【astm標(biāo)準(zhǔn)】d 7078 - d 7078m - 12

1、Designation: D7078/D7078M ? 12Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method1This standard is issued under the fixed designation D7078/D7078M; the number immediately follo

2、wing the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (´) indicates

3、 an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the shear properties of high-modulus fiber-reinforced composite materi- als by clamping the ends of a V-

4、notched specimen between two pairs of loading rails. When loaded in tension, the rails introduce shear forces into the specimen through the specimen faces. In comparison, the specimen of Test Method D5379/ D5379M is load

5、ed through its top and bottom edges. Face loading allows higher shear forces to be applied to the specimen, if required. Additionally, the present test method utilizes a specimen with a larger gage section than the V-not

6、ched specimen of Test Method D5379/D5379M. In both test methods, the use of a V-notched specimen increases the gage section shear stresses in relation to the shear stresses in the vicinity of the grips, thus localizing t

7、he failure within the gage section while causing the shear stress distribution to be more uniform than in a specimen without notches. In comparison, Test Method D4255/D4255M utilizes an un- notched specimen clamped betwe

8、en two pairs of loading rails that are loaded in tension. Also in contrast to Test Method D4255/D4255M, the present test method provides specimen gripping without the need for holes in the specimen. The composite materia

9、ls are limited to continuous-fiber or discontinuous-fiber-reinforced composites in the following ma- terial forms: 1.1.1 Laminates composed only of unidirectional fibrous laminae, with the fiber direction oriented either

10、 parallel or perpendicular to the fixture rails. 1.1.2 Laminates of balanced and symmetric construction, with the 0° direction oriented either parallel or perpendicular to the fixture rails. 1.1.3 Laminates composed

11、 of woven, braided, or knitted fabric filamentary laminae. 1.1.4 Short-fiber-reinforced composites with a majority of the fibers being randomly distributed.1.2 The values stated in either SI units or inch-pound units are

12、 to be regarded separately as standard. Within the text the inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the oth

13、er. Combining values from the two systems may result in nonconformance with the standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility

14、 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 f

15、or Density and Specific Gravity (Rela- tive Density) of Plastics by DisplacementD883 Terminology Relating to Plastics D2584 Test Method for Ignition Loss of Cured Reinforced ResinsD2734 Test Methods for Void Content of R

16、einforced Plastics D3171 Test Methods for Constituent Content of Composite MaterialsD3878 Terminology for Composite Materials D4255/D4255M Test Method for In-Plane Shear Properties of Polymer Matrix Composite Materials b

17、y the Rail Shear MethodD5229/D5229M Test Method for Moisture Absorption Prop- erties and Equilibrium Conditioning of Polymer Matrix Composite MaterialsD5379/D5379M Test Method for Shear Properties of Com- posite Material

18、s by the V-Notched Beam MethodD6856 Guide for Testing Fabric-Reinforced “Textile” Com- posite MaterialsE4 Practices for Force Verification of Testing Machines E6 Terminology Relating to Methods of Mechanical Testing E111

19、 Test Method for Young’s Modulus, Tangent Modulus,1 This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.04 on Lamina and Laminate T

20、est Methods. Current edition approved July 15, 2012. Published December 2012. Originally approved in 2005. Last previous edition approved in 2005 as D7078/D7078M-05. DOI: 10.1520/D7078_D7078M-12.2 For referenced ASTM sta

21、ndards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website.

22、Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Pmax = maximum force carried by test coupon before failure r = notch radius Sn-1 = standard deviati

23、on statistic of a sample popu- lation for a given property w = overall coupon width xi = test result for an individual specimen from the sample population for a given property X ¯ = mean or average (estimate of mean

24、) of a sample population for a given property γ = engineering shear strain ε = indicated normal strain from strain transducer or extensometer σ = normal stress τ = shear stress θ = ply orientation angle4. Summary of Test

25、 Method4.1 A material coupon in the form of a flat rectangle with symmetrical centrally located V-notches, shown schematically in Fig. 3, is clamped to two fixture halves (pictured in Fig. 4, and shown schematically in F

26、ig. 5 and in more detail in the machining drawings of ASTM Adjunct ADJD7078).5 When loaded in tension using a mechanical testing machine, this fixture introduces shear forces in the specimen that produce failures across

27、the notched specimen.4.2 The specimen is inserted into the two fixture halves with the notches located along the line of the applied force. The two halves of the assembled fixture are extended by a testing machine while

28、monitoring force. The relative displacement between the two fixture halves produces shear stresses in the notched specimen. By placing two strain gage elements, oriented at 645º to the loading axis, in the middle of

29、 thespecimen and along the loading axis, the shear strain response of the material can be measured.4.3 The notches influence the shear strain distribution in the central region of the coupon, producing a more uniform dis

30、tribution than without notches. As a result of the reduced specimen width due to the notches, the average shear stress is increased relative to the unnotched width.5. Significance and Use5.1 This shear test is designed t

31、o produce shear property data for material specifications, research and development, quality assurance, and structural design and analysis. Either in-plane or interlaminar shear properties may be evaluated, depending upo

32、n the orientation of the material coordinate system relative to the loading axis. Factors that influence the shear response and should therefore be reported include: material, methods of material preparation and lay-up,

33、specimen stacking sequence, specimen preparation, specimen conditioning, environment of testing, specimen alignment and gripping, speed of testing, time at temperature, void content, and volume percent reinforcement.5.2

34、In anisotropic materials, properties may be obtained in any of the six possible shear planes by orienting the testing plane of the specimen with the desired material plane (1-2 or 2-1, 1-3 or 3-1, 2-3 or 3-2). Only a sin

35、gle shear plane may be evaluated for any given specimen. Properties, in the test direction, which may be obtained from this test method, include the following: 5.2.1 Shear stress versus engineering shear strain response,

36、 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 contro

37、l of fiber alignment, and damage induced by improper specimen machining are known causes of high material data scatter in composites.6.2 Elastic Modulus Measurement—Shear modulus calcula- tions in this test method assume

38、 a uniform distribution of shear stress and shear strain in the region of the specimen between the notch tips. The actual uniformity is dependent on the material orthotropy, the direction of loading, and the notch geomet

39、ry (notch angle, notch depth, and notch radius). Refer- ring to the fiber orientations in Fig. 6, detailed stress analysis (1)6 has shown that [0]n specimens produce an elastic modulus measurement that is too high (5-10

40、% too high for carbon/ epoxy), whereas [0/90]ns specimens produce a relatively accu- rate elastic modulus measurement. Further, stress analysis has shown that specimens with between 25 % and 100 % 645º plies produce

41、 relatively accurate elastic laminate modulus measurements.6.3 Specimen Geometry Modifications—Variations in the notch geometry (notch angle, notch depth, and notch radius)5 The fixture and specimen were developed at the

42、 University of Utah (1 and 2). This work followed an earlier investigation on an improved rail shear test method at the University of Wyoming Composite Materials Research Group (3 and 4). The numbers in parentheses refer

43、 to the references listed at the end of the standard.6 The boldface numbers in parentheses refer to the list of references at the end of this standard.FIG. 2 Illustration of Modulus and Offset Strength DeterminationD7078