Dynamic properties of polyurea-milled glass composites part II: Micromechanical modeling

In Part I, the results of experimental evaluation of the mechanical properties of pure polyurea (PU) and polyurea with milled glass composites (PU-MG) in low (1-20 Hz) and high (0.5-1.5 MHz) frequency ranges (Nantasetphong et al., 2016a) have been reported, focusing on the dependence of these properties on frequency, temperature, and the milled glass volume fraction. Here, we report the results of the corresponding micromechanical modeling. The models are developed, based on three different approximations: (1) dilute random, (2) non-dilute random, and (3) non-dilute periodic distributions of inclusions. Different orientation distributions of fibers, e.g., uniaxial parallel, in-plane random, and 3D random are considered and their results are compared with experimentally measured data presented in (Nantasetphong et al., 2016a). Moreover, the computational results are used to construct master curves of dynamic Young's storage and loss moduli and compare these with those constructed from experimental data. The 3D random and in-plane random calculation results are compared with the dynamic longitudinal and shear moduli of PU-MG composites obtained from ultrasonic wave measurements. These comparisons demonstrated that, as expected, the orientation distribution of the short fibers was affected by the thickness of the composite sample, and this effect was manifested in overall elasticity tensor of the composite.