号数	ばね論文集 59 号（ 2014 年）
ページ数	pp.13-18
種類	論文
論文名	ショットピーニングによる高強度鋼における表面欠陥の無害化（き裂形状の影響）
Title	Improvement in Fatigue Limit By Shot Peening for High-strength Steel Containing Crack-like Surface Defect (Influence of Surface Crack Aspect Ratio)
著者	中川真樹子 1)，高橋宏治 1)，長田俊郎 2)，岡田秀樹 3)，古池仁暢 1)
Author	Makiko NAKAGAWA 1), Koji TAKAHASHI 1), Toshio OSADA 2), Hideki OKADA 3) and Hitonobu KOIKE 1)
抄録	ショットピーニング(SP)による高強度鋼(SUP9A)の表面欠陥の無害化に対するき裂形状の影響を調査するために，アスペクト比0.4の深さ0.1,0.2,0.3mmの表面き裂を模擬した半だ円スリットを有する試験片を用いて応力比R=0の条件で平面曲げ試験を行った．その結果，半だ円スリットの深さが0.2mm以下のSP材の疲労限度はSPを施した無欠陥材の疲労限度と同等の値にまで向上した．このことから，SPによる無害化可能欠陥寸法は0.2mmであることがわかった． 本実験結果と応力拡大係数を用いた無害化可能欠陥寸法の予測値は一致した．そこで本予測方法によりアスペクト比の異なるき裂についても無害化可能欠陥寸法を算出し，無害化可能欠陥寸法領域図を作成した．
Abstract	Effect of shot peening (SP) on bending fatigue limit of high strength steel (SUP9A) containing a semielliptical surface slit was investigated. SP was conducted on the specimens containing a semi-elliptical surface slit with aspect ratio, a/c = 0.4, where a was the slit depth (a=0.1, 0.2 and 0.3mm), and c was the half of surface length of slit. Bending fatigue tests were carried out under stress ratio, R = 0. The result showed that the fatigue limit of the shot-peened specimens having the slit under 0.2 mm in depth was almost same as that of the shot-peened smooth specimens. Meanwhile, some of the specimens fractured from the surface other than the slit. Thus, the maximum depth of slit which could be rendered harmless by SP was 0.2 mm. The maximum depth of crack with various aspect ratios which can be rendered harmless by SP was predicted, assuming that the crack was arrested when apparent stress intensity factor at the slit tip was less than threshold stress intensity factor of the material. The estimated values were in good agreement with experimental values. According to the estimation method, the harmless crack assessment diagram was proposed.
著者の所属	1)横浜国立大学　 2)物質・材料研究機構 3)日本発条（株）
Belonging	1)Yokohama National Universuty 2)NIMS 3)NHK SPRING CO LTD.
Key Words	Shot peening, Residual stress, Fracture mechanics, Surface defect, Aspect ratio