The simulation of rubber viscoelasticity with the tube reptation model for topological interactions is investigated for large dynamic strains. The chemically crosslinked (CC) system of molecules acts as a constraint box per unit volume for the physically constrained (PC) system and carries the PC system during the deformation process. A stick—slip model is used to simulate the interaction between the CC and PC systems Stretch ratios describe the history of the PC system's energy. Rubber energy density functions for both the CC and time dependent PC systems are shown to model large strain viscoelastic deformations. In this approach the energy is split into two terms. The long term energy function for the CC molecules represents one part and a time dependent energy function for the PC molecules comprises the second part. The PC systems' stretches then appear as internal variables in the expression of the total energy. The relaxation of the PC molecules during a general deformation is determined by the history of the CC system's strain state and the box (tube) stick—slip relaxation equation(s). Examples are presented in which step-strain relaxation test data and strain rate data are simulated for large deformations of a rubber compound with differing short and long term energy functions.
Four cyclopropene fatty acids, having the double bond of the cyclopropene ring at the 8,9, 9,10, 10,11 and 11,12 positions, respectively, were tested as inhibitors of stearic acid desaturation by the desaturase enzyme system of hen liver. The first three were powerful inhibitors, but the last was not. The cyclopropene acids with the 9,10 and 10,11 double bonds were equally strong inhibitors, while the acid with the 8,9 double bond was less effective. To account for the specificity of those cyclopropene fatty acids in which the C9 or C10 carbon atom is included in the cyclopropene ring, it is suggested that the conformation and structure of the CoA derivatives of these acids is such that they can irreversibly occupy the site on the enzyme responsible for 9,10-desaturation.
Constitutive models for large strain isothermal viscoelastic deformations of rubber are reviewed. The models discussed are for materials which have separable long and short term stresses, and for which the short term stresses have separable time and strain effects. They include the history integral model, an internal stress variable model, an internal stretch variable model, and an internal solid model. The internal stretch variable model and the internal solid model were motivated by molecular descriptions of rubber viscoelasticity. The material tests required to determine the constants for these large strain models are discussed. The classical problem of determining a rubber energy density function, used to describe both the long term and short term energy in these models, is reviewed. A method to assure Drucker stability, a commonly overlooked issue, is presented for experimentally determined Rivlin energy density function expansions. Also, an improved method for determining the coefficients of a Prony series, which defines a material's relaxation time spectrum, from experimental relaxation data is presented.
The issues are the effect of the rate of inflation, the effect of residual air, and the effect of gravity. The results of the deployment analyses reveal that the time and amount of inflation gas required to achieve a full deployment are related to these issues.
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