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A new method for determining the spring and damping constants for elastomer materials is presented. The method relies on three concepts-measurement of force and displacement or velocity across the test specimen, precise control of differential phase shift and sensitivity in transducers and electronics over the full operating frequency and amplitude range, and automatic optimal identification of K and C using analog hardware. The technique may be used in conjunction with either a resonant beam or electrohydraulic system, as demonstrated in the paper. Typical error sources are presented for both systems with indications given of their elimination by the new technique. Hardware implementing the concepts is described and calibration test results given. It is concluded that the system provides an automatic test procedure which has the potential to reduce errors and maintain consistent results for rubber properties, relatively independent of the test machines and operators.

Dynamic analysis of the resonant beam machine is presented. Equations typically used to determine the dynamic properties of a rubber product are derived from a simplified model. A complex mathematical model representing a more realistic parametric system identification is formulated. Using the complex model as standard, the errors in the results from the simplified model are identified quantitatively, and it is shown they can be considerable. The sensitivity of the errors to the system parameter variations is also shown. These machine errors may be virtually eliminated by measuring the transmitted force and displacement across the sample.

An instrumentation system is described which provides on-line computation and direct readout of C and K. The system relies on the measurement of force and displacement or velocity across the sample and is independent of the type of test machine. Errors introduced by unwanted phase shift in any instrumentation system are discussed. This is overcome in this measurement system by phase compensation. Calibration of the system is described in which an overall system accuracy can be determined independent of test machine or rubber sample. This system has been specifically designed for measurement of dynamic properties of rubber and provides the operator with direct readout of C and K scaled to engineering units, thereby reducing potential operator error.