100 K.-S. Kim et al. Fig. 16.3 High toughness of polyurea with reduce strength in tension at high rate of loading is plotted on an Ashby map [5] 16.4 Conclusion Dynamic toughness of polyurea PU1000 is measured with a newly developed L-ISI, applying plane-wave loading of a centercracked specimen with plate impact. The toughness is measured 5500 J/m2 under a very high rate of crack-tip loading, ˙K ∼ 10 7MPa√m/s. The toughness is relatively high. The strength under high strain rate is found substantially lower, ~220 MPa, at a tensile loading than that, ~2GPa, at a compressive shear loading. However, polyurea PU1000 has enough cohesive ductility, ~50 μm, to exhibit high toughness under the reduced strength in tension. This result shows that the high nominal strength of polyurea at high strain-rate under high pressure, ~2GPa, is mainly due to high hydrostatic pressure. The underlying strengthening mechanisms under a wide range of hydrostatic pressure are to be further investigated with the newly developed tapping-mode AFM DIC [6]. Acknowledgments This work is supported by grant N00014-18-1-2513, from the US Office of Naval Research. References 1. Grujicic, M., et al.: Experimental and computational study of the shearing resistance of polyurea at high pressures and high strain rates. J. Mater. Eng. Perform. 24(2), 778–798 (2014) 2. Kim, K.-S.: Pressure- and rate-dependent plastic flow of nano-phase segregated polyurea copolymer (IMECE Paper # -13559). Drucker Medal Symposium, ASME 2019 IMECE (November 2019) 3. Jiao, T., et al.: Pressure-Sensitivity and Tensile Strength of an Elastomer at High Strain Rates. In: Elert, M., Furnish, M.D., Chau, R., Holmes, N., Nguyen, J. (eds.) Shock Compression of Condensed Matter, pp. 707–710 (2007) 4. Ravichandran, G., Clifton, R.J.: Dynamic fracture under plane wave loading. Int. J. Fracture. 40, 157–201 (1989) 5. Bolton, W., Higgins, R.A.: Materials for Engineers and Technicians. Newnes, London (2010) 6. Kim, K.-S.: Digital Image Correlation at a Small World of Nano Science and Technology (Plenary). iDICs Annual Conference, October 2019
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