Лако-красочные материалы — производство

As indicated in Table 7, the wood moisture content had a major effect on the shear strength of epoxy FRP-wood specimens with RF coupling agent (approximately 42.8%

decrease for wet samples). The epoxy FRP-wood specimens with HMR coupling agent showed a 26.2% decrease in shear strength due to moisture. The HMR/epoxy FRP-wood specimens showed higher shear strengths than the RF/epoxy FRP-wood for both dry and wet conditions (approximately 8.4% for dry and 28.9% for wet). The results indicate that the HMR coupling agent enhances the strength of interface bond. The material or cohe­sive failure of the epoxy FRP-wood specimens occurred entirely in wood. The average percent material failure for the HMR/epoxy FRP-wood samples increased by 15.6%, from about 77.6% for dry to 89.7% for wet. In contrast, the average percent material failure for the RF/epoxy FRP-wood samples exhibited cohesive failures of 26.6% for dry and 21.1% for wet, due to the poor performance of the RF coupling agent. The HMR/ epoxy FRP-wood specimens showed a large percentage of material failure, which indi­cated an improved interface bond.

The favorable results obtained for both dry and wet epoxy FRP-wood samples with HMR in relation to the epoxy FRP-wood samples with RF are due mainly to the enhanced bond strength imparted by the coupling agent. The failure for the epoxy FRP-wood samples with HMR occurred primarily in the wood layer and, therefore, the response of these samples was governed by the shear strength of wood, and consistent percent material or cohesive failures for both the dry and wet samples (77.8% and 89.7%, respectively) were obtained. Moreover, these percent material failures are close to accep­table allowable values (approximately 80%) for wood failure. The failure for the epoxy FRP-wood samples with RF happened mainly at the interface between the epoxy FRP and wood, which resulted in lower shear strength and lower percent material failure, especially for wet samples.