7 fibre pull out

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Click on the different energy absorbing mechanisms to see how they operate

Click on the different energy absorbing mechanisms to see how they operate

Matrix Deformation

For tough matrices a high interfacial strength is desirable in order to favour matrix deformation. Conversely, for brittle matrices a low interfacial strength is desirable so that interfacial debonding, crack deflection, fibre fracture, and fibre pull-out can occur.

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Fibre Pull-out

Fibre Fracture

Interfacial Debonding

Displacement

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Crack Deflection

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Crack Deflection

The transverse stress at a crack tip in an axially loaded composite is roughly 20% of the axial stress and so crack deflection occurs if the interface strength is less than 20% of the fibre strength.

Stress field approach

Axial stress at crack tip

Transverse stress at crack tip

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Crack Deflection

Applied
load
generates
interfacial
shear stress

For a finite Weibull Modulus, there is a
finite probability that fibre fracture will
occur remote from the crack plane.

Fibre Strength Variation

Stress Distribution

Fibre fracture
probability

Fibre Fracture

Interfacial Debonding

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Crack deflection occurs if the energy release rate during interfacial debonding, G_i, exceeds the critical energy release rate, G_ic, (interfacial fracture energy).

Energy approach