Toughness of Composite Materials (Fibre Reinforced Composites)

This video defines toughness and fracture toughness of materials. After this, the concept of toughness in fibre reinforced composites is developed and the analysis is presented. Data on toughness and fracture toughness for different materials are also presented and discussed.
Summary:
Toughness of a material is the amount of energy the material absorbs for the creation of a unit new crack area.
For a fibre composite, the energy in fracturing or breaking the composite is mostly consumed by two events, fibre pull-out and fibre fracture. These energies are much larger than the energy of the new crack surface area created.
The composite toughness analysis says that a composite will be tougher if the fracture strength of the fibre is high and if the interfacial shear strength between the fibre and the matrix is low.
Composite fracture mechanism consists of crack growth and multiple crack diversions in the direction of the fibre length during fibre pull-out and fibre fracture. This process is an energy consuming one and this is the reason for very high toughness of composites, even though the fibre and the matrix, both, may be of brittle type.