Polyurea (PU) is a microphase-segregated elastomer synthesized through bulk polymerization of isocyanates and amines. Polyurea has previously been shown to be an excellent medium in absorbing energy from blast and shock waves, especially when layered with metallic components. Due to its toughness and ease of application, it has been studied as a potential protective coating in cavitation erosion conditions.  The focus of the present work is to evaluate the thermo-mechanical properties of polyurea considering a number of different formulations that quantitatively may differ in terms of the proportion of hard phase as well as qualitatively in terms the nano-morphology of the copolymer. Standard formulations PU-105 and PU-605, are copolymers of Isonate 143L diisocyanate with two distinct diamines: long chain length Versalink P-1000 and medium chain length Versalink P-650, respectively. A base hybrid formulation, that has the same phase proportion as PU-605, is synthesized using a mixture of long and short chain length diamines (Versalink P1000 and P250; 76:24% weight ratio). Other hybrid polyurea specimens are synthesized by reacting a blend two diamines with weight ratios of 70:30% and 80:20%. A particulate reinforced PU composite is fabricated by mixing the medium length diamine VP650 and milled carbon fibers with Isonate 143L. Thermal phase transition (DSC) and thermal conductivity measurements (MDSC) are performed to better comprehend the thermal characteristics of the proposed formulations. DMA tests are conducted to construct the storage and loss moduli master curves. Stress-strain curves under uniaxial loading at high strain rates are obtained using split Hopkinson pressure bar (SHPB). The high strain rate experiments are performed in unconfined and confined configurations to estimate shear and bulk responses of material. The results may be used as calibrating parameters in non-linear pressure- and temperature-dependent constitutive model of elastomers. The overall objective of this approach is to explore potential fine-tuned blend formulations that may provide a balanced stiff and tough elastomeric response under high velocity impact and to assess the feasibility of improving elastomer-based coatings for protection against harsh cavitation erosion conditions.

Thermo-mechanical characterization and constitutive modeling of polyurea variants

2019 Spring National Meeting

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