A nonlinear visco-hyperelastic model for spray polyurea and applications

Spray polyurea (SPUA) is widely used as a protective coating material for engineering structures subjected to the intensive impulsive loadings attributed to its large deformation and viscoelastic properties. Both experimental and theoretical studies of the hyperelastic and viscoelastic behaviors of SPUA, as well as the applications in the numerical simulations of the SPUA retrofitted structures under impact and blast loadings were conducted. Firstly, the reasonable geometries and dimensions of specimens are designed, and the complete compressive stress-strain curves of SPUA with the strain rate ranging from 10-3-103 s-1 were experimentally derived. The dependences of the dynamic initial elastic modulus, stress and fracture strain on the strain rate are formulated. It indicates that the initial elastic modulus and stress increase as the strain rate increases, while the fracture strain is linearly negatively correlated with the logarithm of strain rates. Then, a twenty-four-parameter nonlinear viscohyperelastic constitutive model composed of a hyperelastic model and seven Prony series terms is established and validated, in which the model parameters are determined through a multi-objective optimization based on genetic algorithm. Finally, by evaluating the existing sixteen constitutive models embedded in finite element program LS-DYNA, the Simplified rubber/foam model is selected for describing the mechanical behavior of SPUA. The Simplified rubber/foam model parameters are further calibrated by the established nonlinear viscohyperelastic model and comprehensively validated by comparisons with six series of impact and explosion tests on the SPUA, SPUA retrofitted steel plate and masonry wall. The present work could provide a helpful reference for the design and evaluation of the SPUA retrofitted structures.