ASTM D7078/D7078M-05

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Designation: D7078/D7078M − 05
StandardTest Method for
Shear Properties of Composite Materials by V-Notched Rail
Shear Method
This standard is issued under the fixed designation D7078/D7078M; the number immediately following 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 an editorial change since the last revision or reapproval.
1. Scope inch-pound units are shown in brackets. The values stated in
each system are not exact equivalents; therefore, each system
1.1 This test method covers the determination of the shear
must be used independently of the other. Combining values
properties of high-modulus fiber-reinforced composite materi-
from the two systems may result in nonconformance with the
alsbyclampingtheendsofaV-notchedspecimenbetweentwo
standard.
pairs of loading rails. When loaded in tension, the rails
1.3 This standard does not purport to address all of the
introduce shear forces into the specimen through the specimen
safety concerns, if any, associated with its use. It is the
faces. In comparison, the specimen of Test Method D5379/
responsibility of the user of this standard to establish appro-
D5379M is loaded through its top and bottom edges. Face
priate safety and health practices and determine the applica-
loading allows higher shear forces to be applied to the
bility of regulatory limitations prior to use.
specimen, if required. Additionally, the present test method
utilizes a specimen with a larger gage section than the
2. Referenced Documents
V-notched specimen of Test Method D5379/D5379M. In both
test methods, the use of a V-notched specimen increases the
2.1 ASTM Standards:
gage section shear stresses in relation to the shear stresses in
D792Test Methods for Density and Specific Gravity (Rela-
the vicinity of the grips, thus localizing the failure within the
tive Density) of Plastics by Displacement
gage section while causing the shear stress distribution to be
D883Terminology Relating to Plastics
more uniform than in a specimen without notches. In
D2584Test Method for Ignition Loss of Cured Reinforced
comparison, Test Method D4255/D4255M utilizes an un-
Resins
notched specimen clamped between two pairs of loading rails
D2734TestMethodsforVoidContentofReinforcedPlastics
that are loaded in tension. Also in contrast to Test Method
D3171Test Methods for Constituent Content of Composite
D4255/D4255M, the present test method provides specimen
Materials
gripping without the need for holes in the specimen.
D3878Terminology for Composite Materials
The composite materials are limited to continuous-fiber or
D4255/D4255MTest Method for In-Plane Shear Properties
discontinuous-fiber-reinforcedcompositesinthefollowingma-
of Polymer Matrix Composite Materials by the Rail Shear
terial forms:
Method
1.1.1 Laminates composed only of unidirectional fibrous
D5229/D5229MTestMethodforMoistureAbsorptionProp-
laminae, with the fiber direction oriented either parallel or
erties and Equilibrium Conditioning of Polymer Matrix
perpendicular to the fixture rails.
Composite Materials
1.1.2 Laminates of balanced and symmetric construction,
D5379/D5379MTest Method for Shear Properties of Com-
withthe0°directionorientedeitherparallelorperpendicularto
posite Materials by the V-Notched Beam Method
the fixture rails.
D6856Guide for Testing Fabric-Reinforced “Textile” Com-
1.1.3 Laminates composed of woven, braided, or knitted
posite Materials
fabric filamentary laminae.
E4Practices for Force Verification of Testing Machines
1.1.4 Short-fiber-reinforced composites with a majority of
E6Terminology Relating to Methods of Mechanical Testing
the fibers being randomly distributed.
E111Test Method for Young’s Modulus, Tangent Modulus,
and Chord Modulus
1.2 The values stated in either SI units or inch-pound units
E122PracticeforCalculatingSampleSizetoEstimate,With
are to be regarded separately as standard. Within the text the
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.04 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Lamina and Laminate Test Methods. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved May 15, 2005. Published August 2005. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7078_D7078M-05. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7078/D7078M − 05
Specified Precision, the Average for a Characteristic of a
Lot or Process
E177Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
E251Test Methods for Performance Characteristics of Me-
tallic Bonded Resistance Strain Gauges
E456Terminology Relating to Quality and Statistics
E1237Guide for Installing Bonded Resistance Strain Gages
E1309 Guide for Identification of Fiber-Reinforced
Polymer-Matrix Composite Materials in Databases
E1434Guide for Recording Mechanical Test Data of Fiber-
Reinforced Composite Materials in Databases
2.2 Other Documents:
ANSI Y14.5M-1982 Geometric Dimensioning and Toler-
ancing
ANSI/ASME B 46.1-1985 Surface Texture (Surface
Roughness, Waviness, and Lay)
2.3 ASTM Adjuncts:
V-Notched Rail Shear Fixture Machining Drawings
FIG. 1 Material Coordinate System
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating
3.2.4.1 Discussion—The offset shear strength is a measure
to high-modulus fibers and their composites. Terminology
of the extent of material stress/strain linearity. (The material
D883definestermsrelatingtoplastics.TerminologyE6defines
non-linearityinthisdefinitionneitherassumesnorprohibitsthe
terms relating to mechanical testing. Terminology E456 and
presence of damage.) When comparing material offset
Practice E177 define terms relating to statistics. In the event of
strengths the same offset strain and modulus definition should
a conflict between terms, Terminology D3878 shall have
be used. For material comparison in the absence of evidence
precedence over the other terminology standards.
suggesting the use of more appropriate values, an offset strain
of 0.2% should be used with the standard chord modulus. A
NOTE 1—If the term represents a physical quantity, its analytical
graphical example of offset shear strength is shown in Fig. 2.
dimensionsarestatedimmediatelyfollowingtheterm(orlettersymbol)in
fundamental dimension form, using the following ASTM standard sym- For design, other offset strain and modulus definition combi-
bology for fundamental dimensions, shown within square brackets: [M]
nations may be more suitable for specific materials and
formass,[L]forlength,[T]fortime,[Θ]forthermodynamictemperature,
applications.
and [nd] for nondimensional quantities. Use of these symbols is restricted
to analytical dimensions when used with square brackets, as the symbols 3.2.5 shear strength [M/(LT )], n—the shear stress carried
may have other definitions when used without the brackets.
by a material at failure under a pure shear condition.
3.2 Definitions of Terms Specific to This Standard:
3.3 Symbols:
3.2.1 in-plane shear, n—shear associated with shear forces
A = cross-sectional area of a specimen
or deformation applied to the 1-2 material plane such that the
CV = coefficient of variation statistic of a sample
resultingsheardeformationsoccurintheplaneofthelaminate.
population for a given property (in percent)
(See also material coordinate system).
d = coupon width between notches
3.2.2 interlaminar shear, n—any of the shear properties
d = notch depth
describing the response resulting from a shear load or defor- su
F = ultimate shear strength in the test direction
mation applied to the 1-3 or 2-3 material planes. (See also u
F = ultimate strength in the test direction
material coordinate system).
F° (offset) = the value of the shear stress at the intersection
3.2.3 material coordinate system, n—a Cartesian coordinate of the shear chord modulus of elasticity and
system describing the principal material coordinate system the stress strain curve, when the modulus is
using 1, 2, and 3 for the axes, as shown in Fig. 1. offset along the shear strain axis from the
origin by the reported strain offset value
3.2.4 offset shear strength [M/(LT )], n—the shear stress a
G = shearmodulusofelasticityinthetestdirection
material sustains at the intersection of the shear stress versus
h = overall coupon thickness
engineering shear strain curve with a line parallel to a defined
L = overall coupon length
modulus and translated from the origin by a specified strain.
n = number of coupons per sample population
P = load carried by test coupon
f
P = load carried by test coupon at failure
max
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St., P = maximum load carried by test coupon before
4th Floor, New York, NY 10036.
failure
AvailablefromASTMHeadquarters,100BarrHarborDr.,POBoxC700,West
r = notch radius
Conshohocken, PA 19428-2959. Order Adjunct ADJD7078.
D7078/D7078M − 05
4.3 The notches influence the shear strain distribution in the
central region of the coupon, producing a more uniform
distribution 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 Use
5.1 This shear test is designed to 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 upon 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,methodsofmaterialpreparationandlay-up,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.
FIG. 2 Illustration of Modulus and Offset Strength Determination
5.2 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
S = standard deviation statistic of a sample popu-
n-1
2-1, 1-3 or 3-1, 2-3 or 3-2). Only a single shear plane may be
lation for a given property
evaluated for any given specimen. Properties, in the test
w = overall coupon width
direction, which may be obtained from this test method,
x = test result for an individual specimen from the
i
include the following:
sample population for a given property
5.2.1 Shear stress versus engineering shear strain response,
¯
X = mean or average (estimate of mean) of a
5.2.2 Ultimate shear strength,
sample population for a given property
5.2.3 Ultimate engineering shear strain,
γ = engineering shear strain
5.2.4 Shear chord modulus of elasticity,
ϵ = indicated normal strain from strain transducer
5.2.5 Transition strain.
or extensometer
σ = normal stress
6. Interferences
τ = shear stress
θ = ply orientation angle
6.1 Material and Specimen Preparation—Poormaterialfab-
rication practices, lack of control of fiber alignment, and
4. Summary of Test Method
damage induced by improper specimen machining are known
4.1 A material coupon in the form of a flat rectangle with
causes of high material data scatter in composites.
symmetrical centrally located V-notches, shown schematically
6.2 Elastic Modulus Measurement—Shear modulus calcula-
in Fig. 3, is clamped to two fixture halves (pictured in Fig. 4,
tionsinthistestmethodassumeauniformdistributionofshear
and shown schematically in Fig. 5 and in more detail in the
stress and shear strain in the region of the specimen between
machining drawings of ASTM Adjunct ADJD7078). When
the notch tips. The actual uniformity is dependent on the
loaded in tension using a mechanical testing machine, this
material orthotropy, the direction of loading, and the notch
fixture introduces shear forces in the specimen that produce
geometry (notch angle, notch depth, and notch radius). Refer-
failures across the notched specimen.
ring to the fiber orientations in Fig. 6, detailed stress analysis
4.2 Thespecimenisinsertedintothetwofixturehalveswith
(1) has shown that [0] specimens produce an elastic modulus
n
the notches located along the line of the applied load. The two
measurement that is too high (5-10% too high for carbon/
halves of the assembled fixture are extended by a testing
epoxy), whereas [0/90] specimens produce a relatively accu-
ns
machine while monitoring load. The relative displacement
rate elastic modulus measurement. Further, stress analysis has
between the two fixture halves produces shear stresses in the
shown that specimens with between 25% and 100% 645º
notched specimen. By placing two strain gage elements,
plies produce relatively accurate elastic laminate modulus
oriented at 645º to the loading axis, in the middle of the
measurements.
specimen and along the loading axis, the shear strain response
6.3 Specimen Geometry Modifications—Variations in the
of the material can be measured.
notch geometry (notch angle, notch depth, and notch radius)
affect the degree of nonuniformity of shear stress and shear
The fixture and specimen were developed at the University of Utah (1-3). This
work followed an earlier investigation on an improved rail shear test method at the
University of Wyoming Composite Materials Research Group (4 and 5). The Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
numbers in parentheses refer to the references listed at the end of the standard. this standard.
D7078/D7078M − 05
Nominal Specimen Dimensions
d = 31.0 mm [1.20 in.]
d = 12.7 mm [0.50 in.]
h = as required
L = 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 Schematic
FIG. 4 Partially Assembled Fixture with Specimen and Spacer Blocks
strain in the region of the specimen between the notches. notch angle, notch depth, and notch radius for the purpose of
Recommendations for notch dimensions versus the degree of increasing the uniformity of the shear stress/shear strain
material orthotropy have not been fully developed. Thus, a distributions for a particular material and laminate are accept-
single notch geometry has been adopted. Variations to the able when the variations are clearly noted in the report.
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