Effect of aspect ratio of test specimens on quasistatic compression loading and stress-relaxation of PDMS and a Cu-filled-PDMS composite

This study reports effects of aspect ratio of test specimens on the stress-strain and stress-relaxation behaviors of polydimethylsiloxane (PDMS) and PDMS composites comprising 5 vol % of micrometer sized Cu powders, Cu(p). PDMS and PDMS-Cu(p) composites of aspect ratio ranging from 0.1 to 0.4 were cyclically loaded in compression at a strain rate of 1.0 × 10−3 s−1. Irrespective of the aspect ratio, the PDMS-Cu(p) composites showed higher stress bearing capacity and also absorbed slightly more energy per cycle as compared to pure PDMS. Interestingly, an increase in the aspect ratio resulted in monotonous decrease in both of these properties for all samples. In addition, the relative rate as well as extent of the stress-relaxation increased with decrease in aspect ratio of samples. Furthermore, addition of micrometer sized Cu particles did not significantly affect the stress-relaxation behavior of PDMS. Finite element analysis revealed that effects of aspect ratio might be attributed to the formation of friction cone or hill, i.e., a low stress regime, in the sample near the ends. A simple methodology to account for aspect ratio in the standard stress-strain and stress-time relationships is also developed.