This paper reports the unique microstructure of polyurea foams that combines the advantages of open and closed cell polymeric foams, which were synthesized through a self-foaming process. The latter was the result of aggressive mechanical mixing of diamine curative, isocyanate, and deionized water at ambient conditions, which can be adjusted on-demand to produce variable density polyurea foam. The spherical, semi-closed microcellular structure has large perforations on the cell surface resulting from the concurrent expansion of neighboring cells and small holes at the bottom surface of the cells. This resulted in a partially perforated microcellular structure of polyurea foam. As a byproduct of the manufacturing process, polyurea microspheres nucleate and deposit on the inner cell walls of the foam, acting as a reinforcement. Since cell walls and the microspheres are made of polyurea, the resulting reinforcement effect overcomes the fundamental interfacial issue of different adjacent materials. The partially perforated, self-reinforced polyurea foam is compared to the performance of traditional counterparts in biomechanical impact scenarios. An analytical model was developed to explicate the stiffening effect associated with the reinforcing microspheres. The model results indicate that the reinforced microcell exhibited, on average, ~30% higher stiffness than its barren counterpart.

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The effect of several mechanical boundary conditions on the dynamic magnetoelectric (ME) effect is analytically investigated for layered cylindrical composites. The study consists of deriving a mechanics-based model for two concentric cylinders made of lead-zirconate-titanate (PZT) and cobalt ferrite (CoFe 2 O 4 ), separated by a thin elastic layer, which is treated as strain mediator with no effect on the functional behavior of the system. Different thicknesses of the cylindrical composites and the elastic layer are considered in this study. For each case, nine sets of boundary conditions, four traditional and five non-traditional, were applied. Results show the dependence of the ME effect on the boundary conditions as well as on the inclusion of the elastic layer between the two cylinders, where both affect the strain transduction between the active layers; namely the piezomagnetic (CoFe 2 O 4 ) and piezoelectric (PZT) layers. It was found that the maximum ME effect is attained for conditions in which the outer boundary is subjected to a uniform mechanical pressure. The inclusion of a thin elastic bonding layer was found to increase the ME response, the thickness of which was further investigated to establish limits of applicability of the reported model.