Polarizing optical behaviour of optically heterogeneous fibre-reinforced composites

Abstract

This paper presents an investigation of the polarizing optical behaviour of fibre-reinforced composites with mismatched refractive indices.

Because of their optical heterogeneous nature, these composites are very poor in transparency and do not present fringe patterns when examined under plane polariscopes. To overcome these difficulties, a Laser Microscopic Analyser (LMA) was developed. The polarizing optical behaviour of the target composites are represented in terms of the curves of transmitted light intensity versus azimuthal angle (I-θ curves).

It was found that these curves are of an unequal-fold pattern; this cannot be described by the Jones calculus.

Some of the factors were studied for their relationships with the special morphology of I-θ curves. The unequal-fold feature was found to exist independently from the optical arrangements of the LMA. Other factors, such as fibre content, temperature and especially stress in the composites had a strong influence on the change of I-θ patterns. The regular changes of these parameters lead to regular changes in the I-θ pattern. The strange I-θ patterns are, therefore, believed to be connected with the optically anisotropic nature of the optically heterogeneous fibre-reinforced composites.

This work is considered to be an important step for the further attempt of establishing a transmissive photoelastic method for optically heterogeneous fibre-reinforced composites.