Ultrasonication is an efective method for dispersing nanoparticles in fabrication of thermoset nanocomposites. Among the various parameters of sonication, the sonication time is the most important one which can directly afect the dispersion of nanoparticles in the matrix. In this study, the efect of sonication time on mechanical properties of the graphene oxide/epoxy nanocomposites is investigated. The nanocomposites were fabricated for 0.05, 0.1, 0.3, 0.5 and 0.7 wt% of graphene oxide (GO). Sonication times of 30–45–60, 40–65–90, 90–120–150, 150–180–210, 210–240–270 min were considered for 0.05, 0.1, 0.3, 0.5 and 0.7 wt% of GO, respectively. Then, the Vickers micro-hardness and compressive response of the samples were examined. The experimental results indicated that the sonication time had considerable efect on the mechanical response of the nanocomposites. For instance, the maximum improvement in yield strength and elastic modulus were 7.55%, 9.83% and were obtained for 0.7 wt% of GO under 270 min of sonication time. The maximum improvement in hardness was 6.83% and was obtained for the sonication time of 120 min for 0.3 wt% of GO. Moreover, a new model was introduced which correlated Vickers micro-hardness of nanocomposites to the compressive properties and the nanofller weight percentage. The energy transferred during the ultrasonication to the mixture was evaluated and a novel curve was presented for selection of ultrasonication parameters. SEM technique was also used to examine the efect of sonication time on the quality of the nanoparticle dispersion
