Residual Strength and Fatigue Lifetime of ... - Solid Mechanics
Residual Strength and Fatigue Lifetime of ... - Solid Mechanics Residual Strength and Fatigue Lifetime of ... - Solid Mechanics
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Chapter 3 Failure of Uniformly Compressed Debond Damaged Sandwich Panels 3.1 Background In the previous chapter a detailed analysis of face/core fracture in sandwich columns under compression was presented. A finite element model of the columns was developed and utilised to determine fracture parameters like the energy release rate and mode-mixity phase angle. In order to predict the crack propagation load, face/core interface fracture toughness of the columns was determined using the TSD specimen. Furthermore, the developed finite element model was validated against compression tests on debonded columns with different cores and debond lengths. The next step in studing the interface fracture of sandwich structures is to extend the analysis from simple geometries like beams and columns to geometries like panels. In recent years, efforts have been made to investigate the effect of face/core debonding on the residual strength of sandwich panels. Berggreen and co-authors (2005) in different studies investigated the failure of debonded sandwich panels loaded with non-uniform compressive and lateral pressure loading. They additionally proposed a new method for determining numerically the mode-mixity at the crack tip. Avilés and Carlsson (2007) focused on sandwich panels containing circular embedded debonds. They conducted uniform compression tests and finite element analysis to determine the residual strength of the damaged panels. Chen and Bai (2002) conducted finite element analysis to study the postbuckling behaviour of face/core debonded sandwich panels on the basis of the von Karman non-linearity assumption and the zigzag deformation theory combined with a debonding model and a multi-scalar damage model. Despite all the numerical and experimental studies, a comprehensive study of debond damaged sandwich panels, and analysis of issues like debond propagation, characterisation of the fracture toughness of the interface at different mode-mixities and finally validation of these methods against experiments is still missing. 39
- Page 10 and 11: Synopsis Sandwich kompositter er i
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- Page 14 and 15: Contents Preface Executive Summary
- Page 16 and 17: 5 Face/core Interface Fatigue Crack
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- Page 20 and 21: H11 bimaterial constant H22 bimater
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- Page 26 and 27: 1.2 Overview of the Thesis In this
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- 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
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- 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
- Page 64 and 65: 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
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- Page 76 and 77: (a) Debonded face sheet Figure 3.16
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- 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 106 and 107: Debond radius (mm) 100 90 80 70 60
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Chapter 3<br />
Failure <strong>of</strong> Uniformly Compressed Debond<br />
Damaged S<strong>and</strong>wich Panels<br />
3.1 Background<br />
In the previous chapter a detailed analysis <strong>of</strong> face/core fracture in s<strong>and</strong>wich columns under<br />
compression was presented. A finite element model <strong>of</strong> the columns was developed <strong>and</strong> utilised to<br />
determine fracture parameters like the energy release rate <strong>and</strong> mode-mixity phase angle. In order<br />
to predict the crack propagation load, face/core interface fracture toughness <strong>of</strong> the columns was<br />
determined using the TSD specimen. Furthermore, the developed finite element model was<br />
validated against compression tests on debonded columns with different cores <strong>and</strong> debond<br />
lengths. The next step in studing the interface fracture <strong>of</strong> s<strong>and</strong>wich structures is to extend the<br />
analysis from simple geometries like beams <strong>and</strong> columns to geometries like panels.<br />
In recent years, efforts have been made to investigate the effect <strong>of</strong> face/core debonding on the<br />
residual strength <strong>of</strong> s<strong>and</strong>wich panels. Berggreen <strong>and</strong> co-authors (2005) in different studies<br />
investigated the failure <strong>of</strong> debonded s<strong>and</strong>wich panels loaded with non-uniform compressive <strong>and</strong><br />
lateral pressure loading. They additionally proposed a new method for determining numerically<br />
the mode-mixity at the crack tip. Avilés <strong>and</strong> Carlsson (2007) focused on s<strong>and</strong>wich panels<br />
containing circular embedded debonds. They conducted uniform compression tests <strong>and</strong> finite<br />
element analysis to determine the residual strength <strong>of</strong> the damaged panels. Chen <strong>and</strong> Bai (2002)<br />
conducted finite element analysis to study the postbuckling behaviour <strong>of</strong> face/core debonded<br />
s<strong>and</strong>wich panels on the basis <strong>of</strong> the von Karman non-linearity assumption <strong>and</strong> the zigzag<br />
deformation theory combined with a debonding model <strong>and</strong> a multi-scalar damage model. Despite<br />
all the numerical <strong>and</strong> experimental studies, a comprehensive study <strong>of</strong> debond damaged s<strong>and</strong>wich<br />
panels, <strong>and</strong> analysis <strong>of</strong> issues like debond propagation, characterisation <strong>of</strong> the fracture toughness<br />
<strong>of</strong> the interface at different mode-mixities <strong>and</strong> finally validation <strong>of</strong> these methods against<br />
experiments is still missing.<br />
39
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