# P w U.S. Department ofTransportation FederalAviation Administfation 

# Advisory

Circular

CONSOLIDATEDREPRINT
IThis consolidated reprint incorporates

Change 1
Subject: QUALITY CONTROLFORTHE

MANUFACTUREOFCOMPOSITE STRUCTURES Date: 6/26/89 ACNo: 21-26 Initiatedby: AIR-2()() Change:

1. PURPOSE. This advisory circular (AC) provides information and guidance concerning anacceptable means, but not the only means, of demonstrating compliance with the requirements of Federal Aviation Regulations (FAR) Part 21, Certification Procedures for Products and Parts, regarding quality control (QC)systems for the manufacture of composite structures involving fiber reinforced materials, e.g., carbon (graphite), boron, aramid (Kevlar), andglass reinforced polymeric materials. This ACalso provides guidance regarding the essential features of QCsystems for composites asmentioned in AC20-107, Composite Aircraft Structure. Consideration will begiven to any other method of compliance the applicant elects to present to the Federal Aviation Administration (FM).
2. RELATEDFARSECTIONS. Sections 21.125, 21.143, 21.303, and 21.605.
3. RELATEDREFERENCEMATERIAL.

a AC21-1, Production Certificates.
b. AC21-6, Production Under Type Certificate Only.

c. AC21-303.1, Certification Procedures for Products and Parts.
d. AC20-107, Composite Aircraft Structure.
4. DEFINITIONS. Appendix 1contains alist of terms commonly used in the manufacture of composite structures.
5. QUALITY CONTROLSYSTEM. fabrication should bebasica established to meet the requ QCsystem should include pro materials, control of in-pro to evaluate the end product AQCsystem lly similar irements of cedures that cess manufac that ise

to any0th FARPart 2 ensure th .turing met for conformi ty to desistablished for compos erQCsystem that has 1. For example, the equality of incoming *hods, andtesting per gnrequirements. Thete been

ormed QC system should include standards to beused for nondestructive anddestructive tests, visual inspection techniques during the fabrication process, and product final acceptance. Thestandards used to determine the acceptance or rejection of manufacturing-induced defects and damage should take into account the process and inspection capability. These standards should bebased on approved data developed asaresult of proof of structure evaluations conducted inaccordance with referenced AC20--107 and applicable FAR airworthiness standards. This ACaddresses those areas of aQCsystem that mayrequire further expansion to accommodate composite fabrication.AC

### 21-26 6/26/89

6. MATERIAL ANDPROCESSSPECIFICATI,ONS. Unlike parts which use metallic materials in the manufacturing process, the material properties of acomposite structure are manufactured into the structure aspart of the fabrication process. Therefore, it is essential that material’ and process specifications used to produce composite structures, contain sufficient information to ensure that critical parameters in the fabrication process are identified to facilitate production and final inspection. Typical material and process SpeMIications, respectively, should contain the following information:

a. Basic fiber, matrix and cured component properties, and required testing including type, number, and frequency of tests.
b. Conditions and requirements during the manufacturing process including fabrication method, specific tooling, environmental conditions, significant parameters during the cure cycle, inspection criteria at each operation, and storage and handling conditions throughout the process. 7. MATERIALS. The FAArequires that all drawings submitted for type design approval contain sufficient information or references to material specifications or other such data that clearly identify the materials and processes that are necessary to ensure production of like articles. When materials for acomposite structure are produced in accordance with a proprietary process, or the composition of the materials is proprietary, the production approval holder or applicant mayprefer to exclude this proprietary data from the type design submitted to the FM. In these instances, the applicable type design drawings should refer to aspecification which contains this proprietary information sothat complete traceability to material composition is possible. These specifications will then bemade available to the FAAfor review and approval under anarrangement between the FAAand the production approval holder or applicant which will protect the proprietary nature of the product. Under FARsections 21.33 and 21.157 (Inspection and tests), the FAAis authorized to review such data upon request. The following are recommendations regarding QCprocedures, chemical characterization, testing techniques, and supplier control of purchased materials:

a. The production approval holder or applicant should have an incoming material acceptance plan that ensures conformity and uniformity of purchased composite materials to specifications identified in the approved type design. Copies of supplier laboratory test reports showing actual test results should accompany each batch of material received for review and approval; however, a material supplier’s test report alone should not beconsidered adequate documentation to substantiate that materials satisfy all specification requirements. Samples of these materials should betaken onabatch-to-batch basis and tested to engineering and manufacturing requirements for conformity of physical, chemical, mechanical, and processing properties to verify the accuracy of suppliers’ laboratory reports. Sample testing could be accomplished bythe production approval holder or applicant at its production facilities or byan independent laboratory approved for such testing under the production approval holder's or applicant’s QCsystem. Such testing maybe decreased once confidence in the quality of products from aparticular source has been established bythe production approval holder.

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### AC21-26CHG1

b. Resin matrix systems: Theproduction approval holder orapplicant should require chemical characterization tests of the matrix material. A typical material specification sets upper and lower limits onthe amount of reactive functional group per unit of material, aswell asother design requirements such asviscosity, color, andmoisture content. The characterization tests should identify and measure the amounts of individual constituents of the resin system such asthe basic epoxide, curing agent, accelerator, hardener, etc., and the reacted constituents caused byresin mixing, storage, fiber impregnation, etc.

c. It is recommended that tests such asHigh Performance Liquid Chromatography (HPLC), Fourier Transform Infrared Spectroscopy (FTIS) and Gelation Permeation Characterization (GPC)for chemical characterization, and Differential Scanning Calorimeter (DSC) and Dynamic Rheological Analysis for thermal analysis and viscosity/flow/tack/gelation characteristics or their equivalent beconducted, and resulting traces compared to the standards specified in the material specification. Experience has shown that one method of testing aparticular sample mayyield the same“fingerprint” asan acceptable sample within specification limits, yet the sample is rejectable when tested using another method. Therefore, it is likely that more than one type of characterization test maybenecessary,, since all chemical ingredients affecting agiven composite’s performance maynot bequantifiable byasingle test method. Accordingly, the production approval holder’s orapplicant’s material specification must define the combinations of acceptable test techniques and test results which adequately demonstrate the material’s conformity andprocess capability. Techniques for chemical characterization are not universal but are strongly dependent upon the resin formulation. Therefore, test methods adapted to each material should bedeveloped considering the sensitivity of the method to detect deviations in formulation.
d

. Reinforcement Fibers: Theproduction approval holder or applicant should establish procedures in coordination with its material suppliers to control the quality of incoming fibrous materials such asroving, tow, and woven fabric. Testing for mechanical properties is the primary method used for fiber characterization. This method is also used toqualify or screen continuous filaments since tensile strength and modulus are sensitive indicators of change in composite material mechanical response. In addition, ameans should bedeveloped to control the quality of fiber surface treatment, sizing, etc.

e. Preimpregnated Material (Prepreg): In applications where prepreg tape, fabric, or roving are primary materials of composite structures, it is necessary to test for the chemical, physical, and mechanical fiber and matrix dominated properties identified in the applicable prepreg material specification. Quality control procedures previously described for resins and fibers maybeused to control the quality of incoming prepreg materials. Chemical characterization should beperformed onresin extracted from the prepeg material to beused for production, where applicable.



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### AC21-26 6/26/89

f

. Adhesives: TheQCprocedures recommended for structural adhesives are similar to those for resin matrix systems; that is, the procedures should provide assurance that each incoming batch conforms to the chemical, physical, and mechanical properties identified in the material specification.
8 MANUFACTURINGCONTROLS. The manufacture of acceptable and reliable composite structures is dependent onthe type of process controls employed during the fabrication cycle. If all pertinent process variables are adequately controlled, there is added assurance that the parts and structures produced will beacceptable. Quality control should, therefore, establish and implement aplan which verifies that: (1) the parameters affecting material integrity andprocess capability are operating under controlled conditions; and (2) individual items, batches, or lots conform to specified quality standards. Toensure that QCobjectives have been met, process procedures should clearly define specific materials, tooling, equipment, cure cycle parameters, quality standards, operator qualifications, storage and handling requirements, traceability records, and anyother special requirements.

a. Genera1: Thefollowing are manufacturing process controls that should beinclu .ded in amanufacturer’s QCsystem:

(1) Theproduction approval holder or applicant should develop integrated quality and production control procedures for operations that define product configuration, selection of materials, tooling and facility equipment, calibration, sequence of fabrication operations, critical inprocess parameters andprocessing tolerances, andconformity toquality standards.(2) Environmental parameters (temperature, humidity, chemical contamination) should bedefined andcontrolled, asrequired, where composite parts and structures will beproduced; in particular, cutting, layup, and bonding areas.(a) Unless otherwise validated for the material system in use, the area should betemperature and humidity controlled such that the minimum temperature is 65degrees Fwith acorresponding relative humidity not greater than 63percent and the maximum temperature is 75degrees Fwith a corresponding relative humidity not greater than 46percent. Thetemperature and relative humidity values between the minimum and maximum acceptable values listed above should form astraight line relationship. Procedures for QCto verify and record temperature and humidity conditions should beestablished to ensure environmental stability.

(b) Contamination restrictions in environmentally controlled areas should prohibit the use of uncontrolled sprays, exposure to dust, handling contamination, fumes, oily vapors, and the presence of other particulate or chemical matter which mayadversely affect the manufacturing process, e,g., release agents or material containing uncured silicon should not bepermitted. Also, conditions under which operators mayhandle materials should bedefined.

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### 21-26
() C Layup and clean room systems should becapable of providing air filtration and pressurization aslight positive overpressure. (3) Theproduction approval holder orapplicant should establish a program to train and/or qualify operators, asappropriate. This program should measure operator performance to production standards andprovide for requalification asnecessary.

(4) Prior to the start of production, manufacturing processes should bequalified bydemonstrating that the combination of materials, tooling, equipment, procedures, andother controls making upthe process will produce parts having consistent material properties that conform to design requirements. Aspart of the process qualification, destructive and/or nondestructive inspection (NDI) of appropriate tool proofing specimens should beconducted to determine conformity to specified design requirements. Destructive tests of specimens verify conformity to the specified physical and mechanical properties. Nondestructive inspection of specimens verify that discrepancies caused byfabrication procedures remain within allowable limits.

(5) Oncethe manufacturing process has been established it should not bechanged unless acomparability study and necessary testing of differences has been completed. In addition, processes should be reviewed and requalified if necessary, whenever anysignificant changes are made to the process such as sources of material, cure cycle, equipment controls, or autoclave loading patterns andtool design changes. Process capability should bedemonstrated by inspection and testing asnecessary to determine conformity to design requirements.

(6) In order to control adhesives andmatrix formulation when resin is mixed during part manufacture, documented procedures should beemployed to cover the identity of required constituents, respective quantities, and mixing methods and techniques. Tests should beperformed oneach resin mix to ensure conformity to specification requirements andshould including sampling methods for chemical testing. Themixing process performed under these procedures should ensure that the sequence of additions and mixing techniques are followed, proper chemical reactions are achieved, aeration of the mix is prevented, andthe mixing equipment isproperly cleaned.

(7) After initial process qualification, testing (process control panels, etc,) for conformity to design requirements should continue onan appropriate frequency to ensure that the manufacturing process, materials, and associated tooling continue to operate in astate of control andproduce conforming parts.

(8) For accepting or rejecting cured structures, NDIequipment and procedures should beused to evaluate specified material defects resulting from fabrication and assembly operations. TheNDItechnique used for inspection should have the sensitivity to detect maximum allowable discrepancy type and size in the part.

(9) Specifications used byQCshould define allowable limits for each discrepancy such as: adhesive voids, porosity, delaminations, damaged core, core node bond separations, potting cracks, short core, lack of adhesive, etc.



### Par 8 5AC 21-26 6/26/89

b. Fabrication of Parts: Thefollowing are manufacturing controls unique to laminate andwet layup, filament winding, andpultrusion that aQCsystem should include:

(1) Laminate Layup. (a) Standards and methods should beestablished to ensure proper orientation, stacking, and nesting of the plies during layup operations. The programs that control tape head andtable motions, and tape feed and tape stacking, should beapproved byQC. Standards should beestablished for such in-process variables astape orientation, gaps, andoverlap.

(b) For automatic and hand layup methods, controls should be established for in-process variables that affect the cured laminate quality: e.g. presin content, ply compaction, laminate density, porosity, which may result from debulking, pre-bleeding, andbagging operations. I

(2) WetLayup. (a) Procedures should beestablished to ensure correct material selection, orientation andstacking, or nesting of the plies during wet layup operations. (b) Procedures should beestablished to control in-process variables such asresin content, aeration andair pockets.

(3) Filament Winding. (a) Preimpregnated filaments for dry winding should bestored and handled according to procedures similar to those for other prepreg materials to ensure that the material’s original properties have been maintained, especially material flow andtack to ensure proper bonding for subsequent winding operations.

(b) Procedures should beestablished to ensure that the working life of the resin system exceeds the anticipated winding time and to ensure that gelation does not take place before completion of winding.

(c) Standards and methods should beestablished to control machine-dominant parameters such asfeed rate, feeder armand mandrel motions, mandrel dwell angle, number of circuits per pattern, total number of circuits for complete coverage, number of plies per layer, winding angle, fiber tension andalignment, band-width, and fiber/resin ratio.

(d) Procedures should beestablished to control process variables during the winding operation such asresin viscosity, fiber wetting, fiber tension, fiber band-width and alignment, air entrapment, degree of compaction, and fiber damage.

Par 86/26/89 AC 21-26
(4) Pultrusion. (a) Procedures should beestablished to control pultrusion start-up, steady state, andshutdown operations including disposition of material produced during start-up and shutdown operations.

(b) Process procedures should define limits for important process parameters that determine product quality such asline speed, die temperature profile for the particular operating conditions and resin system, clamping pull-through lead, resin temperature, die input temperature, material orientation for preform operation, and material tension.

c. Assembly of Components: Thefollowing are manufacturing controls unique to the assembly of fabricated composite parts and structures that a manufacture’s QCsystem should include:

(1) Sandwich Construction. (a) Core material should be inspected for cell damage, crush, correct length andthickness, and should beproperly cleaned and protected against contamination.

(b) Cured laminates should beinspected for dimensional conformity. Faying surfaces should beproperly cleaned andprotected from contamination before subsequent assembly and bonding operations.

(c) Uncured laminates used for subsequent co-curing operations should beproperly protected andstored to prevent contamination and to retard chemical advancement.

(d) Procedures should beestablished to control those critical parameters of the assembly process that affect the integrity and uniformity of the end item such as: bondline thickness, bondline pressure andtemperature distribution, and part “floating” within the tooling when the resin or adhesive is in the liquid Hate during cure cycle (bagging and tooling requirements). (e) Theperformance of the sandwich construction process should beevaluated for each autoclave oroven load bytesting specimens of the sandwich construction. Test specimens should bemadefrom specially prepared panels that have been fabricated from the samematerials, and using the same production methods, environmental working conditions, andcure cycle asthe production parts they represent. Whenco-curing of laminates is required to fabricate anassembly, asolid laminate process control panel should also be prepared for specimen testing. Cutouts or cutoffs from production parts may also beused providing they are representative of the product.ion part configuration.

(2) Curing Process. 

## (4 pr parameters of the pracedures s, nashouId bedeveloped to control the critical .mely chemical reactions of the resin and

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### 21-26 6/26/89

consolidation of the plies to achieve manufacturing consistency and quality parts which are of uniform consolidation, within void tolerances, andof correct fiber volume.

(b) Procedures should identify the equipment and materials which will beused to bag the uncured laminate or sandwich construction. This will ensure the proper control of resin flow, volatile content, andply consolidation during the cure cycle since such materials (e.g., peel plies) mayalter properties of the structure.

(c) Procedures should define the relationship of the variables (time, temperature, pressure) in the cure cycle (and post-cure cycles) which control compaction and consolidation and cure reaction. These controls should include the acceptable limits of variables during the cure cycle andaction to betaken when such limits are exceeded; e.g., submit cured parts to QC(MRB) for evaluation anddisposition.

(d) Procedures should beestablished to ensure that, when the autoclave or oven is loaded with uncured parts having different configurations, materials, bagging configurations, and tooling heat-up characteristics, each part is properly cured.

(e) Procedures should describe actions to betaken when heating, cooling, vacuum, orpressure interruptions are experienced during autoclave/oven cure; e.g., submit to QC(MRB)for disposition.

(f) The performance of the curing process should beevaluated for each autoclave or oven load bytesting specimens representative of the composite structure. Test specimens should befabricated from the same materials, and using the sameproduction methods, environmental working conditions, andcure cycle asthe production parts they represent. Cutouts or cutoffs from production parts mayalso beused provided that they are representative of the production part configuration. The useof validated direct-cure monitoring techniques mayalso beused if found directly applicable.(3) Secondary Bonding.

(a) Cleaning procedures for surfaces to bebonded together should specify the chemicals and abrasive to be used onfaying surfaces. Standards for determining properly cleaned surfaces and methods for protecting clean surfaces from contamination (including peel plies) should beavailable at the place of fabrication.

(b) Quality control standards should establish adhesive bondline thickness andpressure to beapplied along the bondline during the cure cycle.

(c) Tool proofing procedures should demonstrate the capability of the tooling to maintain correct bondline thickness, equal pressure distribution along the bondline, andproperly cured adhesive.

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(d) Before the application of adhesives, the production parts should bepreassembled and inspected in the tooling to determine that the expected bondline thickness and pressure distribution onthe bondline will be within design limits. Shims required to fill bonding gaps should only beused in accordance with anapproved QCprocedure.

(f) Methods for applying adhesive films should preclude the formation of defects such asvoids dueto air entrapment, bridging, andgaps between adjacent films.

(g) Standards for the application of adhesives (e.g., pastes) should require acomplete and even coating of adhesive with wetting of surfaces andexclusion of air in the adhesive.

(h) Controls for high temperature curing adhesives should be recorded and should include heat-up and cool-down rates, cure time and temperature, vacuum, and pressure parameters.



### . (1) Controls for room temperature curing of adhesives should specify:
mating, 1. Minimum and maximum time between mixing of adhesive and

clamping, or tooling of parts into final configuration.

2. - Minimum time at particular temperatures to achieve adequate handling strength for subsequent processing, and the conditions (time and temperature) for achieving full cure.

. (J) Theconditions under which bonded structures maybe subjected to asubsequent curing operation should specify:
1. - 2. - Maximum allowable temperature.

Maximum number of subsequent curing cycles.
3. delaminations, etc,, Procedures to prevent bond line separation, blistering, of the structure when subsequent curing temperatures approach that of the previous cure temperature.

(4) Other Holding Methods. I? or techniques such asresin injection, compression, andtransfer molding processes, specific ations should define the limits for all critical process parameters that deter mine product quality. Such parameters are, for example, resinmix, feed-rat eandtemperature, mold temperature, and back pressure or vacuurn. In additio n, molding process specifications should identify the timing andsequent eof automatic operations. These critical parameters should bedefi ned in the process specification and identified in the associated operat ion sheets.
9. FINAL ACCEPTANCE.

a. Final acceptance procedures and quality control standards should provide added assurance that the completed structure meets its functional and design requirements.

Par 8 9AC21-26 6/26/89

b. Final acceptance records should provide evidence that the following significant production andQCactivities, specifically designed to assure the quality of composite structures, have been completed:



### (2) (3) (4) Incoming material acceptance. In-process fabrication and assembly controls.
Maintenance of tooling and facility equipment.
Calibration of inspection and laboratory test equipment. (5) Inspection acceptance of functional characteristics at detail and assembly levels.

(6) Nondestructive inspection acceptance. (7) Configuration control. (8) Material Review Board disposition.

c J

. Nondestructive Inspection (NDI). There are several ND1techniques used in detecting discrepancies in composite structures; however, the most commonly used techniques are visual, audio sonic (coin tapping), radiography, ultrasonics, and mechanical impedance testing.

(1) Visual. Visual inspection is the most widely used NDI method. Discrepancies that can usually beobserved include: Discoloration (due to overheating), foreign matter, crazing, cracks, scratches, blisters, dents, orange peeling, pitting, air bubbles, porosity, resin rich and resin poor areas, and surface wrinkles. Reflected light is used for observing surface irregularities and other defects, while transmitted light (assuming both surfaces are accessible and the material is translucent) helps to reveal discrepancies within the specimen.

produce aconsistent tapping rate and force are available and can beused for this test.(3) Radiography. Radiography is generally used in composite fabrication for the detection of bondline defects. In addition, radiography mayalso beused to inspect for the presence of foreign material, adhesive voids, location of internal parts, honeycomb core defects, mislocated or misdrilled holes, poor fit-up, thick bonds, fiber discontinuities, poor tape lwup, or lack of adhesive fillets. In the case of carbon/epoxy,

10 Par 96/26/89 AC 21-26

glass/epoxy, and aramid (kevlar)/epoxy, the resolution differences are low and defect detection becomes difficult due to the low contrast in the film. Radiography is usually performed through the thickness of the product for detection of anomalies.



### (4) Ultrasonic. In this technique, the attenuation of sound wave energy is used for flaw detection. Twomethods of ultrasonic techniques are available: through transmission, and pulse echo. Three methods of recording and display generally used are: A-scan, B--scan, and C-scan. An A-scan is anamplitude versus time display for aspecific point onthe part inspected. It generally lends itself to the contact pulse-echo methods. B-scans display along cross-sectional view of the part under test and show discovered discrepancies. C-scans display the effect in aplane view usually onapaper that is rolled across the printer bar. C-scans provide nodefect depth or orientation information; however, they are capable of detecting defects in the magnitude of 0.01 square inch. Ultrasonic techniques can generally be used to detect porosity, laminar inclusions, delaminations, and fastener hole flaws. The disadvantage of the ultrasonic method is the inability of the method to distinguish between voids and small delaminations since the attenuation characteristics of the two flaws are identical.

(5) Mechanical Impedance. These are methods in which structural response to strain excitation is measured to detect delaminated areas or disbonds. The sensitivity of this method decreases with increasing structural flexibility or discrepancy depth.

e. Controlling Nondestructive Inspection Techniques. In order for nondestructive inspection techniques to beeffective, repeatable, and reliable, certain controls are required. These controls should beapproved by the production approval holder or applicant. The following controls are recommended:

(1) AQCapproved ND1specification and procedure to be used. (2) Periodic qualification of personnel conducting the inspection technique. This would normally include regularly scheduled vision examinations and inspection of astandard with aknown defect.

(3) Establishment of realistic acceptance standards for use by in-process and final inspection personnel.

(4) Calibration of equipment used in the inspection technique including any QCstandards with known defects that maybe used. The calibration system should provide for periodic requalification of any such equipment at specific time intervals.

(5) Aninternal audit program for validating the effectiveness of the ND1program.



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10. STORAGEANDHANDLING. Composite materials and adhesives maybesubject to deterioration if not stored under proper environmental conditions. Storing these materials at low temperatures (e.g., 0degrees) in freezers retards partial curing of polymer materials and extends their shelf life. Therefore, it is essential that composite material handling and storage procedures are established, followed, and subjected to periodic independent auditing to ensure continued conformity to the materials’ chemical, physical, and specified mechanical properties.

a. Uncured Material Storage. Because composite structures are made from polymeric materials (resins, prepregs, adhesives), procedures which ensure that these materials are acceptable at the time of use in the manufacturing area should beestablished.

(1) Material suppliers should provide documents with each shipment that identify the environmental conditions under which the purchased materia! waspreviously stored and shipped, i.e., temperature and humidity conditions and accumulated time in and out of refrigeration.

(2) Material should bestored under envir onmentally controlled conditions and m

onitored for compliance with specification requirements. Historical records for all stored material should bemaintained, i.e., periodic recording of storage conditions, time in and out of storage, etc.



### 13) Materials are generally stored in sealed plastic bags or containers to prevent moisture from condensing on the cold material and migrating into the polymer when it is removed from the freezer and allowed to warm to ambient temperature. The time interval from when the material is removed from the freezer to the time when the material bag or container maybe opened is generally empirically determined. Physical characteristics such as material roll, stacking height thickness, or material type (e.g., tape vs broadgoods) must beconsidered when determining this time interval. Therefore, the production approval holder or applicant should establish the minimum time interval between removal of material from its freezer and its use to prevent premature removal of materials from storage bags or containers before material temperature stabilization occurs. b. Handling of Cured Parts. Composite materials and structures require specific handling procedures to protect them from damage during production and storage. Accordingly, procedures for handling and storing composite materials and structures should beestablished and followed. These procedures should be an integral part of the manufactures’ QCsystem and should provide protection during receiving inspection, material. storage, material handling, manufacturing process, cure cycle, final inspection, and final product storage.

William J. Sullivan, Acting Director, Aircraft Certification Service

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APPENDIX 1. DEFINITIONS AC 21-26 Appendix 1

Adhesive. Asubstance capable of holding two materials together bysurface attachment. Structural adhesives produce attachments capable of transmitting significant structural loads.
Chemical Characterization. Aseries of chemical examinations to identify and/or quantify the critical constituents of amaterial and thereby establish afingerprint of the material which can beused asabasis for future comparison. Composite. Amaterial containing two or more distinct materials (fillers, reinforcing materials, and compatible plastic resin) designed to exhibit specific performance properties.
Cure. Tochange the physical properties of amaterial bychemical reaction, bythe action of heat and catalysts, alone or in combination, with orwithout pressure. Delamination. The separation of layers in alaminate through failure of the matrix.
Fiber. Asingle homogeneous strand of material used asaprincipal constituent in advanced composite materials because of its high axial strength and modulus.
Filament. -- Fiber of extreme length, used in yarns and other compositions.

arotating mandrel Process in which resin impregnated strands are applied over to produce high strength, reinforced cylindrical shapes.
Laminate. Aproduct obtained bybonding together two or more laminae of the same material or of different materials. Layupe Afabrication process involving the placement of successive layers of materials. Also, the arranged set of laminae.
Gelation. The formation of agel, which is ajelly like semi solid material state formed byanetwork of solid aggregates retaining aliquid phase.
Hand Layup. Method of positioning successive layers of reinforcement material (which mayor maynot bepreimpregnated with resin) onamold byhand. Resin is used to impregnateor coat the reinfor cured to permane ntly fix the formed Shapecement material. The resin is

Matrix. The essentially homogeneous material in which the fibers or filaments of acomposite material are imbedded. Polymer. Ahigh molecular weight organic material (natural or synthetic) formed by linking together alarge number of repeating chemical units (monomers). Whentwo or more monomers are involved, the product is called a copolymer.AC

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Appendix 1 6/26/89



### Preiapregnated Material 

### (Prepregl. Atermgenerally used to describe fibrous material which has been preimpregnated with aliquid resin andcured to the Bstage. Pultrusjon. Aprocess bywhich continuous lengths of fiber are pulled through apre-shaper of the desired cross-section andonthrough aheating source from which they emerge fully cured.
Resin. 

### Anyofthe various solid or semi-solid amorphous natural or synthetic organic substances with indefinite and usually high molecular weights and no sharp melting point.
Reinforcement Fibers. Materials 

### suchasroving, tow, andwoven fabric used to produce 

### astructural material superior to the base resin. Sandwich 

### Construction. Astructural panel concept consisting in its simplest form 

### oftwo relatively thin, parallel sheets (face sheets) of structural material bonded to, and separated by, arelatively thick, lightweight core. 

### Wetlayup. Aprocess inwhichdry fabric is laid into amold and impregnated with liquid resin 

### aspart of the layup process.