Viscoelastic properties of medical grade silicones in tension

Storage, E', and loss, E", moduli of three medical grade silicone elastomers were measured, in tension, in the frequency, f, range 0.02-2 Hz. The materials were tested when immersed in physiological saline solution at 37 degrees C. The dependence of E' and E" on log (10)f was represented, for each of the three grades of silicone, by second-order polynomials. These results were compared with published results for the same elastomers tested in compression. For each silicone tested, there was a very small, but statistically significant, difference between the E' values measured in tension and compression. However, overall for the three silicones tested, there was no systematic difference observed, since for only two of the three silicones was the value of E' greater when measured in tension. E' increased more rapidly, with increasing log(10)f when measured in compression than when measured in tension. Graphs of E" plotted against log(10)f were shallow curves passing through a minimum at frequencies in the range 0.17-0.21 Hz, when measured in tension; when measured in compression, E" increased steeply, but non-linearly, in this frequency range.