1、Designation: D6415/D6415M 06a (Reapproved 2013)Standard Test Method forMeasuring the Curved Beam Strength of a Fiber-ReinforcedPolymer-Matrix Composite1This standard is issued under the fixed designation D6415/D6415M; the number immediately following the designation indicates theyear of original ado
2、ption 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 determines the curved beam strength ofa continuous fib
3、er-reinforced composite material using a 90curved beam specimen (Fig. 1 and Fig. 2). The curved beamconsists of two straight legs connected by a 90 bend with a6.4-mm 0.25 in. inner radius. An out-of-plane (through-the-thickness) tensile stress is produced in the curved region of thespecimen when for
4、ce is applied. This test method is limited touse with composites consisting of layers of fabric or layers ofunidirectional fibers.1.2 This test method may also be used to measure theinterlaminar tensile strength if a unidirectional specimen isused where the fibers run continuously along the legs and
5、around the bend.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
6、.1.4 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 value
7、sfrom the two systems may result in nonconformance with thestandard.2. Referenced Documents2.1 ASTM Standards:2D792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD883 Terminology Relating to PlasticsD3171 Test Methods for Constituent Content of Composit
8、eMaterialsD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for MoistureAbsorption Prop-erties and Equilibrium Conditioning of Polymer MatrixComposite MaterialsD5687/D5687M Guide for Preparation of Flat CompositePanels with Processing Guidelines for Specimen Prepara-tionE4 Practices
9、for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE122 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 Metho
10、dsE456 Terminology Relating to Quality and StatisticsE1309 Guide for Identification of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in DatabasesE1471 Guide for Identification of Fibers, Fillers,
11、and CoreMaterials in Computerized Material Property Databases3. Terminology3.1 DefinitionsTerminology D3878 defines terms relatingto high-modulus fibers and their composites. TerminologyD883 defines terms relating to plastics.Terminology E6 definesterms relating to mechanical testing. Terminology E4
12、56 andPractice E177 define terms relating to statistics. In the event ofa conflict between terms, Terminology D3878 shall haveprecedence over the other terminologies.3.2 Definitions of Terms Specific to This Standard:NOTE 1If the term represents a physical quantity, its analyticaldimensions are stat
13、ed immediately following the term (or letter symbol) infundamental dimension form, using the following ASTM standard sym-bology for fundamental dimensions, shown within square brackets: Mfor mass, L for length, T for time, for thermodynamic temperature,and nd for nondimensional quantities. Use of th
14、ese symbols is restrictedto analytical dimensions when used with square brackets, as the symbolsmay have other definitions when used without the brackets.3.2.1 applied moment, M ML2T2, nthe moment appliedto the curved test section of the specimen.1This test method is under the jurisdiction of ASTM C
15、ommittee D30 onComposite Materials and is the direct responsibility of D30.06 on InterlaminarProperties.Current edition approved Oct. 1, 2013. Published October 2013. Originallyapproved in 1999. Last previous edition approved in 2006 as D6415 06A1. DOI:10.1520/D6415_D6415M-06AR13.2For referenced AST
16、M standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohoc
17、ken, PA 19428-2959. United States13.2.2 curved beam strength, CBS ML1T2, nthe momentper unit width, M/w, applied to the curved test section whichcauses a sharp decrease in applied load or delamination(s) toform.3.2.3 interlaminar tensile strength, F3uML1T2, nthestrength of the composite material in
18、the out-of-plane (through-the-thickness) direction.3.3 Symbols:3.3.1 CBS = curved beam strength (see 3.2.2).3.3.2 CV = coefficient of variation statistic of a samplepopulation for a given property (in percent).3.3.3 dx,dy= horizontal and vertical distances between twoadjacent top and bottom loading
19、bars, respectively.3.3.4 D = diameter of the cylindrical loading bars on thefour-point-bending fixture.3.3.5 Er,E= moduli in the radial and tangential directions,respectively.3.3.6 F3u= interlaminar tensile strength (see 3.2.3).3.3.7 g = parameter used in strength calculation.3.3.8 lb= distance betw
20、een the centerlines of the bottomloading bars on the four-point-bending fixture.3.3.9 l0= distance along the specimens leg between thecenterlines of a top and bottom loading bar.3.3.10 lt= distance between the centerlines of the toploading bars on the four-point-bending fixture.3.3.11 M = applied mo
21、ment (see 3.2.1).3.3.12 P = total force applied to the four-point-bendingfixture.3.3.13 Pmax= maximum force applied to the four-point-bending fixture before failure.3.3.14 Pb= force applied to the specimen by a singleloading bar.3.3.15 r, = cylindrical coordinates of any point in thecurved segment.3
22、.3.16 ri,ro= inner and outer radii of curved segment.3.3.17 rm= radial position of the maximum interlaminar(radial) tensile stress.3.3.18 Sn1= standard deviation statistic of a sample popu-lation for a given property.3.3.19 t = average thickness of specimen.3.3.20 w = width of the specimen.3.3.21 x1
23、= test result for an individual specimen from thesample population for a given property.3.3.22 x= mean or average (estimate of mean) of a samplepopulation for a given property.3.3.23 = relative displacement between the top andbottom halves of the four-point-bending fixture.3.3.24 = parameter used in
24、 strength calculation.3.3.25 = parameter used in strength calculation.3.3.26 = angle from horizontal of the specimen legs indegrees.3.3.27 i= angle from horizontal of the specimen legs at thestart of the test in degrees (0.5 angle between the legs).3.3.28 r= radial stress component in curved segment
25、.4. Summary of Test Method4.1 A90 curved-beam test specimen is used to measure thecurved beam strength of a continuous-fiber-reinforced compos-ite material (Fig. 1 and Fig. 2). The curved beam strengthrepresents the moment per unit width which causes a delami-nation(s) to form. If the curved beam is
26、 unidirectional with allfibers running continuously along the legs and around the bendand an appropriate failure mode is observed, an interlaminar(through-the-thickness) tensile strength may also be calculated.The curved beam is uniform thickness and consists of twostraight legs connected by a 90 be
27、nd with a 6.4-mm 0.25-in.inner radius. The curved beam is loaded in four-point bendingto apply a constant bending moment across the curved testsection.An out-of-plane tensile stress is produced in the curvedregion of the specimen to cause the failure.5. Significance and Use5.1 Out-of-plane stress an
28、alyses are not easily performed.Failure criteria are varied and poorly validated. Interlaminarallowables are not readily available. However, stress analystsroutinely encounter structural details in which they cannotignore the out-of-plane loads. This test method is designed toproduce out-of-plane st
29、ructural failure data for structural de-sign and analysis, quality assurance, and research and devel-opment. For unidirectional specimens, this test method isdesigned to produce interlaminar tensile strength data. Factorsthat influence the curved beam strength and should therefore bereported include
30、 the following: material, methods of materialpreparation, methods of processing and specimen fabrication,specimen preparation, specimen conditioning, environment oftesting, speed of testing, time at temperature, void content, andvolume percent reinforcement.FIG. 1 Test Specimen Geometry (SI units)FI
31、G. 2 Test Specimen Geometry (inch-pound)D6415/D6415M 06a (2013)26. Interferences6.1 Failure in non-unidirectional specimens may be initiatedfrom matrix cracks or free edge stresses. Consequently, theinterlaminar strength calculated from non-unidirectional speci-mens may be in error.6.2 The stress st
32、ate of a curved beam in four-point bendingis complex. Circumferential tensile stresses are produced alongthe inner surface, and circumferential compressive stresses areproduced on the outer surface. The radial tensile stress rangesfrom zero at the inner and outer surfaces to a peak in the middlethir
33、d of the thickness. Consequently, the failure should becarefully observed to ensure that a delamination(s) is producedacross the width before the failure data are used.6.3 Since stresses are nonuniform and the critical stress stateoccurs in a small region, the location of architectural charac-terist
34、ics of the specimen (for example, fabric weave, and towintersections) may affect the curved beam strength.6.4 Nonlaminated, 3-D reinforced, or textile compositesmay fail by different mechanisms than laminates. The mostcritical damage may be in the form of matrix cracking or fiberfailure, or both, ra
35、ther than delaminations.6.5 Material and Specimen PreparationPoor material fab-rication practices, lack of control of fiber alignment, anddamage induced by improper coupon machining are knowncauses of high material data scatter in composites in general.Important aspects of specimen preparation that
36、contribute todata scatter include thickness variation, curve geometry, sur-face roughness, and failure to maintain the dimensions speci-fied in section 8.26.6 The curved beam and interlaminar strengths measuredusing this test method are extremely sensitive to reinforcementvolume and void content. Co
37、nsequently, the test results mayreflect manufacturing quality as much as material properties.Both reinforcement volume and void content shall be reported.6.7 Specimens with low bending stiffness, or high values ofinterlaminar strength, or both, may exhibit excessive bendingof the specimen legs durin
38、g flexural loading. This can createlarge errors in the calculated bending moment, resulting inunconservative strength calculations. A recommended limita-tion on crosshead displacement is provided in Section 12.Although outside of the scope of this test method, a doublermay be added to the legs to re
39、duce the flexure.7. Apparatus7.1 Testing MachineThe testing machine shall be in con-formance with Practices E4, and shall satisfy the followingrequirements:7.1.1 Testing Machine ConfigurationThe testing machineshall have both an essentially stationary head and a movablehead.7.1.2 Drive MechanismThe
40、testing machine drive mecha-nism shall be capable of imparting to the movable head acontrolled velocity with respect to the stationary head. Thevelocity of the movable head shall be capable of beingregulated in accordance with 11.3.7.1.3 Force IndicatorThe testing machine force-sensingdevice shall b
41、e capable of indicating the total force beingcarried by the test specimen. This device shall be essentiallyfree from inertia lag at the specified rate of testing and shallindicate the force with an accuracy over the force range(s) ofinterest of within 61 % of the indicated value.7.1.4 GripsEach head
42、 of the testing machine shall have ameans to hold half of the four-point-bending fixture firmly inplace.Aconvenient means of providing an attachment point foreach fixture half is through the use of a metal “T” in each grip.The lower part of the “T” is clamped in the grips, and the toppart of the “T”
43、 provides a flat attachment surface for eachfixture half.7.2 Four-Point-Bending FixtureA four-point-bending testapparatus as shown in Fig. 3 shall be used to load the specimen.Machine drawings for example fixtures are shown in theappendix. Other designs that perform the necessary functionsare accept
44、able. The cylindrical loading bars shall have diam-eters. D, of 6 to 10 mm 0.25 to 0.40 in. and be mounted onroller bearings. The distance between the bar centers shall be100 6 2 mm 4.00 6 0.05 in. (lb) for the bottom fixture and75 6 2 mm 3.00 6 0.05 in. (lt) for the top fixture.7.3 Displacement Ind
45、icatorThe relative axial displace-ment between the upper and lower fixtures may be estimated asthe crosshead travel provided the deformation of the testingmachine and support fixture is less than 2 % of the crossheadtravel. If not, this displacement shall be obtained from aproperly calibrated extern
46、al gage or transducer located betweenthe two fixtures. The displacement indicator shall indicate thedisplacement with an accuracy of 61 % of the thickness of thespecimen.7.4 Force Versus Displacement (P Versus ) RecordAnX-Y plotter, or similar device, shall be used to make apermanent record during t
47、he test of force versus displacement.Alternatively, the data may be stored digitally and postpro-cessed.7.5 MicrometersThe micrometer(s) shall usea4to6mm0.16 to 0.25 in. ball-interface on irregular surfaces such as theFIG. 3 Curved Beam in Four-Point BendingD6415/D6415M 06a (2013)3bag-side of a lami
48、nate, and a flat anvil interface on machinedor very-smooth tooled surfaces. The accuracy of the instru-ments shall be suitable for reading to within 1 % of the samplewidth and thickness. For typical specimen geometries, aninstrument with an accuracy of 625 m 60.001 in. isdesirable for both thickness
49、 and width measurements.7.6 CalipersThe caliper(s) shall use a knife-edge interfaceon the curved surfaces of the specimen and a flat anvil interfaceon machined or very-smooth tooled surfaces. The accuracy ofthe instruments shall be suitable for reading to within 1 % ofthe sample width and thickness. For typical specimengeometries, an instrument with an accuracy of 625 m60.001 in. is desirable for both thickness and width mea-surements.7.7 Conditioning ChamberWhen conditioning materialsat non-laborator
