Results are presented from an investigation undertaken to explore new opportunities for the evaluation of rubber from stress-strain characteristics obtained with an lnstron testing machine. The resistance strain gage load recording system, and the flexibility of control of the crosshead motions introduce a variety of possibilities not available with the usual pendulum type of rubber tester.
Accurate recording of the load-elongation curves for low elongations is .of particular interest for many technical applications. Reproducible deformation histories can be applied readily to test specimens and the e?ects on load-elongation curves observed. The transient character of the first-stretch load-elongation curve usually used in rubber testing is apparent by comparison with equilibrium curves after repeated cycling. The facility with which such data is obtained makes use of equilibrium curves feasible. Load relaxation at either constant elongation or constant compression may be recorded directly. Creep at constant load can also be determined. The e?ect of rate of longation on the load-elongation curves can be correlated with creep curves. The low load ranges available and the smooth crosshead motion give reproducible recording of load-elongation curves for raw rubber and raw compounds. These results have significance for some phases of processibility. The use of a small ring-shaped test specimen secured with a rotary cutter provides an elegant technique for sampling the tensile properties of the rubber in vulcanized rubber articles. Hysteresis may be evaluated by recording the decay of the vibratory load for the free vertical vibrations of a test specimen and attached mass. Hysteresis determinations can also be made over large ranges of amplitude by recording load-elongation cycles and measuring areas. Compressive as well as tensile loading may be used.
Results from these various procedures are given to illustrate the versatility and flexibility in testing with this equipment. They indicate important fields of usefulness for it in rubber testing other than routine testing for ultimate elongation and tensile strength, for which it is not particularly well adapted.