APPLICATION OF THE IITRI COMPRESSION TEST FIXTURE AT ELEVATED TEMPERATURE.

In the reported research program, the IITRI test fixture was used to determine compressive material properties of HTS/PMR-15 graphite/polyimide material at elevated temperatures (589K (600 degree F)). A total of seventy-nine test specimens of various laminate orientations and widths were tested to verify feasibility of the IITRI technique at such temperatures, and to determine the effect of specimen width and temperature on modulus and ultimate strain values. The IITRI specimen was analyzed using three-dimensional finite elements to determine the magnitude and location of stress concentrations to assess their potential effects of measured moduli and ultimate strains. The ultimate strain and modulus data obtained in the study indicate that graphite/polyimide is an attractive material for use at temperatures up to 589K (600 degree F). All lamiantes tested exhibited nonlinear behavior. The variation of modulus values with strain was sufficiently large that design moduli should be based on operating strain levels. Theoretical considerations are included.