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

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Figure 5.14: Kinking of the crack into the face sheet in an STT specimen with H250 core. Figure 5.15: Fiber bridging in the rear side of an STT specimen with H250 core. A 4 Mpix Digital Image Correlation (DIC) measurement system (ARAMIS 4M) was utilized to monitor 2D surface major strains and locate the crack tip position by the strain concentration at the crack tip in the measured 2D strain contours. To ensure the accuracy of the measurement a tape ruler was glued to the bottom side of the specimens to locate the crack tip as well and measure the crack length by a calliper with an accuracy of ±0.05 mm. Figure 5.16 shows a majore strain contour from an STT specimen with H45 core used to locate the crack tip position by the DIC system. Fatigue crack growth length vs. load cycle diagrams for the STT specimens from both the visual measurements and the measurements using the DIC system are presented in Figure 5.17. The crack length measurements by the DIC system agree well with the physical crack measurements, as shown in Figure 5.17. Crack growth length vs. load cycle results from the two repetitions of each type of STT specimens are shown in Figure 5.18. It is seen that for all core densities the crack initially grows fast, but the crack growth rate decreases as the crack propagates further. This can be attributed to increasing membrane forces and subsequent decreasing energy release rates for the H100 and H45 specimens and fully developed fibre bridging resisting the crack growth for the H250 specimens. For both STT specimens with H45 core, unstable crack propagation was observed during the initial load cycles where the crack propagated unstably 100
around 150 mm. After the unstable crack propagation, the crack continued to propagate in a stable manner. A small deviation between the two test repetitions is observed for the H45 and H100 specimens. However, Figure 5.18 (c) illustrates a large deviation between the two test repetitions for the STT specimens with H250 core, which can be attributed to the different scales of fibre bridging in H250 specimens. Crack length [mm] Figure 5.16: Surface major strain contour of the STT specimens from the DIC system. 250 200 150 100 50 0 Strain concentration at the crack tip 200 (a) (b) 0 20000 40000 60000 80000 Cycles, N Visual DIC 101 Crack length [mm] 160 120 80 40 0 Visual DIC 0 20000 40000 60000 80000 100000 Cycles, N
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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
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
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 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 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
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
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
Page 168 and 169: Out-of-plane displacement (mm) 1 0.
Page 170 and 171: 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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