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High Performance Composites

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Presentation on theme: "High Performance Composites"— Presentation transcript:

1 High Performance Composites
Ray Loszewski Frequently, presenters must deliver material of a technical nature to an audience unfamiliar with the topic or vocabulary. The material may be complex or heavy with detail. To present technical material effectively, use the following guidelines from Dale Carnegie Training®. Consider the amount of time available and prepare to organize your material. Narrow your topic. Divide your presentation into clear segments. Follow a logical progression. Maintain your focus throughout. Close the presentation with a summary, repetition of the key steps, or a logical conclusion. Keep your audience in mind at all times. For example, be sure data is clear and information is relevant. Keep the level of detail and vocabulary appropriate for the audience. Use visuals to support key points or steps. Keep alert to the needs of your listeners, and you will have a more receptive audience. 03/09/05

2 Purpose of Presentation
Overview of boron, carbon, and silicon carbide fibers, prepregs and composite fabrication Differences in fiber structures, how made and used Performance characteristics; strengths/limitations Tailored coatings, surface treatments, and sizing Prepregs, preforms, and composite fabrication Hybrids; design and synergistic combinations Aging characteristics and composite repair Specialized applications; friction, re-entry, and etc. Important to understand the micromechanics In your opening, establish the relevancy of the topic to the audience. Give a brief preview of the presentation and establish value for the listeners. Take into account your audience’s interest and expertise in the topic when choosing your vocabulary, examples, and illustrations. Focus on the importance of the topic to your audience, and you will have more attentive listeners. 03/09/05

3 Disclaimer/Information Sources
Requirement to show/discuss only information or hardware that is in the public domain All photos/illustrations are from Internet sources or current owners (Textron originally), e.g. Nat'l Academies Press, High Performance Synthetic Fibers for Composites (1992) Some information is taken directly from websites and/or edited to fit slide format, e.g. 03/09/05

4 Methods of Reinforcing Plastics, Metals, and Ceramics
Particulates Short or long fibers, flakes, fillers Continuous fibers or monofilaments 03/09/05 Source of sketches:

5 Fiber Types Covered Herein
Boron (B) and silicon carbide (SiC) fibers are relatively large diameter (typically 2 – 8 mils) monofilaments produced by chemical vapor deposition onto a core material, usually a 0.5 mil tungsten-filament or a 1.3 mil CMF (carbon monofilament). Carbon fibers are produced by the pyrolysis of an organic precursor fiber, such as PAN (polyacrylonitrile), rayon or pitch, in an inert atmosphere at temperatures above 982°C/1800°F, typically 1315°C/2400°F, and contain 93-95% carbon. Carbonized fibers can be converted to graphite fibers by graphitization at 1900°C to 2480°C (3450°F to 4500°F) to yield >99% carbon. 03/09/05 Definitions adapted from: High-Performance Composites Sourcebook 2004 Glossary

6 Fiber Size Comparison Chart
1.3 mil ( 33 µ ) .5 Dia .47 mil ( 12 µ ) .28 mil ( 7 µ ) 1.0 Dia 4 mil 5.6 mil CVD Fibers Carbon Fibers Kevlar Fibers or Tungsten Filaments Carbon Monofilaments (CMF) (Scale 1000/1) 03/09/05

7 Fiber Spinning Process Steps
Melt or Solution Spinneret Stretch (Orient) and Solidify Take-up or Idler V0 V1 V1>V0 V2 V2≈V1 Packaging Heat or Chemical Treatment 1st Step 2nd Step 03/09/05

8 Orientation During Spinning
(e.g. Nylon) (e.g. Kevlar) (e.g. Vectran) (Source: Dupont Kevlar® and Celanese Vectran ® Brochures) 03/09/05

9 PAN Based Carbon Fiber Process
PAN Based Carbon Fiber Process Polymerization Spinning Precursor Stabilization Graphitization Carbonization Surface Treat Sizing Carbon Fiber °C 03/09/05

10 PAN/Pitch Process Comparison
Polyacrylonitrile (PAN) Pitch Carbon/Graphite 03/09/05 (Source: A. R. Bunsell, Fibre Reinforcements for Composite Materials, Amsterdam, The Netherlands: Elsevier Science Publishers B.V., 1988, p. 90.)

11 Complete PAN Based Process
03/09/05 (Source:

12 Carbon Fiber Properties
03/09/05 (Photo Source: A. R. Bunsell, Fibre Reinforcements for Composite Materials, Amsterdam, The Netherlands: Elsevier Science Publishers B.V., 1988, p. 203.)

13 Carbon Fiber Vs High Tensile Steel
Carbon fibers per se are not very useful A matrix is needed to transfer load from fiber to fiber and to hold everything together to form a composite An oxidative surface treatment is often needed to provide functionality or attachment points for bonding A coating or “sizing” protects fiber and facilitates wetting 03/09/05

14 Specific Property Comparison*
*Note: composite materials at 60% fiber volume with epoxy 03/09/05

15 Kevlar® Fiber Structure
(Source: Dupont Kevlar® Brochure 12/92) 03/09/05

16 Kink Bands and Fibrillation
Microfibril is the fundamental building block in highly oriented, high modulus fibers. These fibers typically have ten times weaker compressive strength than tensile strength. Local high angle bending or folding causes compressive strain and results in local, microfibrillar misorientation or kink bands. Once enough microfibrils are broken within the kink band, the entire fiber will fail. (Internet Source – Lost Reference) 03/09/05

17 Photomicrograph of Kink Band
(Internet Source – Lost Reference) 03/09/05

18 Why Boron or Boron Hybrids?
Typically, graphite or microfibrillar unidirectional lamina are compression strength limited High tensile strength is unavailable when cyclic loads and stresses limit the strength to the compression strength allowable Graphite fiber + Boron fiber are often matched to yield improved balance between tension and compression strength and modulus Increased strength efficiency translates to weight and cost savings 03/09/05

19 Boron Fiber Structure The fiber surface is nodular, with nodules oriented axially along the length. Fiber crystal structure is fine and complex with crystallite size on the order of 2 nanometers (amorphous). Large diameter and lack of well-defined crystalline structure leads to high compression properties. 03/09/05

20 Boron Reactor Schematic
Boron fiber is produced via CVD using the hydrogen reduction of boron trichloride on a tungsten filament in a glass tube reactor. The basic reaction, carried out at 1350°C, is as follows: 2BCl3(g) + 3H2 (g) = 2 B (s) HCl 03/09/05

21 Boron Filament Production

22 CVD Fiber Structural Limitation
CVD fibers are actually micro-composites Fiber structure depends on deposition parameters temperatures, gas composition, flow dynamics, etc. Theoretically, mechanical properties are limited by the strength of the atomic bonds that are involved Practically, strengths are limited by residual stresses and structural defects that are built in during CVD Residual stresses caused by volume differences in chemical reaction products, CTE mismatches during cool-down, etc. Structural defects caused by temperature gradients, power fluctuations, impurities/inclusions, gas flow instabilities, etc. Must maintain compressive stresses on fiber surface 03/09/05

23 Boron Fiber Properties
Tensile Strength 520 ksi (3600 MPa) Tensile Modulus 58 msi (400 GPa) Compression Strength ~1000 ksi (6900 MPa) Coefficient of Thermal Expansion 2.5 PPM/°F (4.5 PPM/°C) Density 0.093 lb/in³ (2.57 g/cm³) 03/09/05

24 Fibers/Monofilaments/Hybrids
4 mil dia (100μ) 0.5 mil dia (12μ) Matrix Boron Tungsten Kevlar Fibers 0.5 mil dia (12 μ) Carbon Fibers 0.3 mil dia (7 μ) Conventional Boron/Graphite (Carbon) Hybrid HyBor® Versus Void 03/09/05 Source of Top Photos:

25 Understanding Hy-Bor®
Hy-Bor® is a mixture of Boron and Graphite fibers commingled as a single ply High compression properties of Boron fiber improve Graphite fiber micro buckling stability Individually, each material is strain limited by the fiber properties Commingled, each fiber contributes and shares load according to principles of micromechanics 03/09/05

26 Hy-Bor® Prepregging Process

27 Hy-Bor® Compression Strength
Compression Strength of Hy-Bor® directly relates to Shear Modulus* Increasing Boron fiber count increases compression strength towards theoretical 600 ksi limit * “The Influence of Local Failure Modes on the Compressive Strength of Boron/Epoxy Composites”, ASTM STP 497, J.A. Suarez, J.B. Whiteside & R.N. Hadcock, 1972 “Influence of Boron Fiber Count on Compressive and Shear Properties of HyBor”, Alliant Techsystems, J.W. Gillespie,1986 03/09/05

28 Benefits of Hy-Bor® Provides the Maximum Compression Strength of any continuous filament-based composite material Tailored to meet specific materials properties and design objectives (Graphite fiber type and Boron fiber ratio) Prepregged to customer resin preferences Analytically treated as another lamina within a laminate stack per Classical Lamination Theory Can be mixed with carbon plies or it can be the total laminate (maximum fiber volume) 03/09/05

29 Aging and Composite Repair
Properties may deteriorate over time by exposure to high temperatures, moisture, UV radiation, or other hostile environments Degradation may be reversible or permanent; chemical (oxidation) or mechanical (fatigue) Cracks may be patched using “doublers” or adhesively bonded reinforced epoxies Aluminum structures cannot be repaired using graphite/epoxy due to galvanic corrosion issues Boron/epoxy doublers gaining acceptance 03/09/05

30 Boron Doubler Reinforcement

31 Boron Doubler Installation

32 SCS Family of SiC Fibers
Boron was ineffective in metal matrices CVD SiC made by similar process using less costly gases SCS offers Improved strength at higher temperatures Optimized surface for handling and bonding SCS-6 (5.6 mil) Developed for titanium and ceramics SCS-9A (3.1 mil) Developed for thin-gauge face sheets for NASP SCS-ULTRA (5.6 mil) Developed to achieve highest strength 03/09/05

33 SCS SiC Fiber Process CMF vs. tungsten Pyrolytic graphite
Complex chemistry and glassware High maintenance Multistage reactor Integral surface coating region Each run optimized 03/09/05

34 Construction of SCS Fiber for Strength and Matrix Compatibility

35 Schematic of SCS-6 CVD SiC

36 Brittle Fracture Characteristics
Distribution of strengths rather than single value Imperfections lead to stress concentrations Fracture initiates because material cannot deform plastically Cracks typically originate at defects on the core, at interfaces or the surface 03/09/05

37 Comparison of SCS SiC Fibers

38 Comparison of SCS SiC Fibers

39 SCS-6 Strength Vs. Temperature

40 Comparison of Strength Vs. Temperature for SiC Fibers

41 Properties of Ti-6-4 Composites

42 Transverse Optical Micrographs
Source: Vassel A., Pautonnier F., “Mechanical Behavior of SiC Monofilaments in Orthorhombic Titanium Aluminide Composites”, ICCM, Pékin (Chine), June 2001 SCS-6/Ti-22Al-27Nb Composite. Ultra SCS Metal Matrix Composite Source: Textron Specialty Materials 03/09/05

43 Carbon/Carbon Composites
Unimpressive properties at ambient but offers combination of high-temperature resistance to 2760°C (5000°F), light weight, and stiffness Expensive due to difficult processing, pore closure Rapid Densification (RD™) Applications Rocket nozzles, Re-entry Brake linings, discs, torque converters (wet friction) 03/09/05

44 Carbon/Carbon Process Flow
Curing of polymer or Carbonization of pitch under pressure High char yield polymer or pitch Impregnation with liquid polymer or pitch Carbonization 1000°C Preform fabrication First Carbonization (~1000°C) Intermediate Graphitization °C C/C composite 1000°C Final graphitization °C C/C composite °C Carbon fiber Impregnation (CVD or RD) 03/09/05

45 Ceramic-Matrix Composites
Major hurdle is to overcome brittleness Traditional reinforcements are not very effective because cracks still propagate Conversely, SCS-6 fibers impart strength and toughness to ceramics because their carbonaceous surface coating layer arrests and/or deflects the energy, which allows for bridging of any cracks 03/09/05

46 Applications Drive Technology
Aerospace/Defense applications emphasize enabling technologies and performance Competition is more effective than consortia Many promising technologies languish due to funding cuts or satisfaction with status quo e.g. NASP and Superconducting Supercollider “chicken/egg” cost dilemma and public apathy Commercial applications emphasize availability and cost, i.e value for the dollar Competitive edge and marketability are important e.g. Sports equipment, fuel cells, solar, and etc. 03/09/05

47 Closing Comments Composite design starts with the reinforcement
Fiber choice depends upon the application; must weigh advantages/disadvantages, cost, etc. Matrix selection (polymeric, metal, carbon, ceramic) often dictates fiber type and material form, i.e. whether to use tow, fabric, tape, and etc. Key to solving most problems is knowledge of: How fibers are made; why they behave as they do Role of coatings, surface treatments, and sizing Reactions at the fiber surface during processing Focus on the micromechanics at interfaces Determine the best close for your audience and your presentation. Close with a summary; offer options; recommend a strategy; suggest a plan; set a goal. Keep your focus throughout your presentation, and you will more likely achieve your purpose. 03/09/05

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