investigation of effects of stress relieving parameters on reduction of austenitic spring free length during periodic loading

after springs production, different residual stresses are created in the inner and outer surfaces of spring wires. some of these stresses for example compressive residual stresses are useful and some are harmful. the effects of vareation of these stresses are caused spring relaxation and decrising in their free length when they are loaded intermittently. for review this phenomena in this research, first a test device with 0.5 hz operational frequency was made. then with the idea of operation mechanism of milling machines dividing attachment and cams mechanism and performance, a fixtures was designed and manufactured in order to apply displacement and preload to springs. in the next step manufactured springs were stress relieved under different temperatures and times.after that they were loaded intermittently and their free lengths after 10,000  cycles were measured. investigation on tests results showed the effects of changes in temperature and time of stress relieving on springs free length decreasing. two approximate equations with first and second degree were extracted from experimental data. finally, optimal operation of stress relieving was obtained .