Major Accomplishments in Composite Materials and Sandwich Structures - An Anthology of ONR Sponsored Research

Preface

Contents

Contributors

Chapter 1

Accelerated Testing for Long-Term Durability of Various FRP Laminates for Marine Use

1 Introduction

2 Accelerated Testing Methodology

2.1 Procedure of ATM

2.2 Applicability of ATM

2.3 Theoretical Verification of TTSP

3 Experimental Procedures

3.1 Preparation of Specimens

3.2 Tests

4 Results and Discussion

4.1 Creep Compliance

4.2 Flexural CSR Strength

4.3 Flexural Fatigue Strength

5 Conclusions

Navy Relevance

References

Chapter 2

Carbon Fiber–Vinyl Ester Interfacial Adhesion Improvement by the Use of an Epoxy Coating

1 Introduction

2 Materials and Methods

2.1 Materials

2.2 Methods

2.2.1 Microindentation Test

2.2.2 Thermogravimetric Analysis (TGA)

2.2.3 Dynamic Mechanical Thermal Analysis (DMTA)

2.2.4 Environmental Scanning Electron Microscopy (ESEM)

3 Preferential Adsorption of Some Constituents of the Matrix on the Carbon Fiber Surface and Its Influence on Interfacial Adhesion

3.1 Evidence of Preferential Adsorption of Some Constituents of the Matrix on the Carbon Fiber Surface

3.2 Influence on Interfacial Adhesion

3.2.1 Influence of the Concentration of the Initiator

3.2.2 Influence of the Concentration of the Promoter

3.2.3 Influence of the Concentration of the Accelerator

4 Influence of Cure Volume Shrinkage on Interfacial Adhesion

5 Improvement of Interfacial Adhesion by the Use of an Epoxy Coating

5.1 Optimization of the Coating Process

5.2 Interactions Between the Epoxy Coating and the Components of the Vinyl Ester Matrix

5.2.1 Influence of the Concentration of the Initiator

5.2.2 Influence of the Concentration of the Promoter

5.2.3 Influence of the Concentration of the Accelerator

5.2.4 Influence of Monomers

5.3 Influence of the Cure Volume Shrinkage with the Use of an Epoxy Coating

5.4 Qualitative Assessment of the Use of an Epoxy Coating on the Mechanical Properties of a Carbon Fiber–Vinyl Ester Composite Cured at High Temperature

5.5 Determination of the Optimal Thickness of the Coating by a Finite Element Analysis

5.6 Determination of the Thickness of the Interdiffusion Zone by a Nanoindentation Scratch Test

6 Conclusion

References

Chapter 3

A Physically Based Cumulative Damage Formalism

1 Introduction

2 Kinetic Crack Based Cumulative Damage and Life Prediction

3 A Special Form

4 Cyclic Fatigue

5 Probabilistic Generalization

6 Examples

7 Extended Life Examples

8 Conclusions

References

Chapter 4

Delamination of Composite Cylinders

1 Introduction

2 Materials and Specimens

3 Delamination Fracture Testing

4 Impact Testing of Cylinders

5 External Pressure Tests of Cylinders

6 Results and Discussion

6.1 Delamination Fracture Test Results

6.2 Influence of Impact

6.3 External Pressure Test Results

7 Conclusions

References

Chapter 5

Modeling of Progressive Damage in High Strain–Rate Deformations of Fiber-Reinforced Composites

1 Introduction

2 Progressive Damage Model

3 Implementation of the Damage Model

3.1 Brief Description of the Numerical Technique

3.2 Simulation of Material Failure

3.3 Energy Dissipation

3.4 Verification of the Code

3.5 Validation of the Mathematical Model

4 Parametric Studies on a Typical Laminated Composite

4.1 Effect of Mesh Size

4.2 Lay-Up Sequence

4.3 Target Thickness

4.4 Fiber Orientation

4.5 Delamination

4.6 Figure of Merit

4.7 Remarks

4.8 Limitations of the Model

5 Conclusions

References

Chapter 6

Post-Impact Fatigue Behavior ofWoven and Knitted Fabric CFRP Laminates for Marine Use

1 Introduction

2 Materials and Testing Methods

2.1 Materials and Molding Method

2.2 Specimens and Impact Test

2.3 Compression After Impact (CAI) Test and Post-Impact Fatigue (PIF) Test

2.4 Water Absorption Condition

3 Approach to Evaluate Damages

4 Impact Damage of CFRP Laminates

4.1 Plain Woven CFRP Laminate

4.2 Multi-axial Knitted CFRP Laminate

4.3 Three-Dimensional Characterization of Impact Damage Within CFRP Laminates

5 Compressive Strength and Fatigue Strength of Impact Damaged CFRP Laminates

5.1 Effect of Water Absorption on Post-Impact Fatigue Properties

5.2 Damage Evolution Mechanism in Plain Woven CFRP Laminates

5.3 Damage Evolution Mechanism in Multi-axial Knitted CFRP Laminates

5 Conclusions

References

Chapter 7

Dynamic Interaction of Multiple Damage Mechanisms in Composite Structures

1 Introduction

2 Modeling Multiple Delamination Fracture in Laminated and Multilayered Systems

2.1 Theoretical Approach

2.2 Energy Release Rate and Stress Intensity Factors in Homogeneous Orthotropic Beams

3 Interaction Effects of Multiple Delaminations on Fracture Parameters

3.1 Amplification and Shielding of the Energy Release Rate

3.2 Interaction Effects on Mode Ratio

3.3 Coupling of Interaction and Dynamic Effects

3.3.1 Dynamic Response of Beams with Single Stationary Delaminations

3.3.2 Dynamic Response of Beams with Multiple Stationary Delaminations

4 Interaction Effects of Multiple Delaminations on Crack Growth Characteristics and Macrostructural Behaviour

4.1 Local Instabilities and Strengthening Mechanisms

4.2 Stability of the Equality of Length of Systems of Equal Length Delaminations

4.2.1 Equally Spaced and Equal Length Cracks in Homogeneous Beams (Static Loading)

4.2.2 Equal Length and Unequally Spaced Cracks in Homogeneous Beams (Static Loading)

4.2.3 Dynamic Loading Conditions

Equally Spaced and Equal Length Cracks in Homogeneous Beams

Delamination Configurations Falling into the Stable Quasi-static Domain

Delamination Configurations Falling into the Unstable Quasi-static Domain

4.3 Crack Growth Characteristics in Systems of Unequal Length Cracks

5 Improving Mechanical Performance Through Controlled Delamination Fracture

5.1 Energy Absorption Through Multiple Delamination Fracture

5.2 Damage and Impact Tolerance

6 Indentation Response of Composite Sandwich Beams in the Presence of Skin Damage

6.1 Continuously Supported Sandwich Beam (F = 0)

6.2 Sandwich Beam with End Restraints (F Not Equal 0)

6.3 Characteristic Lengths

7 Conclusions

References

Chapter 8

A Review of Research on Impulsive Loading of Marine Composites

1 Introduction

2 Outline

3 Experimental Studies

3.1 Underwater Tests

3.1.1 Test Procedures and Instrumentations

3.1.2 Response of Marine Structural Materials to Underwater Blast Loading

3.2 In-Air Tests

3.2.1 Test Procedures and Instrumentations

3.2.2 Response of Marine Structural Materials to In-Air Shock and Blast Loading

4 Theoretical and Computational Studies

4.1 Analysis of Marine Panels

4.1.1 Panel Response to Free Field Blast Loading

4.1.2 Fluid–Structure Interaction in Sandwich Composites

4.2 Analysis of Full-Scale Marine Structures

5 Closing Remarks

References

Chapter 9

Failure Modes of Composite Sandwich Beams

1 Introduction

2 Sandwich Materials Investigated

2.1 Facesheet Materials

2.2 Core Materials

3 Facesheet Failure

4 Facesheet Debonding

5 Core Failures

6 Indentation Failure

7 Facesheet Wrinkling Failure

8 Failure Mode Interaction

9 Conclusions

References

Chapter 10

Localised Effects in Sandwich Structures with Internal Core Junctions: Modelling and Experimental Characterisation of Load Response, Failure and Fatigue

1 Introduction

2 Prediction of Failure in Sandwich Structures with Core Junctions

2.1 Failure Criteria for Sandwich Core Materials

3 Core Junctions in Sandwich Panels Subjected to In-Plane Loading

3.1 Test Specimens

3.2 Material Properties

3.3 Experimental Investigation – Part 1: Quasi-static Tests

3.4 Finite Element Analyses (FEA)

3.5 Experimental Investigation – Part 2: Fatigue Tests

3.6 Discussion and Conclusions (In-Plane Loading)

4 Core Junctions in Sandwich Panels Subjected to Transverse Shear Loading

4.1 Sandwich Test Specimens

4.2 Experimental Results – Part 1: Quasi-static Tests

4.3 Finite Element Analyses (FEA)

4.4 Experimental Results – Part 2: Fatigue Tests

4.5 Discussion and Conclusions (Transverse Shear Loading)

5 Summary and Conclusions

References

Chapter 11

Damage Tolerance of Naval Sandwich Panels

1 Introduction and Background

2 Fracture of Foam Core Materials

3 Disbonds in Sandwich Beams

4 Impact Damage in Sandwich Beams

5 Interface Disbonds in Sandwich Panels

6 Impact Damage in Sandwich Panels

7 Damage Tolerance Scheme for Naval Sandwich Structures

References

Chapter 12

Size Effect on Fracture of Composite and Sandwich Structures

1 Introduction

2 Size Effect on the Tensile Strength of Notched Fiber–Composite Laminates [23]

2.1 Introduction

2.2 Experimental

2.3 Size Effect

2.4 Conclusions

3 Size Effect on the Flexural Strength of Fiber–Composite Laminates [34]

3.1 Introduction

3.2 Size Effect

3.3 Experimental Studies

3.4 Conclusions

4 Size Effect on the Compression Strength of Fiber–Composite Laminates [42]

4.1 Introduction

4.2 Experimental

4.3 Conclusions

5 Size Effect on Fracture of Polymeric Foams [45]

5.1 Introduction

5.2 Experimental

5.3 Size Effect

5.4 Conclusions

6 Size Effect on Compressive Strength of Sandwich Panels [54]

6.1 Introduction

6.2 Experimental

6.3 Size Effect

6.4 Conclusions

7 Size Effect of Cohesive Delamination Fracture Triggered by Sandwich Skin Wrinkling [55]

7.1 Introduction

7.2 Size Effect

7.3 Conclusions

References

Chapter 13

Elasticity Solutions for the Buckling of Thick Composite and Sandwich Cylindrical Shells Under External Pressure

1 Introduction

2 Formulation

3 Pre-buckling State

4 Perturbed State

5 Solution of the Eigen-Boundary-Value Problem for Differential Equations

6 Results and Discussion

References

Chapter 14

An Improved Methodology for Measuring the Interfacial Toughness of Sandwich Beams

1 Introduction

2 Test Methods Considered

3 Geometries Considered

4 Finite Element Modeling

5 MCSB Evaluation

6 Preliminary Evaluation of the TSD Test

7 Data Reduction in the MP Test

8 TSD and MP Experiments

9 Mechanical Attachments

10 Conclusions

References

Chapter 15

Structural Performance of Eco-Core Sandwich Panels

1 Introduction

2 Design of Test Specimens

2.1 Short Beam Shear Test Specimen

2.2 Four-Point Flexure Test Specimen

2.3 Edgewise Compression Test Specimen

3 Fabrication of Sandwich Panel and Specimen

4 Tests

4.1 Short Beam Shear Test

4.2 Four-Point Flexure Test

4.3 Edgewise Compression Test

5 Test Results and Discussion

5.1 Short Beam Shear Test

5.2 Four-Point Flexure Test

5.3 Edgewise Compression Test

6 Concluding Remarks

References

Chapter 16

The Use of Neural Networks to Detect Damage in Sandwich Composites

1 Introduction

2 Nondestructive Evaluation

2.1 Thermography Based NDE

2.1.1 Modeling

2.1.2 Validation

2.1.3 Test Cases and Results

2.2 Vibrations Based NDE

2.2.1 Modeling

2.2.2 Validation

2.2.3 Test Cases and Results

3 Artificial intelligence (AI) in Damage Detection

3.1 Neural Network Based Damage Detection

3.1.1 Thermographic Based NN Implementation

3.1.2 Curvature Based NN Implementation

3.1.3 Multi-component NN Implementation

3.2 Testing and Evaluation

4 Conclusions

References

Chapter 17

On the Mechanical Behavior of Advanced Composite Material Structures

1 Introduction

2 High Strain Rate Effects on Composite Material Properties

3 Composite Sandwich Structures

References

Chapter 18

Application of Acoustic Emission Technology to the Characterization and Damage Monitoring of Advanced Composites

1 Background

2 Sample Acoustic Emission Applications

2.1 Edgewise Compression Tests of Polycore Sandwich Material

2.1.1 Background

2.1.2 Testing

2.1.3 Discussion of Results

2.1.4 Concluding Remarks

2.2 Isogrid Construction

2.2.1 Background

2.2.2 Testing

2.2.3 Discussion of Results

2.2.4 Concluding Remarks

2.3 Flexural Fatigue of Foam-Cored Composite Sandwich

2.3.1 Background

2.3.2 Testing

2.3.3 Results and Discussion

2.3.4 Concluding Remarks

3 Conclusion

References

Chapter 19

Ballistic Impacts on Composite and Sandwich Structures

1 Introduction

2 Models Based on Assumptions Regarding the Penetration Resistance

2.1 Constant Penetration Resistance

2.2 Assumption 2: Kinetic Energy Absorbed by Ejecta

2.3 Poncelet’s Assumption

2.4 Penetration Force Increases Linearly with the Velocity

2.5 Penetration Force Varies with v and v2

2.6 Summary

3 Projectile-Target Interaction Models

3.1 Normal Pressure on the Surface of the Projectile

3.2 Blunt-Ended Projectile

3.3 Conical-Tipped Projectile

3.4 Spherical Tipped Projectile

3.5 Effect of Friction

4 Factors Affecting the Ballistic Limit

4.1 Effect of Laminate Thickness and Projectile Diameter

4.2 Effect of Stacking Sequence

4.3 Effect of Obliquity

4.4 Effect of Projectile Density

5 Models Based on Static Test Results

6 Energy – Balance Models

7 Numerical Models

8 Impact on Sandwich Structures

9 Conclusions

References

Chapter 20

Performance of Novel Composites and Sandwich Structures Under Blast Loading

1 Introduction

2 Material Systems

2.1 Laminated Composites

2.1.1 E-Glass Vinyl Ester Composite (EVE)

2.1.2 Carbon Fiber Vinyl Ester Composite (CVE)

2.2 Layered Composites

2.2.1 Polyurea Layered Materials

2.3 Sandwich Composites

2.3.1 Polyurea Sandwich Composites

2.3.2 Sandwich Composites with 3D Woven Skin

2.3.3 Core Reinforced Sandwich Composites

2.3.4 Sandwich Composite with a Stepwise Graded Core

2.3.5 Pre-damaged Sandwich Composite

3 Experimental Setup

3.1 Shock Tube

3.2 Loading and Boundary Conditions

3.3 Pre-damage Procedure

3.4 High Speed Imaging

3.5 Blast Energy Calculation Procedure

4 Results and Discussion

4.1 Blast Resistance of Laminated Composites

4.2 Blast Resistance of Layered Composites

4.2.1 PU/EVE Layered Material

4.2.2 EVE/PU Layered Material

4.3 Blast Resistance of Sandwich Composites

4.3.1 Polyurea Based Sandwich Composites

4.3.2 Sandwich Composites with 3D Skin and Polymer Foam Core

4.3.3 Sandwich Composite with E-Glass Fiber and Polymer Foam Core

4.3.4 Sandwich Composites with Stepwise Graded Foam Cores

4.3.5 Pre-damaged Sandwich Composites

5 Summary

References

Chapter 21

Single and Multisite Impact Response of S2-Glass/ Epoxy Balsa Wood Core Sandwich Composites

1 Introduction

2 Experimental

2.1 Specimen Fabrication

2.2 High Velocity Impact Set Up

3 Model Description

3.1 Mesh Generation and Contact Definition

3.2 Composite Progressive Failure Model and Strain Softening Characteristics

3.2.1 Wood Material Model

4 Results and Discussion

4.1 Single Site Projectile Impact

4.1.1 Single Project Impact: Balsa Wood Core Only

Experiment

Simulation

4.1.2 Single Projectile Impact: Sandwich Composite

4.2 Simultaneous 0.30 and 0.50 Caliber Three Projectile Impact on the Sandwich Specimens

4.3 Delamination Factor, Sd for Multisite Impact Prediction

4.4 Fiber and Wood Damage

5 Summary and Conclusions

References

Chapter 22

Real-Time Experimental Investigation on Dynamic Failure of Sandwich Structures and Layered Materials

1 Introduction

2 Experimental Procedure

2.1 Materials and Specimens

2.2 Experimental Setup

3 Results and Discussion

3.1 Failure Process of Short Model Sandwich Specimens with Equal Layer Widths

3.2 Failure Process in Long Model Sandwich Specimens

3.3 Effect of Impact Speeds

3.4 Dynamic Failure Mode Transition

3.5 Dynamic Interface Debonding Ahead of a Main Incident Crack

3.6 New Progress on Dynamic Crack Branching

3.6.1 Special Experiments for Dynamic Crack Kinking and Branching

3.6.2 Dynamic Crack Branching and Kinking from aWeak Interface

3.6.3 Dynamic Crack Branching Initiated from a Notch Subjected to High Impact Loading

3.7 Dynamic Crack Kinking and Penetration at an Interface

3.7.1 Weak Interfaces with Different Interfacial Angles

3.7.2 Modeling of Dynamic Failure Modes Across an Interface

3.7.3 Mode Mixity of the Kinked Interfacial Crack

3.8 Two-layer Specimens with Direct Impact on the BrittlePolymeric Layer

4 Conclusions

References

Chapter 23

Characterization of Fatigue Behavior of Composite Sandwich Structures at Sub-Zero Temperatures

1 Introduction

2 Experiments

2.1 Specimens

2.2 Static Flexure Tests

2.3 Flexural Fatigue Tests

3 Finite Element Modeling

4 Results

4.1 Static 4-Point Bending

4.2 Flexural Fatigue

4.3 Fatigue Life at Low Temperatures

4.4 Stiffness and Damping at Low Temperatures

4.5 Fatigue Failure Modes

5 Finite Element Analysis

6 Conclusions

References

Chapter 24

Impact and Blast Resistance of Sandwich Plates

1 Introduction

2 Response to Uniform Pressure

3 Response to Impact

3.1 Medium Velocity Impact at Different Contact Locations

3.2 Response to Impact at Support

3.3 Effect of Indenter Shape, Interlayer Moduli and Thickness

3.4 Energy Released by Interfacial Cracks

4 Response to Impulse or Blast Loads

4.1 Geometry and Material Properties

4.2 Finite Element Models

4.3 Response to a Full Span Pressure Impulse

4.4 Energy Absorption

4.5 Effect of Change in Total Mass

4.6 Performance Comparison of Polyurea and Polyurethane

5 Conclusions

References

Chapter 25

Modeling Blast and High-Velocity Impact of Composite Sandwich Panels

1 Introduction

2 Impulsively-Loaded Sandwich Panels

2.1 Phase I – Through-Thickness Wave Propagation

2.1.1 Transmission and Reflection at Interfaces

2.1.2 Elastic and PlasticWaves in Foam

2.1.3 Local Indentation

2.2 Phase II – Global Bending/Shear

2.2.1 System Lagrangian

2.2.2 Bending/Shear Strain Energy Potential

2.2.3 Equations of Motion

2.3 Transient Deformations

2.3.1 Local Core Crushing: Phase I Response

2.3.2 Global Bending/Shear: Phase II Response

2.4 Damage Initiation

3 High-Velocity Impact of Sandwich Panels

3.1 Phase I: Local Indentation

3.1.1 Through-Thickness Wave Propagation

3.1.2 Local Indentation

Kinetic Energy

Potential Energy

Equation of Motion

3.2 Phase II: Global Bending/Shear

3.2.1 Kinetic Energy

3.2.2 Global Bending/Shear Energy

3.2.3 Equations of Motion

3.3 Comparison with Finite Element Analysis

4 Conclusions

Appendix A Uniaxial StrainWave Speed in an Orthotropic Plate

Appendix B Momentum and Kinetic Energy of Core During Phase I

Appendix C Elastic Strain Energy and Plastic Work in Core

References

Chapter 26

Effect of Nanoparticle Dispersion on Polymer Matrix and their Fiber Nanocomposites

1 Introduction

2 Effect of Dispersion on Polymer Matrix

2.1 Materials

2.2 Fabrication

2.3 Microstructural and Mechanical Characterization Techniques

2.4 Morphological Characterization

2.5 Mechanical Characterization

3 Mechanical Behavior of FRP Nanocomposites

3.1 Materials and Fabrication

3.2 Mechanical Characterization Techniques

3.2.1 Compression

3.2.2 Tension

3.2.3 DCB

3.2.4 ENF

3.2.5 Low Velocity Impact

3.3 Compressive Properties

3.3.1 Off-Axis Compressive Strength

3.3.2 Longitudinal Compressive Strength

3.4 Tensile Properties

3.5 Fracture Toughness

3.6 Impact Resistance

4 Conclusion

References

Chapter 27

Experimental and Analytical Analysis of Mechanical Response and Deformation Mode Selection in BalsaWood

1 Introduction

2 Experimental

2.1 Microstructural Features of Balsa Wood

2.2 Specimen Preparation and Geometry

2.3 Quasi-Static Testing Method

2.4 Dynamic Testing Method

3 Results and Discussion

3.1 Stress–Strain Response

3.1.1 End Effects

3.1.2 Initial Failure and Progressive Deformation

3.1.3 Densification

3.1.4 Energy Dissipation Capacity

3.2 Failure Modes

3.3 Strength Models Based on Failure Modes

3.3.1 Elastic Buckling

3.3.2 Plastic Buckling

3.3.3 End-Cap Collapse

3.3.4 Kink Band Formation

3.4 Comparison with Quasi-Static Experiments

3.5 Models for Inertial Stress Enhancement

3.5.1 Background

3.5.2 Buckling

Model Parameters

3.5.3 Kink Band Formation

Model Parameters

3.6 Comparison of Inertia-Based Models with Dynamic Data

4 Conclusions

References

Chapter 28

Mechanics of PAN Nanofibers

1 Introduction

2 Experimental Methods and Materials

2.1 Nanofiber Fabrication

2.2 Mechanical Experiments with Single Polymeric Nanofibers

2.2.1 Background

2.2.2 Nanoscale Tension Experiments with Individual Polymeric Nanofibers

2.2.3 Resolution in Force and Nanofiber Extension Measurements

2.2.4 Loadcell Calibration

3 Fabrication vs Mechanical Behavior of PAN Nanofibers

4 Mechanical Instabilities During Cold Drawing of PAN Nanofibers

5 Effect of Strain Rate on the Mechanical Deformation of Nanofibers

6 Origins of Surface Rippling in Electrospun PAN Nanofibers

7 Molecular Alignment in Electrospun PAN Nanofibers

8 Conclusions

References

Chapter 29

Characterization of Deformation and Failure Modes of Ordinary and Auxetic Foams at Different Length Scales

1 Introduction

2 The Multi-scale Speckle Photography Technique

3 Studies of Ordinary Foams

3.1 Size Effect on Mechanical Properties of Foam Composites

3.2 Crack Tip Deformation in Foam at Different Length Scales

4 Studies of Auxetic Foams

4.1 Introduction

4.2 Auxetic Polyurethane Foam

4.3 Auxetic PVC (H45) Foam

4.3.1 Manufacturing the Auxetic PVC Foam

4.3.2 Mechanical Properties of Auxetic PVC Foam

Uniaxial Test

Shear Test

Impact Test

Indentation Tests

References

Chapter 30

Fracture of Brittle Lattice Materials: A Review

1 Introduction

1.1 Fracture Mechanics Concepts

1.2 Outline of this Review

2 Classical Beam Theory

2.1 The Hexagonal Lattice

2.2 Other 2D Lattices

2.3 Statistics of Brittle Failure

3 Generalised Continuum Theories

4 Finite Element Modelling

4.1 Stress Analysis

4.2 Boundary Layer Analysis

4.2.1 Extrapolation of 2D Results to 3D Lattices

4.2.2 Sensitivity of Fracture Toughness to Imperfections

5 Atomic Lattice Models for Crack Dynamics

6 Representative Cell Method

7 Experimental Studies on Fracture Toughness

8 Concluding Remarks

References

Author Index