STRESS DISTRIBUTION-OPTICAL RELATIONSHIP STUDY OF OPTICALLY HETEROGENEOUS FIBER COMPOSITE DISK DIAMETRICALLY COMPRESSED

This paper reports the application of Laser Microscopic Analyser (LMA) to the stress analysis of optically heterogeneous fibre reinforced composites.The composite samples were all disks of 20mm diameter and diametrically compressed in experiments.The transmitted polarised light intensity under the bright field of plane polariscope (I_‖) were measured.The light intensity vs.azimuth curve(I_‖-θ) was analysed with Fourier transform.The relative intensity of the 4th amplitude,e.g.the amplitude of cos (4θ),A_‖4,of the I_‖-θ curve was found to be proportional to the brightness of the isochromatic line under the dark field of circular polariscope for optically homogeneous birefringent model,including transparent photoelastic composites with well matched refractive indices between fiberes and resin matrix.On the condition of optically heterogeneous fibre composites,the transparency was too low to show any photoelasic pattern.The 4th amplitude,however,was still readily available with the use of LMA.By the means of A_‖4,the stress distrbution on the radius perpendicular to the compressing direction was obtained.The results agree with the theoretic results from H.Okabo.The material used for this measurement is E-glass fibre reinforced rubber-epoxy resin,with fibere volume fraction of 60%,and with an apparent transparency of only 0.06%.