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.