Ceramic Matrix Composites In Design

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Ceramic Matrix CompositesIn Design
Lance L Snead
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Conventional Matrix Processes for SiC/SiC

• Chemical vapor infiltration (CVI) makes a good
  reference material
• Stoichiometric crystalline matrix
• Very good interface (interphase) control
• Alternate matrix processes need a lot more
  developmental work to be considered for
  fusion-grade materials
• Melt-infiltration (MI, RS, LSI, MSI, )
• Unreacted Si imposes creep and chemical
  instability issues
• Dual-phase SiC/Si matrix may cause severe
  irradiation damage
• Polymer impregnation and pyrolysis (PIP)
• Microporous nono-crystalline matrix results in
  very poor thermal conductivity
• Non-stoichiometric nano-crystalline matrix causes
  severe irradiation damage

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Fundamental Issues with Design
Currently there is a lack of uniform design
methodology for structural design with ceramic
composites. - ASTM procedures are lacking -
ASME approval 10 years following ASTM
data-basing - Prototyping or design-code?
Composite properties are intrinsically
anisotropic and unique to composite system.
QA of composites requires attention. At
present there have been no application of SiC
composites in nuclear systems. They have had
only limited application as structural material
in non-nuclear systems.
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ASTM Test Standards for Ceramic Matrix Composites
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First Nuclear Application? Gen IV Articulated
Composite Control Rod Segment
Control Rod Tube Architecture 45 braid (for
SiC variant)
SiC/SiC Nicalon Type S Fiber /
CVI SiC Matrix
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Reference NGNP-Grade SiC/SiC
Manufactured by Hypertherm, Inc Nicalon Type-S,
Multilayer SiC Interphase ICVI SiC Matrix
Density 2.9 g/cm3 Porosity 7 Fiber volume
fraction 40
20mm
SiC matrix
SiC/PyC multilayer
300mm
PyC
1mm
Hi-Nicalon Type-S fiber
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Joining SiC to SiC
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Joining Technology Integration for NITE-SiC/SiC
Kohyama
(a) NITE-process Joining
(b) Mechanical Joining
Kyoto University
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Definition of Key Tensile Parameters PLS

• Proportional Limit Stress (PLS)
• Matrix Cracking Stress (smc)
• Transition stress from elastic to quasi-ductile
  fracture.
• Depends on Youngs moduli of fiber, matrix and
  composites, interfacial friction stress, matrix
  fracture energy and misfit stress.

UTS

PLS
E
E. Vagaggini, et al., J. Am. Ceram. Soc. 78
(1995) 2709-2720.
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Definition of Key Tensile Parameters Tensile
Strength

• Ultimate Tensile Strength (UTS)
• Fracture strength
• Closely dependent on fiber strength and fiber
  volume fraction.

UTS

PLS
E
E. Vagaggini, et al., J. Am. Ceram. Soc. 78
(1995) 2709-2720.
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Evaluation on Damage Accumulation

• Matrix Crack Saturation Stress (ss)
• End of progressive matrix cracking.
• Beyond this stress, composite strength simply
  depends on fiber strength.
• Magnitude of matrix cracks can be estimated by
  damage parameter.
• Damage Parameter (D)
• Defined by elastic unloading (E).
• No damage when D0.
• Maximum Loop Width (demax)
• Enlarged hysteresis loop width implies the lower
  sliding stress (tf) and/or higher crack density
  (d).

UTS

Matrix Crack Saturation Stress (ss)
Maximum Loop Width (demax)
Elastic Unloading (E)
E. Vagaggini, et al., J. Am. Ceram. Soc. 78
(1995) 2709.
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Stress Criterions in Composite Failure
sx
s22
Longitudinal fiber direction
Tensile loading direction
q
s11
t12
1) s11 gt smc( a critical stress to initiate
transverse cracking, i.e., matrix cracking) 2)
s22 gt sdetach ( a critical stress to initiate
tunneling cracking by fiber detachment) 3) t12 gt
tshear ( a critical stress to initiate tunneling
cracking by in-plane shear)
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Axial and Off-axis Tensile Fracture Behavior
S/W-0º/90º
S/W-45º
Straight bar specimen 20L x 4W x 2.5T mm3

• PLS ( first matrix cracking stress) is
  recognized as a critical limit stress for the
  component design.

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First Matrix Cracking vs. Transverse Matrix
Cracking
? S/W-0/90 ? S/W-45
? S/W-0/90 ? S/W-45
? S/W-0/90 ? S/W-45
smc
sPLS
smc
smc

• Proportional limit tensile stress (first matrix
  cracking stress) indicates an initiation of
  microcracks in CMCs. The PLS of 2D CMCs is
  identical to a stress to initiate tunneling
  cracking in off-axis bundles.
• Secondary damage accumulation by transverse
  matrix cracking in the axial fiber bundles.

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Typical Properties of Orthogonal 2D CVI SiC/SiC
Composites (RT - 1200ºC)
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Anisotropy of Proportional Limit Stress
Vf 0.30.4, uni- or bi-axial CVI composites
Transverse matrix cracking stress (smc) of
unidirectional CMCs. cf.) smc of 2D composites
would be much lower.
? Braid, ? Braid ? S/W, ? UD ? P/W, S/W
Proportional limit in-plane shear stress, which
depends significantly on the fiber volume
fraction normal to the fracture plane.
Tunneling crack initiation stress of 0º/90º
CMCs.
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Design Stress Criteria

• Ceramic matrix composites, in the absence of
  environmental effects, will endure very long
  periods of service at stress below the point of
  matrix microcracking.
• Above matrix microcracking thermal conductivity
  and static and fatigue mechanical properties
  begin to degrade.
• Design should be based on operating stress below
  the matrix microcraking (or alternate failure
  mode) with an appropriate safety factor. Given
  the Weibull nature of CMC failure this safety
  factor should be generous.
• Design Stress lt 0.5 ?mc or lt 0.5 ?ILS
• Design Basis Accident lt 0.75 ?u ?

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Fracture Behavior of Composites and Irradiation

• Reinforcing fibers are the structural backbone.
• Fiber/matrix interface plays an important role.
• Composite performance is determined by various
  constitute properties.

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Radiation-induced electrical conductivity in SiC
7000 ohm-cm
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Typical Properties for 2D SiC/SiC ITER TBM Flow
Channel Insert Applications
No data available very rough estimate.
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Youngs Modulus of Composites Rule of Mixtures
E Youngs modulus n Poissons ratio V volume
fraction k transverse bulk modulus G transverse
shear modulus
Hi-Nicalon Type-S / CVI-SiC
10 uncertainty
Subscripts 1 embedded material 2 surrounding
material Superscripts A axial T transverse
1.8dpa 380C
1.0, 7.7dpa 800C
1.0dpa 800C
1.0dpa 1000C
7.7dpa 800C
1.0dpa 800C
1.0dpa 1000C
Open symbols indicate non-irradiated specimens
1.0dpa 1000C

• Transversely isotropic composite system.
• Fibers with carbon coating embedded in matrix.
• Matrix is assumed to have columnar pores, which
  are homogeneously distributed along the fiber
  bundles.

Z. Hashin, J. Appl. Phys. 46 (1979) 543-550.
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Strength of Composites Rule of Mixtures
E Youngs modulus n Poissons ratio V volume
fraction k transverse bulk modulus G transverse
shear modulus
Stress
Subscripts 1 embedded material 2 surrounding
material Superscripts A axial T transverse
Strain
.
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Irradiation Effect on Matrix Fracture Toughness
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Neutron Dose Dependent of Interfacial Shear
Strength Implications from Model Analysis
Hi-Nicalon Type-S / CVI-SiC

• Interfacial debond shear strength (IDSS) and
  interfacial friction stress (IFS) probably have a
  peak around the neutron dose level of 1 dpa,
  i.e., turn around.
• Turn-around of the shear properties are due
  primary to the differential swelling induced
  residual stress at the interface.
• Swelling behavior of PyC, which depends strongly
  on fast neutron fluence, has a significant
  influence on the turn-around behavior.
• Irradiation creep may relieve residual stresses
  at the interface, reducing the gap in the actual
  case.

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Irradiation Effect on Proportional Limit Stress
(PLS)

• Irradiation effect on PLS is very complicated
  issue
• Elastic moduli of fiber, matrix and composites
  are almost unchanged or slightly decreased.
• Matrix fracture energy may increase at higher
  temperature irradiation.
• Interfacial friction stress may change depending
  on neutron dose.
• Probably have relaxation of misfit stress by
  irradiation creep.

UD Hi-Nicalon Type-S / CVI-SiC
Non-irradiated
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Irradiation Effect on Fiber Strength

• No significant deterioration was reported for
  Hi-Nicalon Type-S SiC fiber up to 7.7 dpa over
  the wide temperature range of 300800ºC.

T. Nozawa, et al., J. Nucl. Mater. 329-333 (2004)
544-548.
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Survival Strength of Various SiC/SiC Composites
under Neutron Irradiation
UD Hi-Nicalon Type-S / CVI-SiC
PyC
Multilayer
Non-irradiated
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Irradiation Effect on Damage Accumulation

• Non-irradiated composites failed before the
  matrix crack saturation.
• Irradiated composites showed lower proportional
  limit tensile stress.
• Higher crack density and reduction of interfacial
  friction give larger loop width upon irradiation.
• Progressive matrix cracking regime for
  irradiated composites with the matrix crack
  saturation.
• ? Increased tensile strength and strain to
  failure by neutron irradiation.

UD Hi-Nicalon Type-S / 720nm PyC / CVI-SiC
Non-irradiated
7.7dpa, 800ºC
Y. Katoh, et al., submitted to J. Nucl. Mater.
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ASTM Test Standards for Ceramic Matrix Composites
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Definition of Key Tensile Parameters Youngs
Modulus

• Youngs Modulus (E) Initial tangent modulus
• Depends on fiber volume fraction and porosity.
• Irradiation-induced dimensional change may
  influence Youngs moduli of the constituents.

UTS

PLS
E
E. Vagaggini, et al., J. Am. Ceram. Soc. 78
(1995) 2709-2720.
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T-3 attaches to basal plane edges and highly
defected structure. More perfect material
and/or high temperature allows less retention.
NRL IFE 2/2001