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In this research, the exponential stretched based hyperelastic strain energy was generalized to the hyper-viscoelastic model using the heredity integral of deformation history to take into account the strain rate effects on the mechanical behavior of materials. The heredity integral was approximated by the approach of Goh et al. to determine the model parameters and the same estimation was used for constitutive modeling. To present the ability of the proposed hyper-viscoelastic model, the stress-strain response of the thermoplastic elastomer gel tissue at different strain rates from 0.001 to 100/s was studied. In addition to better agreement between the current model and experimental data in comparison to the extended Mooney-Rivlin hyper-viscoelastic model, a stable material behavior was predicted for pure shear and balance biaxial deformation modes. To present the engineering application of current model, the Kolsky bars impact test of gel tissue was simulated and the effects of specimen size and inertia on the uniform deformation were investigated. As the mechanical response of polyurea was provided over wide strain rates of 0.0016–6500/s, the current model was applied to fit the experimental data. The results were shown more accuracy could be expected from the current research than the extended Ogden hyper-viscoelastic model. In the final verification example, the pig skin experimental data was used to determine parameters of the hyper-viscoelastic model. Subsequently, a specimen of pig skin at different strain rates was loaded to a fixed strain and the change of stress with time (stress relaxation) was obtained. The stress relaxation results were revealed the peak stress increases by applied strain rate until the saturated loading rate and the equilibrium stress with magnitude of 0.281 MPa could be reached. [ABSTRACT FROM AUTHOR]

The National Council on Radiation Protection and Measurements (NCRP)in NCRP Report Number 106 recommended a limit of 1010 beta particles emitted from radioactive particles with sizes less than 1mm (hot particles) to prevent acute deep ulceration. This recommendation was determined, in part, by regressing the diameter of the scabsinduced by fissioned 235UC2 hot particles as afunction of the logarithm of the number of beta particles emitted from the sources for one study. To validate this recommendation and theapproach used by the NCRP, external irradiations of pig skin using radioactive sources of less than 600 mum in the largest dimension werecarried out. The hot particles used included fissioned 235UC2 and activated 170Tm, 175Yb, and46Sc. Results indicated a strong correlation between scabdiameter and dose for scabs induced using fissioned 235UC2, activated 170Tm, and 46Sc, but not for 175Yb. The correlation value decreased with decreasing beta particle energy, with the exception of 46Sc, whichhad scabs with diameters greater than twice the maximum beta particle range. The larger scabs from 46Sc are thought to be due to dose contributions from the gamma rays. The results also give an ulceration threshold less than that given by NCRP to prevent acute deep ulceration. It was concluded that regression analysis of scab diameter as a function of either number of beta particles emitted from thehot particles or dose did not yield either precise or accurate thresholds but was useful in determining probable ranges of doses which lead to scab induction. [ABSTRACT FROM AUTHOR]