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

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Contents Preface Executive Summary Synopsis (in Danish) Publications Contents Symbols 1. Introduction 1 1.1 Background and Motivations ……………………………………………….. 1 1.2 Thesis Overview ……………………………………………………………. 3 1.3 Linear Elastic Fracture Mechanics …………………………………………. 5 1.4 Linear Elastic Fracture Mechanics in the Interfaces ……………………….. 7 1.5 Fatigue Crack Propagation in Sandwich Composites ……………………… 10 2 Face/Core Debond Propagation in Sandwich Columns 16 2.1 Background and Objectives ………………………………………………… 16 2.2 Experimental Set-up ………………………………………………………... 17 x i iii vi ix x xv
2.3 Experimental Results ……………………………………………………….. 19 2.4 Characterization of Face/Core Interface Fracture Resistance ………………. 22 2.5 Finite Element Model of the Debonded Columns ………………………….. 29 2.6 Comparison of Numerical and Experimental Results ………………………. 31 2.7 Conclusions …………………………………………………………………. 37 3 Failure of Uniformly Compressed Debond Damaged Sandwich Panels 39 3.1 Background …………………………………………………………………. 39 3.2 Test Specimens ……………………………………………………………... 40 3.3 Characterization of Face/Core Interface ……………………………………. 43 3.4 Panel Tests ………………………………………………………………….. 49 3.5 Panel Analysis ………………………………………………………………. 53 3.6 Conclusion …………………………………………………………………. 60 4 Fatigue Crack Growth Simulation in a Bimaterial Interface 63 4.1 Background …………………………………………………………………. 63 4.2 Cycle Jump Method ………………………………………………………… 65 4.3 2D Face/Core Fatigue Crack Growth in Sandwich Beams ………………… 67 4.4 3D Face/core fatigue crack growth in sandwich panels ……………………. 74 4.5 Conclusion ………………………………………………………………… 85 xi
Page 1: Residual Strength and Fatigue Lifet
Page 4 and 5: Published in Denmark by Technical U
Page 6 and 7: This page is intentionally left bla
Page 8 and 9: method to accelerate the simulation
Page 10 and 11: Synopsis Sandwich kompositter er i
Page 16 and 17: 5 Face/core Interface Fatigue Crack
Page 20 and 21: H11 bimaterial constant H22 bimater
Page 24 and 25: These peculiar damage modes often r
Page 26 and 27: 1.2 Overview of the Thesis In this
Page 28 and 29: Figure 1.3: Fracture modes, from Be
Page 30 and 31: In Equations (1.5) and (1.6) H11, H
Page 32 and 33: Figure 1.6: Schematic illustration
Page 34 and 35: The compact tension specimen (CT) i
Page 36 and 37: A Figure 1.10: CSB, DCB, TSD, DCB-U
Page 38 and 39: Chapter 2 Buckling Driven Face/Core
Page 40 and 41: (DIC) measurement system (ARAMIS 2M
Page 42 and 43: corresponds to the onset of debond
Page 44 and 45: Figure 2.7: Crack kinking into the
Page 46 and 47: (2.2) where and for plane str
Page 48 and 49: A modified version of the tilted sa
Page 50 and 51: previous observations of crack path
Page 52 and 53: of contact elements (CONTACT173 and
Page 54 and 55: the debond opening initially increa
Page 56 and 57: Table 2.4: Instability loads determ
Page 58 and 59: G (J/m2) 600 400 200 0 H100 IMP=0.1
Page 62 and 63: 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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This page is intentionally left bla
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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
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The strain energy release rate, G,
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high growth rate of G (see Figure 4
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4.4 Face/Core Fatigue Crack Growth
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Debond 310 mm Symmetry B. C. a Figu
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B 2 1/ 2 ( S44 S55 S45) (4.17) wh
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75), which illustrates possible ina
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Figure 4.18 (a) presents the deflec
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Debond radius (mm) 100 90 80 70 60
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using the cycle jump method, more t
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Chapter 5 Face/Core Interface Fatig
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of this chapter, sandwich panels wi
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H250 Specimen H100 Specimen H45 Spe
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Figure 5.5: Test setup. Initially,
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H100 Specimen Fibre bridging Figure
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propagation, the crack continues to
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Figure 5.14: Kinking of the crack i
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Crack length [mm] Crack length [mm]
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mode-mixity phase angle was chosen
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should be taken into account for a
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Figure 5.25: Kinking of the crack i
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log (da/dN) (mm/cycle) 10 log G (J/
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erroneous extrapolations in the tra
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compared to the 65% efficiency obta
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the case of uneven debond growth, t
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Load (kN) 2 1.5 1 0.5 0 Panel 1 Pan
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Figure 5.42: Zero and ninety degree
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G(J/m 2 ) 180 150 210 120 150 100 5
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110 q=qG=0.4 Test #1 100 Test #2 Te
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panels were determined for differen
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Chapter 6 Conclusion and Future Wor
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toughness using MMB fracture toughn
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For the specimens with H250 core th
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Development of testing methods for
Page 158 and 159:
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Bezazi A., Mahi A. E., Berthelot J.
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Kanny K. and Mahfuz H. (2005), Flex
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Ratcliffe J. and Cantwell W. J. (20
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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
Page 188:
DTU Mechanical Engineering Section
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