Modeling the Effect of Damage in Composite Structures: Simplified Approaches

ISBN-13: 9781119013211 / Angielski / Twarda / 2015 / 248 str.

Christos Kassapoglou

Opis

Comprehensively covers new and existing methods for the design and analysis of composites structures with damage present

• Provides efficient and accurate approaches for analysing structures with holes and impact damage
• Introduces a new methodology for fatigue analysis of composites
• Provides design guidelines, and step by step descriptions of how to apply the methods, along with evaluation of their accuracy and applicability
• Includes problems and exercises
• Accompanied by a website hosting lecture slides and solutions

Recenzje

"This will help the readers engineers who will be designing the next generation of airframe structures to develop not only better understanding of underlying damage mechanisms, but also critical thinking and
open–mindedness needed for evaluation of any new simplified approaches that may emerge in the future" Professor Maria Kashtalyan, University of Aberdeen on behalf of the Aeronautical Journal, Oct 2017

Spis treści

Series Preface ix

Preface xi

1 Damage in Composite Structures: Notch Sensitivity 1

1.1 Introduction 1

1.2 Notch Insensitivity 2

1.3 Complete Notch Sensitivity 4

1.4 Notch Sensitivity of Composite Materials 5

Exercises 6

References 7

2 Holes 9

2.1 Stresses around Holes 13

2.2 Using the Anisotropic Elasticity Solution to Predict Failure 16

2.3 The Role of the Damage Zone Created Near a Hole 17

2.4 Simplified Approaches to Predict Failure in Laminates with Holes: the Whitney Nuismer Criteria 19

2.5 Other Approaches to Predict Failure of a Laminate with a Hole 24

2.6 Improved Whitney Nuismer Approach 25

2.7 Application: Finding the Stacking Sequence Which Results in Good OHT Performance 34

Exercises 35

References 39

3 Cracks 41

3.1 Introduction 41

3.2 Modelling a Crack in a Composite Laminate 42

3.3 Finite–Width Effects 45

3.4 Other Approaches for Analysis of Cracks in Composites 46

3.5 Matrix Cracks 49

Exercises 52

References 56

4 Delaminations 57

4.1 Introduction 57

4.2 Relation to Inspection Methods and Criteria 60

4.3 Modelling Different Structural Details in the Presence of Delaminations 63

4.3.1 Buckling of a Through–Width Delaminating Layer 63

4.3.2 Buckling of an Elliptical Delaminating Layer 69

4.3.3 Application Buckling of an Elliptical Delamination under Combined Loads 73

4.3.4 Onset of Delamination at a Straight Free Edge of a Composite Laminate 75

4.3.5 Delamination at a Flange Stiffener Interface of a Composite Stiffened Panel 84

4.3.6 Double Cantilever Beam and End Notch Flexure Specimen 88

4.3.7 The Crack Closure Method 92

4.4 Strength of Materials Versus Fracture Mechanics Use of Cohesive Elements 96

4.4.1 Use of Cohesive Elements 99

Exercises 100

References 103

5 Impact 105

5.1 Sources of Impact and General Implications for Design 105

5.2 Damage Resistance Versus Damage Tolerance 109

5.3 Modelling Impact Damage as a Hole 111

5.4 Modelling Impact Damage as a Delamination 114

5.5 Impact Damage Modelled as a Region of Reduced Stiffness 117

5.6 Application: Comparison of the Predictions of the Simpler Models with Test Results 121

5.6.1 Modelling BVID as a Hole 122

5.6.2 Modelling BVID as a Single Delamination 123

5.6.3 Modelling BVID as an Elliptical Inclusion of Reduced Stiffness 124

5.6.4 Comparisons of Analytical Predictions to Test Results Sandwich Laminates 124

5.7 Improved Model for Impact Damage Analysed as a Region of Reduced Stiffness 125

5.7.1 Type and Extent of Damage for Given Impact Energy 125

5.7.2 Model for Predicting CAI Strength 148

Exercises 163

References 168

6 Fatigue Life of Composite Structures: Analytical Models 171

6.1 Introduction 171

6.2 Needed Characteristics for an Analytical Model 175

6.3 Models for the Degradation of the Residual Strength 177

6.3.1 Linear Model 177

6.3.2 Nonlinear Model 180

6.4 Model for the Cycles to Failure 183

6.4.1 Extension to Spectrum Loading 196

6.5 Residual Strength and Wear–Out Model Predictions Compared to Test Results 200

6.5.1 Residual Strength Predictions Compared to Test Results 200

6.5.2 Cycles to Failure Predictions Compared to Test Results (Constant Amplitude) 202

6.5.3 Cycles to Failure Predictions Compared to Test Results (Spectrum Loading) 204

6.6 A Proposal for the Complete Model: Accounting for Larger Scale Damage 206

6.6.1 First Cycle, Tension Portion 207

6.6.2 First Cycle, Compression Portion 207

6.6.3 Subsequent Load Cycles 208

6.6.4 Discussion 208

6.6.5 Application: Tension Compression Fatigue of Unidirectional Composites 209

6.6.6 Application: Tension Tension Fatigue of Cross–Ply Laminates 214

Exercises 218

References 219

7 Effect of Damage in Composite Structures: Summary and Useful Design Guidelines 221

Index 227

O autorze

Christos Kassapoglou received his BS degree in Aeronautics and Astronautics and two MS degrees (Aeronautics and Astronautics and Mechanical Engineering) from Massachusetts Institute of Technology and his PhD degree from Delft University of Technology. Since 1984 he has worked in industry, first at Beech Aircraft on the all–composite Starship I and then at the Structures Research Group at Sikorsky Aircraft specializing on analysis of composite structures for the all–composite Comanche and other helicopters and leading internally funded research and NASA and the US Army funded program. Since 2001 he has been consulting with various companies in the US and Europe on applications of composites, damage tolerance and certification. He joined the Aerospace Engineering Department of the Delft University of Technology (Aerospace Structures) in 2008 as an Associate Professor. His interests include fatigue and damage tolerance of composites, design and optimization for cost and weight, and technology optimization. He has over 60 journal papers and 3 patents on related subjects. He is a member of AIAA, AHS, and SAMPE.

Blurb

Modeling the Effect of Damage in Composite Structures: Simplified Approaches
Christos Kassapoglou – Delft University of Technology, The Netherlands

With the ever increasing application of composites, the need to understand how composite structures in aerospace, automotive, marine and construction applications behave over prolonged periods of service becomes more pronounced. In particular, understanding how damage affects the performance of such structures and how one can design them realizing that damage and defects are inevitable, becomes a priority.

Modeling the Effect of Damage in Composite Structures: Simplified Approaches goes past traditional knockdown or safety factors used in design, and suggests models that can be used to more accurately quantify the effect of damage on composite structures. At the same time it minimizes the use of detailed computationally intensive numerical methods that cannot easily be used in preliminary design. It presents simplified approaches that provide insight on the effect of various types of damage from holes and cracks to delaminations and impact. These approaches allow relatively rapid analysis and generation of alternative designs for optimization and trade–off studies. This helps down–selection of robust and efficient design candidates for more detailed and more expensive analysis. Finally, the methods are combined into a framework for developing promising analytical fatigue models for composite structures.

Key features:

• Presents efficient, accurate, analytical models for predicting the effect of damage on strength of composite structures
• Provides design guidelines, and step by step descriptions of how to apply the methods, along with evaluation of their accuracy and applicability
• Includes problems and exercises
• Accompanied by a website hosting lecture slides and solutions

By presenting reliable approaches that assist design and analysis without the need for expensive numerical methods, Modeling the Effect of Damage in Composite Structures: Simplified Approaches is an invaluable reference for graduate students and practising engineers in the field.