1. Test Methods for Fiber Reinforced Polymer (FRP) Composites
John J. “Jack” Lesko
Department of Engineering Science & Mechanics
(540)
Introduction to Polymeric Adhesives and Composites Short Course
Copyright, 2004, J J Lesko, ESM, Virginia Tech,
Blacksburg, Virginia. All rights reserved.

2. Partial List of Standardization Groups
USA
American Society for Testing and Materials (ASTM)
MIL-HDBK-17 Committee (
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)

3. ASTM Standard Test Methods*
Definitions
D3878--Definitions of Terms Relating to High-Modulus Reinforcing Fibers and Their Composites
Fiber/Matrix Prepreg
C613--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 of ASTM Annual Book of Standards

4. Key to Successful FRP Testing
Stress Concentrations
Alignment
Uniformity of Stress

5. Damage & Strength of Composites

6. Composite Damage Modes
Matrix Cracking
& Delamination
Tensile Failure
Compression Failure

7. Tensile Strength

8. The tensile strength of a composite is controlled by the interface/phase, influencing the local stress concentrations and the size of the “ineffective length - d”.... f
 f   f 1 2 3 4 5 6 7 8

9. Tensile Stress Concentration at a Fiber Break

10. Tensile Strength Models
A very crude approximation of tensile strength from the Rule of Mixtures
More sophisticated models include
Batdorf, S. B. “Tensile strength of unidirectional reinforced composites--I,” Journal of Reinforced Plastics and Composites, Volume 1 (1982), pp
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
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.

11. Stresses Around Filler Particles
Monette, et al, J. Appl. Physics, 75 (3), 1994,

12. Pultrusion Fabrication Flaw
Microcrack -1.2mm long by .25mm wide
90º Tow
0º Tow
“As received” pultruded cross ply laminate (E-glass/Derakane )

13. Transverse Strength Models
Gibson, R. F. Principles of Composite Material Mechanics, McGraw Hill, New York (1994)

14. 0° and Laminate Tension Testing of Composites
Concerns in the Assessment of Modulus and Strength
Uniformity 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 s concentration (common problem in all specimens)
Tab geometry
Grip region geometry
Grip pressure

15. 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°

16. Straight-Sided Specimen
Advantages: No specimen tapering required; better results with cross-reinforced materials
Disadvantages: Tabbing required; tab s-concentration; tight tolerances in thickness

17. 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)

18. Typical Tab Failures in Straight-Sided Coupons

19. ASTM D 638 Type I “Dogbone” Specimen
Advantages: No tabbing required; load introduction less of an issue
Disadvantages: Careful specimen machining required; not suitable for unidirectional material

20. Streamline Specimen
Advantages: No tabbing required; load introduction less of an issue; comparable to straight-sided
Disadvantages: 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

21. Linear-Taped “Bowtie” Specimen
Advantages: No tabbing required; load introduction less of an issue
Disadvantages: Careful specimen machining required; not suitable for unidirectional material; large specimen

22. Effect of Misalignment in Unidirectional Specimens

23. Compression Strength

24. Compression
L = 41.8 mm

25. Compression Strength
An approximation of crushing strength from the Rule of Mixtures
Crushing
Compression Strength
Buckling
Slenderness ratio (r/L)

26. Compression Strength
Xu, Y. and Reifsnider, K. L. “Micromechanical modeling of composite compressive strength,” Journal of Composite Materials, Vol. 27 (6), (1993), pp

27. Compression Strength Ramberg-Osgood shear response
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

28. Compression Testing of Composites
Concerns in the Assessment of Modulus and Strength
Uniformity of stress state
End loaded
Shear loaded
Gage section dimensions
Sandwich beam
Gripping
Stress concentration
Tab geometry
Tabbing material
Alignment
Buckling
Failure modes
Specimen machining tolerance
Fixture characteristics

29. Compression Testing of Composites
Classes of Test Methods
Shear Loaded - Preferred
Celanese & Wyoming modified Celanese
IITRI (Illinois Institute of Technology Research Institute) & Wyoming modified IITRI
End Loaded
Boeing Compression ASTM D695 & Wyoming modified D695
Wyoming End Loaded Side Supported (ELSS)
RAE (Royal Aircraft Establishment)
Short Block Compression
Sandwich Beam
ASTM D3410, Method C--Flexure
Axially Loaded Sandwich Column

30. IITRI - ASTM D3410
Advantages: Alignment; high data averages and low scatter; large specimens possible
Disadvantages: Expense; specimen tabbing & machining critical; tab s-concentration

31. Celanese: ASTM D3410
Advantages: Alignment; high data averages and low scatter; long-standing test fixture
Disadvantages: Specimen tabbing & machining critical; tab s-concentration; sensitive to fixture accuracy; expense (latter two concerns addressed in Wyoming-modified)

32. Boeing Modified ASTM D695
Advantages: Small, thin specimen; reduced material; highly supported against buckling
Disadvantages: No s-e curve; untabbed for modulus; tabbed for strength; tab s-concentration

33. Wyoming End Loaded Side Supported (ELSS)
Advantages: No tabbing required; simple fixture; inexpensive; simple alignment; some shear loading
Disadvantages: End crushing for highly orthotropic specimens; support s-concentration; specimen tolerances critical

34. Sandwich Beam Flexure - ASTM D3410 (ASTM C 393)
Advantages: Simple fixture; reliable results with proper specimen (core) design
Disadvantages: Large specimens (materials expense); failure must occur in compressive face sheet

35. Axially Loaded Sandwich Column
Advantages: Simple fixture; simple data analysis; standard compression fixture
Disadvantages: Expense in fabricating sandwich panel; end crushing; end s-concentration

36. Other Compression Tests
Block Compression Test
Advantages: Simple untabbed specimen; simple fixture; inexpensive
Disadvantages: Thick specimen required; end crushing; end s-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

37. Shear Strength

38. Shear Strength Models
Gibson, R. F. Principles of Composite Material Mechanics, McGraw Hill, New York (1994)

39. Shear Testing of Composites
Concerns in the Assessment of Modulus and Strength
In-plane: t12
Interlaminar: t13
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 s concentration (common problem in all specimens)
Loading arrangement and assessment of results
Grip region geometry

40. Shear Testing of Composites
In-plane: t12
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: t13
Short Beam Shear ASTM D2344
Iosipescu ASTM D5379 (experimental)
bonded laminates

41. Shear Directions 3 S13 S12 S23 2 S12 S23 1 Material Coordinate System
1, 2, 3
S13

42. Iosipescu Shear Test ASTM D5379
Advantages: Excellent shear strength measurement; small specimen; 0°, 90°, [0°/90°]ns layups
Disadvantages: Tight tolerances on specimen; alignment; twist failure; quality fixture required; expense

43. (45)ns Tension ASTM D3518
Advantages: Simple; uniform stress state; no fixture; damage growth representative of laminates
Disadvantages: Tabbing; alignment; strength dependent on layup; scissoring; t12 and t13 failure; edge delamination; s-concentration due to tabs

44. Short Beam Shear ASTM D2344
Advantages: Simple test and fixture; small specimen
Disadvantages: Load introduction; no strain measurement; no modulus measurement; improper assumption of parabolic stress distribution; mixed mode failure

45. Stress Distribution in a Short Beam Shear Specimen
Elasticity Solution
Beam Theory

46. Interlaminar Fracture

47. Double Cantilever Beam (DCB) Test Data – ASTM D5528P D a1 a2 a3 an

48. DCB Data Reduction: Modified Beam Theory
b=width
y = x R 2 =
0.01
0.02
0.03
0.04
0.05
0.06
0.07
-0.05
0.1
0.15
0.2
Crack Length, a [m]
Cube Root of Compliance
C 1/3 (J/m2)1/3 x 1 m a P D
Find C:
Plot C1/3 vs a
Find fit:

49. DCB Data Reduction: Compliance Calibration Method
b=width a P D
log(C)
Find C:
Plot log(C) vs log(a)
Find the slope m2 m2 1
log(a)

50. DCB Data Reduction: Compliance Calibration Method
b=width a P D
Find C:
Plot a/h vs C1/3
Find the slope m3 m3
a/h 1
C1/3

51. Edge Notch Flexure (ENF)P
1/C
PMax
P95%
Pnl
95% of 1/C
Load, P a L L
Mid-span Displacement, D
b=width
Of the uncracked region

52. QUESTIONS