High strain rate material properties and constitutive equations are essential for the development of numerical and physical models to assess the performance of soft materials subject to high rate deformation, with potential applications including protective equipment and vehicle crashworthiness. However, these properties are not available for many soft tissues. This is because specialized testing methods must be employed to obtain the necessary data. Fresh bovine tissue from the semimembranosis muscle was obtained and tested using a polymeric Split Hopkinson Pressure Bar. Samples were tested from 1.4 to 200 hours post mortem to observe the effect of rigor and other possible temporal effects on the material properties. Since this muscle had relatively uniform fiber orientation, it was possible to obtain specimens with fiber directions parallel, perpendicular, and at 45 degrees to the compression axis. The stress-strain curves for the muscle were concave upwards, as is typical of soft tissues at high strain rates. Fiber orientation was determined to have negligible effect at the tested strain rates. The testing revealed that the stiffness of the tissue increased with post mortem time until approximately 6 hours. At times greater than 200 hours post mortem, the tissue properties were found to be very similar to the properties of fresh tissue. These findings suggest that properties of fresh tissue might be estimated using more easily obtained post-rigor tissue.
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