1 test methods for fiber reinforced polymer (frp) composites john j. “jack” lesko department of...
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Test Methods for Fiber Reinforced Polymer (FRP) Composites
John J. “Jack” LeskoDepartment of Engineering Science & Mechanics
[email protected] (540) 231-5259
Introduction to Polymeric Adhesives and Composites Short Course
Copyright, 2004, J J Lesko, ESM, Virginia Tech, Blacksburg, Virginia. All rights reserved.
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Partial List of Standardization Groups
_ USA– American Society for Testing and Materials (ASTM)– MIL-HDBK-17 Committee (http://www.mil17.org/)– Suppliers of Advanced Composite Materials Association (SACMA)
_ Europe– Deutsches Institut Fur Normung (DIN)– Association Francaise de Normalization (AFNOR)– British Standards Institute (BSI)
_ East– Japanese Industrial Standards
_ International– International Organization for Standardization (ISO)
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ASTM Standard Test Methods*
DefinitionsD3878--Definitions of Terms Relating to High-Modulus Reinforcing Fibers and Their
Composites
Fiber/Matrix PrepregC613--Test Method for Resin Content of Carbon and Graphite Prepregs by Solvent Extraction
D3379--Test Method for Tensile Strength and Young’s Modulus for High Modulus Single-Filament Materials
D3529--Test Method for Resin Solids Content of Carbon Fiber-Epoxy Prepreg
D3530--Test Method for Volatiles Content of Carbon Fiber-Epoxy Prepreg
D3531--Test Method for Resin Flow of Carbon Fiber-Epoxy Prepreg
D3532--Test Method for Gel Time of Carbon Fiber-Epoxy Prepreg
D3544--Guide for Reporting Test Methods and Results on High Modulus Fibers
D3800--Test Method for Density of High-Modulus Fibers
D4102--Test Method for Thermal Oxidative Resistance of Carbon Fibers
* Found in Vol. 15.03 of ASTM Annual Book of Standards
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The tensile strength of a composite is controlled by the interface/phase, influencing the local stress concentrations and the size of the “ineffective length - ”....
f
f
0f
1 2 3 4 5 6 7 8
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Tensile Strength Models
fm
tff
tt V1XVXX
A very crude approximation of tensile strength from the Rule of Mixtures
More sophisticated models includeBatdorf, S. B. “Tensile strength of unidirectional reinforced composites--I,” Journal of Reinforced Plastics and Composites, Volume 1 (1982), pp.153-176.
Gao, Z. and Reifsnider, K. L. “Micromechanics of tensile strength in composite systems,” Composite Materials: Fatigue and Fracture, Fourth Volume, ASTM STP 1156, W. W. Stinchcomb and N. E. Ashbaugh, Eds., ASTM, Philadelphia, (1993), pp. 453-470.
Reifsnider, K., Iyengar, N., Case, S. and Xu, Y. “Kinetic Methods for Durability and Damage Tolerance Design of Composite Components,” Keynote Address, Conference on Composite Materials, Japan Society for Mechanical Engineers, June 26, 1995, Tokyo.
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Pultrusion Fabrication Flaw
90º Tow
0º Tow
“As received” pultruded cross ply laminate (E-glass/Derakane 441-400)
Microcrack -1.2mm long by .25mm wide
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Transverse Strength Models
f2
m2
ffm
ttE
E1VV1YY
11
E
Er
E
YEY
f2
m2
hm2
mt
2t rV
hf 2
3
11
E
Er
E
YEY
f2
m2
sm2
mt
2t rV
sf 4
Gibson, R. F. Principles of Composite Material Mechanics, McGraw Hill, New York (1994)
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0° and Laminate Tension Testing of Composites
Concerns in the Assessment of Modulus and StrengthUniformity of stress state• Failure in the gage section (common problem between test specimens)
• Failure modes• Material misalignment (1° misalignment can yield a 30% strength reduction)
• Specimens with cross reinforcement
Gripping• Transition region concentration (common problem in all specimens)• Tab geometry• Grip region geometry• Grip pressure
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0° and Laminate Tension Testing of Composites
Specimen Types Used in Tensile Testing Straight-Sided Coupon--MRG Preferred
With and without tabs ASTM D638 Type I “Dogbone” Specimen Linear Tapered “Bowtie” Specimen
30% lower 0° strength compared to straight-sided specimen 10% lower 0° strength compared to dogbone specimen Woven cross-ply strengths dogbone or tabbed specimen
Streamline Specimen Comparable to straight-sided for 0°
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Straight-Sided Specimen
Advantages: No specimen tapering required; better results with cross-reinforced materialsDisadvantages: Tabbing required; tab s-concentration; tight tolerances in thickness
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Typical Failure Modes in Straight-Sided Coupons
(Acceptable & common in unidirectional specimens)
(Acceptable & common
in 90° or 90° dominated layups)
(May be found in crossply layups; unacceptable)
(Unacceptable)
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ASTM D 638 Type I “Dogbone” Specimen
Advantages: No tabbing required; load introduction less of an issueDisadvantages: Careful specimen machining required; not suitable for unidirectional material
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Streamline Specimen
Advantages: No tabbing required; load introduction less of an issue; comparable to straight-sidedDisadvantages: Careful specimen machining required; not suitable for unidirectional material; large specimen (12” [0°/90°]s; 24” [0°]) in order to keep the shear stresses low at the transition region
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Linear-Taped “Bowtie” Specimen
Advantages: No tabbing required; load introduction less of an issueDisadvantages: Careful specimen machining required; not suitable for unidirectional material; large specimen
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Compression Strength
fm
cff
cc V1XVXX
An approximation of crushing strength from the Rule of Mixtures
Co
mp
ress
ion
Str
eng
th
Crushing
Buckling
Slenderness ratio (r/L)
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Compression Strength
L
S S
Matrix
Fiber
Origin of Buckling Fiber's Sine Wave
c
c
2sin
2
GG2
r
kLG
L12
rE
E
V1EVEX
m12m
1232f
2m
122
32ff
1f1
fm
1ff
1c
L
s
4 ff
1
k
IEL 0L1
Ebk
fm
2ff
2
f2
m2
V1EVE
EEE
fm
12ff
12 V1V
Xu, Y. and Reifsnider, K. L. “Micromechanical modeling of composite compressive strength,” Journal of Composite Materials, Vol. 27 (6), (1993), pp. 572-588.
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Compression Strength
Fleck, N. A. and Budiansky, B. “Compressive failure of fibre composites due to microbuckling,” IUTAM Symposium, Troy, New York, May 29-June 1, (1990), pp. 235-273.
fiber
kink band T
T
L
L
1n
y7
31
G
n
1n
yn
1c
1n7
3n1
GX
Ramberg-Osgood shear response
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Compression Testing of Composites
Concerns in the Assessment of Modulus and StrengthUniformity of stress stateEnd loadedShear loadedGage section dimensionsSandwich beamGrippingStressconcentrationTab geometryTabbing materialAlignmentBucklingFailure modesSpecimen machining toleranceFixture characteristics
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Compression Testing of Composites
Classes of Test MethodsShear Loaded - PreferredCelanese & Wyoming modified Celanese IITRI (Illinois Institute of Technology Research Institute) & Wyoming modified IITRI
End LoadedBoeing Compression ASTM D695 & Wyoming modified D695Wyoming End Loaded Side Supported (ELSS)RAE (Royal Aircraft Establishment)Short Block Compression
Sandwich BeamASTM D3410, Method C--FlexureAxially Loaded Sandwich Column
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IITRI - ASTM D3410
Advantages: Alignment; high data averages and low scatter; large specimens possibleDisadvantages: Expense; specimen tabbing & machining critical; tab s-concentration
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Celanese: ASTM D3410
Advantages: Alignment; high data averages and low scatter; long-standing test fixtureDisadvantages: Specimen tabbing & machining critical; tab s-concentration; sensitive to fixture accuracy; expense (latter two concerns addressed in Wyoming-modified)
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Boeing Modified ASTM D695
Advantages: Small, thin specimen; reduced material; highly supported against bucklingDisadvantages: No s-e curve; untabbed for modulus; tabbed for strength; tab s-concentration
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Wyoming End Loaded Side Supported (ELSS)
Advantages: No tabbing required; simple fixture; inexpensive; simple alignment; some shear loadingDisadvantages: End crushing for highly orthotropic specimens; support s-concentration; specimen tolerances critical
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Sandwich Beam Flexure - ASTM D3410 (ASTM C 393)
Advantages: Simple fixture; reliable results with proper specimen (core) designDisadvantages: Large specimens (materials expense); failure must occur in compressive face sheet
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Axially Loaded Sandwich Column
Advantages: Simple fixture; simple data analysis; standard compression fixtureDisadvantages: Expense in fabricating sandwich panel; end crushing; end s-concentration
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Other Compression Tests Block Compression Test
Advantages: Simple untabbed specimen; simple fixture; inexpensive
Disadvantages: Thick specimen required; end crushing; end -concentration; misalignment sensitive
RAE Compression Test Advantages: No tabbing required; simple fixture;
inexpensive; shear and end loading Disadvantages: Not widely used; tolerance sensitive
for thickness taper; misalignment upon debonding; specimen buckling
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Shear Strength Models
rV
hf 2
3
rV
sf 4
Gibson, R. F. Principles of Composite Material Mechanics, McGraw Hill, New York (1994)
f12
m12
ffm
G
G1VV1SSSS
11
G
Gr
G
SSGSS
f12
m12
hm12
m
12
11
G
Gr
G
SSGSS
f12
m12
sm12
m
12
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Shear Testing of Composites
Concerns in the Assessment of Modulus and Strength
In-plane: 12
Interlaminar: 13
Uniformity of Stress State Failure in the gage section (common problem between test specimens) Failure modes: buckling out of plane; scissoring Material alignment Uniform shear
Load Introduction Transition region concentration (common problem in all specimens) Loading arrangement and assessment of results Grip region geometry
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Shear Testing of CompositesIn-plane: 12 Iosipescu ASTM D5379 (Preferred for shear strength) (45)ns Tension ASTM D3518 (Preferred for modulus) Off-axis Tension Rail Shear ASTM D4255 Torsion of bar (circular/rectangular) Torsion of a tube ASTM D5448
Interlaminar: 13 Short Beam Shear ASTM D2344 Iosipescu ASTM D5379 (experimental)
bonded laminates
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Iosipescu Shear Test ASTM D5379
Advantages: Excellent shear strength measurement; small specimen; 0°, 90°, [0°/90°]ns layupsDisadvantages: Tight tolerances on specimen; alignment; twist failure; quality fixture required; expense
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(45)ns Tension ASTM D3518
Advantages: Simple; uniform stress state; no fixture; damage growth representative of laminatesDisadvantages: Tabbing; alignment; strength dependent on layup; scissoring; t12 and t13 failure; edge delamination; s-concentration due to tabs
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Short Beam Shear ASTM D2344
Advantages: Simple test and fixture; small specimenDisadvantages: Load introduction; no strain measurement; no modulus measurement; improper assumption of parabolic stress distribution; mixed mode failure
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0
100
200
300
400
500
600
700
0 0.01 0.02 0.03 0.04
Displacement, m
Load
, P(N
)Double Cantilever Beam (DCB) Test Data – ASTM D5528
a
P
a1a2
a3
an
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DCB Data Reduction: Modified Beam Theory
y = 0.429941x + 0.001997R2 = 0.9997
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
-0.05 0 0.05 0.1 0.15 0.2
Crack Length, a [m]
Cub
e R
oot o
f Com
plia
nce
C 1/
3 (J
/m2 )
1/3
x
1m
•Find C:
•Plot C1/3 vs a
•Find fit:
a
P
PC
)xa(mC / 31
23 23( )
2I
Pm a x
b G b=width
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DCB Data Reduction: Compliance Calibration Method
2
2I
m P
ba
G
m2
1
•Find C:
•Plot log(C) vs log(a)
•Find the slope m2
PC
a
P
log(C
)
log(a)
b=width
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DCB Data Reduction: Compliance Calibration Method
3
2/33
2I
PC
m bhG
m3
1
•Find C:
•Plot a/h vs C1/3
•Find the slope m3
PC
a
P
a/h
C1/3
b=width
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Edge Notch Flexure (ENF)P
a
L L
b=widthLo
ad,
P
Mid-span Displacement,
95% of 1/C
1/CPMax
P95%Pnl
3
3
4bCh
LEflex
313
3
8/
flexcorr
CbhEa
2
3 3
9
2 (2 3 )corr i
IIcorr
Ca P
b L a
G
Of the uncracked region