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, ${\displaystyle W_{d}={\frac {\pi \;d^{2}\;\sigma _{f}^{2}\;l_{d}}{24\;E_{f}}}}$ ^[3]

where

• ${\displaystyle d}$ is fiber diameter
• ${\displaystyle \sigma _{f}^{2}}$ is failure strength of the fiber
• ${\displaystyle l_{d}}$ is the length of the debonded zone
• ${\displaystyle E_{f}}$ 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][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. 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". 6th Ed. Prentice Hall, Inc. 2009, p. 223. ISBN 0136081681
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, doi:10.1002/9783527622412 ISBN 978-3-527-31361-7