tesi R. Valiante.pdf - EleA@UniSA

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$3Eterov e)ce(te/rou sofo\v to/ te pa/lai to/ te nu=n. Ou ... - EleA@UniSA$

6 Fig. 4.2 - Explicit scheme diagram ............................................................ 112 Fig. 4.3 - Skin geometry ............................................................................ 114 Fig. 4.4 - Item profile including skin and stringers.................................... 115 Fig. 4.5 - Panel geometry (view from above) ............................................ 115 Fig. 4.6 - Panel geometry (frontal view).................................................... 115 Fig. 4.7 - Panel geometry (lateral view) .................................................... 116 Fig. 4.8 - Cut-off of the total panel meshed............................................... 118 Fig. 4.9 - Enhancement of meshing. .......................................................... 118 Fig. 4.10 - Pure modes by excitation of the plate on both sides ................ 120 Fig. 4.11 - Input excitation signal in time and frequency domain, 5.5 cycles at 270 kHz.................................................................................................. 121 Fig. 4.12 - Loads and constrains on the model .......................................... 122 Fig. 4.13 - Details of previous image......................................................... 122 Fig. 4.14 - Property set name scalar plot ................................................... 123 Fig. 4.15 - Field output of the out of plane velocity V 1 for stiffened plate with delamination, modeled with shell elements....................................... 125 Fig. 4.16 - Cut-off of the total panel meshed with hex8 elements............. 126 Fig. 4.17 - Enhancement of meshing. ........................................................ 126 Fig. 4.18 - Field output of the out of plane velocity V 3 for stiffened plate with delamination, modeled with solid elements....................................... 129 Fig. 4.19 - Plot of the velocity recorded from the laser vibrometry at different time instants. ............................................................................... 130
ABSTRACT OF DISSERTATION 7 ABSTRACT OF DISSERTATION Aerospace industry is characterized by continuously growing safety cost requirements. This fact leads to the exponential increase in the use of composite materials. With such feature as high strength-to-weight and stiffness to weight ratios, these materials allow the manufacturing of lighter and more efficient structure, with respect to aluminum alloys, in order to increase the payload and to reduce the fuel consumption. However, composite structures are very vulnerable to structural damage, in particular to the delamination that can be introduced during manufacturing or service. The occurrence of delamination could potentially lead to a catastrophic failure of the whole structure, if it accumulates above a critical level. Cost saving must never be considered without safety. For this reason, in the last years researchers have been developing ever more sophisticated damage monitoring systems, which are able to evaluate the health of a structure in real-time. This branch of research is known as Structural Health monitoring (SHM). This study investigates the use of Lamb waves and laser vibrometry for the identification and localization of damage/defects occurring within critical components of aircraft structure. In the present study, a SHM strategy based on dynamic structural analysis performed over a wide frequency range is presented. The frequency band of investigation spans from the lowest mode of the structure up to the low ultrasonic range, and so, potentially, it allows the detection of various sizes of defects. The tests are performed using a single actuator/sensor pair: piezoelectric discs are employed as actuators, while a Scanning Laser Doppler Vibrometer is used as a sensing device. The piezoceramic discs are inexpensive and easy to operate and the Scanning Laser Doppler Vibrometer measures the velocity of the structure at points on a user-defined grid, thus providing an unprecedented amount of information.
Page 1: Unione Europea Università degli St
Page 5 and 6: RINGRAZIAMENTI E’ per me doveroso
Page 7: Vorrei, infine, disporre del vocabo
Page 11 and 12: CONTENTS Abstract of dissertation .
Page 13 and 14: LIST OF FIGURES AND TABLES Fig. 1.1
Page 15: Fig. 3.32 - : RMS of the field of r
Page 19 and 20: ABSTRACT OF DISSERTATION 9 are: The
Page 21 and 22: INTRODUCTION 11 Ideally, routinely
Page 23 and 24: INTRODUCTION 13 Feature extraction
Page 25 and 26: INTRODUCTION 15 1.3. GLOBAL VERSUS
Page 27 and 28: INTRODUCTION 17 damage. These inves
Page 29 and 30: INTRODUCTION 19 between shifts at v
Page 31 and 32: INTRODUCTION 21 Space Shuttle Orbit
Page 33 and 34: INTRODUCTION 23 1.6. GUIDED WAVES-B
Page 35 and 36: INTRODUCTION 25 Fig. 1.3 - Differen
Page 37 and 38: INTRODUCTION 27 Considering the arg
Page 39 and 40: INTRODUCTION 29 Fig. 1.6 - Differen
Page 41 and 42: INTRODUCTION 31 2 ω c 2 k = 2 ω
Page 43 and 44: INTRODUCTION 33 Fig. 1.8 - Frequenc
Page 45 and 46: INTRODUCTION 35 where 1 1 p1 c k =
Page 47 and 48: INTRODUCTION 37 Fig. 1.12 - Group v
Page 49 and 50: INTRODUCTION 39 Fig. 1.13 - Directi
Page 51 and 52: INTRODUCTION 41 for very simple cas
Page 53 and 54: INNOVATIVE SHM TECHNIQUES BASED ON
Page 63 and 64: EXPERIMENTAL ANALYSIS 53 3. EXPERIM
Page 65 and 66: EXPERIMENTAL ANALYSIS 55 Fig. 3.3 -
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EXPERIMENTAL ANALYSIS 57 same point
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EXPERIMENTAL ANALYSIS 59 Fig. 3.5 -
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EXPERIMENTAL ANALYSIS 61 Fig. 3.8 -
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EXPERIMENTAL ANALYSIS 63 of the ene
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EXPERIMENTAL ANALYSIS 65 Fig. 3.13
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EXPERIMENTAL ANALYSIS 69 Analysis g
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EXPERIMENTAL ANALYSIS 71 Analysis g
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EXPERIMENTAL ANALYSIS 73 and in spa
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EXPERIMENTAL ANALYSIS 75 and are tr
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EXPERIMENTAL ANALYSIS 77 obtained w
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EXPERIMENTAL ANALYSIS 81 (a) t = 68
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EXPERIMENTAL ANALYSIS 97 The data p
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EXPERIMENTAL ANALYSIS 101 To increa
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EXPERIMENTAL ANALYSIS 103 Both of t
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EXPERIMENTAL ANALYSIS 107 Complete
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FINITE ELEMENT MODELING OF WAVE PRO
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CONCLUSIONS AND FUTURE WORK 131 5.
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CONCLUSIONS AND FUTURE WORK 133 cas
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REFERENCES 135 [6] Rose, J. L. “A
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REFERENCES 137 [20] Ko, J. M., Wong
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REFERENCES 139 [35] J. D. Achenbach
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