6 - Computational Simulation, Multi Scale Computations, and Issues Related to Behavioral Aspects of HSREP

Abstract

We present singlescale and multiscale models of polyurea and high-density polyethylene (HDPE) subjected to high strain rates. The high strain rate polymer behavior is described by a variant of the viscoplasticity model based on overstress (VBO), hereafter referred to as the generalized VBO or GVBO. The singlescale material properties of the GVBO are identified from the experimental data using a combination of global and local inverse methods for various impact loading conditions. The multiscale model of polyurea/HDPE is based on the reduced order homogenization theory, where the unit cell of a polymer is modeled as a heterogeneous material with ellipsoidal inclusions. The reduced order multiscale model has been further enhanced by incorporating dispersive mechanism aimed at capturing reflection and refraction of stress waves at high strain rates that give rise to dispersion and attenuation of waves within the polymer microstructure. We present a one-parameter macroscopic model of distributed damage and dynamic fracture of polymers. Key characteristics of the model include its simplicity and suitability for straightforward and efficient numerical implementation. The damage model can be derived from a micromechanical model of chain elasticity and failure by recourse to optimal scaling methods and fractional strain gradient elasticity. As a result of the optimal scaling analysis, micromechanical parameters can be linked to the material’s critical energy release rate, which constitutes the single material parameter of the macroscopic fracture model. The model can be integrated into numerical simulations of polymeric materials within the framework of material point eigenerosion. The scope and fidelity of the model is demonstrated in an example of application, namely, Taylor-impact experiments of polyurea specimens.