号数ばね論文集55号（2010年）
ページ数pp.13-18
種類論文
論文名ショットピーニングしたばね鋼のねじり疲労強度と回転曲げ疲労強度の関係
TitleRelationship between Torsional Fatigue Strength and Rotating Bending FatigueStrength for High Strength Spring Steel with Shot Peening
著者脇田将見1）久野隆紀1）久保埜貴文2）猿木勝司3）田中啓介3）
AuthorMasami WAKITA1) Takanori KUNO1) Takafumi KUBONO2) Katsushi SARUKI3) Keisuke TANAKA3)
抄録自動車サスペンション用懸架コイルばねの疲労設計法を検討するため，ぱね鋼の疲労強度に関する基礎的な研究として，焼戻し温度により硬さを変化させたばね鋼SUP7にショットピーニングを施行して，ねじり疲労試験および回転曲げ疲労試験を行ない，ねじり疲労強度および回転曲げ疲労強度に及ぼすショットピーニングの効果について比較した．また，破面観察により，ねじり疲労および回転曲げ疲労それぞれの破壊形態の違いについて検討を加えた．その結果，次の事項が明らかになった．（1）ショットピーニング施行材のねじり疲労限度はいずれの硬さについても無施行材を上回るが，回転曲げ疲労限度は最大硬さの場合を除き，無施行材と差はなかった．（2）ねじり疲労限度と回転曲げ疲労限度の関係は，無施行材の場合はせん断ひずみエネルギー説に最も近いが，ショットピーニング施行材の場合は最大主応力説とせん断ひずみエネルギー説のほぼ中間の値となった．（3）破面観察の結果，ねじり疲労試験において，ショットピーニング無施行材は軸線に平行にせん断破壊を生じ，その後，主応力方向に破壊が進展したが，ショットピーニング施行材では主応力方向である軸線に45度方向に破壊が発生し，進展した．一方，回転曲げ疲労限度試験ではいずれも主応力方向に破壊が発生し，進展した．
AbstractTo study fatigue strength design method for suspension coil springs for automobile, especially as thefundamental study of fatigue strength for spring steel, torsional fatigue and rotating bending fatigue tests wereconducted for shot-peened spring steel of SUP7 having various Vickers hardness through temperingtemperature variation. The effect of shot peening on the torsional fatigue strength and rotating bending fatiguestrength were studied. Furthermore, the difference between the morphology of torsional fatigue failure androtating bending fatigue failures were also studied.As a result, following findings came to light. (1) The torsional fatigue limit of peened specimen exceeded thatof non-peened one in any hardness condition. On the other hand, as for rotating bending fatigue limit, therewas no difference between non-peened and peened specimen, with the exception of specimen with maximumhardness. (2) The relationship between torsional fatigue limit and rotating bending fatigue limit for non-peened specimen was well explained by the shear strain energy theory. On the other hand, as for peenedspecimen, the relationship was explained by the combination of the maximum principal stress and the shearstrain energy theories. (3) The fatigue failure morphology for non-peened specimen due to torsional fatigueindicated that shear fatigue failure initiated parallel to the axial line and then the failure propagated towardprincipal stress direction. As for peened specimen, the fatigue failure initiated along the 45 degree direction tothe axial line (principal stress direction), and then propagated. On the other hand, as for all specimen due torotating bending fatigue tests, the fatigue failure initiated toward principal stress direction, and thenpropagated.
著者の所属1) 中央発條株式会社　2) 名城大学大学院　3）名城大学
Belonging1) CHUO SPRING CO.,LTD.　2) Meijyo University　3) Meijyo University
Key WordsShot peening, Spring steel, Torsional fatigue, Rotating bending fatigue, Residual stress