Chemistry:Fiber pull-out
Fiber pull-out is one of the failure mechanisms in fiber-reinforced composite materials.[1] Other forms of failure include delamination, intralaminar matrix cracking, longitudinal matrix splitting, fiber/matrix debonding, and fiber fracture.[1] The cause of fiber pull-out and delamination is weak bonding.[2][page needed]
Work for debonding, [math]\displaystyle{ W_d = \frac{\pi\; d^2\; \sigma_f^2\; l_d}{24\; E_f} }[/math] [3]
where
- [math]\displaystyle{ d }[/math] is fiber diameter
- [math]\displaystyle{ \sigma_f^2 }[/math] is failure strength of the fiber
- [math]\displaystyle{ l_d }[/math] is the length of the debonded zone
- [math]\displaystyle{ E_f }[/math] is fiber modulus
In ceramic matrix composite material this mechanism is not a failure mechanism, but essential for its fracture toughness,[4] which is several factors above that of conventional ceramics.
The figure is an example of how a fracture surface of this material looks like. The strong fibers form bridges over the cracks before they fail at elongations around 0.7%, and thus prevent brittle rupture of the material at 0.05%, especially under thermal shock conditions.[5][page needed] This allows using this type of ceramics for heat shields applied for the re-entry of space vehicles, for disk brakes and slide bearing components.
References
- ↑ 1.0 1.1 WJ Cantwell, J Morton (1991). "The impact resistance of composite materials -- a review". Composites 22 (5): 347–62. doi:10.1016/0010-4361(91)90549-V.
- ↑ Serope Kalpakjian, Steven R Schmid. "Manufacturing Engineering and Technology". International edition. 4th Ed. Prentice Hall, Inc. 2001. ISBN:0-13-017440-8
- ↑ PWR Beaumont. "Fracture mechanisms in fibrous composites". Fracture Mechanics, Current Status, Future Prospects. Edited by RA Smith. Pergamon Press: 1979. p211-33 in WJ Cantwell, J Morton (1991). "The impact resistance of composite materials -- a review". Composites 22 (5): 347–62. doi:10.1016/0010-4361(91)90549-V.
- ↑ V. Bheemreddy et al. "Modeling of fiber pull-out in continuous fiber reinforced ceramic composites using finite element method and artificial neural networks," Computational Materials Science, Vol. 79, pp.663-676, 2013.
- ↑ W. Krenkel, ed.:Ceramic Matrix Composites, Wiley-VCH, Weinheim, 2008, doi:10.1002/9783527622412 ISBN:978-3-527-31361-7
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