号数	ばね論文集 57 号（ 2012 年）
ページ数	pp.59-79
種類	共同研究
論文名	ばね及びばね鋼のX線残留応力測定法
Title	Method for X-ray Residual Stress Analysis in Springs and Spring Steel
著者	X線によるばねの残留応力評価法研究委員会
Author	Research Committee for Evaluation in Residual Stress of Spring by X-ray Diffraction
抄録	Ｘ線応力測定法は残留応力測定に広く適用されている技術である．しかし現在，ばねの残留応力測定に限定した適切なＸ線応力測定方法はない．それ故，日本ばね学会ではばねのＸ線応力測定法に関する研究委員会を2008年に設立した．委員会では，まずばね関連業界におけるＸ線応力測定の実態をアンケート調査した．委員会ではこの調査結果から，次の4つの課題を研究した．A)ショットピーニングされた平板の残留応力測定方法，B)ショットピーニングされた丸棒の残留応力測定方法，c)回析角2θ- sin2 Ψ線図の評価法，d) フェライト系ばね鋼のＸ線応力定数． 結果として，次の成果が得られた． （1）ばね関連企業の通常業務で設定しているＸ線応力測定条件で測定されたショットピーニング平板のその残留応力の誤差68.3％信頼限界値は測定残留応力の平均値の6％以下である．したがって，68.3％信頼限界値を基準にしたＸ線応力測定の条件を提案した． （2）コイルばねのように測定表面が曲面の場合，測定誤差が10％以下の残留応力値を得るには，コリメータ径をワイヤ径の20％以下にする必要がある．ファインショットピーニングを施した丸棒には，2θ- sin2 Ψ線図は非直線となり，また回析強度- sin2 Ψ線図にはうねりが現れることが分かった． （3）2つの統計的なアプローチと3軸応力状態を仮定したシミュレーションによる sin2 Ψ線図の評価法について検討した． sin2 Ψ線図の評価に曲がり度ＣＢ，うねり度Ｃｗという新たなパラメーターを提案した． sin2 Ψ線図のうねり度の評価を行うためにはＸ線入射角は少なくとも7点以上設定する必要がある．また，回析角2θ- sin2 Ψ線図のシミュレーションを用いると，ＣＢとＣｗを用いた評価法の有効性を確認できる． （4）フェライト系ばね鋼ＳＵＰ9Ａ，ＳＵＰ12のＸ線応力定数を評価するためにラウンドロビンテストを行った．結果として2つのファライト系鋼平均Ｘ線応力測定はＫ＝ -338±13.1 MPa/degであることを明らかにした．
Abstract	X-ray stress measurement is a technique which has been widely applied to residual stress. However, a satisfactory method for measuring residual stress in springs has not been appropriately developed yet. Thus, a research committee in Japan Society of Spring Engineers was established to research the X-ray based stress measurement of springs in 2008. The first item accomplished by the committee was an exploratory investigation to understand the measuring conditions of X-ray stress measurement being used in spring industries. By referring to these results obtained, four subjects were investigated as follows: a) development of a method of residual stress measurement in shot-peened plate, b) development of a method of residual stress measurement in shot-peened round-bar, c) evaluation method for 2θ-sin2 Ψ diagrams, d) characterization of an X-ray stress constant in ferrous spring steels. The following results were obtained: (1) The errors for 68.3% confidence limits in the residual stress of the shot-peened plate specimen, which were observed by X-ray stress measurement under routine measurement conditions in participating companies, were within 6% of the average residual stress values obtained. Therefore, X-ray stress measurement conditions based on a 68.3% confidence limit were proposed. (2) In a sample with a curved surface, such as a coil spring, the diameter of an X-ray collimator should be less than 20% of the diameter of the spring wire so that the error of the residual stress can be less than 10%. It turned out that the nonlinearity of the 2θ-sin2Ψ diagrams and wave-like fluctuation in diffraction intensity-sin2Ψ diagrams were observed in the surface of fine-shot-peened round-bars. (3) An evaluation method for 2θ-sin2Ψ diagrams showing the pattern of bowing or waving using two statistical approaches and simulations in tri-axial stress states has been investigated. Two parameters CB and Cw representing degrees of the bowing and waving in 2θ-sin2Ψ diagrams have been suggested. At least seven diffraction angles in the 2θ-sin2Ψ diagram are necessary to evaluate waving. A simulation of the 2θ-sin2Ψ diagram enables us to confirm effectiveness of the evaluation technique with CB and Cw. (4) A round robin test (RRT) for characterization of an X-ray stress constant in ferrous spring steels such as SUP9A and SUP12 was carried out. As a result, it appears that the average X-ray stress constant K in the two spring steels was -338±13.1 MPa/deg.
著者の所属
Belonging
Key Words	X-ray stress measurement, Residual stress, Shot peening, X-ray stress constant, 2θ｜sin2 diagram, Ferrous　spring steel