GMNA GM9914P PDF

This Procedure is used to determine the physical behavior of a sealer material under pressure conditions. The materials compressibility/rebound characteristics are determined by this procedure. This test is of particular value for materials containing fragile filler components such as glass microspheres or plastic microspheres as the results can be used to predict the crush or damage to these components under hydrostatic pressure.

A Johnstone Sep-Check test apparatus, or equivalent (ref: SAE J1864), is used to conduct this test. A sealed steel cylinder (of initial volume 9.2 inches³) is completely filled with material to be tested, loaded into the Sep-Check load frame and subjected to a progressive increase in loading upon the pressure cap. This load is applied in a manner which increases the internal hydrostatic pressure of the material by a measured increment (usually 200 psi). Any displacement of the pressure cap is measured by means of a dial extensometer or LVDT. Two (2) measurements are taken at each pressure increment – the air pressure in the loading cylinder (total applied load) and the displacement of the pressure cylinder cap (total compression). By calculating and plotting the material can be constructed and used to determine effective compressive modulus (resistance to compression) and filler yield point (failure limit of pressure sensitive filler components). Finally, the total material compression for a peak loading pressure can be separated into rebound (elastic) and crush (permanent) compressive elements.