Grain Strain Measurement Method Research

It's the large strain of propellant grain under load condition that plays an important role in the evaluation of solid motor's working safety properties. Nowadays, the main focuses of domestic research lie in the stage of numerical analysis. The experimental analysis and research, however, are developing at a low pace. Therefore, it's necessary to study the strain measurement method of the propellant grain in experiments.This paper analyses the generating mechanism of strain, and demonstrates the characteristic and measurement speciality of the grain's strain on the basis of the properties of solid motor and grain. Meanwhile, the measurement methods of large strain in general use are discussed, and the feasibility is discussed qualitatively that these methods are applied in the strain measurement of the propellant grain inside the motor. The temperature impact and tensile tests to the research object are made by means of resistance strain gauge. Besides, its feasibility is discussed deeply. As the research shows, it's practical to measure the large strain of modified double base propellant grain by means of large strain gauge, while the measurement methods for HTPB propellant still needs further study. This paper theoretically analyses the output nonlinearity which results from the case when the large strain is measured by means of resistance strain gauge. And two methods for the nonlinearity compensation are discussed as well. The measurement method for large strain based on bow beam is put forward, since there exist certain problems when the grain strain of some materials such as HTPB propellant are measured by means of resistance strain gauge. The working principle of bow-shape strain sensors is shown, and its mechanical characters are demonstrated precisely. What's more, the numerical simulation analysis is acquired by the finite element software of ANSYS, and the strain sensors of four specifications are manufactured in the designed parameters. The bow-shape strain sensor calibration system of large strain is structured, and the designed sensors got calibrated statically. The parameters of static characteristic are obtained and the experiments of test feasibility for sensors are made, with the consideration of the grain. As the results show, this method can accomplish the large strain measurement of the propellant grain as expected, and it is possible to be turned into practice.