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Implementation Challenges for High-Temperature Composites (1997) / Chapter Skim
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Life-limiting Mechanisms
Pages 16-21

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From page 16...
... Then, the key issue is that delaminations initiate subject to weakest-link scaling, with extreme variability arising from manufacturing flaws; that is, in this orientation, CMC performance is dominated by the low toughness matrix. Manufacturing flaws and other transverse cracks induce local temperature variations.
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From page 17...
... These stresses would cause premature failure. FIGURE 13 The shakedown and ratchetting regions in a TMC subject to transverse loads, AT, and cyclic temperature, AT: here, 60 is the matrix yield strength.
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From page 18...
... But even though ~ diminishes and increases AKtip, the crack growth rates are considerably lower than those for the monolithic alloy, because of the strong fiber bridging (LSB) effect [70,711.
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From page 19...
... However, this is a benign phenomenon, since matrix cracking is stable and, moreover, is the source of the inelastic strain that imparts stress redistribution capacity to the material. Corrosion Fatigue High-temperature forms of stress corrosion with attendant embrittlement pose major materials development and life prediction challenges [73,741.
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From page 20...
... When they have degraded sufficiently to fail, the surface cracks extend across the weakened zone and form new crack segments bridged by pristine reinforcements (see Figure 17~. This new bridged region again gradually weakens and fails.
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From page 21...
... Local oxidation interacts with the stress concentrations on the fibers to diminish their failure strength, causing the fibers to fail at the matrix crack. This process repeats, and the crack extends in a manner analogous to stress corrosion.
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Key Terms

  • manufacturing flaws
  • energy release
  • matrix cracks
  • release rate
  • matrix crack

  • friction stress
  • crack growth
  • hoop stresses
  • rapid crack
  • relatively rapid

  • corrosion cracking
  • using hysteresis
  • life prediction
  • transverse loads
  • fiber failure

  • matrix toughness
  • approach zero
  • thermal strains
  • imparts stress
  • crack acceleration

  • transverse cracks
  • yield strength
  • cmc performance
  • local temperature
  • oxygen gradients

  • premature fiber
  • flaw size
  • crack extends
  • degraded sufficiently
  • variability arising


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