N94-36399 Astm Test Methods For Composite Characterization And Evaluation

Composite Characterization Materials Test Characterization A list of test methods commonly in the following table. contained Type Tests employed in materials Properties : characterization Measured tests is Environmental Condition 0 Tension Strength, Ratio 90 Tension Strength, Ratio 0 Compression Strength, 90 Compression Strength, /- 45 Tension Modulus In-Plane Strength RTA Shear Modulus, Modulus, Poisson's Poisson's Modulus Modulus CTA, RTA, ETW CTA, RTA, ETW CTA, RTA, ETW CTA, RTA, ETW CTA, ETW RTA, Interlaminar Shear Strength RTA Intedaminar Tension Strength RTA Compression Strength, Laminate Open Hole Tension Open Hole Tension Modulus Strength (Fatigue) CTA, RTA, ETW CTA, ETW RTA, S - N Data RTA RTA Filled Hole Tension Strength Open Hole Compression Strength Filled Hole Compression Strength RTA Strength RTA Strength RTA GIC RTA GIIC RTA Compression after Bolt Bearing Tension Mode I Delamination Mode II Delamination Note: 2O Material : and Evaluation Bold CTA RTA ETW Impact Resistance Resistance Type indicates tests performed in Screening Evaluation indicates -65 o F/Ambient Moisture Conditions indicates Room Temperature/Ambient Moisture Conditions indicates Elevated Temperature/Saturated Moisture Conditions CTA, RTA, ETW

Composite Characterization Development Material : and Evaluation Of Design Allowables Objective: Develop Complete Design and Certification. Database Same Types of Tests Used in Materials Characterization Evaluations. Test Matrix Expanded : to Include for Screening Additional Configurations, Alternate Specimen Geometries Width/Diam. Ratios), Additional Environmental Conditions, More Replicate Tests on Samples Several Batches of Material. Could Total Certification Thousands of Tests Final Depending and Laminate (e.g. taken from on Requirements. 21

Composite Characterization Tests Applied TEST TYPE Material : and Evaluation to Laminated Tape Composites TE ;T METHOD TENSION: Unnotched ASTM D3039, D3518 MISC. COMPANY METHODS Notched SACMA SRM 5 NASA 1142- B9 COMPRESSION: Unnotched ASTM 3410 SACMA SRM1 NASA SHORT BLOCK MISC. COMPANY METHODS Notched SACMA SRM 3 NASA 1092 ST-4 MISC. COMPANY METHODS SACMA SRM 2 COMPRESSION AFTER IMPACT MISC. COMPANY BOLT BEARING INTERLAMINAR NASA 1142 Bll TENSION METHODS FLATWlSE TENSION CURVED BEAM INTERLAMINAR SHEAR ASTM D2344 MODE I DELAMINATION DOUBLE CANTILEVER MODE II DELAMINATION END NOTCHED FLEXURE BEAM Note: SACMA Indicates Test Methods Developed by the Suppliers of Advanced Composite Materials Association 22 :

Composite Characterization Physical Properties Prepreg Measured : Tape: Resin Content Fiber Content Volatile Cured Material : and Evaluation Content Laminates: Resin Content Fiber Content Void Content Density/Specific Gravity Glass Temperature Transition Equilibrium Thermal Heat Moisture (Dry and Wet) Content Conductivity Capacity Coefs. Thermal of Thermal Oxidative Expansion Stability 23

Development of Test Methods Textile Composites Program Objective As indicated below, develop a set of test methods physical properties Investigations developed address conducted largely Develop Test Techniques 24 materials to date have reinforced that existing lnstrumen For Textile stated, textile methods, preforms. which were may not adequately Mechanical ta tion Composites is to the mechanical forms. Recommended And simply with fibrous tape type composites, new material And Verify effort, to be used to measure indicated laminated of these Procedures of this on-going and guidelines to evaluate the subtleties : the objective of composite for and

Development Textile Statement of Problem The problem below. Simply composite reinforced tape. program. response accurately to be addressed stated, evaluate significantly of Test Methods Composites materials formed the braided, The fiber of these reflect textile TEST LAMINATED and stitched materials statements given were developed of pre-impregnated materials to be evaluated roll in determining methods to fiberdiffers in this the mechanical and practices materials? DEVELOPED FOR COMPOSITES ARCHITECTURE MATERIAL figures composite Will existing of these TAPE layers laminated materials. response METHODS TEXTILE in the previous will play a prime composite the material of these woven, architecture listed in the two bullet by laminating The microstructure from : is summarized the test methods for CONTROLS RESPONSE 25

Development of Test Methods Textile Composites Textile Composites Testing for Issues : It is not difficult to identify a number of specific testing issues relative to textile composites. Several of these concerns, which are applicable to virtually all of the test methods listed on the previous page, are listed below. The fin'st two reflect the unique size effects these materials may present. A unit cell is defined as the smallest unit of repeated fiber architecture. It may be considered the building block of the material. The size of the unit cell is dependent on a number of factors including the size of the yarns, the angle at which they are intertwined or interwoven, and the intricacy of the braid or weave pattern. A representative volume of material must be tested and monitored to accurately reflect true material response. Specimen geometry and strain gage sizes must be reexamined in terms of unit cell size. The effect of the sizes of the yarn bundles must also be considered since they may also affect the performance and the measurements. This is expressed in the third statement. The final three items on the list reflect concerns over specimen geometry. Test specimen dimensions established for tape type composites may not be applicable to textile composites. The degree of heterogeneity present in the latter materials is quite different than that encountered in the former. The potential effects of these differences must be also quantified. textile Moire A limited amount of relevant data has been developed for 2-D triaxially braided composites. These results will be reviewed in the following section. They include interferometry and strength and modulus measurements. EFFECT OF UNIT CELL SIZE ON MECHANICAL PERFORMANCE EFFECT GAGE EFFECT OF UNIT CELL OF TOW SIZE ON MECHANICAL ON STRAIN MEASUREMENTS AND FIBER ARCHITECTURE PERFORMANCE EFFECT OF FINITE WIDTH OPEN-HOLE SPECIMENS EFFECT OF EDGE PERFORMANCE ON UNNOTCHED CONDITIONS EFFECT OF TEXTILE PERFORMANCE 26 SIZE AND DISPLACEMENT THICKNESS AND ON MECHANICAL ON MECHANICAL

Development of Test Methods Textile Composites Program Approach A straightforward previous figure. the concerns braided, An extensive listed and stitched The general methods are supplied approach earlier. : has been test program The program, preform IDENTIFY AND/OR below. DESIGN Details AND MECHANICAL AND TEXT TEST Variety of Test Variety of Instrumentation Full Field Analytical IDENTIFY will include will consider IDENTIFY to meet the objective to gather outlined data a wide variety several loading of material tested in the addressing of woven, conditions. and test pages. CONFIGURATIONS CONDUCT which is outlined in the following adopted will be conducted architectures, approach for Strain DEVELOP SPECIMEN FIXTURES PROGRAM Methods Techniques Measurements Support SMALLEST LEVEL APPROPRIATE INSTRUMENTATION OF HOMOGENEITY TEST METHODS AND GUIDELINES 27

Development of Test Methods Textile Composites for Description of Material Tested : Preforms and Textile Parameters Studied Fifteen The preform indicated types type. braided, are listed in parentheses. each preform evaluated woven, The and stitched below in the table; the number reflects manufacturers TEXTILE will be evaluated table also lists the braid The list of materials by the aircraft preforms PREFORM parameter forms program. BRAIDS - (4) Size % Longitudinal Braid Tows Angle 3-D INTERLOCK Weave Warp, STITCHED WEAVE Type Weft, - (6) - (3) and Weaver UNIWEAVE Stitch Material Stitch Spacing Stitch Yarn - (5) Size MATERIALS 28 that will be varied TYPES 2-D TRIAXIAL Tow of each type to be tested the material in the ACT FIBER: HERCULES RESIN: SHELL 1895 AS4 in the program. Tow Size that are being is for

Development of Test Methods Textile Composites Description Triaxial of Material Braid Tested for : Pattern The specimens studied in this investigation featured 2-D triaxially braided AS4 graphite fiber preforms impregnated with Shell 1895 epoxy resin. In a triaxially braided preform three yarns are intertwined to form a single layer of 0"/ O" material. In this case, the braided yarns are intertwined in a 2 x 2 pattem. Each yam crosses alternatively over and under two - O yarns and vice versa. The 0 yams were inserted between the braided yarns. This yields a two dimensional material. The figure below schematically illustrates the fiber architecture and establishes the nomenclature used in the paper. The yams were braided over a cylindrical mandrel to a nominal thickness of 0.125 in. The desired preform thickness was achieved by overbraiding layers; there are no through-the-thickness fibers. After braiding, the preforms were removed from the mandrel, slit along the 0" fiber direction, flattened, and border stitched to minimize fiber shifting. The resin was introduced via a resin transfer molding process. ;in Braider olding yams Axial loading direction I Axial yarns Braid Transverse angle Ioading direction 29

Development of Test Methods Textile Composites Triaxial Braid Three preform in this study. angle per yarn. The parameters, proportion and yarn size. The AS4 fibers longitudinal yarns The preform parameters incorporating spacing. These MATERIAL Yarn expressed yarn were formed of carriers parameters in terms yarns they differed were in braid and is a function of filaments diameter in all cases. angle varied of 0 yarns. of the number have a nominal than the braided sizes; : as a percentage yarns to total yarn content size is expressed are listed 72 longitudinal the number is typically of longitudinal were larger had the same The fabrics listed Tested yarn size, and 0 yarn content, used in these materials architectures Since braid angle, The last parameter It is the volumetric of braid Configurations for of 7 microns. The B 1 and B2 and 0 yarn content. in the table. with a 144 cartier yarns. The mandrel was constant, New England diameters Butt triaxial varied this had the effect braider, for each architecture. of changing the yarn are also listed in the table. BRAID BRAIDER 0 YARN PATTERN YARN SIZE 0 YARN 0 YARN BRAID CONTENT SPACING YARN (Yarn/In.) SPACING SIZE (%) (Yarn/In.) A1 0/ 63 12K 24K 31.5 4.17 9.16 B1 0/ 66.5 6K 18K 37.6 4.77 11.98 B2 0/ 70 6K 18K 34.0 4.37 12.74 Note: K indicates microns 3O thousands. in diameter For the AS-4 yarns, each filament is 7

Development of Test Methods Textile Composites Unit Cell Definition for : A convenient way to describe textile preforms is to identify a unit cell of material - a repeatable unit of fabric geometry. The unit cell represents the complete yarn intertwinement pattern. The unit cell approach has become the foundation of textile analysis and serves as a convenient framework in which to interpret experimental data. The rhombic flame show in the figure defines a unit cell for the 2-D triaxially braided material studied in this program. For computational purposes, it is desirable to define the smallest unit cell possible. In some analyses, rectangular unit cells are also required. The rectangular section shown in the figure represents the smallest unit cell identified. The table shown below contains the dimensions of the unit cells for the three architectures tested. The unit cell width is dependent on the mandrel diameter and the number of yarns braided. The height of the unit cell is dependent on the cell width and the braid angle. Even though a conservative definition of the unit cell was applied in this case, the data in the table indicate that the unit cells can be quite large compared to typical specimen and strain gage dimensions. lUll UNIT MATERIAL CELL DIMENSIONS WIDTH (in.) HEIGHT A1 0.48 0.12 B1 0.42 0.09 B2 0.46 0.08 (in.) 31

MOIRI Axial Load INTERFEROMETRY - Vertical Displacement Field As indicated earlier, Moird interferometry was used to define the fullfield strain distribution in these braided specimens. The technique defines deformation patterns in both the vertical and horizontal directions. The technique was applied to specimens subjected to longitudinal and transverse loading. These results are shown in this and the following figures. The figure below illustrates the specimen geometry and highlights the section studied. The vertical displacement field that resulted when a specimen was loaded to 1200 micro-strain along the 0" fiber direction is also shown in the figure. The vertical displacement fields (V fields) consist of basically horizontal fringes; this indicates specimen extension where points along one fringe have been displaced vertically with respect to points along a neighboring fringe. For a uniform extension the fringes should be evenly spaced and straight. The fringes for the specimens tested, however, are wavy and the spacing between them varies. The variation is cyclic and coincides with the repeated unit of the textile architecture. ' - 1.50 N in. O* Fiber Direction iiii iiiiiii iiiii!iii iiiii i i!i iiii{iiii iiiiiiiii .:.:. iiiiii iiiiiiiii .50 in. :: :? : : :?!:? : : : : :? : : : : :;:;: : : : :? O Vertical 32 Displacement Field

MOIR] INTERFEROMETRY Axial Load - Horizontal Displacement Field The horizontal displacement patterns (U fields) consist of zigzag vertical fringes that display the Poisson's effect. For uniform conwacdon the fringes should be straight and the spacing constant. The fringes however display a variation which is cyclic, and matches that Of the braid geomen-y. The sharp kinks in the U field fringes reveal the presence of shear strains between the fiber bundles. - J 1.50 in. tO Direction Fiber N Horizontal Displacement Field 33

ENLARGED The figure that consists oudine shows bundles patterns as the distance presence of the resin of the width the resin rich zones Cy. Additionally, unit cell. within of the fiber between bundle the U field shows The and is nearly clearly shows was about constant Vertical Horizontal width Displacement Displacement and the at interfaces is consistent with the that the shear applied strain fringe y varies spacing. all of the resin Field Field The strain rich of one Txy in normal was nearly'constant that the strain in the was on the order 2 to 1. The normal throughout bundles is illustrated that of the average effect of specimen deformation which U field shows region fiber This bundles, by the nonuniform strain This lines. that the Poisson pattern ey to minimum bundles the fiber was on the order of 0.5 times unit cell as can be seen strain width. spaced itself. adjacent that the shear over a finite the closely rich areas The V displacement each maximum between OF SPECIMEN magnified between It was revealed occurred of the fiber of a highly The boundaries of the cells are marked. the fiber OF TWO UNIT CELLS (Axial Loading) the V and U fields of two unit cells. between fifth VIEW strain across the significantly ratio of varies zones. on top

SPECIMEN SECTION COINCIDING MOIRE FRINGE PATTERNS (Transverse Loading) Interferomeu-y direction these figure. was also performed on specimens (i.e. at 90" to the axial direction). This figaa'e specimens. The pattern The deformation fields of the surface that developed braided loaded shows yarns in these WITH in the transverse the re#on is shown coupons investigated schematically are shown in in the in the next two figures. 0 Fiber Direction 35

MOIRI Transverse Load. INTERFEROMETRY Vertical Displacement Field In general, the inte, erometry results indicate that greater variations in normal shear strains existed in specimens loaded in the transverse direction than in the axial dix tion. and This figure displays the vertical displacement fieId for a coupon loaded in the transverse direction. The location of the yarns is evident in the vertical displacement fi-inge patterns, where sudden jogs in the fringes represent strong shear strains in the resin rich regions between the yarns. From the V displacement pattern, the spacing of the fi'inges in the vertical direction displays a cyclic variation. The strains are highest over the region where there are 90 fibers under the braider yams. They are lowest over the regions where the braider yarns cross. The difference between the average strains in these areas is on the order of 3 times. Unlike the axial loading case, the cyclic variation is not confined to the dimensions of the unit ceil. The variation breaches the unit cell to form a global material response that covers the entire specimen. This is illustrated by the horizontal bands seen in the figure. They span several unit cetis and extend across the specimen width. 0 Fiber Direction Vertical 36 Displacement Field

Development Textile Effect of Strain of Test Methods Composites Gage for Size on Modulus : The inhomogeneity in the strain fields demonstrated in the Moir6 interferometric results discussed in the previous slides has significant implications with regard to specimen instrumentation. The large strain gradients seen within the unit cell graphically illustrate the need to measure strain over a truly representative volume of material to get an accurate determination of the global material response. Local strain readings can be misleading and confusing. The data shown in the figure below demonstrate these points. The figure plots the measured transverse modulus of several B 1 laminates vs. the size of the gages used to measure the strain. The gages ranged in length from 0.062 in. to 1.0 in.; the preform's unit cell measures 0.42 in. in this direction. The average modulus and the standard deviation of the data are shown in the figure. As the figure indicates, significant scatter was evident in the results obtained using the small gages. These effects are reduced as the length decreased of the gage increased. The results as strain gage size increased. The results instrumentation illustrate the n

astm d3039, d3518 misc. company methods sacma srm 5 nasa 1142- b9 astm 3410 sacma srm1 nasa short block misc. company methods sacma srm 3 nasa 1092 st-4 misc. company methods sacma srm 2 nasa 1142 bll misc. company methods flatwlse tension curved beam astm d2344 double cantilever beam end notched flexure