ON RESOLUTION OF RELAXATION MECHANISM IN FIBER-REINFORCED COMPOSITE

Abstract

In order to elucidate the mechanism of mechanical dispersion in fiber-reinforced composite, temperature dependence of the dynamic viscoelastic properties in simple extention was studied for the epoxy resin composite reinforced with satin woven glass cloth, in which the symmetrical angle between the directions of extension and each fiber axis of warp and woof was adjusted to ±67.5° (COA67.5), ±45° (COA45), and ±22.5° (COA22.5).The composite reinforced with the cloth in which the fiber axis of warp coincided with the direction of extension (COA0), and that reinforced with uniaxially aligned continuous glass fiber to the direction of extension (ROA0) were also used as samples.Although the primary transition is merely observed for COA67.5 and COA45, a sub-transition appears at a temperature above the primary transition for COA22.5 and COA0. The sub-transition for COA0 appears more distinctly separated from the primary transition as compared with the case of COA22.5. E″ and tan δ vs. temperature curves for ROA0 are hardly distinguishable from those for COA0.Our results are similar to those reported by Reed6), in which mechanical dispersion in flexural deformation is studied for the unidirectional epoxy-glass fiber composite at various fiber orientation angles.This implies that the effect of fiber intersection has no serious influence on the mechanical dispersion behaviors. The present and Reed's results can be explained by the mechanism proposed by Lipatov et al.7) that the separation of the sub and primary transitions occurs if the boundary layers formed on the surface of reinforcement and the bulk polymer phase are aligned parallel to the direction of deformation. The sub-transition reported earlier by us for composites reinforced with randomly distributed short glass fiber is also clearly explained by the mechanism proposed by Lipatov et al.