Dynamic Mechanical Spectroscopy (DMS)
DMS measures the ability of a material to store and dissipate mechanical energy. DMS measurements are based on the differences in response of the viscous and elastic components to an applied strain. This imposed strain is generally applied by twisting or pulling a sample and measuring the resultant stress.

Dynamic mechanical measurements are done by varying the temperature at constant frequency. Dynamic mechanical properties vary as a function of temperature and frequency, which have opposite effects on molecular motion. Therefore, the dependence of the measured responses to frequency is inverse to that for temperature.

DMS data often correlate to other dynamic test methods and actual field performance, but there are times when the small strain deformations may not accurately predict performance in high-load/high-strain applications. Dynamic mechanical testing is an easy way to screen a series of formulations prior to casting costly prototype parts.

Compressive Fatigue Hysteresis
A typical compressive fatigue hysteresis test uses either a servohydraulic Instron or MTS testing machine. An elastomer is cycled between two loads at a specified frequency with hysteretic energy loss measured several times throughout the test. Internal temperature is also monitored by a thermocouple inserted into the elastomer. Like DMS, this test requires some costly equipment investment. Cycle times can be long, but material requirements are low and compressive fatigue hysteresis is an effective screening tool. Unlike DMS, compressive fatigue hysteresis can simulate the high loads and strains often found in real-life applications.

Dynamic mechanical testing and the resultant measurement of hysteretic heat buildup is affected by the prepolymer technology, the polyol backbone type, the curative used and the percent stoichiometry selected.