Читать книгу Properties for Design of Composite Structures - Neil McCartney - Страница 72

Owing to the use of the far-field in Maxwell’s method for estimating the properties of fibre composites, it is possible to consider multiple fibre reinforcements. Suppose in a cluster of fibres that there are N different types such that for i = 1, …, N, there are ni fibres of radius ai. The properties of the fibres of type i are denoted by a superscript i. The cluster is assumed to be homogeneous regarding the distribution of fibres, and this leads to transverse isotropic effective properties.

For the case of multiple phases, relation (4.85) is generalised to the following form:

(4.86)

When this result is applied to a single fibre of radius b having effective properties corresponding to the multiphase cluster of fibres, it follows that

(4.87)

The cluster of all types of fibre is now considered to be enclosed in a cylinder of radius b such that the volume fraction of fibres of type i within the cylinder of radius b is given by Vfi=niai2/b2. The volume fractions must satisfy the relation

(4.88)

It then follows that (4.86) may be written in the form

(4.89)

The coefficients of the 1/r terms in relations (4.87) and (4.89) must be identical so that

(4.90)

It then follows on using (4.1) that the effective axial shear modulus for the multiphase composite may be written as

(4.91)