| 号数 | ばね論文集４８号（２００３年） |
| ページ数 | pp.15-20 |
| 種類 | 論文 |
| 論文名 | コイルばねの遅れ破壊におよぼす残留応力分布の影響 |
| Title | Influence of Residual Stress Distribution on Delayed Fracture of Coil Springs |
| 著者 | 丹後 公一・杉山 充弘・鈴木 健・綾田 倫彦 |
| Author | Koichi TANGO, Mitsuhiro SUGIYAMA, Takeshi SUZUKI, Michihiko AYADA |
| 抄録 | 遅れ破壊は，ばね鋼の高強度化〜自動車の軽量化において重要な問題の一つである． 耐遅れ破壊性の改善に対し，ショットピーニングによる圧縮残留応力が有効であることが既に報告されている． しかし，圧縮残留応力がき裂発生の抑制に効くのか，き裂進展の抑制に効くのか明らかとなっていない． そこで我々は，独自で開発したAE法を用いたコイルばねの遅れ破壊試験法により，遅れ破壊に対する圧縮残留応力の影響を調べた． ショットピーニングの有無に拘わらず，遅れ破壊試験初期から微小き裂を生じた． しかし，ショットピーニングで圧縮残留応力を付加することにより，拡散性水素量は増加するものの，遅れ破壊寿命は向上した． 破面観察の結果，表面圧縮残留応力値が高く，圧縮残留応力の作用する深さが 深いほど，擬へき開割れの領域は深くなった． 擬へき開深さを破断時間で除して求めた平均き裂進展速度は，表面圧縮残留応力値が高く，圧縮残留応力の作用する深さが深いばねが最も小さな値となった． これ らのことより，ショットピーニングによる圧縮残留応力は，き裂の進展を抑制する効果があり，遅れ破壊寿命を向上させたと考えられた． |
| Abstract | Delayed fracture is one of the most important problems for strengthening spring steels
and reducing the weight of coil springs. It has already been reported that the compressive
residual stress by shot peening lengthens the delayed fracture life. However, whether the compressive residual stress suppresses the crack initiation or the crack propagation has not been clarified. Therefore, we researched the effect of compressive residual stress on the occurrence of crack and its propagation by using the newly developed AE (Acoustic Emission) system. First, it was clarified that the shot peened spring had a long life for delayed fracture, even if increasing the diffusible hydrogen. It was also clarified that the crack occurred as soon as the experiment started, regardless of shot peening. From the observation of delayed fracture surface, it was also clarified that the QC (Quasi-Cleavage) region became deeper as the surface magnitude and the depth of compressive residual stress became larger. The mean growth rate of crack was estimated by dividing the depth of QC region by the total time to delayed fracture. The mean growth rate of crack became smaller for larger surface compressive residual stress and its depth. It can be concluded that the compressive residual stress caused by the shot peening suppresses the propagation of crack, and contributes to enhance the delayed fracture strength. |
| 著者の所属 | 日本発条（株） |
| Belonging | NHK Spring CO., LTD |
| Key Words | Delayed fracture, Acoustic Emission, Coil springs, Residual stress, Quasi-Cleavage fracture |