あり」の場合には同一測定者における破壊靭性の測定値のばらつきが低下することが明らかになった。例えば、測定者Ｃでの破壊靱性は、最小値が2.37MPa・ｍ1/2から、最大値で2.73MPa・m1／2まで、約0.36MPa・m1／2のばらつきがあるのに対し、「透明被膜あり」の測定では、最低値が2.26ＭＰａ・ｍ1/2に対して最大値は2.37ＭＰａ・ｍ1/2と、わずか0.11MPa・m1／2のばらつきに収まっており、再現性が著しく改善された。また、測定者間の破壊靭性の平均値のばらつきも、若干ではあるが、「透明被膜あり」の方が小さくなる傾向が見られた。非特許文献１において、高倍率観察により高精度で求めた同一試料の破壊靭性は新原の式を用いて算出されたものが記載されているが、同一データを用いてJIS R1607の式を用いて求められた破壊靭性は2.39±0.03MPa・m1／2であり、本実施例での「透明被膜あり」の場合の破壊靭性〜2.3MPa・m1／2とよく一致している。このことから、本発明による測定手法は、非特許文献１に示した先行技術による高精度測定法と同程度の、高い信頼性のある破壊靭性の測定手法であることが明らかとなった。
＜実施例４＞光学顕微鏡観察における亀裂識別を容易にする混合溶液の濃度の検討
実施例１〜３で用いたものと同じ炭化ケイ素測定試験片（イビセラム SC―850）を供試材に用いた。測定試験片表面にビッカース圧子を荷重196N（20kgf）にて押し込み、圧痕及び亀裂を形成し、10倍の対物レンズと10倍の接眼レンズを装着した光学顕微鏡を用いて亀裂を観察し、亀裂識別を容易にする混合溶液の濃度範囲を検討した。
As shown in Table 5, in the case of “with transparent film”, it became clear that the variation in measured values of fracture toughness among the same measurers was reduced. For example, the fracture toughness of Measurer C varies from a minimum value of 2.37 MPa · m 1/2 to a maximum value of 2.73 MPa · m 1/2 , while it is approximately 0.36 MPa · m 1/2. In the measurement of “With transparent coating”, the minimum value is 2.26 MPa · m 1/2 and the maximum value is 2.37 MPa · m 1/2, which is within a variation of only 0.11 MPa · m 1/2 . The reproducibility was significantly improved. In addition, variation in the average value of fracture toughness among the measurers was slightly, but there was a tendency for “with transparent coating” to be smaller. In Non-Patent Document 1, the fracture toughness of the same sample obtained with high accuracy by high-magnification observation is described using Niihara's formula, but using the same data, the formula of JIS R1607 is used. The required fracture toughness is 2.39 ± 0.03 MPa · m 1/2, which is in good agreement with the fracture toughness in the case of “with transparent coating” to 2.3 MPa · m 1/2 in this example. From this, it was clarified that the measurement method according to the present invention is a highly reliable fracture toughness measurement method comparable to the high-precision measurement method according to the prior art shown in Non-Patent Document 1.
<Example 4> Examination of concentration of mixed solution facilitating crack identification in optical microscope observation The same silicon carbide measurement test piece (IBICERAM SC-850) as used in Examples 1 to 3 was used as a test material. . A Vickers indenter is pushed into the surface of the measurement specimen with a load of 196 N (20 kgf) to form indentations and cracks, and the cracks are observed using an optical microscope equipped with a 10x objective lens and a 10x eyepiece. The concentration range of the mixed solution that facilitates the study was studied.
まず、圧痕導入後に何も塗布しないで観察を行った。鏡筒に取り付けたデジタルカメラで撮影した観察像を図２に示す。図２を見てわかるように、亀裂の先端に近づくに従いコントラストが薄くなってゆき、どこが亀裂先端であるのか識別し難いことが分かる。 First, observation was performed without applying anything after indentation introduction. An observation image taken with a digital camera attached to the lens barrel is shown in FIG. As can be seen from FIG. 2, the contrast becomes thinner as the crack tip is approached, and it is difficult to identify where the crack tip is.
次に、樹脂の最適濃度範囲を求めるために、混合溶液中の樹脂濃度を変化させた混合溶液を作製して圧痕及び亀裂に塗布して乾燥させ、圧痕及び亀裂の観察を行った。樹脂と非極性溶媒の混合溶液として、市販のワニス（ロックペイント、フタル酸樹脂ワニス、樹脂成分４８%）を塗料用シンナー（ロックペイント ペイント薄め液）で適宜希釈した混合溶液を作製し、これを染み込ませた綿棒を用いて、圧痕及び亀裂を覆うように試験片表面に混合溶液を薄く均一に塗布し、約１分ほど放置して乾燥させ、透明被膜を形成させ、光学顕微鏡で観察を行った。 Next, in order to obtain the optimum concentration range of the resin, a mixed solution in which the resin concentration in the mixed solution was changed was prepared, applied to the indentations and cracks and dried, and the indentations and cracks were observed. As a mixed solution of resin and non-polar solvent, prepare a mixed solution of commercially available varnish (rock paint, phthalic acid resin varnish, resin component 48%) appropriately diluted with paint thinner (lock paint paint thinning solution). Using a soaked cotton swab, apply the mixed solution thinly and evenly on the surface of the test piece so as to cover the indentation and cracks, leave it to dry for about 1 minute, form a transparent film, and observe with an optical microscope. It was.
その結果、樹脂濃度が１重量%未満と極端に低い場合、数回塗り重ねても十分な厚みの透明被膜が形成されず、亀裂識別の改善効果は見られなかった。一方、濃度が25重量％を超える濃度においては、透明被膜が厚すぎて亀裂自体が見え難くなってしまった。この結果、混合溶液中の樹脂の重量濃度は、１％〜２５％の範囲が好ましいことが分かった。 As a result, when the resin concentration was extremely low, less than 1% by weight, a transparent film having a sufficient thickness was not formed even after repeated coating, and an effect of improving crack identification was not observed. On the other hand, at a concentration exceeding 25% by weight, the transparent film was too thick and it was difficult to see the cracks themselves. As a result, it was found that the weight concentration of the resin in the mixed solution is preferably in the range of 1% to 25%.
さらに、図２で示した同じ圧痕に、樹脂濃度が4重量％の混合溶液を塗布した後の観察像を図３に示す。 Furthermore, the observation image after apply | coating the mixed solution whose resin concentration is 4 weight% to the same indent shown in FIG. 2 is shown in FIG.
図３に示したように、亀裂先端のコントラストがくっきりとして、亀裂先端の位置が明瞭に特定できた。この場合の、透明被膜の厚みをエリプソメーターで測定したところ、約１００ｎｍの透明被膜が形成されていたことが分かった。このように、混合溶液中の樹脂濃度が4〜12重量％の範囲であると、明瞭に亀裂が識別可能であり、亀裂長さの測定精度が向上することが確認された。 As shown in FIG. 3, the crack tip contrast was clear and the crack tip position could be clearly identified. In this case, when the thickness of the transparent film was measured with an ellipsometer, it was found that a transparent film of about 100 nm was formed. Thus, it was confirmed that when the resin concentration in the mixed solution is in the range of 4 to 12% by weight, cracks can be clearly identified and the measurement accuracy of the crack length is improved.
１ 試験片
２ ビッカース圧子
３ 圧痕
４ 亀裂
1 Test piece 2 Vickers indenter 3 Indentation 4 Crack
Claims (6)
（１）試験片の表面にビッカース圧子を圧入して圧痕および亀裂を生じさせる工程、
（２）試験片の表面に樹脂と溶媒を含む混合溶液を塗布し、圧痕および亀裂を覆う透明被膜を形成する工程、
（３）前記透明被膜が形成された試験片表面の圧痕の対角線長さおよび亀裂長さを顕微鏡で計測する工程、
を含むことを特徴とする破壊靭性測定方法。 A test method for fracture toughness of a test piece, comprising the following steps:
(1) a step of pressing a Vickers indenter into the surface of the test piece to generate indentations and cracks;
(2) A step of applying a mixed solution containing a resin and a solvent to the surface of the test piece to form a transparent film covering the indentations and cracks,
(3) a step of measuring the diagonal length and crack length of the indentation on the surface of the test piece on which the transparent film is formed with a microscope,
Fracture toughness measuring method characterized by containing.
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| KR101660705B1 (en) * | 2015-06-03 | 2016-09-28 | 울산과학기술원 | Manufacturing method of specimen |
| CN108225901A (en) * | 2018-03-13 | 2018-06-29 | 核工业理化工程研究院 | For measuring the device of fracture toughness specimen crack length |
| CN109406280A (en) * | 2018-12-05 | 2019-03-01 | 航天科工防御技术研究试验中心 | A kind of quantitative detecting method of coating material impression fracture toughness |
| KR20220151411A (en) * | 2021-05-06 | 2022-11-15 | 대한민국(관리부서: 행정안전부 국립과학수사연구원장) | Footprint generator capable of applying constant force and footprint generation method using the same |
| CN108225901B (en) * | 2018-03-13 | 2024-05-31 | 核工业理化工程研究院 | Device for measuring crack length of fracture toughness test sample |
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