銅合金条材の疲労強度および疲労き裂進展特性に関する研究 (本文)
概要
銅合金条材の疲労強度および疲労き裂進展特性
に関する研究
2023年度
三田夏大
学位論文
博士(工学)
銅合金条材の疲労強度および疲労き裂進展特性
に関する研究
2023年度
慶應義塾大学大学院理工学研究科
三田夏大
目次
図目次 ................................................................................................................................................. iv
表目次 ............................................................................................................................................... viii
第1章
序論 .................................................................................................................................. 1
1.1
研究背景 .............................................................................................................................. 1
1.2
先行研究 .............................................................................................................................. 3
1.3
本研究の目的 ...................................................................................................................... 5
第2章
銅合金条材のための高サイクル疲労試験機の改良と疲労特性の評価 .................. 8
2.1
緒言 ...................................................................................................................................... 8
2.2
供試材と試験片 .................................................................................................................. 8
2.2.1
供試材 .......................................................................................................................... 8
2.2.2
試験片 .......................................................................................................................... 9
2.3
試験装置の改良 ................................................................................................................ 10
2.3.1
疲労試験機と試験手法の概要 ................................................................................ 10
2.3.2
試験時間の短縮化とサイクル負荷 108 回を満たすための各種提案 ................ 12
2.3.3
疲労試験 .................................................................................................................... 17
2.4
銅合金条材の疲労寿命特性評価 .................................................................................... 18
2.4.1
材質別,圧延方向違いの条材疲労試験 ................................................................ 18
2.4.2
き裂発生個所の確認 ................................................................................................ 28
2.4.3
厚さ違いの条材疲労試験 ........................................................................................ 29
2.5
結言 .................................................................................................................................... 32
第3章
Cu-Ni-Si 銅合金条材における平均応力が及ぼす疲労強度への影響 ..................... 34
3.1
緒言 .................................................................................................................................... 34
3.2
実験方法 ............................................................................................................................ 35
3.2.1
供試材 ........................................................................................................................ 35
3.2.2
試験片 ........................................................................................................................ 35
3.2.3
繰返し疲労試験機の構成 ........................................................................................ 39
3.2.4
U 字端子試験片の表面粗さ条件出しの為の評価方法 ........................................ 40
i
3.2.5
疲労限度線の評価方法 ............................................................................................ 40
3.2.6
表面メッキ処理の評価方法 .................................................................................... 44
3.3
結果,考察 ........................................................................................................................ 44
3.3.1
U 字端子試験片の検証 ............................................................................................ 44
3.3.2
疲労限度線の推定 .................................................................................................... 50
3.3.3
表面メッキ処理後の疲労特性 ................................................................................ 53
3.4
結言 .................................................................................................................................... 56
第4章
薄板 Cu–Sn–P 銅合金条材における疲労き裂進展特性 ......................................... 58
4.1
緒言 .................................................................................................................................... 58
4.2
実験方法 ............................................................................................................................ 58
4.2.1
供試材 ........................................................................................................................ 58
4.2.2
実験方法 .................................................................................................................... 59
4.2.3
画像処理によるき裂長さの測定方法 .................................................................... 62
4.2.4
直流電位差法によるき裂長さの測定方法 ............................................................ 64
4.2.5
ΔJ の特定方法 ........................................................................................................... 68
4.2.6
破面,断面観察 ........................................................................................................ 70
4.3
き裂長さ測定方法の比較 ................................................................................................ 71
4.3.1
き裂長さの測定法違いの結果 ................................................................................ 71
4.3.2
き裂長さ測定方法の考察 ........................................................................................ 71
4.4
き裂進展特性 .................................................................................................................... 73
4.4.1
き裂進展特性の結果 ................................................................................................ 73
4.4.2
破面,断面観察の結果 ............................................................................................ 77
4.4.3
き裂進展特性の考察 ................................................................................................ 77
4.5
結言 .................................................................................................................................... 82
第5章
薄板銅合金条材の圧延方向が及ぼす疲労き裂進展特性への影響 ........................ 84
5.1
緒言 .................................................................................................................................... 84
5.2
実験,解析方法 ................................................................................................................ 84
5.2.1
供試材 ........................................................................................................................ 84
5.2.2
実験方法 .................................................................................................................... 87
5.2.3
DIC からの J 積分計算方法..................................................................................... 88
ii
5.2.4
破面,断面観察 ........................................................................................................ 89
5.2.5
3 次元 FEM 計算のモデルと境界条件 ................................................................... 89
5.2.6
3 次元 FEM と DIC 的手法に基づく J 積分の計算 .............................................. 90
5.3
結果及び考察 .................................................................................................................... 91
5.3.1
DIC から求めたき裂進展特性 ................................................................................ 91
5.3.2
LD,TD の破面,断面観察........................................................................................ 92
5.3.3
3 次元 FEM による J 積分と DIC 的手法による J 積分の結果 ........................... 96
5.4
第6章
結言 .................................................................................................................................. 100
結論 .............................................................................................................................. 102
6.1
各章のまとめ .................................................................................................................. 102
6.2
全体のまとめ及び今後の展望 ...................................................................................... 104
謝辞 .................................................................................................................................................. 108
参考文献 ........................................................................................................................................... 110
本研究に関連する掲載論文および学会発表 ............................................................................... 117
iii
図目次
1-1 DC-DC converter for Automotive. ......................................................................................... 2
1-2 Examples of connector. .......................................................................................................... 2
1-3 Failure case of an electric part made from a copper alloy strip used in a car navigation. ..... 3
1-4 Relationship of each chapter in this dissertation. ................................................................... 7
2-1 Shape of specimen (mm). ....................................................................................................... 9
2-2 Basic structure of fatigue cycle jig. ...................................................................................... 10
2-3 Fatigue test machine and jigs. ...............................................................................................11
2-4 Circuit schematic for measuring the resistance of specimen to judge the specimen failure. 12
2-5 Observation of fixed brock jigs. ........................................................................................... 14
2-6 Relationship between stress amplitude and the number of cycles to failure for Cu-Ni-Si
copper alloy specimen (LD direction, t = 0.12 mm). ....................... ...