Optimum recovery time for cyclic compression tests on bovine brain tissue

In conducting mechanical tests on the brain tissue, it is preferred to perform multiple tests on the same sample. In this study, we investigated the behavior of the bovine brain tissue in repeated compression tests with 6 recovery periods (namely, 10, 60, 120, 180, 240, and 300 s). Compression tests were performed on cylindrical samples with average diameter and height of 18.0 mm and 15.0 mm, respectively. Two testing protocols were employed; the first one comprised experiments with 5, 25, and 125 mm/min loading speeds up to 33% strain and the second one consisted of tests with 25 and 125 mm/min loading speeds up to 17% strain. Each experiment was conducted in two cycles separated by a specic recovery period. Stress-strain data from the first and second cycles were compared using 3 criteria, namely Normalized Root-Mean-Square Error (NRMSE), coeffcient of variation (R2), and Effective Height Ratio (EHR). The analysis suggested that the optimum recovery periods for the first and second protocols were 120 s and 180 s, respectively. Moreover, differences between the first and second cycles in medium- and high-speed tests were found to be smaller than those in the low-speed experiments.