The effect of micropores on mechanical properties of laminates
Polimery 2000, No 4, 271
SummaryThe conventional and the S-RIM techniques were used to prepare laminates with varying void contents generated by a blowing agent added during the hardening reaction. Pore-free laminates were prepared by a modified RTM technique. Epoxy and polyurethane resins (Table 1) were used to make the foamed laminates and glass, carbon or aramide fiber (mat or roving) was used as reinforcement (Table 2). Mechanical properties (mostly dynamic and static) of the laminates were examined in relation to resin type, nature and amount of the blowing agent, reinforcement type, technique used to make the laminate, and micropore (void) content (Figs. 5–16). The static properties were found to be only slightly dependent on the void content The dynamic properties were found to be related to the (uniform) distribution of micropores throughout the laminate. The cumulative loss energy was measured and used as a new parameter to interpret the dynamic data (eqns. 1, 2; Table 3). This energy is a precise parameter (Fig. 15) that helps us indirectly evaluate the structural changes occurring in the laminate. It enables the dynamic strength of the material to be determined, and to relax from the lengthy and less accurate Wöhler fatigue tests. The laminates were examined microscopically to evaluate the effect of micropores on the size and course of crack propagation in the resin matrix on delamination under bending and dynamic loads (Figs. 17–20).