PHOTOELASTIC IMAGE COMPUTATION OF A COMPR ESSED SINGLE-FIBER COMPOSITE

Based a compressed single embedded fiber composite, constituted with a 7 mu m or 49 mu m fiber in an epoxy matrix, photoelasticity observabl es images are calculated. The microbuckling model, first developped by Lee and Harris [21] and their completed by Grandsire-Vincon [14] (O.N .E.R.A.) is used. From it, it is possible to obtain the principal defo rmations, their difference as well as the principal directions. In add ition to the active layer which contains the fiber microbuckling plane , some additional layers, corresponding to those which are situated ab ove and below the fiber microbuckling plane, have also been taken into account. In the case of T300 fiber (7 mu m of diameter), and for an i nitial undulation of 0.5 mu m of amplitude, an oscillation period of 5 0 or 100 mu m, and a global compression taken between 1 and 3%, the re sults of the simulation, with or without additional layers and with or without quarter wave plates, show relatively dark images. The contras t is low and the amplitude of the deformations are rather the same all over the images. In the case of the C49 fiber (49 mu m of diameter), the contrast is more pronounced and the results of the simulation show significant modifications with the variations of some parameters and are quite in agreement with experiment. In particular, the difference of the principal deformations decrease over a distance similar to the fiber diameter around the latter; we obtain a color alternance when th e angle between the polarizer and the fiber axis changes, and finally, the local strain is larger near concave part of the undulation than n ear the convex one.