SHORT TIME CREEP-RUPTURE PROPERTIES OF LAMP WIRE

Short time tensile creep rupture tests were made on 7 mil lamp filament wire and on 7 mil undoped tungsten wire at 2500 to 3100 K. Steady-state creep rate was described by an expression having the form: epsilon equals AD( sigma /E)**m, where A is a constant, D is the self-diffusion coefficient, sigma is the creep stress, E is the elastic modulus, and m is 5 for undoped tungsten and 25 for lamp grade wire. Activation energy for time to failure of lamp wire was found to vary from 150 to 185 kcal. Failure modes and reasons for the very high creep strength observed for lamp wire are suggested.