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1 Test Methods for Fiber Reinforced Polymer (FRP) Composites John J. “Jack” Lesko Department of Engineering Science & Mechanics (540) 231-5259.

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Presentation on theme: "1 Test Methods for Fiber Reinforced Polymer (FRP) Composites John J. “Jack” Lesko Department of Engineering Science & Mechanics (540) 231-5259."— Presentation transcript:

1 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 2 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)

3 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 4 Key to Successful FRP Testing

5 5 Damage & Strength of Composites

6 6 Composite Damage Modes Tensile FailureCompression Failure Matrix Cracking & Delamination

7 7 Tensile Strength

8 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 -  ”.... ff ff  0 ff  

9 9 Tensile Stress Concentration at a Fiber Break

10 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 11 Stresses Around Filler Particles Monette, et al, J. Appl. Physics, 75 (3), 1994,

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

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

14 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  concentration (common problem in all specimens) Tab geometry Grip region geometry Grip pressure

15 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 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 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 18 Typical Tab Failures in Straight-Sided Coupons

19 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 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 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 22 Effect of Misalignment in Unidirectional Specimens

23 23 Compression Strength

24 24 Compression L = 41.8  m

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

26 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 27 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 Ramberg-Osgood shear response

28 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 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 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 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 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 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 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 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 36 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

37 37 Shear Strength

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

39 39 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

40 40 Shear Testing of Composites In-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

41 41 Shear Directions Material Coordinate System 1, 2, 3 S 23 S 12 S 13

42 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 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; t 12 and t 13 failure; edge delamination; s-concentration due to tabs

44 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 45 Stress Distribution in a Short Beam Shear Specimen Elasticity Solution Beam Theory

46 46 Interlaminar Fracture

47 47 Double Cantilever Beam (DCB) Test Data – ASTM D5528 a P  a1a1 a2a2 a3a3 anan

48 48 DCB Data Reduction: Modified Beam Theory y = x R 2 = Crack Length, a [m] Cube Root of Compliance C 1/3 (J/m 2 ) 1/3 x 1 m Find C: Plot C 1/3 vs a Find fit: a P  b=width

49 49 DCB Data Reduction: Compliance Calibration Method m2m2 1 Find C: Plot log(C) vs log(a) Find the slope m 2 a P  log(C) log(a) b=width

50 50 DCB Data Reduction: Compliance Calibration Method m3m3 1 Find C: Plot a/h vs C 1/3 Find the slope m 3 a P  a/h C 1/3 b=width

51 51 Edge Notch Flexure (ENF) P a L L b=width Load, P Mid-span Displacement,  95% of 1/C 1/C P Max P 95% P nl Of the uncracked region

52 52 QUESTIONS


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