Abstract: A device for, and a method of, applying an incremental strain to a test specimen of a solid propellant which is at the stress-free temperature, while simultaneously subjecting the test specimen to an incremental temperature change above and below the stress-free temperature. The device includes a frame assembly in which a captive "strain multiplier" is used to apply the thermally induced loads to the test specimen of the solid propellant that is mounted within the device. Temperature changes, above or below the stress-free temperature, cause volume changes of the rubber members of the "strain multiplier" and result in the "strain multiplier" axially loading the mounted test specimen in simulation of the loading conditions that occur in a case-bonded solid rocket grain. When the temperature is raised, the rubber members expand and exert an axial compressive load on the mounted specimen; and, when the temperature is lowered, the rubber members contract and exert an axial tensile load on the mounted specimen.