03/09/051 high performance composites ray loszewski
Post on 29-Mar-2015
238 Views
Preview:
TRANSCRIPT
03/09/05 1
Systems
High Performance Composites
Ray Loszewski
03/09/05 2
Systems
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
03/09/05 3
Systems
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. http://www.nap.edu/execsumm/0309043379.html http://www.specmaterials.com/
03/09/05 4
Systems
Methods of Reinforcing Plastics, Metals, and Ceramics
Particulates
Short or long fibers, flakes, fillers
Continuous fibers or monofilaments
Source of sketches: http://www.nd.edu/~manufact/pdfs/Ch09.pdf
03/09/05 5
Systems
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.
Definitions adapted from: www.compositesworld.com High-Performance Composites Sourcebook 2004 Glossary
03/09/05 6
Systems
Fiber Size Comparison Chart
1.3 mil( 33 µ )
.5 Dia
.47 mil( 12 µ )
.28 mil( 7 µ )
1.3 mil1.0 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
Systems
Fiber Spinning Process Steps
Melt or Solution
Spinneret
Stretch(Orient)
and Solidify
Take-upor Idler
V0
V1
V1>V0
V2
V2≈V1 Packaging
Heat or Chemical Treatment
1st Step 2nd Step
03/09/05 8
Systems
(e.g. Nylon) (e.g. Kevlar) (e.g. Vectran)
(Source: Dupont Kevlar® and Celanese Vectran ® Brochures)
Orientation During Spinning
03/09/05 9
Systems
PAN Based Carbon Fiber Process
Polymerization
Spinning
Precursor
Stabilization
GraphitizationCarbonization
Surface Treat
Sizing
Carbon Fiber
1000-3000°C
03/09/05 10
Systems
PAN/Pitch Process Comparison
(Source: A. R. Bunsell, Fibre Reinforcements for Composite Materials, Amsterdam, The Netherlands: Elsevier Science Publishers B.V., 1988, p. 90.)
Polyacrylonitrile (PAN)
Pitch
Carbon/Graphite
03/09/05 11
Systems
Complete PAN Based Process
(Source: http://www.harperintl.com/carbon2.htm)
03/09/05 12
Systems
Carbon Fiber PropertiesTreatment Step (PAN)
Carbon (wt%)
Nitrogen (wt%)
Hydrogen (wt%)
Oxygen (wt%)
Untreated 68 26 6 -Thermoset 65 22 5 8Carbonized >92 <7 <0.3 <1Graphitized 100 - - -
GPa 106 psi GPa ksi
High Strength / Intermediate Modulus
228-283 33-41 3.45-4.83 500-700
High Modulus
379 55 2.41 350
Very High Modulus
517 75 2.07 300
Ultrahigh Modulus
690-827 100-120 2.24-2.41 325-350
Modulus StrengthFiber Grade
(Photo Source: A. R. Bunsell, Fibre Reinforcements for Composite Materials, Amsterdam, The Netherlands: Elsevier Science Publishers B.V., 1988, p.
203.)
03/09/05 13
Systems
Carbon Fiber Vs High Tensile Steel Density
(GPa) (ksi) (GPa) 106 psi (g/ccm) (GPa) 106 psiStandard Grade Carbon Fiber
3.5 500 230 33 1.75 2 290
High Tensile Steel
1.3 190 210 30 7.87 0.17 25
Tensile Strength Tensile Modulus Specific Strength Material
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
Systems
Specific Property Comparison*
http://www.advancedcomposites.com/technology.htm#properties
*Note: composite materials at 60% fiber volume with epoxy
03/09/05 15
Systems
(Source: Dupont Kevlar® Brochure 12/92)
Kevlar® Fiber Structure
03/09/05 16
Systems
(Internet Source – Lost Reference)
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.
03/09/05 17
Systems
(Internet Source – Lost Reference)
Photomicrograph of Kink Band
03/09/05 18
Systems
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
Systems
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
Systems
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)
+ 6HCl
03/09/05 21
Systems
Boron Filament Production
03/09/05 22
Systems
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
Systems
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)
0
10
20
30
40
50
300 450 600 750
Strengths (ksi)
Tensile Histogram
03/09/05 24
Systems
Fibers/Monofilaments/Hybrids
4 mil dia (100μ)0.5 mil dia (12μ)MatrixBoronTungsten
MatrixKevlar Fibers0.5 mil dia (12 μ)
Carbon Fibers0.3 mil dia (7 μ)
Conventional Boron/Graphite (Carbon) Hybrid
HyBor®
Versus
Void
Source of Top Photos: http://www.nd.edu/~manufact/pdfs/Ch09.pdf
03/09/05 25
Systems
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
Systems
Hy-Bor® Prepregging Process
03/09/05 27
Systems
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
Systems
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
Systems
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
Systems
Boron Doubler Reinforcement
03/09/05 31
Systems
Boron Doubler Installation
03/09/05 32
Systems
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
Systems
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
Systems
Construction of SCS Fiber for Strength and Matrix Compatibility
03/09/05 35
Systems
Schematic of SCS-6 CVD SiC
03/09/05 36
Systems
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
Systems
Comparison of SCS SiC Fibers
03/09/05 38
Systems
Comparison of SCS SiC Fibers
03/09/05 39
Systems
SCS-6 Strength Vs. Temperature
03/09/05 40
Systems
Comparison of Strength Vs. Temperature for SiC Fibers
03/09/05 41
Systems
Properties of Ti-6-4 Composites
Ti-6Al-4V SCS-6™Composite @ 35 v/o Ultra SCS
Composite* @ 29 v/o
Strength 120 Ksi 550 Ksi 225-250 Ksi 940 Ksi 318-324 Ksi
Modulus 16 Msi 56 Msi 28-30 Msi 60 Msi 28-29 Msi
Density .16 lb./in.³ .12 lb./in.³ .14 lb./in.³ .12 lb./in.³ .14 lb./in.³
* Similar properties were obtained for Ultra SCS/Ti-22Al-23Nb for improved oxidation and creep resistance
03/09/05 42
Systems
Transverse Optical Micrographs
Source: Vassel A., Pautonnier F., “Mechanical Behavior of SiC Monofilaments in Orthorhombic Titanium Aluminide Composites”, ICCM, Pékin (Chine), 25-29 June 2001
SCS-6/Ti-22Al-27Nb Composite. Ultra SCS Metal Matrix Composite
Source: Textron Specialty Materials
03/09/05 43
Systems
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
Systems
Carbon/Carbon Process Flow
High char yield polymer
or pitch
Carbon fiber
Preform fabrication
First Carbonization
(~1000°C)
Impregnation (CVD or RD)
Intermediate Graphitization 2500-3000°C
Carbonization 1000°C
Curing of polymer or Carbonization of pitch
under pressure
Impregnation with liquid
polymer or pitch
Final graphitization 2500-3000°C
C/C composite 1000°C
C/C composite
2500-3000°C
03/09/05 45
Systems
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
Systems
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
Systems
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
top related