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Table of Contents

Structural Sandwich Composites

Table of Contents

Preface and Front Material

CHAPTER l - Introduction

l.1 Scope 1-1
1.2 Basic Design Principles 1-2
1.3 Fundamental Formulas 1-4

1.3.1 Sandwich Bending Stiffness 1-5
1.3.2 Sandwich Extensional Stiffness 1-6
1.3.3 Sandwich Shear Stiffness 1-6

CHAPTER 2 - MATERIALS

2.1 Facing Materials 2-1

2.1.1 Functions, Descriptions, Usual Forms 2-l
2.2 Sandwich Cores 2-3

2.2.1 Description of Cures 2-3
2.2.2 Mechanical Properties of Cores 2-10
2.3 Adhesives 2-17

2.3.1 Types 2-18
2.3.2 Available Sources 2 -24
2.3.3 Forms 2 -24
2.3.4 Storage and Mixing of Adhesives 2-25
2.3.5 Strength of Adhesive Bonds 2-26

CHAPTER 3 - WRINKLING OF SANDWICH FACINGS UNDER EDGEWISE LOAD

CHAPTER 4 - DIMPLING OF SANDWICH FACINGS UNDER EDGEWISE LOAD

CHAPTER 5 - DESIGN OF FLAT RECTANGULAR SANDWICH PANELS UNDER EDGEWISE COMPRESSION LOAD

5.1 Basic Principles 5-1
5.2 Determining Facing Thickness 5-2
5.3 Determining Core Thickness and Core Shear Modulus 5-2

5.3.1 Determination of Minimum Values of h 5-4
5.3.2 Determination of Actual Values of h 5-6
5.3.3 Checking Procedure for Determining Buckling Stress, FCR 5-7

CHAPTER 6 - DESIGN OF FLAT RECTANGULAR SANDWICH PANELS UNDER EDGEWISE SHEAR LOAD

6.1 Basic Principles 6-1
6.2 Determining Facing Thickness 6-1
6.3 Determining Core Thickness and Core Shear Modulus 6-2

6.3.1 Determination of Minimum Values of h 6-4
6.3.2 Determination of Actual Values of h 6-6
6.3.3 Checking Procedure of Determining Buckling Stress, FCR 6-7

CHAPTER 7 - DESIGN OF FLAT RECTANGULAR SANDWICH PANELS UNDER EDGEWISE BENDING MOMENT

7.1 Basic Principles 7 -l
7.2 Determining Facing Thickness 7-l
7.3 Determining Core Thickness and Core Shear Modulus 7-3

7.3.1 Determination of Minimum Values of h 7-5
7.3.2 Determination of Actual Values of h 7-5
7.3.3 Checking Procedure for Determining Buckling Stress, FCR 7-6

CHAPTER 8 - DESIGN OF FLAT RECTANGULAR SANDWICH PANELS UNDER COMBINED LOADS

CHAPTER 9 - DESIGN OF FLAT SANDWICH PANELS UNDER UNIFORMLY DISTRIBUTED NORMAL LOAD

9.1 Basic Principles 9-1
9.2 Determining Facing Thickness, Core Thickness, and Core Shear Modulus for Simply Support4 Flat Rectangular Panels 9-1

9.2.1 Use of Design Charts 9-4
9.3 Determine Core Shear Stress 9-6
9.4 Checking Procedure 9-6
9.5 Determining Facing Thickness, Core Thickness, and Core Shear Modulus for Simply Supported Flat Circular Panels 9-7

9.5.1 Use of Design Charts 9-9
9.6 Determine Core Shear Stress 9-10
9.7 Checking Procedure 9-10

CHAPTER 10 - DESIGN OF SANDWICH CYLINDERS UNDER EXTERNAL RADIAL PRESSURE

10.1 Basic Principles 10-1
10.2 Determining Facing Thickness, Core Thickness, and Core Shear Modulus for Sandwich Cylinders Under External Radial Pressure 10-2

10.2.1 Determination of Minimum Values of h 10-4
10.3 Final Design 10-4

CHAPTER 11 - DESIGN OF SANDWICH CYLINDERS UNDER TORSION

11.1 Basic Principles 11-1
11.2 Determining Facing Thickness 11-2
11.3 Determining Core Thickness and Core Shear Modulus 11-3

11.3.1 Determination of Minimum Values of d 11-4
11.3.2 Determination of Actual Values of d 11-5
11.3.3 Checking Procedure for Determining Buckling 11-6
11.4 Check to Determine Whether Sideways Buckling Will Occur 11-6

CHAPTER 12 - DESIGN OF SANDWICH CYLINDERS UNDER AXIAL COMPRESSLON OR BENDING

CHAPTER 13 - DESIGN OF SANDWICH CYLINDERS UNDER COMBINED LOADS

CHAPTER 14 - FABRICATION

14.1 Fabrication of Cores. 14-1

14.1.1 Preparation for Use 14-l
14.2 Fabrication of Bonded Construction 14-5

14.2.1 Preparation for Bonding. 14-6
14.2.2 Method of Applying Adhesives . 14-14
14.3 Brazed OT Welded Sandwich Construction. 14-20
14.4 Sandwich Production Techniques 14-21

14.4.1 Means of Applying Pressure. 4-22
14.4.2 Techniques for Curved Parts 14-30
14.4.3 Mold-Release Agents. 14-32
14.4.4 Attachment Details 14-34
14.4.5 Trimming 14-36
14.4.6 Safety Precautions 14-36
14.4.7 Specifications 14-37

CHAPTER 15 - INSPECTION AND TEST METHODS

15.1 Inspection of Raw Materials 15-1

15.1.1 Cores 15-2
15.1.2 Facings. 15-2
15.1.3 Adhesives and Resins. 15-2
15.2 Inspection of Completed Parts 15-4

15.2.1 Visual Inspection. 15-4
15.2.2 Tapping. 15-5
15.2.3 Spur Wheel . 15-6
15.2.4 Ultrasonic Inspection. 15-6
15.2.5 Radiographic Inspection 15-6
15.2.6 Vibrator .Amplifier Inspection 15-6
15.2.7 Thermographic Inspection 15-7
15.3 Proof Loading Devices. 15-7

15.3.1 Exposure to Vacuum 15-7
15.3.2 Vacuum-induced Concentrated Load Tester 15-8
15.3.3 Multiple Proof Loader 15-8
15.4 Specifications 15-9
15.5 Test Methods 15-10

15.5.1 Test Methods for Core Materials 15-10
15.5.2 Test Methods for Adhesives and for Bonded Joints 15-10
15.5.3 Lap-Joint Metal-to-Metal Shear Test. 15-10
15.5.4.Lap-Joint Shear Test at Various Temperatures 15-12
15.5.5 Lap-Joint Shear Ted After Exposure 15-13
13.5.6 Lap-Joint Specimens in Fatigue Testing 15-13
15.5.7 Use of Lap-Joint Specimens in Long-Time Loading. 15-13

CHAPTER 16 - REPAIR

16.1 General. 16-1
16.2 Principles of Repair 16-1
16.3 Classes of Repair 16-3
16.4 Repair of Plastic Sandwich Parts (ref. 16-l) 16-4

16.4.1 Repair Materials. 16-4
16.4.2 Preparing Parts for Repair 16-5
16.4.3 Repair Techniques 16-6
16.4.4 Special Considerations 16-10
16.5 Repair of Adhesive-Bonded Metal Sandwich [ref. 16-2). 16-11

16.5.1 Repair Materials 16-11
16.5.2 Repair Techniques 16-13
16.6 Repair of Brazed or Welded Sandwich 16-23

16.6.1 Adhesive Injection Repairs 16-23
16.6.2 Potting Repairs 16-26
16.6.3 Brazed Patch Repair 16-26

CHAPTER 17 - DURABILITY

17.1 General 17-1

17.1.1 Environmental Exposure of Adhesive-Bonded Joints 17-1
17.1.2 Environmental Evaluation of Sandwich Constructions 17-2
17.2 Rain Erosion of Plastic Leading Edges 17-4

CHAPTER 18 - OPTIMUM SANDWICH

CHAPTER 19 - DESIGN OF SANDWICH STRIPS UNDER TORSION LOAD

CHAPTER 20 - DESIGN OF CIRCULAR SANDWICH PANELS LOAD AT AN INSERT

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