1. 6061-T6 Effects of Tool Size on Fracture and Fatigue Behaviors of Friction Stir SpotWelds of 6061-T6 Aluminum Sheets

2. 6061-T6T1 T2 T3T1 T2 T3 T3 T1T2T3SEM : 6061-T6I 3. Abstract Effects of tool size on fracture and fatigue behaviors of friction stir spot welds (FSSW) in cross-tensile specimens of 6061-T6 aluminum sheets were investigated based on experimental observations. Welds made by three tools with different sizes, T1, T2 and T3, at different rotational speed, dwelling time and indentation depth were tested under quasi-static opending conditions. The nugget pullout, interfacial and mixed type failure modes can be observed. The experimental results indicate that the failure strengths and failure modes of goodwelds made under different processing conditions show significant dependence on the tool size.Then, welds made by the three tools at the optimum processing parameters of T3 tool were tested under cyclic opening conditions. Under cyclic loading conditions, the fatigue lives and failure modes of the welds strongly depend on the tool size and applied load amplitude. For T1 tool, the mixed mode failure mode can be found. For T2 tool, when the welds are subjected to high and low cycle fatigue loading conditions, the upper-sheet and lower-sheet nugget pullout failure modes can be found, respectively.For T3 tool, except the two failure modes mentioned above, another transient failure mode can be found between them.Finally, optical and scanning electron micrographs of the welds made by the three tools before and after failure were examined and micro indentation tests of these welds were conducted. Keywords : aluminum 6061-T6, friction stir spot weld, tool size, fracture, fatigue, failure mode II 4. ................................................................................................................IABSTRACT ......................................................................................................... II ..................................................................................................................... III .................................................................................................................VI ............................................................................................................... VII......................................................................................................... 1 1-1............................................................................................................. 11-2 ......................................................................................... 3 ................................................................................................. 4 2-1 6061-T6 ................................................................. 42-2 ..................................................................................... 5 2-2-1 .................................................................. 6 2-2-2 .......................................................... 7 2-2-3 .................................................................. 7 2-2-4 .......................................................................... 92-3 ................................................................................... 12 2-3-1 .................................................................................... 12 2-3-2 .................................................................... 12 2-3-3 -................................................................................... 13 2-3-4 ................................................................ 14 ................................................................................... 17 3-1................................................................................................... 17III 5. 3-1-1 ............................................................................................ 173-1-2 ............................................................................ 173-1-3 ............................................................................ 183-1-4 .................................................................... 193-1-5........................................................................................ 193-1-6 (Design of Experiment, DOE) ............................................ 20 3-2 ................................................................................... 33 3-3.................................................................. 36 3-4................................................................................................... 373-4-1 ............................................................................................ 373-4-2 ............................................................................ 373-4-3 EDS..................................................................... 383-4-4........................................................................................ 383-4-5 ............................................................................................ 38................................................................... 444-1................................................................................................... 44 4-2 ............................................... 47 4-3........................... 494-3-1 T3 ............................... 494-3-2 T3 SEM ...................... 504-3-3 T1T2T3 .............. 50 4-4.................................................................. 56 4-5 ................................................... 60 4-6 ............................... 72 4-7........................... 80 4-8SEM ........................... 86 IV 6. ........................................................................... 895-1................................................................................................... 89 5-2 ............................... 93 5-3 ........................... 99 5-4 SEM ......................... 108 ..................................................................................................... 116........................................................................................................... 118 V 7. 3-1 6061-T6 ........................................................... 233-2.......................................................................................... 233-3 L 9 (34)............................................................................................ 233-4 .............................................................................................. 393-5 .............................................................................................. 394-1T3................................................ 45VI 8. 2-1 [7]................................................................. 102-2 (A) (B) .......................... 102-3............................................................. 112-4................................................................. 142-5 .............................................................................. 152-6 .............................................................................. 152-7 ...................................................................................... 152-8-.................................................................................... 163-1 .......................................................................... 243-2 .......................................................................................... 243-3 ...................................................................................... 253-4 .......................................................................... 253-5 .................................................................................. 263-6................................. 263-7 .......................................................................... 283-8 ......................................................... 293-9..................................................................... 303-10 ............................................................................................ 313-11................................................................................ 323-12 ................................................................... 32VII 9. 3-13............................................................................................ 353-14 ........................................................... 403-15EDS ............................................................ 413-16........................................................................................ 413-17 .................................................................................... 423-18 (MTS)......................................................................... 423-19........................................................................ 434-1 T3........................................................................ 464-2 T1........................................................ 484-3 T3........................................ 524-4 T3 ............ 534-5 T1T3.................................. 544-6 T1T3 .................. 554-7 T3............................................ 574-8 T2............................................ 584-9 T1............................................ 594-10T1 ...... 654-11T2 ...... 674-12T3 ...... 694-13T1T2 T3 ..................................................................................................................... 714-14T1.............................. 75 VIII 10. 4-15 T2.............................. 754-16 T3 .............. 764-17 T31400RPM........ 764-18 T32000RPM........ 774-19 T30.......... 774-20 T315 ........ 784-21 T31.6 MM .... 784-22 T31.9 MM .... 794-23 ............................................................... 824-24 T3.................................................. 834-25 T3.......................................... 844-26 T3.......................................... 854-27 T1 SEM.................................................. 874-28 T3SEM ...................... 884-29 T3SEM ...................................... 884-30 T1...................................... 914-31 T2...................................... 914-32 T3...................................... 924-33 T1 T2T3 ............. 924-34 T1.............................. 964-35 T2.............................. 964-36 T2.............................. 97 IX 11. 4-37 T3.............................. 974-38 T3.............................. 984-39 T3.............................. 984-40................................. 1024-41 T1............................ 1034-42 T2............................ 1044-43 T2............................ 1054-44 T3............................ 1064-45 T3............................ 1074-46 T1 SEM .................................... 1114-47 T2 SEM .................................... 1124-48 T2 SEM .................................... 1134-49 T3 SEM .................................... 1144-50 T3 SEM .................................... 115 X 12. 1-1 (resistance spot welding, RSW) Lin [1] Thornton[2] KHI () MAZDA ( ) (friction stir spot welds, FSSW) [3,4] (FSSW) (RSW) (1) (2)(3) (4)(5)(6) (7) (8) (9) 1 13. 2 14. 1-2 (lap-shear specimen) 6061-T6 (1mm) (cross-tension specimen) 3 15. 2-1 6061-T6(FCC) [5]Al-Mg-Si 6061-T6 2.71600 1539 2 79.6 cal/g 3-42 T66000 2000 70003C 4 16. 2-2 (friction stir spot welding, FSSW) (The Welding Institute, TWI) 1991 (friction stir welding, FSW)[6]2-1[7] 1. Plunge 2. Complete 3. Retract2000 5000 60007000[8](dynamic recrystallization, DRX)5 17. [9][10] 2-2-12-2[11] 1. 2. 3. 4. 5. 6. Tozaki [12] Tran[13]6 18. Lin Arul [1,14] Tozaki[15] [16] 6061-T6 2-2-2WangLee[17](base metal, BM) (thermal-mechanical affected zone, TMAZ) (stir zone, SZ)2-3 2-3 2-2-3(porosity) (crack)(integrity)7 19. [18] 1.2.3.4.5.6.7. : 1.2. [19] 8 20. 2-2-4 2004 RX-8 [20] 3C9 21. 2-1 [7] 2-2 (a)(b) 10 22. WeldCentral Hole UpperLower BM HAZ TMAZHAZ BM (TMAZ+SZ) (base metal, BM)(heat affected zone, HAZ) (thermal-mechanicalHAZ SZ affected zone, TMAZ) (stir zone, SZ) 2-3 11 23. 2-3 (mechanical fatigue)(creep-thermal fatigue) 2-3-12-4 a m R : max min max min minmax min , a , m , R2 2 maxa m RR 0.1 2-3-22-52-5 [21] 2-6 12 24. 2-6 2-6 1 2 34 5 2-7 2-3-3 -( ) ( )(high-cycle fatigue)-(stress-life approach) ( )()-(S-N curve)2-8(a)-aNf-10 3106 (fatigue limit) (endurance limit)e- 2-8(b) 106 10 7 (fatigue strength)[21] 13 25. 2-3-4[22] LinTran[13] Uematsu [23]2-414 26. 2-5 2-6 2-7 15 27. (a) (b) 2-8 -16 28. 3-1 3-1-1 1 mm 6061-T6SAE 152 mm50 mm(cross-tention specimen)3-1 3-1-2CNC FSW 5HP3-13-21 3-3 CNC 17 29. (1) 3000 rpm 2000 rpm 700~2000 rpm (2)(3)(4) 3-1-3 T1 T2 T3 3-4SKD11SKD1160HRc 3-5 1.(tool holder) 18 30. 2.(tool shoulder) 3.(tool pin) 3-61 122 D11.5 3S1 S2 3-1-43-7(a)(b) (S45C) 51 mm 1 mm2 mm10 mm18.5 mm101.6 mm 3-7(c) 152 mm50 mm 8 mm14 16 18 mm3-8 3-9(a) ( ) 3-9(b) 3-1-519 31. (NT-411) 3-10 0.1~999.9/DIP SWICH ENCODER L:0~3V, H:6~30VRelay RESETRESETRESET RESET3-114 mm (Switching Frequency) 600 MHz () 3-1-6 (Design of Experiment, DOE)3-12 L 9 (34) (Orthogonal Arrays, OA, 3-3)Minitab 1960 20 32. C. R. Rao1947[24](parameter design) [25,26] 1. /(subsystems) 2. / (ideal function/response)(input signal, M)(output response, y) (ideal function)y = bMb(sensitivity) 3. (signal and noise factor SN)(signal levels and ranges) (noise factors) (noise strategy) 4. (control factors and levels) (orthogonal array) 3L 9 (34)3-3 5.(collect data) 6.(conduct data analysis)SN ratios / /(response tables/graphs ) 7.(confirmation run) 8. 1.(Main effects plot for means)N x 1 , ..., x i21 33. N 1xxi N i 12. (Main effects plot for StDevs) n1 s ( xi x)2n 1i 1 3. (Main effects plot for SN ratio)y2 SN 10 log( 2 ) s 22 34. 3-1 6061-T6Si Fe Cu Mn Mg Cr Zn Ti % 0.4-0.80.7 0.15-0.40.150.8-1.2 0.04-0.350.25 0.15T6 ASTM (515-550C) (155-165C)18hr 3-2(mm)(mm) (mm) T1 8 3 1.5 T210 4 1.5 T312 5 1.5 3-3 L 9 (34)No. of FactorRunABCD111 11 212 22 313 33421 23 522 32 623 11731 32 832 13 933 21 ABC D23 35. 3-1 (a) (b)(c) (d) 3-224 36. (a)X (b)Y(c)Z3-3 T1 T2 T3 000 (mm) 8 10 12 (mm) 3 45 (mm)1.51.51.53-4 25 37. 3-5 3-6 26 38. (b) (c) 27 39. (c) 3-7 28 40. 3-8 29 41. (a) (b) 3-930 42. 3-1031 43. 3-11 Value Tool rotation speed Holding time Tool displacement0 t Time 3-12 32 44. 3-2 1 mm 6061-T6 (DOE)3-130.2 mm/s (1)(2) 10~15 (3)(4)(5)(6)(7)5 (8) 36 152 mm 50 mm (9) (10) 27 SEM33 45. 6061-T6:1.2. 3. 6061-T6: (DOE)1.2.3.4. NG SEM ( ) ()34 46. 3-1335 47. 3-3 (DOE)T3 100 10 90 % 80 % 70 % 60 % 50 % 40 % 30 % 20 % R 0.1 5 Hz P(proportional) I(integration) D(derivative) F(feed forward) (1). MTS (2). MTS (3).(4).(5).(6).(7). SEM 36 48. 3-43-4-1 (EHOMA3SR300) (BUEHLER ISOMET2000) 3-14 ( ) 815 2(BUHLER ECOMET6) #120 #240 #400 #600 #1000 #2000 1 m 0.3 m(HF) (H 3 PO 4 ) 3-4 6061-T6 3-4-2Zeiss Axiotech 25HD 50 100 200 5001000Nikon Coolpix 99037 49. 3-4-3EDS3-15EDS(S3500N) 3-4-4(micro vickers hardness) Matsuzawa MHT2 ( 3-16)10g 25g100g 200g 300g 500g 1000g0.01mm 100400 200 g 400 15 (micro Vickers hardness) 3-4-5(SHIMADZU AG-I)5 kN 10 kN 3-17 MTS (647 Hydraulic Wedge Grip)100 kN / 22 kip 21 MPa / 3000 psi3-18 3-19MTS 38 50. 3-4 (ml)HF(44%)15 H 3 PO 4 (85%)10water75 3-5 Load cell Styles Model 45 (Order Code AL116)Range5000 lb Excitation10 VDCStatic Overload Capacity 300% F.S. Bridge Resistance350Operating Temperature -65F to 200F 39 51. 3-1440 52. 3-15 EDS3-16 41 53. 3-17 3-18(MTS)42 54. 3-1943 55. 4-1 T3T3 T1 T2 T3 (DOE) T3(1)700 1350 2000 rpm (2)1.7 1.8 1.9 mm(3)0 7 14 sec. (4)0.2 mm/s 4-14 4-1700 rpm 1.7 mm 0 sec800 rpm1.65 mm1 sec. T1 T2 T3 1321 1701 2372N44 56. 4-1T3(rpm) (mm)(sec)1 700 1.7 02 700 1.8 73 700 1.9 144 13501.7 75 13501.8 146 13501.9 07 20001.7 148 20001.8 09 20001.9 745 57. (a)(b) SN 4-1T3 46 58. 4-24-2T1T3 4-2(a)T1 4-2(b)4-2(c) T2T347 59. (a) (b)(c) 4-2 T1 48 60. 4-3T1 T2 T3 4-3-1 T34-3 T34-3(a) 4-3(c)4-3(a) I II III IV T3 (1) 800 rpm (2) 1.65 mm (3) 1 sec.4-3(a) 2-3(stir zone) (TMAZ)(HAZ)4-3(a) 49 61. Thornton [2]4-3(c) I (base metal) II(thermal-mechanical affected zone)III (stir zone)Lin[1] 4-3(c)IV 4-3-2T3SEM4-6 T3SEM 4-4(a) A B 4-4(b) A500 2000 4-4(c)B 500 2000 4-3-3T1 T2 T34-5T3 50 62. 4-5T2T3T1 T1 T2 T3 4-6T1 T2T3T34-6 T1 T2T1T351 63. (a)(c) 4-3T3800 rpm1 1.65 mm52 64. (a)(b)(c) 4-4 T353 65. 4-5 T1 T3 800 rpm1 1.65 mm 54 66. 4-6T1 T3 800 rpm 1 1.65 mm55 67. 4-4(BM) (HAZ) (TMAZ) (SZ) 200 g 40015 (micro Vickers hardness)4-9 0.5 mm 1.5 mm 6061-T6 120 Hv (HAZ) (TMAZ) (SZ)4-7 T3 85~90 Hv 4-84-9 T2 T1 T356 68. 4-7 T357 69. 4-8 T258 70. 4-9 T159 71. 4-5DOE T3 800 rpm1 sec. 1.65 mm 2372N T1 T2 T3 1321N 1701NT3 3 T14-10(a) T1 1 sec.1.65 mm 0.2 mm/sec.400~2000 rpm 700~1000 rpm1300~1400 N700 rpm T3800 rpmT1 T1T11400 rpm 700 rpm 2000 rpm 4-10(b)800 rpm1.65 mm 3 sec.60 72. 1341 N6sec. 15 sec. T115 4-10(c)800 rpm 1 sec.1.65 mm1.7 mm 1325N 1.6 mm1.7 mm 1.9 mm T24-11(a) T21 sec. 1.65 mm0.2 mm/sec. 400~2000 rpm 700 rpm 1731 NT3 800 rpmT2T2 T2 800 rpm1400 rpm1400 rpm 4-11(b) 800 rpm1.65 mm 1 sec.1700 N214 sec.~15 sec. 61 73. 4-11(c)800 rpm 1 sec. 1.65 mm1700 N 1.6 mm1620 N1.7 mm ~ 1.9 mm 1.9 mm.T3 4-12(a)T31 sec. 1.65 mm 0.2 mm/sec. 400~2000 rpm800 rpm 2372 N 900 rpm 1000~1400 rpm 2000 rpm4-12(b)800 rpm 1.65 mm1 sec. 2372 N24-12(c)800 rpm 1 sec. 1.65 mm2372 N 1.6 mm2078 N1.7 mm ~ 1.9 mm1.9 mm. 62 74. 4-13T1 T2 T3 T3 800 rpm T1T2700 rpm T1 T2T3 T1T2 T1T21400 rpm~2000 rpmT31 sec. T2T3 T1T1 T1T31.65 mmT2T3 T11.6~1.7 mm1.8~1.9 mm 63 75. (a) (b)64 76. (c) 4-10 T1 65 77. (a) (b) 66 78. (c) 4-11 T2 67 79. (a) (b)68 80. (c) 4-12 T3 69 81. (a) (b)70 82. (c) 4-13 T1 T2 T371 83. 4-6T3 T1 T2T3T3T14-146061-T6T1T3 4-14(a) 4-14(b) 4-14(c)(nugget pullout failure mode)T24-15T2 T34-15(a) 4-15(b) 4-15(c) T1 (nugget pullout failure mode)T34-16T34-16(a) 4-16(b)4-16(c) (nugget pullout failure mode) 72 84. 4-17 T3 1400 rpm4-17(a)4-17(b) 4-17(c) (interface fracture)4-18 T32000 rpm 4-18(a)4-18(b) 4-18(c)4-17(c) 4-18(c) 2000 rpm (nugget pullout failure mode) 2000 rpm 1400 rpm 4-19 T30 4-19(a) 4-19(b) 4-19(c) (nugget pullout failure mode)4-20 T3 15 4-20(a)4-20(b)4-20(c)4-19(c)4-20(c)0 15 4-10(b) 4-11(b) 4-12(b) 4-21 T31.6 mm 4-21(a) 4-21(b)4-21(c) 73 85. (nugget pullout failure mode)4-22 T3 1.9 mm 4-22(a)4-22(b)4-22(c)4-21(c)4-22(c) 1.6 mm 1.9 mm 4-10(c)4-11(c)4-12(c) 74 86. (a)(b)(c)4-14T1800 rpm 1 1.65 mm (a)(b)(c)4-15T2800 rpm 1 1.65 mm 75 87. (a) (b) (c)4-16T3800 rpm11.65 mm (a) (b)(c)4-17 T3 1400rpm76 88. (a) (b)(c)4-18 T3 2000rpm (a) (b)(c)4-19 T3077 89. (a)(b)(c)4-20 T315 (a)(b)(c) 4-21T3 1.6 mm 78 90. (a) (b)(c) 4-22 T3 1.9 mm 79 91. 4-7 4-34-23 T1 T2 T3 4-23(a) 4-23(b) 4-23(c)4-1 4-234-24 T3 4-24(a) 4-24(b) 4-24(c) 700 rpm1400 rpm 2000 rpm90 4-24(a) 4-24(b) 4-24(c) 4-24 4-12(a)Tozaki [14,27]80 92. 4-25T3 4-25(a)0 sec4-25(c)4-25(b)0 sec 12 sec 4-26T34-26(a)1.6 mm4-26(b)(d)1.7 mm1.9 mm 81 93. (a)T1(b)T2(c)T3 4-23 800 rpm 11.65 mm82 94. (a) (b) (c) 4-24 T3 83 95. (a) (b) (c) 4-25 T3 84 96. (a) (b) (c) (d) 4-26 T3 85 97. 4-8 SEM T14-27 T1SEMA40 500 (Dimple)[28,29] (necking)B40 500T34-28SEM A 40 500 4-29SEM A60 200 2000 86 98. 4-27 T1SEM 87 99. 4-28T3 SEM4-29T3SEM 88 100. 5-1T1T1 T31001349N 90% 80%70% 60% 50%40%30%20%R 0.15 Hz T2T3 4-30 T1T3 -10 3 10 32 10 32 10 3106 106 106 T24-31 T2 T3 -10 489 101. 10 4 106106 T34-32T3 - 4-31 10 410 4 106106 4-33-T2 T3T1 2 10 3 10 5 T2 T390 102. 4-30 T1 4-31 T2 91 103. 4-32 T3 4-33T1 T2T3 92 104. 5-2 T1 T2 T3T3T14-34 T1 50%16074 4-34(a)4-34(b) 4-34(c) (mixed failure mode) 40%~90% 50%T1T1 T34-24-10T1 700rpm 3 sec. T1T24-35 T2 60%10843 4-35(a)4-35(b)93 105. 4-35(c)4-35(b)(nugget pullout failure mode)4-36T240%94366 4-36(a) 4-36(b)4-36(c)4-36(a)4-36(b) (c) 4-36(c) (nugget pullout failure mode)4-354-36 (nugget pullout failure mode)80%~60% 50%~30%T3 4-37T360%11768 4-37(a) 4-37(b)4-37(c)4-37(b)4-38T350%21458 4-38(a) 94 106. 4-38(b)4-38(c) 4-38(a) 4-38(b) 4-38(b)4-39T340%51981 4-39(a)4-39(b)4-39(c) 4-39(a)4-39(b)(c)4-39(c) T3 80%~50% 50% 50%~30%T1 T2 T3 (nugget pullout failure mode) (mixed failure mode) 95 107. (a)(b)(c)4-34 T1 50% (a)(b) (c)4-35 T2 60% 96 108. (a)(b) (c)4-36 T2 40% (a)(b)(c)4-37 T3 60%97 109. (a) (b)(c) 4-38 T350% (a) (b)(c) 4-39 T340%98 110. 5-3 T14-404-41T1 (4-40 A-A)60% 17664-41(a)4-41(b) (c)A-A B-B4-41(d) (e) (f) 4-41(b)III 4-41(c) III4-41(d) (e) 4-41(f) 4-41(e) III4-41(d) (e) B-BT24-42 T2(4-40A-A)60% 103884-42(a) 4-42(b) (c)A-A B-B4-42(d) (e) (f) 4-42(b) I II 4-42(c) III4-42(d)(e) 4-42(f)4-42(e) III 4-42(d) (e)99 111. B-B 4-43T2 ( 4-40 A-A) 40% 83019 4-43(a) 4-43(b) (c) A-AB-B 4-43(d) (e)(f) 4-43(b) III4-43(c) III4-43(d) 4-43(e)4-43(f)4-43(e) III 4-43(d) (e) 4-43(d) (e) T34-44T3 ( 4-40 A-A) 60% 12187 4-44(a) 100 112. 4-44(b) (c) A-AB-B 4-44(d) (e) (f)4-44(b)III4-44(c) III4-44(d)4-44(e) 4-44(f) 4-44(e) III4-44(d) (e) B-B 4-45T3 (4-40A-A)40% 47632 4-45(a) 4-45(b) (c)A-A B-B4-45(d) (e) (f)4-45(b)I II4-45(c)III4-45(d) (e) 4-45(f)4-45(e)III 4-45(d)(e) 4-45(d) (e) 101 113. 4-40102 114. (a)(b)A-A(c) B-B (d)A-A(e)A-A(f)B-B 4-41T160%1400 cycles 103 115. (a) (b) A-A (c) B-B (d) A-A (e) A-A (f) B-B4-42T2 60%8500 cycles 104 116. (a) (b) A-A (c) B-B (d) A-A (e) A-A (e) B-B4-43T240%66500 cycles 105 117. (a) (b) A-A (c) B-B (d) A-A (e) A-A (f) B-B4-44T360%10000 cycles 106 118. (a) (b) A-A (c) B-B4 (d) A-A (f) A-A (e) B-B4-45T340%35000 cycles 107 119. 5-4 SEM T14-46T1SEM 60% 1960 4-46(a)4-46(b) A SEM 304-46(c) 5000(fatigue striation) 4-46(d)BSEM30 4-46(e) 1000T24-47T2SEM 60% 108434-47(a)4-47(b)A SEM30 4-47(c)2000 (fatigue striation) 4-47(d)BSEM30 4-47(e) 300108 120. T1 B4-48T2SEM40%67408 4-48(a) 4-48(b) ASEM 304-48(c)2000 4-48(d) B SEM 304-48(e) 1000 T34-49 T3 SEM60% 15639 cycles4-49(a)4-49(b)A SEM 30 4-49(c)30004-49(d)B SEM 304-49(e)500T1 B 4-50 T3 SEM40% 42605 cycles4-50(a)4-50(b)ASEM109 121. 404-50(c)10004-50(d)B SEM 40 4-50(e)5000 110 122. (a) (b)(c) (d)(e) 4-46T1 SEM60%111 123. (a) (b)(c) (d)(e) 4-47T2 SEM60%112 124. (a) (b)(c) (d)(e) 4-48T2 SEM40%113 125. (a) (b)(c) (d)(e) 4-49T3 SEM60%114 126. (a) (b)(c) (d)(e) 4-50T3 SEM40%115 127. 6061-T6[16] T1 T2 T3 T3T1 T2 T3 T3SEM 1. T3 :(1)800 rpm (2) 1.65 mm (3)1 sec. (4) 0.2 mm/s 2.T1 T2 T3T31321N 1701N2372N 3. 4. T1T2T3T3 > T2 > T1 5.116 128. 80Hv 6. T1 T2 T3 T3T1(mixed failuremode)T2T3 T2 7. SEM117 129. 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