shear test, +45 ° tension test, and 10° off-axis tension test were highly ranked by .... (0.15") with a notch tip radius 1.3mm (0.05"). .... notch roots and notch flanks for 90 ° and 0° specimens, respectively ... of ICCM VIII, July 15-19, SAMPE, 36-L, 1991. 9. .... to Specimen Along the Load. Introduction. Region. /I r. ;_'. 11.5m. G 2 w.
-x
NASA-CR-190660
if," ".,>._ - of,_--
0-3 AN
//5
FOR THE IOSIPESCU MODIFIED WYOMING
EXPERIMENTAL PROCEDURE SPECIMEN TESTED IN THE
6_I
COMPOSITE FIXTURE
H. Ho, M.Y. Tsai, J. Morton Department of Engineering Science and Mechanics Virginia Polytechnic Institute and State University Blacksburg, VA 24061-0219
_= E
and G.L. Farley US Army Aerostructures Directorate NASA Langley Research Center Hampton, VA 23665-5225
ABSTRACT
A detailed specimens
description
in the modified
gage instrumentation With
the proper
properties
of the experimental Wyoming
Interpretation
setup
for testing composite
f'Lxmre is presented.
are addressed.
experimental
procedure
Specimen
preparation
of the experimental
and procedure,
consistent
Iosipescu and strain
results
and repeatable
is discussed. shear
are obtained.
INTRODUCTION
Characterization mechanical shear
behavior
test methods
measurements Iosipescu
obtained pure
effect
of a laminated
composite
[1-6] have been
for composite
based
structures. to perform
Among
analysis stress
is needed
Since
these many
none of these
The
specimen, to account
10 ° off-axis
strengths
correction
test also produced
failed under for the coupling lower N92-31566
(NASA-CR-190660) AN EXPERIMENTAL PROCEDURE FOR THE IOSIPESCU COMPOSITE SPECIMEN TESTED IN THE MODIFIED WYOMING FIXTURE (Virginia Polytechnic 24
Inst.
and
State
by
test methods
for the shear-extension
tension
the
no specimen
an after-test
numerous
highly ranked
and the shear
because
of the
and strength
test were
fields in the test section
tension
the late 1960's,
shear test methods,
tension
[7]. However,
[9] in order
by the end constraints.
to the understanding
shear stiffness
were also questionable
For the 10 ° off-axis
shear modulus
is essential
test, and 10 ° off-axis
shear
from these test methods
caused
developed
materials.
on a decision
pure and uniform
shear [8-10].
apparent
shear properties
shear test, +45 ° tension
Lee & Munro produced
of the in-plane
Unclas
Univ.)
p G3/24
0115541
failure
stresses
shear
due to the bi-axial
strain distribution
neighboring
therefore,
+45 ° tension
specimens
in-plane
sequence
(sublaminate
and ply-level
fabric composites,
is attributed
widely
and simple
graphite-epoxy
specimen
investigators Nevertheless, from either
For example,
0 ° or 90 ° specimens
the shear moduli
between
stress-strain
a pure shear
in the 0 ° specimen
longitudinal
different
with the Iosipescu
that occurs
[10,16-19]
stiffness. because
[10,16]
\
\
using the Fig.2,
their specimens.
is caused
shear modulus
studies
strain distributions
showed
that,
were inconsistent.
are: (1) the inability
[10,16],
(2) the different
and (3) the large difference
by the specimen's
shear moduli
[10,16-19],
data for either fiber
shear test method
[10,16-19],
are
different
between
of the 0° specimens
2 \
between
for both 0 ° and 90 ° specimens
The measured the shear
test fixture,
from the 0 ° and 90 ° specimens
the 0° and 90 ° specimens
response
AS4/3501-6
were tested and the results
shear modulus
test
shear modulus
[13-15]
In recent
shear
procedure
was found in the measured
cut from the same panel
associated
of composite
and ease of
for unidirectional
from the same investigator.
obtained
must be used.
experimental
fractions
shear
short fiber
and inconsistent
shear moduli
of data scatter
the in-plane
systems
Wyoming
and +45 °
of the Iosipescu
of investigators
fiber volume
a pure shear state in the test section
shear moduli
large
of the measured
by different
a very large degree
The main problems
shear
by a number
to the large scatter in the measured
orientation,
to obtain
the shear modulus
the
that is, the
measurement
careful
than
and the stacking
composites,
of material
inaccurate
rather
measurement,
to measure
property
without
Fig. 1, and modified
The variations
may be caused
results,
measured
geometry,
both 0 ° and 90 ° specimens in addition
However,
with the
of the 10 ° off-axis
The popularity
a wide range
instrumentation.
composites
in Fig.3.
of testing
associated
is a laminate
test methods
shear test for shear
of the experimental
data can be obtained.
other shear
a_dused.
test, the
thickness
For multi-directional
investigated
to its capability
and interpretation
shown
the Iosipescu
+45 ° tension
effect [ 11,12];
The usefulness
the tests can only be applied
and woven
has been
Iosipescu
because
scaling
on the specimen
scaling).
composites.
In the past decade,
handling
is dependent
specimen
[8]. For strength
to a specimen
of unidirectional
composites,
materials
to free edge effects
shear strength
In the
local fluctuations
the +45 ° tension
are susceptible
tests is limited
properties
layers contained
[8]. In addition, it is subject
measured
tension
in the surface
sub-layer
a lamina;
stress state in the specimen.
[14-19].
The lack of
low transverse
for the 0 ° and 90 ° specimens in the test section
in
and are
of the 0 ° and
90° specimens arenonuniformandareof differentforms. Thelargeloaddistributionarea in thespecimen/fixture contactregionof the0° specimen[17]andpossiblelocalhardness alongthespecimen/fixture contactregionof the0° specimen's long edgesresultin inconsistentloadpointsbetweenspecimens.The variationin themeasuredshearmoduli for the 0° specimenis attributedto theeffectof theuncertaintyof loadpoints[10,17]. Due to thehigh transverse stiffnessof the90" specimen,twistingcanoccurwhenloadis applied [10]. Specimentwistingcausesdifferentshearstress-strain responses in thefront and backfacesof the specimen.Thevariationin themeasured shearmodulifor the90° specimenis causedby specimentwisting,whichis materialpropertyandspecimen dependent. In this paper,generalguidelines,ascurrentlypracticedby theauthors,for testingthe Iosipescucomposite specimen in the modified Wyoming fixture are presented. The above mentioned
problems
experimental
are addressed
setup, experimental
in the guidelines procedure,
TEST
in terms of specimen
and proper
interpretation
preparation,
of experimental
data.
PROCEDURE
Specimen Both unidirectional the in-plane
elastic
ply composite
(0 ° or 90 °) and cross-ply shear modulus
panels
The in-plane notches
at the opposite
3.8mm
(0.15")
2.5mm
(0.1")
to 6.3mm parallel
and 90 ° specimens,
Unidirectional comparison Due
tip radius
(0.25")
1.3mm
and perpendicular
Fig. 1. To avoid
in the specimens,
of the uncertainty shear
(0.05").
material.
are machined
Specimen
possible
and cross-
specifications.
(3" x .75") with two V-
axis, Fig. 1. The notch thickness
handling.
depth
variations
Specimens
modulus
is inevitable
[10].
from with
as the 0°
in the resin content
are trimmed.
from the same panel to render
on shear
is
ranging
axis are designated
of the panels
of how load is wansferred
modulus
Unidirectional
x 19.1ram
to facilitate
the edges
can be used to determine
to the manufacturer's
to the longitudinal
of the effect of fiber orientation
of the measured
center
is recommended
0 ° and 90 ° specimens
to the effect
variation
are 76.2mm
ends of the transverse
respectively,
and poor fiber alignment
according
of the specimen
with a notch
fiber directions
(G12) of a composite
are laid up and cured
dimensions
(00/90 °) specimens
measurement
direct
[10,16-19].
into the 0 ° specimens, The uncertainty
of load transfer
for the0° specimenis aninherentpropertyandtheeffectvariesbetweenspecimens. Therefore,the90° specimenis recommended for accurateshearmodulusmeasurement. Specimens werecutusinga diamondimpregnatedwheelsaw. The longedgesof the specimenweregroundflat andparallelto a toleranceof 0.0254mm(0.001"). Several specimens with backingmaterialwereheldin a viseon a grindingmachinetofacilitate cuttingthenotch. A 150mm(6") diameterabrasivegrindingwheelwith a tip radiusof 1.3ramwaspositionedatthecenterof the specimens heldin thevise. The rotationalspeed andthefeedrateof thegrindingwheelwere2,950RPMand0.4m/rain,respectively.The feedrateof thegrindingwheelshouldbekeptlow to preventdelaminationandsplitting nearthenotches.It hasalsobeendeterminedthata variationin measuredshearmodulus canoccurif thenotchesarenotlocatedatthecenterof thespecimen. Beforeattachmentof thestraingagerosettesto thespecimen,thetestsectionof the specimen(theregionbetweenthetop andbottomnotches)is sandedflat with finegrade sandpaper(600grit). Thespecimenthickness,t, in thetestsectionis thenmeasuredalong with thenotchwidth, w. Usually,threethicknessandwidthmeasurements aretakenand theaveragevalueis usedto calculatethetestsectioncross-section area(A=tw). Foreachfiber orientation,atleastfive specimens areprepared.Becausethethicknessof thepanelmaynot beuniformacrossthepanelandtheedgesof thepanelmayhave irregularities,suchaswavyfibers,thespecimenlocationon thepanelandspecimen thicknessarerecordedfor furtherreference.Any variationin specimenthicknessresultsin local changesin fibervolumefractionwhichcouldresultin changesin mechanical response.The authorsrecommendthepanelsshouldhaveno morethana 3 percent variationin thickness. Specimentwistinghasbeenshowntobea significantproblemwhentestingmaterial with a 90° ply (i.e.90° or 00/90° laminates).Toreducethetwistinginducedstrainsa compliantlayer(maskingtape)is appliedalongtheedgesof thespecimen,seeFig.1. The front andbackshearresponses of a 90° AS4/BMIPES(bismaleimidethermosetmatrixwith polysulfonethermoplasticadditive)Iosipescuspecimenbeforeandaftertheapplicationof themaskingtapesareshownin Fig.4. Theamountof specimentwistingdecreases after the applicationof thetape.In general,thedegreeof twistingdependsonthetransverse 4
stiffnessof the specimen.Formaterialwith low transverse stiffness,the distancebetween thedistributedforces[10]alongtheloadintroductionregionof the specimenandthe specimenmid-planedecreases astheappIiedloadincreases.Thusfor AS4/3501-6 graphite-epoxy compositematerials,the90° specimen(Ey=138GPa)twistswhilethe0° specimen(Ey=8.96GPa)doesnot [20]. Forisotropicmaterials,analuminumalloy specimen(Ey=E=70GPa)twistswhileanaluminumparticulatefilled epoxycomposite specimen(Ey=E=7.75GPa)doesnot [20]. Typicalshearstress-strain dataon thefront andbackfacesof the90° graphite-epoxy andaluminumspecimens areshownin Figs.5and 6. In Fig.5a,the shearstress-strain curvesareobtainedfromthefront andbackfacesof the samespecimenwhentestedfour differenttimesin thefixture. Thatis, thespecimen wasloadedwith onerosettefacingthefrontof thefixture andtheotherfacingthebackof thefixture. Thespecimenwasthenunloadedandrotated180° abouta horizontalor vertical axis, andloadedagain. Thewide separation of theshearstress-strain curvesindicatesthat the specimentwistingis sensitivetohowthespecimencontactsthetestfixture. By taking the averageof thefront andbackshearstrains,thevariabilityof the shearstress-swain data correspondingto thefour specimen-to-fixture contactpositionsof the samespecimenis greatlyreduced,Fig. 5b. Theresponseof analuminumalloy specimenis shownin Fig.6a. The significanttwisting,which is observedin Fig.6a,is eliminatedby the averagingtechnique,seeFig.6b. Thusthetwistingeffectis nota resultof material anisotropy. Instrumentation Measuring oriented
shear
strain in the test section
at +45 ° relative
expressed
to the longitudinal
of the specimen
requires
axis of the specimen.
at least two gages
The shear strain is
as
(1)
7xy = E+45 - E-45
where
e+45 and e...45 are the extensional
recommend
that for each panel,
gage rosettes
relative
expensive
unstacked
can be used.
at least one specimen
on the front and back
directions
surfaces.
to the longitudinal two-gage
The recommended
strains in the +45 ° strain gages.
rosettes
be instrumented
The authors with stacked
The three gages are orientated
axis of the specimen. oriented
at +45 ° and 0 °
practice,
at +45 ° to the specimens
gage length of the strain
5
For general
gages is 1.5ram.
three-
less
longitudinal
axis
The advantage
of usingthe stackedthree-gage rosettesrelativeto theunstackedtwo-gagerosettesis that the0° gageprovidesa meansof measuringspecimenout-of-planebending.Furthermore, the stackedthreegagerosettemeasures thestrainsovera commonregionin thetestsection whereastheunstackedtwo gagesmeasurethestrainsat two differentlocations[17]. For 0° Iosipescucompositespecimens, thestrainsrecordedby thetwo gagesin the_+45 ° directionsarenot equalin magnitudeandoppositein signasis thecasefor the90° specimens, Fig. 7. Thelackof symmetryin the+45 ° gage readings is attributed to the presence strain
of transverse
field is found
reference
normal
to be uniform
20 (orthotropic
calculated
using
direction
ratio ranging
equation
shear
To identify
(1) [17].
response
and quantify
to have
variations
in the measured
2. When
between
the bearing
rotate
forward.
which
can cause
the twisting surface
the shear
consistent
gages.
Specimen
studied
in
strain still can be at the 45 ° or-45
slides along
occurs.
would
axis.
stiffness
°
post is large, the movable portion
the in-plane
The magnitude is applied
be obtained.
effect
portion
induced
by averaging
6
to
having
of the fixture
induces
90 ° Fig. post
will
an eccentric
is different
on the back between
large variations
the front and back shear between
load
of the specimen,
strains whereas
of the specimen,
can be obtained
specimens.
is attributed
point to the guide
On the front surface
to one surface
responses
unequal
of specimens
of the effect of twisting
However,
to cause
is worn or if the tolerance
of the fixture
shear
it is
a guide post via roller bearing,
If the bearing
to slip in the fixture.
shear stress-strain
[10] by producing
of the load application
of the movable
strains reduce
has been shown
The twisting
and high transverse
about the horizontal
and the guide
on the shear response
twisting
for 90 ° specimens
the eccentricity
If only one rosette modulus
systems
gage is attached
and its influence
of the fixture
the specimen
the converse
specimens.
strains,
portion
The rotation
induced
normal
the value of the single gage strain, an
of the specimen.
of the test fixture
a moment
if a single
twisting
shear moduli
the load is applied,
will produce
for all the material
by doubling
strain
on the front and back surfaces
The movable
The transverse
from 1.0 to 15.4), thus, the shear
However,
specimen
back-to-back
rigid body rotation
[16].
will be obtained.
necessary
plies.
in the Lest section
and the shear strain calculated
erroneous
strains
strain ey in the test section
successive
of
:\
Strain weave
gages may be inadequate
fabric
weave,
composites.
cross-ply
Based
([0/9012s)
Figs.8a-Sb,
moire
distribution
across
architecture
of the woven
cross-ply
shear
fringe
upon
woven
bands
The she_
fabric
two gage rosettes.
Even
responses
Experimental
Wyoming
fixture,
configuration
which
provides
Wheatstone
bridge
is converted
about
using back-to-back strains,
the
see Fig. I0.
through
wall.
pin is lifted to engage
secured
in the fixture
with the adjustable
portion
of the fixture
which
is constrained
completion
controlled
box.
data acquisition
the specimen
portion
using
in the specimen,
wedge clamps.
system.
parts of the fixtures
is centered
is
should
be
of the fixture
an alignment
pin.
and the specimen
Load is applied
to move vertically
analog
The circuit
of the movable
The specimen
The
and the amplified
openings,
and stationary
the lower notch
with a half bridge
amplifier
any rotation
using a cross
of the strain gages.
into the fixture
The movable
the guide rod after load is applied.
Experimental
a circuit
is inserted
to be in the same plane to prevent
The alignment
bridge
compensation
to a micro-computer
specimen
the fixture
to the testing machine
to a signal conditioning
to digital signal
box is connected
against
downward
is
to the movable along a guide
rod.
procedure
An aluminum surfaces
with the
of six plain-weave,
were obtained
to a Wheatstone
temperature
is connected
the composite
adjusted
in
strain
is associated
the front and back shear
Fig.2, is attached
gages are connected
placed
for a plain-
shear
in strain
responses
specimens
are also inconsistent,
Strain
After
to undulating
stress-strain
after averaging
head adapter.
completion
fringe patterns
This variation
composite
of coarse
setup
The modified
signal
determination
[20] with 12k AS4 fiber, shown
correspond
see Fig.9.
fabric.
moire
composite
occur which
woven
stress-strain
shear modulus
u- and v-field
fabric
the test section,
([0°/90°]2s)
unstacked
for accurate
alloy specimen
of the specimen
test setup
produces
machine.
Agreement
any test setup errors.
with stacked
is tested
consistent between
three-gage
within the linear elastic
results
rosettes response
each time the test apparatus
subsequent
on the front and back
tests of the aluminum
region is placed
to ensure
that the
in the test
alloy specimen
minimize
Thereactionforcefromthespecimen,whichis alsotheequivalentappliedshearforce, P, in thetestsection,is obtainedfrom theloadcell connectedto thefixture. The shear stressis calculatedby dividing theshearforceP by thecross-sectional areaA (A=tw) in the testsection.A crosshead loadingrateof 0.5mm/minute(0.02irdminute)is used. Data
interpretation
The shear
stress-strain
on the minimum equivalent
cross-section
area covered
are nonuniform. specimens,
plotted
correction
factors
The correction
factors
forms
depend
for the material
Problems
shear fields
be applied
obtained
in question.
orthotropy
It has been shown
developed
swains over the
arise when
the shear fields
for either 0 ° or 90 °
of shear
modulus
[ 10,17-
from the 0 ° and 90 ° specimens
of the shear stress/swain
on the material
stresses
shear
in the test section
in calculation
shear moduli
shear
of the average
gage rosettes.
should
in the apparent
are the average
as a function
by the strain
due to the different
analysis
in Figs.4-6,
Due to the nonuniform
19]. The difference largely
responses,
distributions
is
in the test section.
and are defined
by a finite element
to be expressed
approximately
[17]
as
CF = 1.036
where
- 0.125
Ex and Ey are the longitudinal
respectively.
The corrected
(2)
x log(Ex/Ey).
shear
and transverse modulus
stiffnesses
G×y is expressed
of the specimen, as
Gxy = CF X G*
where
G* is the apparent
front and back
shear
the 90 ° specimens of the specimen. However,
increased
Iosipescu
specimens
using
The measured
shear
shear moduli
of load points between
the shear modulus
of the 0° specimen
and the difference greatly,
see Fig. 11.
Zave]Ygage, with '_ave = P/A and'Ygage = average
The distribution
is obtained
the measured
to uncertainty
shear modulus,
strains.
and 90 ° graphite-epoxy
reduced
(3)
between
of the measured is shown
the averaged moduli
for several
for several specimens. reduced
shear
modulus
in Fig. 11. The
90 ° specimens
shear modulus
0°
for
application
shear moduli
are consistent.
show a range
of values
of correction
while the shear modulus
the measured
for several
swain of the front and back surfaces
0 ° specimens After
shear
of
due
factors,
of the 90 ° specimen
of 0 ° and 90 ° specimens
is
Twistinghasbeenidentifiedasplayinganimportantrolesfor specimenswith high transversestiffness,(i.e.,90° and00/90° specimens).In additionto differentfrontand backshearstress-strain responses, twistingalsocauseslow failure stresses. Iosipescuspecimens (isotropic,0° or 90° unidirectionalcompositematerials)donot fail atthenotchaxiswherethecross-section areais a minimum. Themixedmodefailure is attributedto thepresenceof thetensilenormalstrains,Ex,andey, notch
roots and notch flanks
inherent
problem
The effect
due to the notch
design
of strain gage transverse
for 90 ° and 2.6%, transverse
for 90 ° and 0 ° specimens,
sensitivity
coefficient
[16,17],
of the
and is an
of the specimen.
sensitivity
for 0 ° graphite-epoxy
respectively
at the intersections
has been found
specimens
instrumented
to be negligible,
about
2%
with strain gages with a
kt = 2% [21].
CONCLUSIONS
For
0 ° and 90 ° graphite-epoxy
measurement
could
the experimental
occur
specimens,
if a proper
guidelines
significant
experimental
variations
procedure
for shear testing of the Iosipescu
in the shear modulus
is not followed. composite
In summary,
specimens
are as
follows.
1. The thickness
of the composite
panel should have
2. The edges of the panel from which constant
fiber
volume
fraction
the specimens
and straight
less than 3% variation. are cut should be trimmed
fibers.
3. Use slow feed rate in the cutting
of the notches.
4. Apply
long edges to reduce
masking
5. For accurate back 6. Apply
rosettes
tape at specimen
shear modulus should
a correction
modulus
measurement,
to ensure
specimen
90 ° specimens
twisting.
are recommended.
Back-to-
be applied. factor
of the composite
to the measured
shear modulus
material.
9
to obtain the corrected
shear
Following theproposedguidelinesandby properinterpretationof experimentalresults, extremelyconsistentin-planeshearmodulusdatausingtheIosipescuspecimentestedin the modifiedWyomingfixturecanbeobtained.
ACKNOWLEDGEMENTS This work hasbeensupportedby U.S.Army Aerostructures DirectorateunderNASA LangleyResearchCenterResearchGrantNAG-l-1053.
10
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11
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12 (3) :
(1990).
16. Ho, H., Tsai, M.Y., Morton, J. and Farley, G.L., "An Experimental Investigation Iosipescu Specimen For Composite Materials," Experimental Mechanics, 31 (4) • 328-336, 1991. 17. Ho, H., Tsai, M.Y., Morton, J. and Farley, G.L., "Numerical Analysis Of The Iosipescu Specimen For Composite Materials," Composite Science and Technology, in press. 18. Pindera, M.J., Choksi, G., I-Iidde, J.S. and Herakovich, C.T.,"A Methodology for Accurate Shear Characterization of Unidirectional Composites," Journal of Composite Materials, 21 (12) • 1164-1184, 1987. 19. Pindera, M.J., Ifju. P. and Post, D.,"Iosipescu and Metal Matrix Composites," Experimental 20.
Shear Characterization of Polymeric Mechanics, 30 (1) • 101-108, 1990.
Ho, H., Tsai, M.Y., Morton, J. and Farley, G.L.,"An Evaluation Specimen For Composite Materials Shear Property Measurement," Virginia Polytechnic Institute and State University, Aug. 1991.
Of The Iosipescu CCMS-91-18,
21. "Errors Due to Transverse Sensitivity in Strain Gages," M-M Tech Note TN-509: Transverse Sensitivity Errors, Measurements Group, Inc., Raleigh, NC.
12
Of
FIGURE CAPTIONS Fig.1 Modified Iosipescushearspecimen. Fig.2 Modified Wyomingfixture. Fig.3 Normalizedvaluesof in-planeshearmoduliobtainedfromIosipescusheartest on AS4/3501-6.Valuesarenormalizedwith respecttoG* 12=5.12GPa,the averageobtainedfrom + 45 ° tension and 10 ° off-axis tests [8]. The ranges shown in the figure are moduli deviation.
of repeatability
[15] or denote
one standard
Fig.4
Typical shear stress-strain data (a) before (b) after application of masking tapes to the specimen along load introduction region of a 90 ° AS4/BMIPES Iosipescu specimen.
Fig.5
(a) Front and back surface shear stress-strain data for a single 90 ° graphite-el_.xy specimen. Specimen was loaded in different orientations by rotating the sp.ecn'nen about the x, y and z axes. (b) Average of front and back surface shear strmns as a function of shear stress for 90 ° graphite-epoxy specimen.
Fig.6
(a) Front and back surface shear stress-strain data for a single aluminum specimen. Specimen was loaded in different orientations by rotating the specimen about the x, y and z axes. (b) Average of front and back surface shear stratus as a function of shear stress for aluminum specimen.
Fig.7
Strain vs. stress for typical (a) 0 ° and (b) 90" graphite-epoxy Gages are aligned at +45 ° and 0 ° directions.
Figs.
8a&b
Typical moire fringe pattems of the plain weave [0/9012s specimen at an applied shear stress of 142 MPa. (a) u-field, (b) v-field. Carrier rotation is applied such that the deformation information is equally contained in the uand v-fields.
Fig. 9 Shear strains across the notches, strain, for plain weave [0/9012s Fig. 10
Fig.11
specimen.
normalized specimens.
with respect
to the average
shear
(a) Shear stress-strain data from front and back faces, (b) average of front and back shear stress-strain data of six plain weave [0/9012s specimens. Calculated application
G12 for three graphite-epoxy of correction factors,
0 ° and 90 ° specimens,
13
before
and after
y
Application of Masking Tape to Specimen Along the Load Introduction Region
/I
/
r
;_'
fiber angle 91Y.
X
11.5m
G 2
/
76.2mm
91
E
/
Masking
w
fiber angle 0_
tape
T
Fig.1.
Modified
Iosipescu
shear
specimen.
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