Viscoelastic materials are widely used in various fields. In order to better use viscoelastic materials in various working conditions, it is necessary to master the material properties of viscoelastic materials. Relaxation modulus is a characterization method of viscoelastic material properties. In this paper, by analyzing that viscoelastic materials are time-domain related parameters, the load-time curves are obtained by using the spherical indentation instrument to carry out the ramp loading indentation test at different speeds. According to the law of ramp strain history loading, the data at different velocities are summarized and a method for judging the linear viscoelastic boundary of viscoelastic materials in spherical indentation tests is obtained. Aggregate the load-time data at different speeds to obtain a set of valid data for a longer period of time. A method of measuring the relaxation modulus using the ramp-constant strain history is proposed. Compared with the ramp loading test method, it is simple and easy to operate, and it can make up for the short time period of the measured data in the ramp loading test. The experiment verifies the feasibility of the method of ramp-constant strain history.

Viscoelastic parameters of viscoelastic materials should be measured to ensure their effective use. Unfortunately, devices for effective and accurate measurement of the relaxation modulus of materials are not currently available. In this study, we designed a mechanical device that can control the spherical indenter to press on the material at a uniform speed to allow measurement of the relaxation modulus of a viscoelastic material. The results showed that the device is accurate and easy to operate. The load expressions of ramp loading (the motion of the indenter is a uniform velocity) and ramp-constant loading (the motion of the indenter is stationary after uniform velocity) were derived for the spherical indenter. The relaxation modulus function of the material was calculated by measuring the displacement and load of the indenter and fitting it using the non-negative least square method. The relaxation modulus expression of viscoelastic materials calculated using the ramp loading experiment was substituted into the derived load expression of ramp-constant loading. The values were compared with the load values obtained using the ramp-constant loading experiment and the error was evaluated. The error was less than 2.5%, indicating high feasibility and practicability of the experimental device designed in this study.

In this paper, the theory of viscoelastic material relaxation modulus testing, testing method, and material relaxation modulus parameter solution method is studied. Based on the IoT sensor test devices and the Hertzian mathematics theory, the relationship between the compression amount, pressure, and relaxation modulus of a rigid spherical indenter pressed into a flat viscoelastic material is studied. In combination with the Boltzmann superposition principle, the relaxation modulus test method and theory for viscoelastic materials are proposed. A good fitting curve was obtained to solve the relaxation modulus parameters of various materials under the three-element Maxwell model. The experimental setup and the results of the parameter fitting were analyzed to verify the feasibility and accuracy of the results.