1、Designation: D 6415/D 6415M 06ae1Standard Test Method forMeasuring the Curved Beam Strength of a Fiber-ReinforcedPolymer-Matrix Composite1This standard is issued under the fixed designation D 6415/D 6415M; the number immediately following the designation indicates theyear of original adoption or, in
2、 the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEIn Paragraph 1.1, 0.25 mm was corrected to 0.25 in. and at the end of Paragraph 7.1.2, r
3、eference to 11.3 was addededitorially in January 2007.1. Scope1.1 This test method determines the curved beam strength ofa continuous fiber-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-
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 force 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
5、used to measure theinterlaminar tensile strength if a unidirectional specimen isused where the fibers run continuously along the legs andaround 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 th
6、is standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.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.
7、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.2. Referenced Documents2.1 ASTM Standards:2D 792 Test Methods for Density and Specific Gravity
8、(Rela-tive Density) of Plastics by DisplacementD 883 Terminology Relating to PlasticsD 3171 Test Methods for Constituent Content of CompositeMaterialsD 3878 Terminology for Composite MaterialsD 5229/D 5229M Test Method for Moisture AbsorptionProperties and Equilibrium Conditioning of Polymer Ma-trix
9、 Composite MaterialsD 5687/D 5687M Guide for Preparation of Flat CompositePanels with Processing Guidelines for Specimen Prepara-tionE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ing1This test method is under the jurisdiction of ASTM Com
10、mittee D30 onComposite Materials and is the direct responsibility of D30.06 on InterlaminarProperties.Current edition approved March 1, 2006. Published March 2006. Originallyapproved in 1999. Last previous edition approved in 2006 as D 6415 06.2For referenced ASTM standards, visit the ASTM website,
11、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.FIG. 1 Test Specimen Geometry (SI units)FIG. 2 Test Specimen Geometry (inch-pound)1Copyright ASTM International, 100
12、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E 122 Practice for Calculating Sample Size to Estimate,With a Specified Tolerable Error, the Average for aCharacteristic of a Lot or ProcessE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456
13、Terminology Relating to Quality and StatisticsE 1309 Guide for Identification of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE 1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in DatabasesE 1471 Guide for Identification of Fibers, Fillers, and
14、CoreMaterials in Computerized Material Property Databases3. Terminology3.1 DefinitionsTerminology D 3878 defines terms relatingto high-modulus fibers and their composites. TerminologyD 883 defines terms relating to plastics. Terminology E6defines terms relating to mechanical testing. TerminologyE 45
15、6 and Practice E 177 define terms relating to statistics. Inthe event of a conflict between terms, Terminology D 3878shall have precedence over the other terminologies.3.2 Definitions of Terms Specific to This Standard:NOTE 1If the term represents a physical quantity, its analyticaldimensions are st
16、ated 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, u for thermodynamic temperature,and nd for nondimensional quantities. Use o
17、f these 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.3.2.2 curved beam strength, CBS ML1T2, nthe momen
18、tper 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 the out-of-plane (through-the-thickness) direction.3.3 Symbols:3.3.1 CBS = curved b
19、eam 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 bars, respectively.3.3.4 D = diameter of the cylindrical loading bars on thefour-po
20、int-bending fixture.3.3.5 Er,Eu= 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 between the centerlines of the bottomloading bars on the four-point-bending fixture.3.
21、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 moment (see 3.2.1).3.3.12 P = total force applied to the four-point-bendingfixture.3
22、.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, u = cylindrical coordinates of any point in thecurved segment.3.3.16 ri,ro= inner and outer radii of curved segment.3.3.17 rm= radial position
23、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= test result for an individual specimen from thesample population for a given p
24、roperty.3.3.22 x= mean or average (estimate of mean) of a samplepopulation for a given property.3.3.23 D = relative displacement between the top andbottom halves of the four-point-bending fixture.3.3.24 k = parameter used in strength calculation.3.3.25 r = parameter used in strength calculation.3.3.
25、26 f = angle from horizontal of the specimen legs indegrees.3.3.27 fi= angle from horizontal of the specimen legs atthe start of the test in degrees (0.5 3 angle between the legs).3.3.28 sr= radial stress component in curved segment.4. Summary of Test Method4.1 A 90 curved-beam test specimen is used
26、 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 unidirectional with allfibers running continuously along the legs
27、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 bend with a 6.4-mm 0.25-in.inner radius. The curved beam is loaded in
28、 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 analyses are not easily performed.Failure criteria are varied and poo
29、rly 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 structural failure data for structural de-sign and analysis, quality
30、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 the following: material, methods of materialpreparation, methods o
31、f processing and specimen fabrication,D 6415/D 6415M 06ae12specimen preparation, specimen conditioning, environment oftesting, speed of testing, time at temperature, void content, andvolume percent reinforcement.6. Interferences6.1 Failure in non-unidirectional specimens may be initiatedfrom matrix
32、cracks or free edge stresses. Consequently, theinterlaminar strength calculated from non-unidirectional speci-mens may be in error.6.2 The stress state of a curved beam in four-point bendingis complex. Circumferential tensile stresses are produced alongthe inner surface, and circumferential compress
33、ive stresses areproduced on the outer surface. The radial tensile stress rangesfrom zero at the inner and outer surfaces to a peak in the middlethird of the thickness. Consequently, the failure should becarefully observed to ensure that a delamination(s) is producedacross the width before the failur
34、e data are used.6.3 Since stresses are nonuniform and the critical stress stateoccurs in a small region, the location of architectural charac-teristics of the specimen (for example, fabric weave, and towintersections) may affect the curved beam strength.6.4 Nonlaminated, 3-D reinforced, or textile c
35、ompositesmay fail by different mechanisms than laminates. The mostcritical damage may be in the form of matrix cracking or fiberfailure, or both, rather than delaminations.6.5 Material and Specimen PreparationPoor materialfabrication practices, lack of control of fiber alignment, anddamage induced b
36、y improper coupon machining are knowncauses of high material data scatter in composites in general.Important aspects of specimen preparation that contribute todata scatter include thickness variation, curve geometry, sur-face roughness, and failure to maintain the dimensions speci-fied in section 8.
37、26.6 The curved beam and interlaminar strengths measuredusing this test method are extremely sensitive to reinforcementvolume and void content. Consequently, the test results mayreflect manufacturing quality as much as material properties.Both reinforcement volume and void content shall be reported.
38、6.7 Specimens with low bending stiffness, or high values ofinterlaminar strength, or both, may exhibit excessive bendingof the specimen legs during flexural loading. This can createlarge errors in the calculated bending moment, resulting inunconservative strength calculations. A recommended limita-t
39、ion 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 reduce the flexure.7. Apparatus7.1 Testing MachineThe testing machine shall be inconformance with Practices E4, and shall satisfy the followingrequirements:
40、7.1.1 Testing Machine ConfigurationThe testing machineshall have both an essentially stationary head and a movablehead.7.1.2 Drive MechanismThe testing machine drive mecha-nism shall be capable of imparting to the movable head acontrolled velocity with respect to the stationary head. Thevelocity of
41、the movable head shall be capable of beingregulated in accordance with 11.3.7.1.3 Force IndicatorThe testing machine force-sensingdevice shall be capable of indicating the total force beingcarried by the test specimen. This device shall be essentiallyfree from inertia lag at the specified rate of te
42、sting 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 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 f
43、oreach 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” 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 t
44、o load the specimen.Machine drawings for example fixtures are shown in theappendix. Other designs that perform the necessary functionsare acceptable. 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 c
45、enters 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 IndicatorThe relative axial displace-ment between the upper and lower fixtures may be estimated asthe crosshead travel provided the deformation of the testingm
46、achine and support fixture is less than 2 % of the crossheadtravel. If not, this displacement shall be obtained from aproperly calibrated external gage or transducer located betweenthe two fixtures. The displacement indicator shall indicate thedisplacement with an accuracy of 61 % of the thickness o
47、f thespecimen.7.4 Force Versus Displacement (P Versus D) RecordAnX-Y plotter, or similar device, shall be used to make apermanent record during the test of force versus displacement.Alternatively, the data may be stored digitally and postpro-cessed.7.5 MicrometersThe micrometer(s) shall usea4to6mm0.
48、16 to 0.25 in. ball-interface on irregular surfaces such as thebag-side of a laminate, and a flat anvil interface on machinedFIG. 3 Curved Beam in Four-Point BendingD 6415/D 6415M 06ae13or very-smooth tooled surfaces. The accuracy of the instru-ments shall be suitable for reading to within 1 % of th
49、e samplewidth and thickness. For typical specimen geometries, aninstrument with an accuracy of 625 m 60.001 in. isdesirable for both thickness and width measurements.7.6 CalipersThe caliper(s) shall use a knife-edge inter-face on the curved surfaces of the specimen and a flat anvilinterface on machined or very-smooth tooled surfaces. Theaccuracy of the instruments shall be suitable for reading towithin 1 % of the sample width and thickness. For typicalspecimen geometries, an instrument with an accuracy of 625m 60.001 in.
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