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

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mode-mixity phase angle was chosen in the finite element model of the MMB specimen to determine the appropriate lever arm distance (c). It is assumed that because of the mode I dominant loading for phase angles more than -20, the characterisation of the face/core interface for only -20 phase angle and using the resulting crack growth rates for the simulation of STT specimens with slightly lower phase angle magnitudes (-20
Displacement controlled static tests with 1 mm/min loading rate were conducted on two MMB specimens of each core type to determine the static crack propagation load. Typical load vs. displacement curves from the static tests are presented in Figure 5.22. The point where the crack starts to propagate is marked with an open circle (“”). The critical failure load is marked according to the ASTM D6671/D 6671M-06 recommendation and complemented by visual inspection. Load (N) 80 60 40 20 0 0 0 1 2 3 0 2 4 6 Displacement (mm) Displacement (mm) (a) (b) Figure 5.22: Typical load vs. displacement curves (“” onset of crack growth) for the MMB sandwich specimens with (a) H45 core and (b) H100 core. Fatigue tests in displacement control with sinusoidal wave form were conducted on three specimens of each core type at a frequency of 2 Hz and with a loading ratio R=0.1. Displacement controlled testing was chosen for better servo-hydraulic control of the loading and to avoid any unstable crack growth in the MMB specimens. To have a stable crack growth, 80% of the static crack propagation load was chosen as the maximum fatigue load after testing a few trial specimens. The crack length was determined every 50 cycles using the compliance of the MMB specimen as 105 ( 5.1) Where c is the lever arm distance, L the half-span length, is the load partitioning parameter. C1, C2 and C3 are compliances of the sub-beams according to Quispitupa et al. (2009) as introduced in Chapter 3. For further details see Chapter 3. Moreover, visual crack length measurement was performed by a calliper with an accuracy of ±0.05 mm. The maximum fatigue load (Pmax) and the corresponding displacement (max) were used to determine the compliance of the MMB specimens and subsequently the crack length. The MMB compliance in Equation (5.1) is a function of the crack length. Knowing the maximum load (Pmax) and displacement (max) from the testing machine, the compliance CMMB=/P can be calculated and subsequently the crack length can be determined, see Chapter 3. Furthermore, since the MMB test rig has several hinge connections and load introduction points, the deflections of the test rig during the fatigue tests Load (N) 160 120 80 40
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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
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
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 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
Page 172 and 173: A.5 Out-of-plane deflection of Debo
Page 174 and 175: (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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