Stress birefringence in compressible polymer fibres with irregular transverse sections

Abstract

From an interferometric point of view a mathematical formula is developed for computing the exact optical path variations associated with a deformed cross-section of a fibre due to the drawing process. Fizeau fringes in transmission crossing Perlon fibres are obtained to illustrate the experimental applicability of the new corrected formula. The correction term is expressed as a function of the material compressibility, applied stress and the draw ratio. The birefringence of Perlon fibres is changed mechanically according to two different mechanisms in successive ranges of draw ratio. The mechanical response of Perlon fibres is found to be dependent on the direction with respect to the fibre axis. Another term is suggested to describe the mechanical anisotropy of a polymer. Microinterferograms are given for illustration.