# ASTM D7078D7078M-12

Designation: D7078/D7078M − 12Standard Test Method forShear Properties of Composite Materials by V-Notched RailShear Method1This standard is issued under the fixed designation D7078/D7078M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the shearproperties of high-modulus fiber-reinforced composite materi-als by clamping the ends of a V-notched specimen between twopairs of loading rails. When loaded in tension, the railsintroduce shear forces into the specimen through the specimenfaces. In comparison, the specimen of Test Method D5379/D5379M is loaded through its top and bottom edges. Faceloading allows higher shear forces to be applied to thespecimen, if required. Additionally, the present test methodutilizes a specimen with a larger gage section than theV-notched specimen of Test Method D5379/D5379M. In bothtest methods, the use of a V-notched specimen increases thegage section shear stresses in relation to the shear stresses inthe vicinity of the grips, thus localizing the failure within thegage section while causing the shear stress distribution to bemore uniform than in a specimen without notches. Incomparison, Test Method D4255/D4255M utilizes an un-notched specimen clamped between two pairs of loading railsthat are loaded in tension. Also in contrast to Test MethodD4255/D4255M, the present test method provides specimengripping without the need for holes in the specimen.The composite materials are limited to continuous-fiber ordiscontinuous-fiber-reinforced composites in the following ma-terial forms:1.1.1 Laminates composed only of unidirectional fibrouslaminae, with the fiber direction oriented either parallel orperpendicular to the fixture rails.1.1.2 Laminates of balanced and symmetric construction,with the 0° direction oriented either parallel or perpendicular tothe fixture rails.1.1.3 Laminates composed of woven, braided, or knittedfabric filamentary laminae.1.1.4 Short-fiber-reinforced composites with a majority ofthe fibers being randomly distributed.1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. Within the text theinch-pound units are shown in brackets. The values stated ineach system are not exact equivalents; therefore, each systemmust be used independently of the other. Combining valuesfrom the two systems may result in nonconformance with thestandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD883 Terminology Relating to PlasticsD2584 Test Method for Ignition Loss of Cured ReinforcedResinsD2734 Test Methods for Void Content of Reinforced PlasticsD3171 Test Methods for Constituent Content of CompositeMaterialsD3878 Terminology for Composite MaterialsD4255/D4255M Test Method for In-Plane Shear Propertiesof Polymer Matrix Composite Materials by the Rail ShearMethodD5229/D5229M Test Method for MoistureAbsorption Prop-erties and Equilibrium Conditioning of Polymer MatrixComposite MaterialsD5379/D5379M Test Method for Shear Properties of Com-posite Materials by the V-Notched Beam MethodD6856 Guide for Testing Fabric-Reinforced “Textile” Com-posite MaterialsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE111 Test Method for Young’s Modulus, Tangent Modulus,1This test method is under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.04 onLamina and Laminate Test Methods.Current edition approved July 15, 2012. Published December 2012. Originallyapproved in 2005. Last previous edition approved in 2005 as D7078/D7078M-05.DOI: 10.1520/D7078_D7078M-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1and Chord ModulusE122 Practice for Calculating Sample Size to Estimate, WithSpecified Precision, the Average for a Characteristic of aLot or ProcessE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE251 Test Methods for Performance Characteristics of Me-tallic Bonded Resistance Strain GagesE456 Terminology Relating to Quality and StatisticsE1237 Guide for Installing Bonded Resistance Strain GagesE1309 Guide for Identification of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases2.2 Other Documents:ANSI Y14.5M-1982 Geometric Dimensioning and Toler-ancing3ANSI/ASME B 46.1-1985 Surface Texture (SurfaceRoughness, Waviness, and Lay)32.3 ASTM Adjuncts:V-Notched Rail Shear Fixture Machining Drawings43. Terminology3.1 Definitions—Terminology D3878 defines terms relatingto high-modulus fibers and their composites. TerminologyD883 defines terms relating to plastics.Terminology E6 definesterms relating to mechanical testing. Terminology E456 andPractice E177 define terms relating to statistics. In the event ofa conflict between terms, Terminology D3878 shall haveprecedence over the other terminology standards.NOTE 1—If the term represents a physical quantity, its analyticaldimensions are stated immediately following the term (or letter symbol) infundamental dimension form, using the following ASTM standard sym-bology for fundamental dimensions, shown within square brackets: [M]for mass, [L] for length, [T] for time, [Θ] for thermodynamic temperature,and [nd] for nondimensional quantities. Use of these symbols is restrictedto analytical dimensions when used with square brackets, as the symbolsmay have other definitions when used without the brackets.3.2 Definitions of Terms Specific to This Standard:3.2.1 in-plane shear, n—shear associated with shear forcesor deformation applied to the 1-2 material plane such that theresulting shear deformations occur in the plane of the laminate.(See also material coordinate system).3.2.2 interlaminar shear, n—any of the shear propertiesdescribing the response resulting from a shear force or defor-mation applied to the 1-3 or 2-3 material planes. (See alsomaterial coordinate system).3.2.3 material coordinate system, n—a Cartesian coordinatesystem describing the principal material coordinate systemusing 1, 2, and 3 for the axes, as shown in Fig. 1.3.2.4 offset shear strength [M/(LT2)], n—the shear stress amaterial sustains at the intersection of the shear stress versusengineering shear strain curve with a line parallel to a definedmodulus and translated from the origin by a specified strain.3.2.4.1 Discussion—The offset shear strength is a measureof the extent of material stress/strain linearity. (The materialnon-linearity in this definition neither assumes nor prohibits thepresence of damage.) When comparing material offsetstrengths the same offset strain and modulus definition shouldbe used. For material comparison in the absence of evidencesuggesting the use of more appropriate values, an offset strainof 0.2 % should be used with the standard chord modulus. Agraphical example of offset shear strength is shown in Fig. 2.For design, other offset strain and modulus definition combi-nations may be more suitable for specific materials andapplications.3.2.5 shear strength [M/(LT2)], n—the shear stress carriedby a material at failure under a pure shear condition.3.3 Symbols:A = cross-sectional area of a specimenCV = coefficient of variation statistic of a samplepopulation for a given property (in percent)d1= coupon width between notchesd2= notch depthFsu= ultimate shear strength in the test directionFu= ultimate strength in the test directionF° (offset) = the value of the shear stress at the intersectionof the shear chord modulus of elasticity andthe stress-strain curve, when the modulus isoffset along the shear strain axis from theorigin by the reported strain offset valueG = shear modulus of elasticity in the test directionh = overall coupon thicknessL = overall coupon lengthn = number of coupons per sample populationP = force carried by test couponPf= force carried by test coupon at failure3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.4Available fromASTM Headquarters, 100 Barr Harbor Dr., PO Box C700, WestConshohocken, PA 19428-2959. Order Adjunct ADJD7078.FIG. 1 Material Coordinate SystemD7078/D7078M − 122Pmax= maximum force carried by test coupon beforefailurer = notch radiusSn-1= standard deviation statistic of a sample popu-lation for a given propertyw = overall coupon widthxi= test result for an individual specimen from thesample population for a given propertyX¯= mean or average (estimate of mean) of asample population for a given propertyγ = engineering shear strainε = indicated normal strain from strain transduceror extensometerσ = normal stressτ = shear stressθ = ply orientation angle4. Summary of Test Method4.1 A material coupon in the form of a flat rectangle withsymmetrical centrally located V-notches, shown schematicallyin Fig. 3, is clamped to two fixture halves (pictured in Fig. 4,and shown schematically in Fig. 5 and in more detail in themachining drawings of ASTM Adjunct ADJD7078).5Whenloaded in tension using a mechanical testing machine, thisfixture introduces shear forces in the specimen that producefailures across the notched specimen.4.2 The specimen is inserted into the two fixture halves withthe notches located along the line of the applied force. The twohalves of the assembled fixture are extended by a testingmachine while monitoring force. The relative displacementbetween the two fixture halves produces shear stresses in thenotched specimen. By placing two strain gage elements,oriented at 645º to the loading axis, in the middle of thespecimen and along the loading axis, the shear strain responseof the material can be measured.4.3 The notches influence the shear strain distribution in thecentral region of the coupon, producing a more uniformdistribution than without notches. As a result of the reducedspecimen width due to the notches, the average shear stress isincreased relative to the unnotched width.5. Significance and Use5.1 This shear test is designed to produce shear propertydata for material specifications, research and development,quality assurance, and structural design and analysis. Eitherin-plane or interlaminar shear properties may be evaluated,depending upon the orientation of the material coordinatesystem relative to the loading axis. Factors that influence theshear response and should therefore be reported include:material, methods of material preparation and lay-up, specimenstacking sequence, specimen preparation, specimenconditioning, environment of testing, specimen alignment andgripping, speed of testing, time at temperature, void content,and volume percent reinforcement.5.2 In anisotropic materials, properties may be obtained inany of the six possible shear planes by orienting the testingplane of the specimen with the desired material plane (1-2 or2-1, 1-3 or 3-1, 2-3 or 3-2). Only a single shear plane may beevaluated for any given specimen. Properties, in the testdirection, which may be obtained from this test method,include the following:5.2.1 Shear stress versus engineering shear strain response,5.2.2 Ultimate shear strength,5.2.3 Ultimate engineering shear strain,5.2.4 Shear chord modulus of elasticity,6. Interferences6.1 Material and Specimen Preparation—Poor material fab-rication practices, lack of control of fiber alignment, anddamage induced by improper specimen machining are knowncauses of high material data scatter in composites.6.2 Elastic Modulus Measurement—Shear modulus calcula-tions in this test method assume a uniform distribution of shearstress and shear strain in the region of the specimen betweenthe notch tips. The actual uniformity is dependent on thematerial orthotropy, the direction of loading, and the notchgeometry (notch angle, notch depth, and notch radius). Refer-ring to the fiber orientations in Fig. 6, detailed stress analysis(1)6has shown that [0]nspecimens produce an elastic modulusmeasurement that is too high (5-10 % too high for carbon/epoxy), whereas [0/90]nsspecimens produce a relatively accu-rate elastic modulus measurement. Further, stress analysis hasshown that specimens with between 25 % and 100 % 645ºplies produce relatively accurate elastic laminate modulusmeasurements.6.3 Specimen Geometry Modifications—Variations in thenotch geometry (notch angle, notch depth, and notch radius)5The fixture and specimen were developed at the University of Utah (1 and 2).This work followed an earlier investigation on an improved rail shear test methodat the University of Wyoming Composite Materials Research Group (3 and 4). Thenumbers in parentheses refer to the references listed at the end of the standard.6The boldface numbers in parentheses refer to the list of references at the end ofthis standard.FIG. 2 Illustration of Modulus and Offset Strength DeterminationD7078/D7078M − 123affect the degree of nonuniformity of shear stress and shearstrain in the region of the specimen between the notches.Recommendations for notch dimensions versus the degree ofmaterial orthotropy have not been fully developed. Thus, asingle notch geometry has been adopted. Variations to thenotch angle, notch depth, and notch radius for the purpose ofNominal Specimen Dimensionsd1= 31.0 mm [1.20 in.]d2= 12.7 mm [0.50 in.]h = as requiredL = 76.0 mm [3.0 in.]r = 1.3 mm [0.05 in.]w = 56.0 mm [2.20 in.]FIG. 3 V-Notched Rail Shear Test Specimen SchematicFIG. 4 Partially Assembled Fixture with Specimen and Spacer BlocksD7078/D7078M − 124increasing the uniformity of the shear stress/shear straindistributions for a particular material and laminate are accept-able when the variations are clearly noted in the report.6.4 Force Eccentricity—Twisting of the specimen duringloading can occur, affecting strength results, and especiallyelastic modulus measurement. Twisting may occur due to anout-of-tolerance fixture, an out-of-tolerance specimen, or froma specimen that is improperly installed in the fixture. It isrecommended that at least one specimen of each sample betested with back-to-back two-element strain ga