The mechanical properties of a composite can be predicted based on the mechanical properties of the fibres and matrix. Important as well in the make up of the composite is the proportion of fibres and matrix and the orientation of the fibres with respect to the applied load.
There are two idealised geometries that we will now examine.
Isostrain – Stress applied parallel to aligned continuous fibres in a matrix.
Isostress – Stress applied perpendicular to aligned continuous fibres in a matrix.
In the isostrain condition the composite is loaded parallel to the plane of the continuous fibres. In this situation both the fibres and matrix are strained the same amount (Isostrain = single strain) even though they may have very different moduli of elasticity.
In the isostress condition the composite is loaded perpendicular to the plane of the continuous fibres. In this situation, the stress in both the fibres and matrix is the same (isostress = single stress). The matrix usually exhibits the largest strain due to its lower modulus.