A new hydrostatic compression tester for anisotropic filled polymers

This paper describes a testing device designed for measuring the isotropic or anisotropic hydrostatic compression properties of filled polymers like solid propellants, including the initial void content and the bulk modulus. The propellant test samples used are either cubical, cylindrical, or rectangular specimens. Three pressure-sealed linear variable differential transformers (LVDTs) are used to monitor the dimensional changes of a cube specimen during hydrostatic pressurization simultaneously in the XYZ directions. The moduli E11, E22, and E33 and the compression strain ratios v21, v32, and v31 can be determined as a function of pressure. The three LVDTs can also be used to measure the length changes of three rectangular or cylindrical test specimens under hydrostatic compression only in the vertical Z direction. The bulk modulus and void content can be computed when isotropic behavior is assumed. The entire test procedure is controlled by an Apple II microcomputer via an AI13 12-bit analog input system. Some typical test results obtained with undamaged and damaged propellant samples are described.