Micromechanism of surface and sub-surface deformation behavior of high density polyethylene containing dispersion of nanoparticles: An electron microscopy study and indenter-substrate interaction

In recent years, the focus of our research has been to obtain insights on microscale deformation mechanisms in thermoplastic materials reinforced with micrometer-sized particles. A perspective of deformation processes occurring over different strain–strain rate regimes was obtained [Dasari, A., Misra, R.D.K., 2004. Acta Mater. 52, 1683; Nathani, H., Dasari, A., Misra, R.D.K., 2004. Acta Mater. 52, 3217; Surampudi, N.L., Pesacreta, T.C., Misra, R.D.K., 2007. Mater. Sci. Eng. A 456, 218]. The objective here is to advance our basic understanding to nanoscale deformation in polymeric systems containing dispersion of nanoparticles, considering the growing use of polymeric materials as functional materials. A Berkovich nanoindenter was used to induce surface damage using a load of 0.5–1 mN and scratch velocity of 1 μm/s. An accompanying objective is to investigate the commonality in surface deformation behavior between nano- and microscale deformation to reinforce the underlying fundamental principles governing surface deformation. An understanding of mechanics of surface deformation is accomplished via electron microscopy analysis of scratch damage at and beneath the surface in conjunction with physical and mechanical properties. The electron microscopy analysis suggests that the understanding of microscale surface deformation can be extended to nanoscale surface deformation. In the intercalated high density polyethylene–nanoclay system, the susceptibility to scratch deformation is significantly reduced because of the shift of von Mises stress from the surface to the sub-surface region, with consequent reduction in the maximum tensile stress induced by the scratch. This conclusion is derived from electron microscopy and supported by the theoretical analysis. To the best of our understanding this is the first electron microscopy study that combines micro- and nanoscale deformation response during scratching of polymer nanocomposites in terms of processes that occur at and beneath the surface.

Research highlights
► Understanding of mechanics of deformation was accomplished by electron microscopy.
► Understanding of microscale deformation can be extended to nanoscale deformation.
► In nanocomposite system, the von Mises stress shifts from surface to sub-surface.