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

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Figure 5.5: Test setup. Initially, to investigate the static behaviour and maximum load carrying capacity of the STT specimens, static tests were carried out on two specimens for each core density. Ramped displacement controlled loading with a piston displacement rate of 1 mm/min was applied to all tests. A sample rate of one image per second was used for the DIC measurements. Figure 5.6 shows typical load vs. axial actuator displacement for the STT specimens, for additional results see Appendix C. The load initially increases linearly until face/core debond crack initiation occurs. After the first crack propagation the load drops, but as the crack propagates further the maximum load remains approximately constant. The maximum load in fatigue tests is chosen as a portion of the average of this mainly constant load. It is also seen that by increasing the core density, the crack initiation and propagation loads increase, which can be attributed to the larger fracture toughness of heavier cores. Force (kN) Measurement area 1.2 0.8 0.4 0 H45 Specimen 0 2 4 6 8 10 Axial displacement (mm) Figure 5.6: Typical axial displacement of the actuator vs. force for specimens with H45, H100 and H250 core densities. 94 Actuator piston Load cell H250 Specimen H100 Specimen H45
Crack growth paths for the STT specimens with H45, H100 and H250 cores from the static tests are shown in the following figures. For the specimens with H45 core, the crack kinks into the core up to 4-5 mm below the interface and then approaches the face/core interface as the crack propagates further. However, since the fracture toughness of the H45 core is low compared to that of the face/core interface, the crack never kinks into the interface and continues to propagate in the core just below the resin-rich region of the core, see Figure 5.7. For the specimens with H100 core, the crack initially kinks into the core and continues to propagate 2-3 mm below the interface. After 45-55 mm of crack growth it eventually kinks into the face/core interface and subsequently into the face sheet, which leads to large-scale fibre bridging, see Figures 5.8 and 5.9. For the specimens with H250 core, the crack starts to propagate in the face/core interface. Subsequently, it kinks into the face sheet after 25-35 mm propagation and continues to propagate in the face sheet, resulting in large-scale fibre bridging, see Figure 5.10. The static crack initiation and propagation loads are listed in Table 5.2. It is seen that the mainly constant crack propagation load is much lower that the crack initiation load, which can be attributed to the initial resistance of the crack due to the accumulation of resin at the crack tip during the manufacturing process at the predefined face/core crack. H45 Specimen Figure 5.7: Static crack growth path for an STT specimen with H45 core at the beginning and end of the test. 95
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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
Page 66 and 67: sheet and the core thickness, respe
Page 68 and 69: Load (N) 250 200 150 100 50 0 H130
Page 70 and 71: Table 3.4: Parameters in the face/c
Page 72 and 73: was used to monitor 3D surface disp
Page 74 and 75: arising due to the junction between
Page 76 and 77: (a) Debonded face sheet Figure 3.16
Page 78 and 79: Figure 3.19 shows the determined en
Page 80 and 81: H130 MMB H130 Panel H250 MMB Interf
Page 82 and 83: 3.6 Conclusion In this chapter the
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Page 86 and 87: composite laminates under thermal c
Page 88 and 89: S S y( t ) y( t ) ( t ) 2 1 12 2
Page 90 and 91: 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
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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
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Page 114 and 115: H250 Specimen H100 Specimen H45 Spe
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]
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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/
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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 142 and 143: Figure 5.42: Zero and ninety degree
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
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Page 150 and 151: Chapter 6 Conclusion and Future Wor
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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
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Out-of-plane displacement (mm) 1 0.
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Out-of-plane displacement (mm) 3 2
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A.5 Out-of-plane deflection of Debo
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(a) Figure A.14: Out-of-plane defle
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(a) (b) Figure A.18: Out-of-plane d
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Load (kN) 250 200 150 100 50 250 30
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Displacement (mm) 4 3 2 1 0 8 9 (a)
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(a) (b) Figure B.11: Out-of-plane d
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(a) (b) Figure B.15: Out-of-plane d
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DTU Mechanical Engineering Section
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Residual Strength and Fatigue Lifetime of ... - Solid Mechanics

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