CMH-17_Vol6_RevG

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Y

Yellow Pages from Monterey up to ellow Pages from Monterey up to and includingand including Salt Lake City - to be first release

Salt Lake City - to be first release

NOT

NOT MEASUREME

MEASUREMENT

NT

SENSITIVE

CMH-17-6

Volume 1 of 6

xx MONTH 2009

COMPOSITE MATERIALS HANDBOOK

VOLUME

VOLUME 6.

6. STRUCTURAL

STRUCTURAL SANDWICH

SANDWICH COMPOSITES

COMPOSITES

Copyright 2009 - Composite Materials Handbook –

Copyright 2009 - Composite Materials Handbook – 17 (CMH-17).

17 (CMH-17). All rights

All rights reserved.

reserved.

Unauthorized duplication or distribution may violate the Copyright Laws of the United

States and of other jurisdictions

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Volume 6, Foreword Volume 6, Foreword

FOREWORD

The Composite Materials Handbook, CMH-17, provides information and guidance necessary to design The Composite Materials Handbook, CMH-17, provides information and guidance necessary to design and fabricate structural components fro

and fabricate structural components from composite materials. m composite materials. Its primary purposes are a) tIts primary purposes are a) the standardi-he standardi-zation of engineering data development methodologies related to testing, data reduction, and data zation of engineering data development methodologies related to testing, data reduction, and data report-ing of property data for current and emergreport-ing composite materials, b) guidance on material and process ing of property data for current and emerging composite materials, b) guidance on material and process specifications and procedures for utilization of the material data presented in the handbook, and c) specifications and procedures for utilization of the material data presented in the handbook, and c) meth-odologies for the design, analysis, certification,

odologies for the design, analysis, certification, manufacture, and field support of composite manufacture, and field support of composite structures. structures. InIn support of these objectives, the handbook includes

support of these objectives, the handbook includes composite materials properties that meet specific datacomposite materials properties that meet specific data requirements.

requirements. The Handbook therefore constituteThe Handbook therefore constitutes an overview of the field of composites technology ands an overview of the field of composites technology and engineering, an area that is advancing and ch

engineering, an area that is advancing and changing rapidly. anging rapidly. As a result, the document will be As a result, the document will be continuallycontinually revised as sections are added

revised as sections are added or modified to reflect advances in or modified to reflect advances in the state-of-the-art.the state-of-the-art.

CMH-17 Mission

The Composite Materials Handbook organization creates, publishes and maintains proven, reliable The Composite Materials Handbook organization creates, publishes and maintains proven, reliable engi-neering information and standards, subjected to thorough technical review, to support the development neering information and standards, subjected to thorough technical review, to support the development and use of composite materials and

and use of composite materials and structures.structures.

CMH-17 Vision

The Composite Materials Handbook will be the authoritative worldwide focal point for technical The Composite Materials Handbook will be the authoritative worldwide focal point for technical informa-tion on composite materials and structures.

tion on composite materials and structures.

Goals and Objectives to Support CMH-17 Mission

•• TTo periodically o periodically meet with meet with experts froexperts from the m the field to field to discuss critical discuss critical technical issues for technical issues for compositecomposite structural applications, with an emphasis on increasing overall product efficiency, quality and structural applications, with an emphasis on increasing overall product efficiency, quality and safety.

safety.

•• TTo proo provide covide comprehensive, pramprehensive, practical engineering ctical engineering guidance that guidance that has phas proven reliable roven reliable for thfor the dee design,sign, fabrication, characterization, test and maintenance of composite materials and structures.

fabrication, characterization, test and maintenance of composite materials and structures.

•• TTo provide o provide reliable data, reliable data, linked to linked to control of control of processes anprocesses and raw d raw materials, tmaterials, thereby being hereby being a com-a com-prehensive source of material property basis values and design information that can be shared prehensive source of material property basis values and design information that can be shared within the

within the industryindustry..

•• TTo provide o provide a resource a resource for composite for composite material and material and structure estructure education with ducation with examples, applicationsexamples, applications and references to supporting engineering work.

and references to supporting engineering work.

•• TTo estao establish guidelines blish guidelines for use for use of information of information in the in the Handbook, identifying Handbook, identifying the limitationthe limitations of s of thethe data and methods.

data and methods.

•• TTo o provide provide guidance guidance on ron references eferences to pto proven roven standards standards and and engineering pengineering practices.ractices.

•• TTo proo provide for vide for periodic updatperiodic updates to es to maintain maintain the all-inclusive the all-inclusive nature nature of thof the informate information.ion.

•• TTo o provide provide information information in in formats formats best-suited best-suited for for user user needs.needs.

•• TTo servo serve the e the needs of needs of the intthe international composites ernational composites community community through meetthrough meetings and ings and dialogue be-dialogue be-tween member industries, which use teamwork and the diverse member engineering skills to tween member industries, which use teamwork and the diverse member engineering skills to pro-vide information for the handbook.

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Volume 6, Foreword Volume 6, Foreword

Notes

1.

1. Every effort has Every effort has been made to reflect been made to reflect the latest information on pthe latest information on polymer (organic), metal, olymer (organic), metal, and ce-and ce-ramic composites.

ramic composites. The handbook is The handbook is continually reviewed and revised continually reviewed and revised to ensure it is to ensure it is completecomplete and current.

and current. 2.

2. CMH-17 provides guidelines and CMH-17 provides guidelines and material properties for material properties for polymer (organic), polymer (organic), metal, and cerametal, and ceramicmic matrix composite materials.

matrix composite materials. The first three volumes of this hanThe first three volumes of this handbook currently focus on, but aredbook currently focus on, but are not limited to,

not limited to, polymeric composites intended polymeric composites intended for aircraft and for aircraft and aerospace vehicles. aerospace vehicles. Metal matrixMetal matrix composites (MMC), ceramic matrix composites (CMC) including carbon-carbon composites composites (MMC), ceramic matrix composites (CMC) including carbon-carbon composites (C-C), and sandwich composites are covered

(C-C), and sandwich composites are covered in Volumes 4, 5, and 6, respectively.in Volumes 4, 5, and 6, respectively. 3.

3. The information contThe information contained in this handbook was ained in this handbook was obtained from materobtained from materials producers, industials producers, industryry companies and experts, reports on Government sponsored research, the open literature, and by companies and experts, reports on Government sponsored research, the open literature, and by contract with research laboratories a

contract with research laboratories and those who participate ind those who participate in the CMH-17 coordination n the CMH-17 coordination activityactivity.. The information in this handbook has undergone vigorous technical review and was subject to The information in this handbook has undergone vigorous technical review and was subject to membership vote.

membership vote. 4.

4. Beneficial comments Beneficial comments (recommendations, (recommendations, additions, deletions) aadditions, deletions) and any nd any pertinent data pertinent data which maywhich may be of use in improving

be of use in improving this document should be this document should be addressed to: addressed to: CMH-17 Secretariat, CMH-17 Secretariat, MaterialsMaterials Sciences Corporation, 135 Rock Road, Horsham, PA 19044, by letter or email, Sciences Corporation, 135 Rock Road, Horsham, PA 19044, by letter or email, [email protected].

[email protected].

ACKNOWLEDGEMENT ACKNOWLEDGEMENT

Volunteer committee members from government, industry, and academia develop, coordinate and review Volunteer committee members from government, industry, and academia develop, coordinate and review all the information provided in this handbook.

all the information provided in this handbook. The time and effort oThe time and effort of the volunteers and the support off the volunteers and the support of their respective departments, companies, and universities make it possible to insure the handbook their respective departments, companies, and universities make it possible to insure the handbook re-flects completeness, accuracy, and

flects completeness, accuracy, and state-of-the-art composite technology.state-of-the-art composite technology.

Support necessary for the development and maintenance of the Composite Materials Handbook Support necessary for the development and maintenance of the Composite Materials Handbook (CMH-17) are provided

17) are provided by the handbook Seby the handbook Secretariat, Materials Sciences cretariat, Materials Sciences Corporation. Corporation. The primary source The primary source ofof funding for the current Secretariat contract is the Federal Avi

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Volume 6, Contents Volume 6, Contents CONTENTS CONTENTS Page Page Foreword...ii Foreword...ii CHAPTER 1

CHAPTER 1 GENERAL GENERAL INFORMATIONINFORMATION ... ... ... ... ... ...1...1

1.1

1.1 INTRODUCTION INTRODUCTION TO TO THE THE HANDBOOKHANDBOOK ...1...1 1.2

1.2 OVERIVEW OVERIVEW OF OF HANDBOOK HANDBOOK CONTENTCONTENT ...1....1 1.3

1.3 INTRODUCTIONINTRODUCTION ...2...2 1.4

1.4 NOTATION...3NOTATION...3 1.5

1.5 BASIC DESIGN PRINCIPLES...4BASIC DESIGN PRINCIPLES...4 REFERENCES...8 REFERENCES...8

CHAPTER 2

CHAPTER 2 GUIDELINES GUIDELINES FOR FOR PROPERTY PROPERTY TESTINGTESTING ...1...1

2.1

2.2 DATDATA A REDUCTREDUCTION ION AND AND PRESEPRESENTANTATIONTION ...33 2.3

2.3 EVALUATION OF CORE MATERIALS...3EVALUATION OF CORE MATERIALS...3 2.3.1

2.3.1 Mechanical properties ...3Mechanical properties ...3 2.3.2

2.3.2 Environmental Environmental effectseffects ...3....3 2.3.3

2.3.3 TTest est methodsmethods ...5...5 2.4

2.4 EVALUAEVALUATION TION OF OF CORE-TO-FACICORE-TO-FACING NG BONDSBONDS ...7....7 2.4.1

2.4.1 Introduction...7Introduction...7 2.4.2

2.4.4 TTest est MethodsMethods ...7...7 2.5

2.5 EVALUATION OF FACING PROPERTIES...7EVALUATION OF FACING PROPERTIES...7 2.5.1

2.6 EVALUATION OF SANDWICH PANELS...8EVALUATION OF SANDWICH PANELS...8 2.6.1

2.6.4 Damage resistance...9Damage resistance...9 2.6.5

2.6.5 Damage Damage tolerancetolerance ...9...9 2.6.6

2.6.6 RepairRepair ...10.10 2.6.7

2.7 EVALUATION OF INSERTS AND FASTENERS...11EVALUATION OF INSERTS AND FASTENERS...11 2.7.1

2.7.3 Environmental Environmental effectseffects ...13..13 2.7.4

2.7.4 TTest est methods methods (references (references to to ASTMs)ASTMs) ...13...13 2.8

2.8 EVALUATION OF OTHER FEATURES...13EVALUATION OF OTHER FEATURES...13 2.8.1

2.8.3 Environmental Environmental effectseffects ...14..14 2.8.4

2.8.4 TTest est methodsmethods ...14...14 REFERENCES...15 REFERENCES...15

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Volume 6, Contents Volume 6, Contents CHAPTER 3

CHAPTER 3 MATERIAL DATA...1MATERIAL DATA...1 3.1

3.1 CORES 1CORES 1 3.2

3.2 FACINGSFACINGS ...11 3.3

3.3 ADHESADHESIVESIVES ...1...1 CHAPTER 4

CHAPTER 4 DESIGN AND ANALYSIS OF SANDWICH STRUCTURES...1DESIGN AND ANALYSIS OF SANDWICH STRUCTURES...1 4.1

4.2 DESIGN DESIGN AND AND CERTIFICACERTIFICATIONTION ...1...1 4.3

4.3 CERTIFICATION ...1CERTIFICATION ...1 4.4

4.4 SANDWICH SANDWICH PAPANEL NEL FAILURE FAILURE MODESMODES ...2...2 4.5

4.5 STIFFNESS AND INTERNAL LOADS ...2STIFFNESS AND INTERNAL LOADS ...2 4.6

4.6 LOCAL LOCAL STRENGTH STRENGTH ANALYSIS ANALYSIS METHODSMETHODS...2.2 4.7

4.7 FLAFLAT PANEL INTERNAL LOADS AND T PANEL INTERNAL LOADS AND STRESSES STRESSES - PRES- PRESSURE LOADING SURE LOADING ...2.2 4.8

4.8 CURVED SCURVED SANDWICH ANDWICH PPANEL INTERNAL ANEL INTERNAL LOADS AND LOADS AND STRESSES STRESSES ...2...2 4.9

4.9 FLAT PANEL STABILITY ANALYSIS METHODS...2FLAT PANEL STABILITY ANALYSIS METHODS...2 4.10

4.10 DESIGN OF FLAT RECTANGULAR SANDWICH PDESIGN OF FLAT RECTANGULAR SANDWICH PANELS UNDER COMBINED ANELS UNDER COMBINED LOADSLOADS...2.2 4.10.1

4.10.1 Combined Combined load load bucklingbuckling ...2..2 4.10.1.1

4.10.1.1 Biaxial Biaxial compression...compression...2....2 4.10.1.2

4.10.1.2 Bending Bending and and compressioncompression ...3...3 4.10.1.3

4.10.1.3 Compression and shear ...3Compression and shear ...3 4.10.1.4

4.10.1.4 Bending and shear ...3Bending and shear ...3 4.10.2

4.10.2 Combined Combined in-plane in-plane and and transverse transverse loads...loads...3...3 4.11

4.11 DESIGN DESIGN OF OF SANDWICH SANDWICH CYLINDERS CYLINDERS ...4...4 4.12

4.12 FINITE ELEMENT FINITE ELEMENT MODELING OF MODELING OF SANDWICH SANDWICH STRUCTURESTRUCTURE ...4...4 4.12.1

4.12.2 Global models...5Global models...5 4.12.3

4.12.3 Layered Layered modelmodelss ...5...5 4.12.4

4.12.4 Solid Solid modelsmodels ...6.6 4.12.5

4.12.5 Sandwich element models ...7Sandwich element models ...7 4.13

4.13 OPTIMUM OPTIMUM SANDWICHSANDWICH ...7...7 4.13.1

4.13.1 Sandwich weight...7Sandwich weight...7 4.13.2

4.13.2 Sandwich Sandwich bending bending stiffnessstiffness ...8....8 4.13.3

4.13.3 Sandwich Sandwich bending bending moment moment capacity...capacity...10...10 4.13.4

4.13.4 Sandwich Sandwich panel panel bucklingbuckling ...12...12 REFERENCES...14 REFERENCES...14 CHAPTER 5

CHAPTER 5 FABRICAFABRICATION OF SANDWICH STRUCTURES (MATERIALS ATION OF SANDWICH STRUCTURES (MATERIALS AND PROCESSES)ND PROCESSES) ....1....1 5.1 5.1 INTRODUCTIONINTRODUCTION ...1...1 5.2 5.2 MATERIALS...3MATERIALS...3 5.2.1 5.2.1 CoresCores ...3...3 5.2.2

5.2.2 Face Face sheetssheets ...44 5.2.3

5.2.3 AdhesiAdhesivesves ...66 5.2.4

5.2.4 Surfacing Surfacing and and sealingsealing ...7....7 5.3 5.3 PROCESSESPROCESSES ...8..8 5.3.1 5.3.1 CoreCore ...8...8 5.3.1.1 5.3.1.1 CleaniCleaningng ...8...8 5.3.1.2 5.3.1.2 Drying...9Drying...9 5.3.1.3 5.3.1.3 FormingForming ... 1111 5.3.1.4 5.3.1.4 Splicing...12Splicing...12 5.3.1.5 5.3.1.5 PottingPotting ...14...14 5.3.1.6 5.3.1.6 SeptumSeptumss ...15...15 5.3.1.7

5.3.1.7 Core Core stabilization stabilization for for machiningmachining ...16....16 5.3.1.8

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Volume 6, Contents Volume 6, Contents

5.3.1.9

5.3.1.9 Tolerances...18Tolerances...18 5.3.2

5.3.2 Face sheets Face sheets - co-cure - co-cure vs. pre-cure vs. pre-cure and resin and resin pressure...pressure...18....18 5.3.3

5.3.3 Adhesive...21Adhesive...21 5.3.3.1

5.3.3.1 Impression Impression checkcheck ...21...21 5.3.3.2 5.3.3.2 BondiBondingng ...23...23 5.3.3.3 5.3.3.3 Filleting...25Filleting...25 5.4 5.4 ASSEMBLY...28ASSEMBLY...28 5.4.1

5.4.1 Core Core crush crush during during curecure ...28...28 5.4.2

5.4.2 Core Core crush crush - - theoretical theoretical discussiondiscussion ...29.29 5.4.3

5.4.3 Core Core crush crush stabilization stabilization for for curecure...31...31 5.4.4

5.4.4 Core Core material material characteristics characteristics and and core core crushcrush ...32...32 5.4.5

5.4.5 Prepreg and adhesive Prepreg and adhesive material characteristics and material characteristics and core crushcore crush ...33..33 5.4.6

5.4.6 Cure Cure cycles cycles and and core core crushcrush...34..34 5.4.7

5.4.7 Quality issues Quality issues including nincluding non-destructive evaluation on-destructive evaluation (NDI)(NDI) ...35..35 REFERENCES...39 REFERENCES...39

CHAPTER 6

CHAPTER 6 QUALITY QUALITY CONTROLCONTROL ...11

6.1

6.2 MAMATERIAL PROCTERIAL PROCUREMENT UREMENT QUALITY ASSURANCE QUALITY ASSURANCE PROCEDURES PROCEDURES ...1.1 6.2.1

6.2.1 Specifications Specifications and and documentation...documentation...1...1 6.2.2

6.2.2 Receiving inspection...1Receiving inspection...1 6.3

6.3 PART FABRICATION VERIFICATION...3PART FABRICATION VERIFICATION...3 6.3.1

6.3.1 Process verification ...3Process verification ...3 6.3.2

6.3.2 Nondestructive inspection ...3Nondestructive inspection ...3 6.3.3

6.3.3 DestructDestructive ive teststests ...3...3 6.4

6.4 STASTATISTICAL TISTICAL PROCESS PROCESS CONTROLCONTROL ...4.4 6.5

6.5 MANAGING MANAGING CHANGE CHANGE IN IN MAMATERIALS ATERIALS AND ND PROCESSES...PROCESSES...4...4 REFERENCES...5 REFERENCES...5

CHAPTER 7

CHAPTER 7 SUPPORTASUPPORTABILITYBILITY ...1...1

7.1

7.2 DESIGN FOR SUPPORTABILITY...1DESIGN FOR SUPPORTABILITY...1 7.2.1

7.2.1 In-service experience ...1In-service experience ...1 7.2.2

7.2.2 Inspectability...2Inspectability...2 7.2.3

7.2.3 Material selection...2Material selection...2 7.2.4

7.2.4 Damage resistance...2Damage resistance...2 7.2.5

7.2.5 Environmental compliance ...3Environmental compliance ...3 7.2.6

7.2.6 Reliability Reliability and and maintainabilitymaintainability ...3.3 7.2.7

7.2.7 Repairability...3Repairability...3 7.3

7.3 SUPPORT IMPLEMENTATION...5SUPPORT IMPLEMENTATION...5 7.3.1

7.3.1 Part inspection...5Part inspection...5 7.3.2

7.3.2 Damage assessment...5Damage assessment...5 7.3.3

7.3.3 Repair design criteria...6Repair design criteria...6 7.3.4

7.3.4 Repair Repair of of composite composite structures...structures...8...8 7.3.4.1

7.3.4.1 Damage Damage removal removal and and site site preparation...preparation...8...8 7.3.4.2

7.3.4.2 Bonded repairs...8Bonded repairs...8 7.3.4.3

7.3.4.3 Repair analysis...10Repair analysis...10 7.3.4.4

7.3.4.4 Repair procedures...10Repair procedures...10 7.3.4.5

7.3.4.5 Repair inspection ...12Repair inspection ...12 7.3.4.6

7.3.4.6 Repair validation ...12Repair validation ...12 7.4

7.4 LOGISTICS LOGISTICS REQUIREMENTSREQUIREMENTS ...13.13 REFERENCES...15 REFERENCES...15

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Volume

Volume 6, Chapter 6, Chapter 1 1 General InformationGeneral Information

CHAPTER

CHAPTER 1

1 GENERAL

GENERAL INFORMATION

INFORMATION

1.1 1.1 INTRODUCTION

INTRODUCTION TO

TO THE

THE HANDBOOK

HANDBOOK

Standardized, statistically-based material property data are essential to the development of Standardized, statistically-based material property data are essential to the development of compos-ite structures; such data are needed by material suppliers, design engineering personnel, manufacturing ite structures; such data are needed by material suppliers, design engineering personnel, manufacturing organizations, and

organizations, and structure end-users structure end-users alike. alike. In addition, reliable, In addition, reliable, proven design and proven design and analysis methodsanalysis methods are essential to the efficient d

are essential to the efficient development and application of composite strevelopment and application of composite structures. uctures. This handbook is in-This handbook is in-tended to provide these through standardization of:

tended to provide these through standardization of: 1.

1. Methods used Methods used to develop, analyze, to develop, analyze, and publish property and publish property data for data for composite materials.composite materials. 2.

2. Statistically-based, Statistically-based, material material property property datasets datasets for for composite composite materials.materials. 3.

3. General procedures for General procedures for designing, analyzing, testing, designing, analyzing, testing, and supporting and supporting composite structures composite structures thatthat utilize the property data published in this handbook.

utilize the property data published in this handbook.

In many cases, this standardization is intended to address the requirements of regulatory agencies, In many cases, this standardization is intended to address the requirements of regulatory agencies, while providing efficient engineering practices for developing structures that meet the needs of customer while providing efficient engineering practices for developing structures that meet the needs of customer organizations.

organizations.

Composites is an evolving and growing technical field, and the Handbook Coordinating Committee is Composites is an evolving and growing technical field, and the Handbook Coordinating Committee is continuously working to incorporate new information and new material properties data as it becomes continuously working to incorporate new information and new material properties data as it becomes available and is proven acceptable.

available and is proven acceptable. While the source and context for much of this inforWhile the source and context for much of this information has comemation has come from experience with aerospace applications, all industries utilizing composite materials and structures, from experience with aerospace applications, all industries utilizing composite materials and structures, whether commercial

whether commercial or military, will or military, will find the handbook ufind the handbook useful. seful. This latest revision This latest revision includes informationincludes information related to broader applications from non-aerospace industries, and incorporation of non-aerospace data related to broader applications from non-aerospace industries, and incorporation of non-aerospace data will increase as development of the handbook continues.

will increase as development of the handbook continues.

Composite Materials Handbook-17 (CMH-17) has been developed and is maintained as a joint effort Composite Materials Handbook-17 (CMH-17) has been developed and is maintained as a joint effort of the Department of Defense and the Federal Aviation Administration, with considerable participation and of the Department of Defense and the Federal Aviation Administration, with considerable participation and input from industry,

input from industry, academia, and other governacademia, and other government agencies. ment agencies. Although initial structural applications ofAlthough initial structural applications of composites tended to be military, recent development trends have seen increasing use of these materials composites tended to be military, recent development trends have seen increasing use of these materials in commercial applications.

in commercial applications. In part because oIn part because of these trends, f these trends, the formal administration othe formal administration of the handbookf the handbook passed from the Department of Defense to the Federal Aviation Administration in 2006 and the handbook passed from the Department of Defense to the Federal Aviation Administration in 2006 and the handbook title was changed

title was changed from Military Handbook-17 from Military Handbook-17 to Composite Mateto Composite Materials Handbook-17. rials Handbook-17. The organization ofThe organization of the Coordinating Committee and the purpose of the

the Coordinating Committee and the purpose of the handbook did not change.handbook did not change.

1.2 1.2 OVERIVEW

OVERIVEW OF HA

OF HANDBOOK CONTENT

NDBOOK CONTENT

Composite Materials Handbook-17 is composed of a

Composite Materials Handbook-17 is composed of a series of six volumes.series of six volumes. Volume 1:

Volume 1: Polymer Matrix Composites - Polymer Matrix Composites - Guidelines for Characterization of Guidelines for Characterization of Structural MaterialsStructural Materials Volume 1 contains guidelines for determining the properties of polymer matrix composite material Volume 1 contains guidelines for determining the properties of polymer matrix composite material systems and their constituents, as well as the properties of generic structural elements, including test systems and their constituents, as well as the properties of generic structural elements, including test planning, test matrices, sampling, conditioning, test procedure selection, data reporting, data reduction, planning, test matrices, sampling, conditioning, test procedure selection, data reporting, data reduction, statistical analysis, and o

statistical analysis, and other related topics. ther related topics. Special attention is given Special attention is given to the statistical tto the statistical treatment andreatment and analysis of data.

analysis of data. Volume 1 contains guidelines for Volume 1 contains guidelines for general development of general development of material characterization dmaterial characterization dataata as well as specific requirements for publication of material data in CMH-17.

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Volume

Volume 6, Chapter 6, Chapter 1 1 General InformationGeneral Information Volume 2:

Volume 2: Polymer Matrix CompPolymer Matrix Composites - Material osites - Material PropertiesProperties Volume 2 contains statistically-based data

Volume 2 contains statistically-based data for polymer matrix composites that meets specific CMH-17for polymer matrix composites that meets specific CMH-17 population sampling and data documentation requirements, covering material systems of general interest. population sampling and data documentation requirements, covering material systems of general interest. As of the publication of Revision G, data published in Volume 2 are under the jurisdiction of the Data As of the publication of Revision G, data published in Volume 2 are under the jurisdiction of the Data Re-view Working Group and

view Working Group and are approved by are approved by the overall CMH-17 the overall CMH-17 Coordinating Committee. Coordinating Committee. New materialNew material systems will be included and additional material data for existing systems will be added as data becomes systems will be included and additional material data for existing systems will be added as data becomes available and are approved.

available and are approved. Selected historical data from previoSelected historical data from previous versions of the handbook tus versions of the handbook that do nothat do not meet current data sampling, test methodology, or documentation requirements, but that still are of meet current data sampling, test methodology, or documentation requirements, but that still are of poten-tial interest to industry are also included in this volume.

tial interest to industry are also included in this volume. Volume 3:

Volume 3: Polymer Matrix Composites - Polymer Matrix Composites - Materials Usage, Design, and AnalysisMaterials Usage, Design, and Analysis

Volume 3 provides methodologies and lessons learned for the design, analysis, manufacture, and Volume 3 provides methodologies and lessons learned for the design, analysis, manufacture, and field support of fiber-reinforced,

field support of fiber-reinforced, polymeric-matrix composite structpolymeric-matrix composite structures. ures. It also provides guidance on ma-It also provides guidance on ma-terial and process specifications an

terial and process specifications and procedures for utilization of d procedures for utilization of the data presentthe data presented in Volume 2. ed in Volume 2. TheThe information provided is consistent with the guidance provided in Volume 1, and is an extensive information provided is consistent with the guidance provided in Volume 1, and is an extensive compila-tion of the current knowledge and experiences of the engineers and scientists who are active in tion of the current knowledge and experiences of the engineers and scientists who are active in compos-ites from industry, government, and academia.

ites from industry, government, and academia. Volume 4:

Volume 4: Metal Matrix Metal Matrix CompositesComposites

Volume 4 publishes properties on metal matrix composite material systems for which data meeting Volume 4 publishes properties on metal matrix composite material systems for which data meeting the specific requirements of

the specific requirements of the handbook are available. the handbook are available. In addition, it provides selected In addition, it provides selected guidance onguidance on other technical topics related to this class of composites, including material selection, material other technical topics related to this class of composites, including material selection, material specifica-tion, processing, characterization testing, data reducspecifica-tion, design, analysis, quality control, and repair of tion, processing, characterization testing, data reduction, design, analysis, quality control, and repair of typical metal matrix composite materials.

typical metal matrix composite materials. Volume 5:

Volume 5: Ceramic Matrix Ceramic Matrix CompositesComposites

Volume 5 publishes properties on ceramic matrix composite material systems for which data meeting Volume 5 publishes properties on ceramic matrix composite material systems for which data meeting the specific requirements of

the specific requirements of the handbook are available. the handbook are available. In addition, it provides selected In addition, it provides selected guidance onguidance on other technical topics related to this class of composites, including material selection, material other technical topics related to this class of composites, including material selection, material specifica-tion, processing, characterization testing, data reducspecifica-tion, design, analysis, quality control, and repair of tion, processing, characterization testing, data reduction, design, analysis, quality control, and repair of typical ceramic matrix composite materials.

typical ceramic matrix composite materials. Volume 6:

Volume 6: Structural SaStructural Sandwich Compositesndwich Composites

Volume 6 is an update to the cancelled Military Handbook 23, which was prepared for use in the Volume 6 is an update to the cancelled Military Handbook 23, which was prepared for use in the de-sign of structura

sign of structural sandwich polymer composites, l sandwich polymer composites, primarily for flight primarily for flight vehicles. vehicles. The information presenteThe information presentedd includes test methods, material properties, design and analysis techniques, fabrication methods, quality includes test methods, material properties, design and analysis techniques, fabrication methods, quality control and inspection procedures, and repair techniques for sandwich structures in both military and control and inspection procedures, and repair techniques for sandwich structures in both military and commercial vehicles.

commercial vehicles.

1.3 INTRODUCTION

The Sandwich Structures Volume of Military Handbook 17, Volume 6, contains seven chapters; The Sandwich Structures Volume of Military Handbook 17, Volume 6, contains seven chapters; Gen-eral Information, Guidelines for Property Testing, Material Data, Design and Analysis, Fabrication, Quality eral Information, Guidelines for Property Testing, Material Data, Design and Analysis, Fabrication, Quality Control, and Supportability

Control, and Supportability. . Chapter 1, General Information, Chapter 1, General Information, provides the objective, background, introduc-provides the objective, background, introduc-tion and notaintroduc-tion utilized in sandwich structu

tion and notation utilized in sandwich structures. res. Chapter 2, Guidelines for Property Chapter 2, Guidelines for Property TTesting discussesesting discusses property testing of sandwich constituent materials; core materials, core-to-facing bonds, and facings (or property testing of sandwich constituent materials; core materials, core-to-facing bonds, and facings (or face sheets); as well as sandwich panels, inserts and fasteners, and other sandwich details such as face sheets); as well as sandwich panels, inserts and fasteners, and other sandwich details such as ramps and close-out

ramps and close-outs. s. Chapter 3, Material DatChapter 3, Material Data, contains core, facina, contains core, facing, adhesive, and self-adhesive fac-g, adhesive, and self-adhesive fac-ing properties.

ing properties. Chapter 4, Design and Chapter 4, Design and Analysis, provides structural design, Analysis, provides structural design, sizing and analysis methodssizing and analysis methods for critical failure modes of

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Volume

Volume 6, Chapter 6, Chapter 1 1 General InformationGeneral Information and processes, and

and processes, and lessons learned. lessons learned. Chapter 6, Quality Chapter 6, Quality Control, discusses in-process and Control, discusses in-process and end-articleend-article inspection, material properties verification, and process controls as applicable to sandwich structures. inspection, material properties verification, and process controls as applicable to sandwich structures. Chapter 7, Supportability, discusses design practice to improve damage tolerance and repair aspects of Chapter 7, Supportability, discusses design practice to improve damage tolerance and repair aspects of sandwich structures.

sandwich structures. Discussions of basic design pDiscussions of basic design principles and fundamental rinciples and fundamental formulas are included in allformulas are included in all sections as appropriate.

sections as appropriate.

1.4 NOTATION

The following notation is used throughout this volume.

The following notation is used throughout this volume. AdditionallyAdditionally, portions of the volume devoted to, portions of the volume devoted to a particular component d

a particular component define the symbols used for the efine the symbols used for the first time in that portfirst time in that portion. ion. An occasional symbolAn occasional symbol not in general use will appear

not in general use will appear in specific areas and not be in specific areas and not be included in this notation. included in this notation. Figure 1.4 shows no-Figure 1.4 shows no-tation for sandwich construction.

tation for sandwich construction.

Units of dimensions, forces, stresses, constants, and other quantities are not specified unless they Units of dimensions, forces, stresses, constants, and other quantities are not specified unless they are employed in formulas

are employed in formulas wherein numerical coefficientwherein numerical coefficients are not non-dimensional. s are not non-dimensional. In applying formulasIn applying formulas for which units are not specified, correct results will not be obtained unless units are consistent – for for which units are not specified, correct results will not be obtained unless units are consistent – for ex-ample:

ample: If thicknesses are given in inches and forces in pounds, then the length and width of a pIf thicknesses are given in inches and forces in pounds, then the length and width of a panel mustanel must be in inches (not feet) to

be in inches (not feet) to give stresses in pounds per square give stresses in pounds per square inch.inch.

FIGURE 1.4

FIGURE 1.4 Sandwich construction notation.Sandwich construction notation.

1

1 - - Subscript Subscript denoting denoting facing facing 1 1 of of a a sandwichsandwich 2

2 - - Subscript Subscript denoting denoting facing facing 2 2 of of a a sandwichsandwich a, b

a, b - - Length Length of of panel panel edge; edge; subscripts subscripts denoting denoting parallel parallel toto aa or or bb edge edge B

B - - Subscript Subscript denoting denoting bond bond or or bendingbending cc - - Subscript Subscript denoting denoting core core or or compressioncompression cr

cr - - Subscript Subscript denoting denoting criticalcritical D

D - - Bending Bending stiffness stiffness or or twisting twisting stiffness stiffness depending depending on on subscriptssubscripts d

d - - TTotal otal sandwich sandwich depth depth or or thicknessthickness E

E - - YYoung's oung's modulus modulus of of elasticity; elasticity; for for orthotropic orthotropic facingfacing E = [EE = [EaaEEbb]]1/21/2

E’

E’ - - Effective Effective modulus modulus of of elasticity; elasticity; for for orthotropic orthotropic facingsfacings E’ = [EE’ = [Eaa’E’Ebb’]’]1/21/2

F

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Volume

Volume 6, Chapter 6, Chapter 1 1 General InformationGeneral Information F

F1212 - - Geometric Geometric view view factor factor between between sandwich sandwich facingsfacings

f

f - - Calculated Calculated stressstress G

G - - Modulus Modulus of of rigidity; rigidity; with with subscriptssubscripts GGabab is the modulus of rigidity associated with shear distortion is the modulus of rigidity associated with shear distortion

of the

of theabab plane plane G’

G’ - - Effective Effective modulus modulus of of rigidityrigidity H

H - - Extensional Extensional stiffnessstiffness h

h - - Distance Distance between between facing facing centroidscentroids K

K - - A A coefficcoefficientient L

L - - Length, Length, core core ribbon ribbon axis axis directiondirection M

M - - Bending Bending moment; moment; subscript subscript denoting denoting behavior behavior of of sandwich sandwich with with thin thin facings facings when when applied applied toto buckling coefficients

buckling coefficients m

m - - Half Half width width of of corrugation corrugation or or number number of of half half waveswaves N

N - - Load Load per per unit unit length length of of edgeedge n

n - - Number Number of of half half waveswaves O

O - - Subscript Subscript denotingdenotingV = 0V = 0 o

o - - Subscript Subscript denoting denoting honeycomb honeycomb core core ribbon ribbon or or core core corrugation corrugation sheetsheet P

P - - LoadLoad p

p - - Intensity Intensity of of distributed distributed loadload

rr - - Radius; Radius; subscript subscript denoting denoting reducedreduced R

R - - RatioRatio S

S - - Shear Shear load load normal normal to to surface surface of of panelpanel

ss - - Core Core cell cell size; size; subscript subscript denoting denoting shear shear when when applied applied to to stress stress and and secant secant when when applied applied toto moduli

moduli T

T - - TTorque; orque; core core axis axis direction; direction; facing facing dissimilarity dissimilarity indexindex T = 1/[1+(ET = 1/[1+(E22’t’t22 /E /E11’t’t11)])]

T

Tmm - - Mean Mean temperaturetemperature

tt - - Thickness; Thickness; without without subscript subscript denotes denotes facing facing thickness; thickness; subscript subscript denoting denoting tangent tangent when when appliedapplied to moduli

to moduli U

U - - Transverse Transverse shear shear stiffnessstiffness u

u - - Subscript Subscript to to stress stress denoting denoting ultimateultimate V

V - - Parameter Parameter relating relating shear shear and and bending bending stiffnessstiffness W

W - - Weight; Weight; core core axis axis direction direction perpendicular perpendicular to to the the ribbon ribbon axis axis L; L; special special parameter parameter relating relating shearshear and bending stiffness for sandwich with corrugated core

and bending stiffness for sandwich with corrugated core w

w - - Density; Density; subscript subscript denoting denoting wrinklingwrinkling x

x - - Axis; Axis; subscript subscript denoting denoting parallel parallel to to x-axisx-axis y

y - - Axis Axis perpendicular perpendicular to to x-axis; x-axis; subscript subscript denoting denoting parallel parallel to to y-axis; y-axis; or or denoting denoting yield yield when when ap- ap-plied to stress

plied to stress

zz - - Axis Axis normal normal to to surface surface of of sandwich; sandwich; subscript subscript denoting denoting parallel parallel to to z-axisz-axis

α

α -- [E[Ebb’/E’/Eaa’]’]1/21/2

β

β -- αµαµabab+2+2γ γ

γ

γ - - Shear Shear strain; strain; elastic elastic property property parameterparameter γ γ = =λ λ GGbaba’/[E’/[Eaa’E’Ebb’]’]1/21/2

δδ - - DeflectionDeflection

εε - - Compression Compression or or extension extension strain; strain; emissivityemissivity

η

η - - Plasticity Plasticity coefficient; coefficient; convective convective heat heat transfer transfer coefficientcoefficient

λ

λ - - One One minus minus the the product product of of two two Poisson's Poisson's ratiosratios λ λ =1- =1-µµababµµbaba

µ

µ - - Poisson's Poisson's ratio; ratio; with with subscriptssubscripts µµabab is the ratio of contraction in the is the ratio of contraction in the bb direction to extension in the direction to extension in the

aa direction direction

ρ

ρ - - Radius Radius of of gyrationgyration

σ

σ - - StefanStefan-Boltzmann -Boltzmann constantconstant

1.5 1.5 BASIC

BASIC DESIGN

DESIGN PRINCIPLES

PRINCIPLES

Structural sandwich is a layered composite formed by bonding two thin facings to a relatively thick Structural sandwich is a layered composite formed by bonding two thin facings to a relatively thick core.

core. It is a type of It is a type of stressed-skin construction in wstressed-skin construction in which the facings resist hich the facings resist nearly all of the applied edge-nearly all of the applied edge-wise (in-plane) loads and flatedge-wise bending moments.

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Volume

Volume 6, Chapter 6, Chapter 1 1 General InformationGeneral Information more effective in

more effective in providing bending stiffness. providing bending stiffness. The core provides most of tThe core provides most of the shear rigidity and trahe shear rigidity and transfersnsfers shear stress between the face shee

shear stress between the face sheets so that they act about a common nts so that they act about a common neutral axis. eutral axis. By proper choice ofBy proper choice of materials for facings and core, constructions with high ratios of stiffness-to-weight and strength-to-weight materials for facings and core, constructions with high ratios of stiffness-to-weight and strength-to-weight can be achieved.

can be achieved.

A basic design concept is to space strong, thin facings far enough apart to achieve a high ratio of A basic design concept is to space strong, thin facings far enough apart to achieve a high ratio of stiffness to weight; the lightweight core that does this

stiffness to weight; the lightweight core that does this also provides the required resistance to shear also provides the required resistance to shear and isand is strong enough to stabilize the facings.

strong enough to stabilize the facings. A bonding medium such as an adhesive layerA bonding medium such as an adhesive layer, braze, or weld at-, braze, or weld at-taches the face sh

taches the face sheets to the eets to the core. core. The sandwich is analogous to an I-bThe sandwich is analogous to an I-beam in which the flanges carryeam in which the flanges carry direct compression and tension loads, as do the sandwich facings, and the web carries shear loads, as direct compression and tension loads, as do the sandwich facings, and the web carries shear loads, as does the sandwich core.

does the sandwich core.

Lightweight sandwich cores are normally designed so that they are made of low-density material, Lightweight sandwich cores are normally designed so that they are made of low-density material, such as honeycomb,

such as honeycomb, foam or balsa wood. foam or balsa wood. As a consequence of As a consequence of employing a lightweight core, wemploying a lightweight core, whichhich normally has a low effectiv

normally has a low effective shear modulus, design methe shear modulus, design methods account for core ods account for core shear deformation. shear deformation. TheThe main difference in design procedures for sandwich structural elem

main difference in design procedures for sandwich structural elements as compared to design proceduresents as compared to design procedures for homogeneous material is the inclusion of the effects of core shear properties on deflection, buckling, for homogeneous material is the inclusion of the effects of core shear properties on deflection, buckling, and stress for the sandwich.

and stress for the sandwich.

There are three local modes of failure that must be investigated in a sandwich panel; wrinkling, There are three local modes of failure that must be investigated in a sandwich panel; wrinkling, dim-pling, and shear crimping.

pling, and shear crimping. Wrinkling, as shown in Figure 1.5D, may occur if sandwich facing Wrinkling, as shown in Figure 1.5D, may occur if sandwich facing subjected tosubjected to edgewise compression buckles as a

edgewise compression buckles as a plate on an elastic foundation. plate on an elastic foundation. The facing may buckle inwaThe facing may buckle inward orrd or outward, depending on the flatwise compressive strength of the core relative to the flatwise tensile outward, depending on the flatwise compressive strength of the core relative to the flatwise tensile strength of the bond betw

strength of the bond between the facing and core. een the facing and core. If the bond between facing aIf the bond between facing and core is strong, facingsnd core is strong, facings can wrinkle and cause t

can wrinkle and cause tension failure in the core. ension failure in the core. Thus, the wrinkling load depends uThus, the wrinkling load depends upon the elasticitypon the elasticity and strength of th

and strength of the foundation system; namelye foundation system; namely, the core and the , the core and the bond between facing and core. bond between facing and core. SinceSince the facing is never perfectly flat, the wrinkling load will also depend upon the initial eccentricity of the the facing is never perfectly flat, the wrinkling load will also depend upon the initial eccentricity of the fac-ing or original w

ing or original waviness. aviness. Dimpling only occurs in Dimpling only occurs in honeycomb core phoneycomb core panels. anels. It is possible It is possible for the facings for the facings toto buckle or dimple into the

buckle or dimple into the spaces between core wspaces between core walls as shown in Figure 1.5C. alls as shown in Figure 1.5C. Dimpling may be severeDimpling may be severe enough so that permanent dimples remain after removal of load and the amplitude of the dimples may be enough so that permanent dimples remain after removal of load and the amplitude of the dimples may be large enough to cause the dimples to grow across the core cell walls and result in a wrinkling of the large enough to cause the dimples to grow across the core cell walls and result in a wrinkling of the fac-ings.

ings. Shear crimping failure, Figure 1.5B, appearShear crimping failure, Figure 1.5B, appears to be a local mode of failure, but s to be a local mode of failure, but is actually a form ofis actually a form of general overall buckling (Figure 1.5A) in

general overall buckling (Figure 1.5A) in which the wavelength of the buckles is very small because which the wavelength of the buckles is very small because of lowof low core shear modulus.

core shear modulus. The crimping of the sandwich occurs suddenly The crimping of the sandwich occurs suddenly and usually causes the core to fail inand usually causes the core to fail in shear at the crimp; it

shear at the crimp; it may also cause shear failure in the bond between may also cause shear failure in the bond between the facing and core. the facing and core. CrimpingCrimping may also occur in cases where the overall buckle begins to appear and then the crimp occurs suddenly may also occur in cases where the overall buckle begins to appear and then the crimp occurs suddenly because of severe local shear stresses at

because of severe local shear stresses at the ends of the overall buckle. the ends of the overall buckle. As soon as the crimp appears,As soon as the crimp appears, the overall buckle

the overall buckle may disappearmay disappear. . Therefore, although Therefore, although examination of texamination of the failed sandwich he failed sandwich indicatesindicates crimping or shear instability, failure may have begun by overall buckling

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Volume

FIGURE 1.5

FIGURE 1.5 Sandwich failure modes.Sandwich failure modes. The local modes of failure may

The local modes of failure may occur in sandwich panels under eoccur in sandwich panels under edgewise loads or normal loads. dgewise loads or normal loads. InIn addition to overall buckling and local modes of failure, sandwich structures should be designed so that addition to overall buckling and local modes of failure, sandwich structures should be designed so that facings do not fail in tension, compression, shear, or combined stresses due to edgewise loads or normal facings do not fail in tension, compression, shear, or combined stresses due to edgewise loads or normal loads, and cores and bonds do not fail in shear, flatwise tension, or flatwise compression due to normal loads, and cores and bonds do not fail in shear, flatwise tension, or flatwise compression due to normal loads.

loads.

The basic design principles can be summarized into four conditions as follows: The basic design principles can be summarized into four conditions as follows: 1.

1. Sandwich facings should Sandwich facings should be at least be at least thick enough tthick enough to withstand o withstand chosen design stresses chosen design stresses under de-under de-sign loads.

sign loads. 2.

2. The core should The core should be thick enough abe thick enough and have sufficient nd have sufficient shear rigidity and shear rigidity and strength so that strength so that overalloverall sandwich buckling, excessive deflection, and shear failure will not occur under design loads. sandwich buckling, excessive deflection, and shear failure will not occur under design loads. 3.

3. The core should The core should have high enough moduli of have high enough moduli of elasticityelasticity, and the , and the sandwich should have greatsandwich should have great enough flatwise tensile and compressive strength so that wrinkling of either facing will not occur enough flatwise tensile and compressive strength so that wrinkling of either facing will not occur under design loads.

under design loads. 4.

4. If the a If the a honeycomb core is used honeycomb core is used and dimpling of the facings and dimpling of the facings is not permissible, tis not permissible, the cell sizehe cell size should be small enough so that dimpling of either facing into the core spaces will not occur under should be small enough so that dimpling of either facing into the core spaces will not occur under design loads.

design loads.

The choice of materials, methods of sandwich assembly, and material properties used for design The choice of materials, methods of sandwich assembly, and material properties used for design should be compatible w

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exam-Volume

ple, facing to core bonding should have sufficient flatwise tensile and shear strength to develop the ple, facing to core bonding should have sufficient flatwise tensile and shear strength to develop the re-quired sandwich panel strength in the expected environment.

quired sandwich panel strength in the expected environment. Environmental effectEnvironmental effects of temperature, was of temperature, wa--ter or moisture, corrosive atmosphere and fluids, fatigue, creep, and any condition that may affect ter or moisture, corrosive atmosphere and fluids, fatigue, creep, and any condition that may affect mate-rial properties should also be included.

rial properties should also be included.

Certain additional characteristics, such as thermal conductivity, resistance to surface abrasion, Certain additional characteristics, such as thermal conductivity, resistance to surface abrasion, di-mensional stability, permeability, and electrical properties of the sandwich materials should be considered mensional stability, permeability, and electrical properties of the sandwich materials should be considered in arriving at a thoroughl

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Volume

REFERENCES REFERENCES

1.2

1.2 MIL-HDBK-23A, MIL-HDBK-23A, "Military "Military StanStandardization dardization Handbook, Handbook, StructStructural ural Sandwich Sandwich Composites",Composites", Department of Defense, December 1968.

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Volume 6,

Volume 6, Chapter 2 Chapter 2 Guidelines for Property TGuidelines for Property Testingesting

CHAPTER

CHAPTER 2

2 GUIDELINES

GUIDELINES FOR

FOR PROPERTY

PROPERTY TESTING

TESTING

2.1 INTRODUCTION

A sandwich structure consists of facings, core, and some means of connecting the two so they work A sandwich structure consists of facings, core, and some means of connecting the two so they work together such as an adhesive or brazing.

together such as an adhesive or brazing. Facing and core properties must be known in order tFacing and core properties must be known in order to designo design the sandwich and the sandwich must be tested to insure the facings are adequately connected to the the sandwich and the sandwich must be tested to insure the facings are adequately connected to the core.

core. This section discusses mechanical properties, environmental effectThis section discusses mechanical properties, environmental effects, test methods, and dats, test methods, and data reduc-a reduc-tion and presentareduc-tion.

tion and presentation.

The main properties of sand

The main properties of sandwich core materials are listed wich core materials are listed below with the ASTM Standard Tbelow with the ASTM Standard Test Methodest Method used to

used to obtain that property.obtain that property.

Core

Core Property Property ASTM ASTM Standard Standard Test Test MethodMethod

Density

Density Density Density of of Sandwich Sandwich Core Core Materials Materials C C 271271 Water

Water Absorption Absorption Water Water Absorption Absorption of of Core Core Materials Materials C C 272272 Shear

Shear Strength Strength and and Modulus Modulus Shear Shear Properties Properties of of Sandwich Sandwich Core Core Materials Materials C C 273273 Flatwise

Flatwise Tensile Tensile Strength Strength Flatwise Flatwise Tensile Tensile Strength Strength of of Sandwich Sandwich Constructions Constructions C C 297297 Core

Core Node Node Bond Bond Strength Strength Node Node Bond Bond Tensile Tensile Strength Strength of of Honeycomb Honeycomb Core Core Materials Materials C C 363363 Compressive

Compressive Strength Strength and and Modulus Modulus Flatwise Flatwise Compressive Compressive Properties Properties of of Sandwich Sandwich Cores Cores C C 365365 Core

Core Thickness Thickness Measurement Measurement of of Thickness Thickness of of Sandwich Sandwich Cores Cores C C 366366 Flexural

Flexural Strength Strength and and Modulus Modulus Core Core Shear Shear Properties Properties of of SandwichSandwich Constructions

Constructions by by Beam Beam Flexure Flexure C C 393393 Facing Properties of Sandwich Constructions by

Facing Properties of Sandwich Constructions by

Long

Long Beam Beam Flexure Flexure D D 72497249

Determining

Determining Sandwich Sandwich Beam Beam Flexural Flexural and and Shear Shear Stiffness Stiffness D D 72507250

Shear

Shear Fatigue Fatigue Strength Strength Shear Shear Fatigue Fatigue of of Sandwich Sandwich Core Core Materials Materials C C 394394 Aging

Aging of of Core Core Laboratory Laboratory Aging Aging of of Sandwich Sandwich Constructions Constructions C C 481481 Water

Water Migration Migration Water Water Migration Migration in in Honeycomb Honeycomb Core Core Material Material F F 16451645

The basic core design properties are compressive strength and modulus and shear strength and The basic core design properties are compressive strength and modulus and shear strength and modulus.

modulus. The shear properties for honeycomb cores are dThe shear properties for honeycomb cores are different in the L and ifferent in the L and W directions depending onW directions depending on the cell geometry

the cell geometry. . For normal hexagonal honeycomb, the L shear properFor normal hexagonal honeycomb, the L shear properties are about two times the Wties are about two times the W shear properties.

shear properties. The balsa and foam core shear prThe balsa and foam core shear properties are about the same operties are about the same in both these directions.in both these directions. The honeycomb core shear

The honeycomb core shear strengths also vary witstrengths also vary with core thickness as shown h core thickness as shown below (Figure 2.1). below (Figure 2.1). TheThe normal thickness for testing aluminum honeycomb is 0.625" and 0.500" (15.875 mm and 12.7 mm) for normal thickness for testing aluminum honeycomb is 0.625" and 0.500" (15.875 mm and 12.7 mm) for non-metallic honeycomb.

non-metallic honeycomb.

The bare compressive stren

The bare compressive strength is obtained on the gth is obtained on the core without any facings. core without any facings. This test is just a quickThis test is just a quick quality control test for

quality control test for honeycomb, but can be honeycomb, but can be used for balsa and foam dused for balsa and foam design properties. esign properties. The adhesiveThe adhesive fillets on the honeycomb core-to-facing bond supports the honeycomb cell

fillets on the honeycomb core-to-facing bond supports the honeycomb cell edges and gives slightledges and gives slightly highery higher values than the unsupported b

values than the unsupported bare compression test. are compression test. When the core has facings bonWhen the core has facings bonded on, the test isded on, the test is called a stabilized compression t

called a stabilized compression test. est. This test specimen is used to This test specimen is used to obtain the honeycomb coobtain the honeycomb compressivempressive modulus.

modulus. The modulus for balsa and foam cores The modulus for balsa and foam cores can be obtained frocan be obtained from either test.m either test. The shear strength

The shear strength and modulus of cores are usually oband modulus of cores are usually obtained from the plattained from the plate shear test. e shear test. This con-This con-sists of bonding the core to steel plates and then loading the plates in either tension or compression with sists of bonding the core to steel plates and then loading the plates in either tension or compression with the load line going through the diagonal corners of the core.

the load line going through the diagonal corners of the core. This core property is probably the most im-This core property is probably the most im-portant as in a sandwich beam

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Volume 6,

FIGURE 2.1

FIGURE 2.1 Honeycomb core shear strength versus core thickness (Reference 2.1).Honeycomb core shear strength versus core thickness (Reference 2.1).

The facings must be well bonded to the core for the sandwich to work togeth

The facings must be well bonded to the core for the sandwich to work together. er. Two of the main teTwo of the main testssts used to evaluate the core-to-facing

used to evaluate the core-to-facing bond are the flatwise tensile and the climbing drum peel testbond are the flatwise tensile and the climbing drum peel tests. s. A newA new cleavage test was just developed for

cleavage test was just developed for thicker faced panels.thicker faced panels.

Panel

Panel Property Property ASTM ASTM Standard Standard Test Test MethodMethod

Flatwise

Flatwise Tensile Tensile Strength Strength Flatwise Flatwise Tensile Tensile Strength Strength of of Sandwich Sandwich Constructions Constructions C C 297297 Peel

Peel Strength Strength Climbing Climbing Drum Drum Peel Peel Test Test for for Adhesives Adhesives D D 17811781 Cleavage

Cleavage Strength Strength Facing Facing Cleavage Cleavage of of Sandwich Sandwich Panels Panels E E 20042004

The flatwise tensile test consists of cutting a small specimen from the panel, usually 2" by 2" (50 mm The flatwise tensile test consists of cutting a small specimen from the panel, usually 2" by 2" (50 mm by 50 mm), and bonding it t

by 50 mm), and bonding it to metal blocks. o metal blocks. The specimen is then fixtured into a test The specimen is then fixtured into a test machine and pulledmachine and pulled apart with the maximum lo

apart with the maximum load and mode of failure recorded. ad and mode of failure recorded. The failure mode is extremely importThe failure mode is extremely important as itant as it can tell if the p

can tell if the panel was made propeanel was made properly. rly. The modes of failure The modes of failure are the following: are the following: core tearing, adcore tearing, adhesion-to- hesion-to-core, adhesion-to-facing,

core, adhesion-to-facing, cohesive failure of the cohesive failure of the core-to-facing adhesive. core-to-facing adhesive. If the bond between If the bond between the blockthe block and the panel fails, this is not co

and the panel fails, this is not considered a valid failure and the test should be repeatednsidered a valid failure and the test should be repeated. . If the failuresIf the failures are adhesion to core or facing, this shows that the core or facing is contaminated and the cleaning are adhesion to core or facing, this shows that the core or facing is contaminated and the cleaning proc-ess should be reviewed.

ess should be reviewed.

The climbing drum peel test consist

The climbing drum peel test consists of peeling off one facins of peeling off one facing from the panel. g from the panel. This test only worksThis test only works well on relatively thin facings,

well on relatively thin facings, and the modes of failure and the modes of failure are the same as are the same as above. above. For thicker facings, tFor thicker facings, thehe new cleavage test may give better results, as

new cleavage test may give better results, as the facing does not have to the facing does not have to be bent around a be bent around a drum.drum.

The facings of a sandwich panel take the bending loads (one facing in compression and the other in The facings of a sandwich panel take the bending loads (one facing in compression and the other in tension) or in some cases the

in-tension) or in some cases the in-plane shear loads. plane shear loads. The major facing properties are tThe major facing properties are the compressive andhe compressive and tensile strengths and moduli.

tensile strengths and moduli. Some ASTM teSome ASTM test methods for composite facings are given below.st methods for composite facings are given below.

Core Thickness – Inch Core Thickness – Inch

C C o o r r r r e e c c t t i i o o n n F F a a c c t t o o r r K K

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Volume 6,

Facing

Facing Property Property ASTM ASTM Standard Standard Test Test MethodMethod

Tensile

Tensile Strength Strength and and Modulus Modulus Tensile Tensile Properties Properties of of Fiber-Resin Fiber-Resin Composites Composites D D 30393039 Compressive

Compressive Strength Strength and and Modulus Modulus Compressive Compressive Properties Properties of of Polymer Polymer Matrix Matrix CompositeComposite Laminates Using a Combined Loading Compr Laminates Using a Combined Loading Compr essionession (CLC)

(CLC) Test Test Fixture Fixture D D 66416641

In-Plane

In-Plane Shear Shear Strength Strength In-Plane In-Plane Shear Shear Stress-Strain Stress-Strain Response Response of of UnidirectionalUnidirectional Reinforced

Reinforced Plastics Plastics D D 35183518

Shear Properties of Composite Materials by the

Shear Properties of Composite Materials by the V-NotchedV-Notched Rail

Rail Shear Shear Method Method D D 70787078

The facing properties, data reduction, and presentation are in Volume 2, therefore, this section will The facing properties, data reduction, and presentation are in Volume 2, therefore, this section will only deal with the sandwich core

only deal with the sandwich core properties. properties. The core properties given in The core properties given in the Chapter 3 tathe Chapter 3 tables are thebles are the following: typical and minimum compressive strength and shear strength, typical compressive and shear following: typical and minimum compressive strength and shear strength, typical compressive and shear moduli, and typical tensile strength.

moduli, and typical tensile strength.

These values are from published test values from th

These values are from published test values from the core suppliers. e core suppliers. The property values given areThe property values given are not design allowables, but values used t

not design allowables, but values used to purchase the core. o purchase the core. It is the general practice in tIt is the general practice in the industry tohe industry to thoroughly test three blocks of a core product for specification qualif

thoroughly test three blocks of a core product for specification qualif ication and then just selected tests forication and then just selected tests for block acceptance.

block acceptance. Normally five specimens for each Normally five specimens for each condition are tested and condition are tested and the average and minimumthe average and minimum values of these five specimens (m

values of these five specimens (minimum individual) must meet the specification requirements.inimum individual) must meet the specification requirements.

2.2 2.2 DA

DATA

TA REDUCTIO

REDUCTION AND PRESENT

N AND PRESENTA

ATION

TION

While core properties have been published by individual suppliers, and some core materials are While core properties have been published by individual suppliers, and some core materials are pur-chased according to industry specifications, a standardized approach to data reduction and presentation chased according to industry specifications, a standardized approach to data reduction and presentation have not been established for

have not been established for inclusion into this volume of CMH-17. inclusion into this volume of CMH-17. The near-term approach tThe near-term approach to addresso address the issue of core data is to provide material property values solely for illustration and comparison so that the issue of core data is to provide material property values solely for illustration and comparison so that the user can get a feel for what kind of properties to expect from a given material.

the user can get a feel for what kind of properties to expect from a given material. The data is clearly la-The data is clearly la-beled regarding its source and published value interpretation (i.e., whether the data represents typical or beled regarding its source and published value interpretation (i.e., whether the data represents typical or minimum values), and is not to be considered as certifiable for official design qualification (or submittable minimum values), and is not to be considered as certifiable for official design qualification (or submittable as “Type Data” for FAA Certification, for example) unless agreed to ex

as “Type Data” for FAA Certification, for example) unless agreed to explicitly by plicitly by that governing agency.that governing agency. The ultimate goal of CMH-17 is to establish protocols and standards for eventual inclusion of core The ultimate goal of CMH-17 is to establish protocols and standards for eventual inclusion of core data for official design use, including thorough peer review and scrutiny with the statistical rigor that is data for official design use, including thorough peer review and scrutiny with the statistical rigor that is currently applied to fiber-reinforced polymer composite materials presented in

currently applied to fiber-reinforced polymer composite materials presented in Volume 2.Volume 2.

2.3 2.3 EVA

EVALUATION

LUATION OF CORE MA

OF CORE MATERIALS

TERIALS

2.3.1

2.3.1 Mechanical Mechanical propertiesproperties

The three main types of cores used in sandwich constructions are honeycomb, foam, and balsa The three main types of cores used in sandwich constructions are honeycomb, foam, and balsa wood.

wood. Each type has its advantages and disadvantages (TEach type has its advantages and disadvantages (Table 2.3.1).able 2.3.1). 2.3.2

2.3.2 Environmental Environmental effectseffects

The hygrothermal stability of sandwich panels is of special interest to the integrity of solar panels, The hygrothermal stability of sandwich panels is of special interest to the integrity of solar panels, an-tenna structures, aircraf

tenna structures, aircraft, and payload fairings. t, and payload fairings. In addition to aluminum cores, a variety oIn addition to aluminum cores, a variety of materials are inf materials are in use, including alloys such as stainless steel, KRAFT paper (softwood), KEVLAR (aramid), TYVEK (high use, including alloys such as stainless steel, KRAFT paper (softwood), KEVLAR (aramid), TYVEK (high density polyethylene), plastic foams, and fiberglass Bias or straight graphite fabrics with phenolic or density polyethylene), plastic foams, and fiberglass Bias or straight graphite fabrics with phenolic or poly-imide resin represent

imide resin represent developmental honeycomb developmental honeycomb materials. materials. Their properties, such Their properties, such as shear modulus,as shear modulus, vary with core density and cell dimensions and directions.