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]

Work for debonding, $W_d = \frac{\pi\; d^2\; \sigma_f^2\; l_d}{24\; E_f}$ ^[3]

where

• $d$ is fiber diameter
• $\sigma_f^2$ is failure strength of the fiber
• $l_d$ is the length of the debonded zone
• $E_f$ 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] 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. 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.
2. Serope Kalpakjian, Steven R Schmid. "Manufacturing Engineering and Technology". International edition. 4th Ed. Prentice Hall, Inc. 2001. ISBN 0-13-017440-8
3. 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.
4. 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.
5. W. Krenkel, ed.:Ceramic Matrix Composites, Wiley-VCH, Weinheim, 2008, ISBN 978-3-527-31361-7