| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 93 === The present study was conducted to investigate the in vitro tensile properties and stress relaxation behavior of sciatic nerves of Sprague-Dawley (SD) and Wistar rats under two different initial strain rates, 0.02 and 0.2 s-1. Results showed that for a strain rate of 0.02 s-1 the ultimate stress, elastic modulus and failure strain are 3.66 �b 1.20 MPa, 6.58 �b 3.22 MPa and 0.91 �b 0.18, respectively. The corresponding values for 0.2 s-1 are 4.72 �b 1.21 MPa, 12.56 �b 4.11 MPa and 0.77 �b 0.27, respectively. Such results indicate that a higher strain rate would result in a greater elastic modulus but ultimate stress and failure strain level would not be affected by strain rate according to statistical analysis. In addition, microstructural analysis showed that perineurium and epineurium were responsible for the tensile strength of rat sciatic nerve.
With regard to the effects of initial strain rate on the stress relaxation behavior, a slower initial stain rate would cause a greater extent of stress relaxation at a constant strain of 33%, but an opposite trend was found for a constant strain of 50%. However, no statistically significant effect of initial strain rate could be found on the stress relaxation behavior of rat sciatic nerve at a constant strain of 66%. It was also found that the extent of stress relaxation under a constant strain of 33% was greater than those under 50% and 66% at a low initial strain rate of 0.02 s-1. Nevertheless, the extents of stress relaxation at a high initial strain rate of 0.2 s-1 were comparable among the given three constant strain levels. Finally, the stress relaxation results at all given testing conditions could be well correlated by a viscoelastic model (the Kelvin model).
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