Viscoelastic characterization of polyurea based polymers
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Several formulations of sprayed polyurea were considered as an alternative to cast polyurea. Based on results from confined compression experiments on these materials, TRI – 25 was selected as the best alternative material on account of its good flow characteristics at lower stresses. The constitutive behavior of this formulation has been determined using confined relaxation and Arcan relaxation experiments. Bulk relaxation modulus and shear relaxation modulus were obtained in the form of Prony series. The thermal shift factor for bulk relaxation was fitted with the Arrhenius equation while for shear relaxation, the trend was fitted with the WLF equation. The nonlinear response at ambient conditions was predicted using the modified free volume model (Park et al., 2004). Calibration factors for the nonlinear model were obtained using bulk data from confined compression under ramp loading and Arcan shear. The prediction of uniaxial tensile test followed the experimental response closely while the compressive response followed it with stress and strain shifts, suggesting that the voids in the material could shift the compressive response of the material.