Abstract
Polyurea is an elastomeric polymer with segregated segmental microstructure and superior mechanical properties that are sensitive to loading time and temperature. In the research leading to this report, the primary goal was to elucidate the contributions of different segmental structures to the time-dependent creep deformation and material properties, such as Poisson’s ratio and the creep modulus. The approach consisted of recording high-resolution digital images and resolving the full-field strain components of creep-loaded polyurea using digital image correlation (DIC) analysis. The resulting normal axial and lateral strains exemplified a typical creep response of incompressible elastomeric polymers, denoting the primary and secondary creep regions. Despite the uniaxial loading conditions, the presence of detectable shear strains demonstrated the occurrence of creep-activated shear softening behavior. The resolved strain contour maps, unique to DIC strain analysis, revealed noteworthy strain localization (demarked as striations on the strain contour plots) in selected regions within the observed regions of interest. The localized strains were separated and organized as functions of elapsed loading time. The high-strain regions were attributed to the soft segments of polyurea with inferior mechanical properties to their hard counterparts. The extracted time history of striations revealed three distinct molecular relaxation processes: one within primary creep attributed to the convoluted contributions of the hard/soft segmental microstructure and two processes within secondary creep associated independently with the hard and soft domains, respectively. The outcomes of this research are important for the development of effective and versatile polyurea-based impact-mitigating structures.
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Acknowledgements
The research leading to these results was supported in part by the United States Department of Defense under Grant Agreement No. W911NF1410039 and W911NF1810477. The National Science Foundation under Award No. 1925539 also supported the research. The authors are also grateful for internal funding from San Diego State University.
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Huynh, N.U., Koohbor, B. & Youssef, G. Localized creep analysis of polyurea elastomer from full-field measurements. Mech Time-Depend Mater 27, 727–741 (2023). https://doi.org/10.1007/s11043-022-09572-x
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DOI: https://doi.org/10.1007/s11043-022-09572-x