Ultimate behavior of dry and water-swollen polymer network/glass bead composites

Tensile properties of a poly(2-hydroxyethyl methacrylate) (PHEMA) network filled with various amounts of glass beads, in the dry and the equilibrium water-swollen states, have been studied below and above T_g. The temperature ranged from 5° C to 170° C and the volume fraction of the filler was up to 50 percent. In the glassy region it has been found that the temperature at which the transition from brittle to ductiel behavior occurs is increased by the presence of the filler. In the brittle zone the strength of the composites is decreased by the presence of the filler and can be predicted by using a finite element method; in the ductile zone, however, the strength of the composites reaches that of the unfilled polymer. In the rubbery region failure envelopes have been obtained for both dry and swollen PHEMA/glass bead composites. Using a double shift procedure all the data have been superimposed to obtain universal failure envelopes for the two different states. The dependence of the shift factors on filler content is discussed.