• shot peening
• parameters’ influence
• residual stress
• characteristics
• AA7449 plates

1 INTRODUCTION 3
2 STATE OF ART: SHOT PEENING PROCESS 5
2.1 PROCESS 5
2.2 SHOT PEENING PARAMETERS 6
2.2.1 Shot type and shot size 7
2.2.2 Peening intensity 9
2.2.3 Shot impact angle 10
2.2.4 Coverage 14
2.2.5 Mass flow rate 16
2.2.6 Nozzle performances 18
3 STATE OF ART: RESIDUAL STRESS MEASUREMENT 20
3.1 X-RAY TECHNIQUE 20
3.2 BORE HOLE DRILLING METHOD 24
4 EXPERIMENTAL PROCEDURES 28
4.1 MATERIAL AND TREATMENTS 28
4.2 SPECIMEN DESCRIPTION 31
4.2.1 Specimen extraction 31
4.2.2 Specimen dimensions 32
4.2.3 Specimen preparation 33
4.3 SHOT PEENING DETAILS 34
4.4 RESIDUAL STRESS INVESTIGATION-HOLE DRILLING METHOD DETAILS 35
4.5 RESIDUAL STRESS MEASUREMENT- XRD TECHNIQUE 36
4.6 ROUGHNESS MEASUREMENT 37
4.7 METALLOGRAPHY AND MICRO-HARDNESS MEASUREMENT 40
4.8 PHYSICAL ANALYSIS: SEM-SCANNING ELECTRON MICROSCOPE 43
5 RESULTS AND DISCUSSION OF THE AA7449 WITHOUT SHOT PEENING 46
6 RESULTS 50
6.1 RESIDUAL STRESS PROFILE 50
6.1.1 Residual stress profile batch No#1 51
6.1.2 Residual stress profile batch No#2 53
6.2 MICROHARDNESS 56
6.2.1 Batch No#1 56
6.2.2 Batch No#2 60
6.3 TOTAL ROUGHNESS DISTRIBUTION 65
6.3.1 Total roughness course in ST direction 65
6.3.2 Total roughness course in LT direction 66
6.3.3 Total roughness course-combination of ST and LT direction 67
6.4 SEM PICTURES 68
6.4.1 Surface topography after steel shots hits 69
6.4.2 Surface topography after glass beads hits 71
7 DISCUSSION 74
7.1 RESIDUAL STRESS DISTRIBUTION 74
7.1.1 Influence of the peening intensity 74
7.1.2 Comparison of batch No#1 and batch No#2 specimens 75
7.2 MICROHARDNESS 76
7.2.1 Influence of the peening intensity for specimens T7651 heat treated 76
7.2.2 Influence of the peening intensity for specimens T7651+SHT heat treated 77
7.2.3 Influence of the heat treatment 78
7.2.4 Influence of the shot type 79
7.3 TOTAL ROUGHNESS DISTRIBUTION 80
7.3.1 Influence of shot type and shot size 80
7.3.2 Influence of the peening pressure 81
7.3.3 Influence of the distance nozzle-target surface and of the coverage 82
7.3.4 Influence of the heat treatment 83
8 CONCLUSIONS 85
9 REFERENCES 86