SynopsisModel substances were prepared of a.polyurethane rubber filled with different amounts of various fractions of sodium chloride. Eight filler fractions were used of sizes in the range of 1-480 pm. The amount of filler was varied between 0 and 50 v01.-%. An experimental method is described by which thermal expansion and bulk modulus of an isotropic material may be simultaneously determined as functions of temperature.The materials were investigated for thermal expansion and bulk modulus. All filled and unfilled samples show a glass-rubber transition, at which temperature the thermal expansion coefficient increases considerably and the bulk modulus decreases sharply. These temperatures do not depend on amount or size of filler. The values of the bulk moduli and the thermal expansion coefficients are independent of filler size, but depend considerably on the volume fraction of filler. These values may be predicted by means of a simple macroscopic theory (Frohlich-Sack-Van der Poel,) describing the bulk modulus, the thermal expansion, and the density of the composite material in terms of the corresponding properties of the components and of their relative amounts.
INTRODUCTIONRecently the mechanical properties of highly filled elastomers have aroused considerable interest in connection with the use of these materials as solid propellants in rocketry. Most composite propellants consist of elastomers highly filled with inorganic oxidizer. Mixing is effected in an uncrosslinked state where the polymer has still low molecular weight and the consistency of a viscous fluid. Then the mixture is cast or extruded into the desired shape and hardened by polymerization and crosslinking. The degrees of loading for those systems are very high and are, depending on composition, between 65 and 85 vol.-%.For the proper understanding of the mechanical behavior of solid propellants, knowledge is essential on the relationship between composition and mechanical properties of these highly fded elastomers. The work described here was undertaken to investigate the influence of filler characteristics, such as size, shape, and content on the mechanical behavior of Wed elastomers.
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VAN DER WAL, BREE, AND SCHWARZLTo avoid complications in the preparation and handling, this investigation was performed with chemically inert fillers. The compounds were prepared on a kilogram scale, and consisted of polyurethane rubber filled with various amounts of fractions of sodium chloride. The size of the fractions ranged from 1 to 480 pm. The amounts incorporated were varied in the range of 0-50 vol.-%.These substances were subjected to,extensive mechanical investigations. Tensile properties and shear moduli of these substances in relation to filler characteristics have been published elsewhere.' The present paper deals with thermal expansion and with the behavior under hydrostatic pressure as related to filler characteristics.
EXPERIMENTAL Technique for the Determination of Bulk Modulus and Thermal ExpansionAn apparatus was developed for the ...
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