Size effect in microcompression of polystyrene micropillars

- Size effect in yield strength of an amorphous polymer, Polystyrene (PS), is investigated.
- PS micropillars have been prepared through a microfabrication route.
- Yield stress of PS is seen to increase with deceasing diameter, for diameters less than 100 μm.
- Experimental artifacts have a significant effect on the rehardening response of PS.

Experiments by He et al. [J.Y. He, Z.L. Zhang, M. Midttun, G. Fonnum, G.I. Modahl, H. Kristiansen, and K. Redford. Size effect on mechanical properties of micron-sized PS-DVB polymer particles. Polymer 2008, 49(18), 3993] have indicated that polymers exhibit enhancement of strength at length scales of the order of microns. This is surprising since size effects, widely reported for FCC metals, owe their origin to the presence of crystalline defects, particularly dislocations. On the other hand, polymers being a material of choice in microfabrication, these results assume technological importance. In this work, we conduct controlled experiments on polystyrene (PS) micropillars to ascertain whether they exhibit size effects. The pillars are microfabricated and hence free of beam damage. The experimental load displacement curves obtained from microcompression experiments are matched with computer simulations on similar samples using a well-calibrated constitutive model. Our results demonstrate significant intrinsic size effect on the yield strength, though effects of size on rehardening response turned out to be an experimental artifact.

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