Residual Strength and Fatigue Lifetime of ... - Solid Mechanics

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Figure 5.42: Zero and ninety degrees positions along the debond front. Initial crack 0 debond section Initial crack 90 debond section Crack growth path Crack growth path Figure 5.43: Fatigue crack growth paths in the tested sandwich panels. 5.3.2 Finite Element Modelling of the Debonded Panels A 3D finite element model of the debonded panels is developed in the commercial finite element code ANSYS. 8-node iso-parametric elements (PLANE45) are exploited for finite element modelling. Because of geometrical and loading symmetry only a quarter of the panel is 120 90 0
generated. Symmetry boundary conditions are imposed in the symmetry planes. The edges of the panels are clamped by imposing a zero displacement boundary condition. The finite element model of the debonded panel is shown in Figure 5.44. The accelerated fatigue crack growth simulation scheme (cycle jump method) developed in the previous chapter is used to simulate fatigue crack propagation in the sandwich panels. The energy release rate and mode-mixity phase angle are chosen as state variables in the cycle jump scheme. Figure 5.45 illustrates the distribution of the energy release rate and the related mode-mixity phase angle during the first cycle along the debond front using the maximum fatigue load amplitude. As expected the energy release rate and mode-mixity phase angle are evenly distributed along the debond front because of the circular shape of the debond and the large distance to the panel boundaries. Figure 5.46 shows the energy release rate and mode-mixity phase angle vs. debond diameter using the maximum fatigue load amplitude. Debond Figure 5.44: Quarter finite element model of the debonded panels with a circular debond. The smallest element size is 10m. 121 Clamp B. C. Symmetry B. C. 310 mm x y
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Residual Strength and Fatigue Lifet
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Published in Denmark by Technical U
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method to accelerate the simulation
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Synopsis Sandwich kompositter er i
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Contents Preface Executive Summary
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5 Face/core Interface Fatigue Crack
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H11 bimaterial constant H22 bimater
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These peculiar damage modes often r
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1.2 Overview of the Thesis In this
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Figure 1.3: Fracture modes, from Be
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In Equations (1.5) and (1.6) H11, H
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Figure 1.6: Schematic illustration
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The compact tension specimen (CT) i
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A Figure 1.10: CSB, DCB, TSD, DCB-U
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Chapter 2 Buckling Driven Face/Core
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(DIC) measurement system (ARAMIS 2M
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corresponds to the onset of debond
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Figure 2.7: Crack kinking into the
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(2.2) where and for plane str
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A modified version of the tilted sa
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previous observations of crack path
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of contact elements (CONTACT173 and
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the debond opening initially increa
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Table 2.4: Instability loads determ
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G (J/m2) 600 400 200 0 H100 IMP=0.1
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Hayman (2007) has described a damag
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Table 3.1: Panel test specimens. La
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sheet and the core thickness, respe
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Load (N) 250 200 150 100 50 0 H130
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Table 3.4: Parameters in the face/c
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was used to monitor 3D surface disp
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arising due to the junction between
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(a) Debonded face sheet Figure 3.16
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Figure 3.19 shows the determined en
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H130 MMB H130 Panel H250 MMB Interf
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3.6 Conclusion In this chapter the
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composite laminates under thermal c
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S S y( t ) y( t ) ( t ) 2 1 12 2
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listed in Table 4.1. The length and
Page 92 and 93: The strain energy release rate, G,
Page 94 and 95: high growth rate of G (see Figure 4
Page 96 and 97: 4.4 Face/Core Fatigue Crack Growth
Page 98 and 99: Debond 310 mm Symmetry B. C. a Figu
Page 100 and 101: B 2 1/ 2 ( S44 S55 S45) (4.17) wh
Page 102 and 103: 75), which illustrates possible ina
Page 104 and 105: Figure 4.18 (a) presents the deflec
Page 106 and 107: Debond radius (mm) 100 90 80 70 60
Page 108 and 109: using the cycle jump method, more t
Page 110 and 111: Chapter 5 Face/Core Interface Fatig
Page 112 and 113: of this chapter, sandwich panels wi
Page 114 and 115: H250 Specimen H100 Specimen H45 Spe
Page 116 and 117: Figure 5.5: Test setup. Initially,
Page 118 and 119: H100 Specimen Fibre bridging Figure
Page 120 and 121: propagation, the crack continues to
Page 122 and 123: Figure 5.14: Kinking of the crack i
Page 124 and 125: Crack length [mm] Crack length [mm]
Page 126 and 127: mode-mixity phase angle was chosen
Page 128 and 129: should be taken into account for a
Page 130 and 131: Figure 5.25: Kinking of the crack i
Page 132 and 133: log (da/dN) (mm/cycle) 10 log G (J/
Page 134 and 135: erroneous extrapolations in the tra
Page 136 and 137: compared to the 65% efficiency obta
Page 138 and 139: the case of uneven debond growth, t
Page 140 and 141: Load (kN) 2 1.5 1 0.5 0 Panel 1 Pan
Page 144 and 145: G(J/m 2 ) 180 150 210 120 150 100 5
Page 146 and 147: 110 q=qG=0.4 Test #1 100 Test #2 Te
Page 148 and 149: panels were determined for differen
Page 150 and 151: Chapter 6 Conclusion and Future Wor
Page 152 and 153: toughness using MMB fracture toughn
Page 154 and 155: For the specimens with H250 core th
Page 156 and 157: Development of testing methods for
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Page 160 and 161: Bezazi A., Mahi A. E., Berthelot J.
Page 162 and 163: Kanny K. and Mahfuz H. (2005), Flex
Page 164 and 165: Ratcliffe J. and Cantwell W. J. (20
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Page 168 and 169: Out-of-plane displacement (mm) 1 0.
Page 170 and 171: Out-of-plane displacement (mm) 3 2
Page 172 and 173: A.5 Out-of-plane deflection of Debo
Page 174 and 175: (a) Figure A.14: Out-of-plane defle
Page 176 and 177: (a) (b) Figure A.18: Out-of-plane d
Page 178 and 179: Load (kN) 250 200 150 100 50 250 30
Page 180 and 181: Displacement (mm) 4 3 2 1 0 8 9 (a)
Page 182 and 183: (a) (b) Figure B.11: Out-of-plane d
Page 184 and 185: (a) (b) Figure B.15: Out-of-plane d
Page 188: DTU Mechanical Engineering Section
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