Figure 1‐2: Structure of the LISA project. ... 3

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ix

List of Figures

Figure 1‐1: Comparison between conventional riveted T‐joint and stationary shoulder friction

stir welded T‐joint ... 2

Figure 1‐2: Structure of the LISA project. ... 3

Figure 2‐1: Rotational Friction Welding in four steps. ... 5

Figure 2‐2: Scheme of the FSW process. ... 6

Figure 2‐3: Denomination in the FSW process. ... 7

Figure 2‐4: Example of macrograph picture with indicated the typical areas generated by a FSW process. ... 8

Figure 2‐5: Various geometries of FSW joints. ... 9

Figure 2‐6: Difference in the surface finishing between FSW (left) and SSFSW (right) ... 11

Figure 2‐7: FSW imperfections due to too hot welds: (a) Surface Galling; (b) Excessive flash. .. 13

Figure 2‐8: FSW cavity imperfection from too cold welds. ... 13

Figure 2‐9: Lack Of Penetration (LOP) in the root area during the FSW process. ... 14

Figure 3‐1: Coordinates, stress and displacement components in the crack tip stress field. ... 19

Figure 3‐2: Modes of crack surface displacements. ... 20

Figure 3‐3: Irwin’s plastic zone correction. ... 21

Figure 3‐4: Definition of the Crack Tip Opening Displacement (CTOD) ... 22

Figure 3‐5: Representation of the ܬ‐integral. ... 23

Figure 4‐1: Schematic representation of the experimental procedure followed in this work. ... 26

Figure 4‐2: Schematic representation of the material disposition. ... 29

Figure 4‐3: HZG FSW Gantry System. ... 33

Figure 4‐4: Standard FSW and SSFSW clamping system on the Gantry System. ... 34

Figure 4‐5: 3D illustration of the FSW tool used for this study. ... 36

Figure 4‐6: Schematic view and section of the SSFSW tool. ... 37

Figure 4‐7: Cutting plan for tensile specimens SSFS welded with 3 different WS. ... 38

Figure 4‐8: Sketch of the sample for macrograph and EDX analysis of SSFSW joint. ... 39

Figure 4‐9: Sketch of the geometry of the FSW and SSFSW root bending specimens. ... 41

Figure 4‐10: Bending Test set up. ... 42

Figure 4‐11: Exemplary microhardness measurement indentations across a FSW joint. ... 43

Figure 4‐12: Standard extensometer for tensile test. ... 44

Figure 4‐13: Sketch of the specimen used for the tensile test. ... 44

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List of Figures

x

Figure 4‐14: Drawing of the center‐cracked tensile specimen M(T). ... 46

Figure 4‐15: Final set‐up for the R‐curve determination test... 48

Figure 4‐16: Example of the 3D map of the fracture surface. ... 49

Figure 5‐1: ARAMIS System. ... 51

Figure 5‐2: 15x15 facets with 2 pixels overlapping. ... 52

Figure 5‐3: Translation and strain of a line element. ... 54

Figure 5‐4: Spray pattern for toughness specimens. ... 56

Figure 5‐5: Calibration Panel. ... 57

Figure 5‐6: Example of definition of measuring area. ... 58

Figure 5‐7: Strain field on the specimen and section...58

Figure 6‐1: Cross section of: (a) FSW‐WS=3‐AA7050 ‐R; (b) FSW‐WS=3‐AA2024‐R. ... 60

Figure 6‐2: Cross section of: (a) FSW‐WS=5‐AS=AA7050 ‐R; (b) FSW‐WS=5‐AA2024 ‐R. ... 62

Figure 6‐3: Cross section of: (a) FSW‐WS=8‐AA7050‐R; (b) FSW‐WS=8‐AA2024‐R. ... 62

Figure 6‐4: Cross section of: (a) FSW‐WS=3‐AA2024‐P; (b) FSW‐WS=3‐AA2024‐R. ... 63

Figure 6‐5: Cross section of: (a) FSW‐WS=5‐AA7050‐P; (b) FSW‐WS=5‐AA7050‐R. ... 64

Figure 6‐6: Microhardness test results for WS=3 mm/s and different positioning of the materials. ... 67

Figure 6‐7: Microhardness test results for WS=5 mm/s and different positioning of the materials. ... 69

Figure 6‐8: Microhardness test results for WS=8 mm/s and different positioning of the materials. ... 70

Figure 6‐9: Microhardness test results for WS=5 mm/s, AA 2024‐T3 in AS and different direction of the materials. ... 71

Figure 6‐10: Microhardness test results for WS=8 mm/s, AA 7050‐T7651 in AS and different direction of the materials. ... 72

Figure 6‐11: Variation of the YS changing the WS and the materials position. ... 73

Figure 6‐12: Variation of the UTS changing the WS and the materials position. ... 74

Figure 6‐13: Variation of the YS changing the WS, the materials position and direction. ... 75

Figure 6‐14: Variation of the UTS changing the WS, the materials position and direction... 76

Figure 7‐1: Cross section of: (a) FSW‐WS=3; (b) FSW‐WS=5; (c) FSW‐WS=8; (d) FSW‐WS=10. .. 80

Figure 7‐2: Results from the SZ area measurement for different WS in the case of FSW. ... 81

Figure 7‐3: Cross section of: (a) SSFSW‐WS=1; (b) SSFSW‐WS=2; (c) SSFSW‐WS=3; (d) SSFSW‐ WS=4. ... 83

Figure 7‐4: Results from the SZ area measurement for different WS in the case of SSFSW. ... 84

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xi

Figure 7‐5: Cross section of: (a) FSW‐WS=8; (b) SSFSW‐WS=3. ... 85

Figure 7‐6: Cross section of a weld plate with a broken probe embedded, taken along the mid‐ plane (parallel to the plate) of the weld plate [1]. ... 85

Figure 7‐7: Comparison of the SZ area in case of SSFSW and conventional FSW for different WS. ... 86

Figure 7‐8: SEM image of a sample showing the scanned line for the EDX test. ... 87

Figure 7‐9: Atomic percentage of zinc through the scanned line for FSW‐WS=3. ... 87

Figure 7‐10: Atomic percentage of zinc through the scanned line for FSW‐WS=5. ... 88

Figure 7‐11: Atomic percentage of zinc through the scanned line for FSW‐WS=8. ... 88

Figure 7‐12: Atomic percentage of zinc through the scanned line for SSFSW‐WS=1. ... 89

Figure 7‐13: Atomic percentage of zinc through the scanned line for SSFSW‐WS=2. ... 89

Figure 7‐14: Atomic percentage of zinc through the scanned line for SSFSW‐WS=3. ... 89

Figure 7‐15: MicroHardness test results for conventional FSW and four different WS. ... 90

Figure 7‐16: MicroHardness test results for SSFSW and three different WS. ... 92

Figure 7‐17: MicroHardness comparison between SSFSW and conventional FSW. ... 93

Figure 7‐18: Hardness distribution through the thickness of the specimens (a) FSW‐WS=8 (b)SSFSW‐WS=3. ... 94

Figure 7‐19: Variation of the Yield Stress changing the WS in the case of SSFSW and conventional FSW. ... 95

Figure 7‐20: Variation of the UTS changing the WS in the case of SSFSW and conventional FSW. ... 96

Figure 7‐21: ARAMIS report for FSW‐WS=8. ... 98

Figure 7‐22: ARAMIS report for SSFSW‐WS=3. ... 98

Figure 7‐23: Local and general Stress‐Strain curves of the specimens SSFSW‐WS=3 and FSW‐ WS=8. ... 99

Figure 7‐24: ARAMIS report for SSFSW‐WS=1. ... 101

Figure 7‐25: ARAMIS report for SSFSW‐WS=2. ... 102

Figure 7‐26: ARAMIS report for SSFSW‐WS=3. ... 102

Figure 7‐27: Local Stress‐Strain curves of the specimens SSFSW‐WS=3; SSFSW‐WS=2 and SSFSW‐WS=1. ... 103

Figure 7‐28: Stress‐Strain curve of the specimen SSFSW‐WS=3. ... 104

Figure 7‐29: Behaviour of the Major Strain through the weld in the YS and UTS. ... 105

Figure 7‐30: MicroHardness measurements in three different lines through the thickness of the

specimen. ... 106

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xii

Figure 7‐31: Local Stress‐Strain curves in different areas of the weld. ... 107

Figure 8‐1: Load‐δ

₅

for WS=1 mm/s and three different crack positions. ... 110

Figure 8‐2: Load‐CMOD

for WS=1 mm/s and three different crack positions. ... 111

Figure 8‐3: Crack resistance curves (R‐Curve) for WS=1 and three different crack positions. . 112

Figure 8‐4: Major strain field for WS=1 mm/s and crack in the AS. ... 113

Figure 8‐5: Major strain field for WS=1 mm/s and crack in the SZ. ... 114

Figure 8‐6: Major strain field for WS=1 mm/s and crack in the RS. ... 114

Figure 8‐7: Major Strain behaviour in front of the crack tip for WS=1 mm/s. ... 115

Figure 8‐8: Load‐δ

₅

for WS=2 mm/s and three different crack positions. ... 117

Figure 8‐9: Load‐CMOD for WS=2 mm/s and three different crack positions. ... 117

Figure 8‐10: Crack resistance curves (R‐Curve) for WS=2 and three different crack positions. 118 Figure 8‐11: Major strain field for WS=2 mm/s and crack in the AS. ... 119

Figure 8‐12: Major strain field for WS=2 mm/s and crack in the SZ... 120

Figure 8‐13: Major strain field for WS=2 mm/s and crack in the RS. ... 121

Figure 8‐14: Major Strain behaviour in front of the crack tip for WS=2 mm/s. ... 121

Figure 8‐15: Load‐δ

₅

for WS=3 mm/s and three different crack positions. ... 122

Figure 8‐16: Load‐CMOD

for WS=3 mm/s and three different crack positions. ... 123

Figure 8‐17: Crack resistance curves (R‐Curve) for WS=2 and three different crack positions. ... ... 124

Figure 8‐18: Major strain field for WS=3 mm/s and crack in the AS. ... 125

Figure 8‐19: Major strain field for WS=3 mm/s and crack in the SZ... 126

Figure 8‐20: Major Strain behaviour in front of the crack tip for WS=3 mm/s. ... 126

Figure 8‐21: Load‐δ

₅

for crack in the SZ and three different WS. ... 128

Figure 8‐22: Load‐CMOD

for crack in the SZ and three different WS. ... 128

Figure 8‐23 Crack resistance curves (R‐Curve) for crack in the SZ and three different WS. ... 129

Figure 8‐24 Major Strain behaviour in front of the crack tip in the SZ for three different WS. ...

... 130