Fig. 2.

Force-time (a and c) and corresponding force-displacement (b and d) indentation data: (a and b) data taken on poly(methyl methacrylate) using a constant $\dot{P}$ loading; (c and d) data taken on polystyrene using constant $\dot{P}/P$ loading. Both data sets include a 10 s hold period between loading and unloading, and the data in (c) and (d) include an additional hold period near the end of the unloading segment.