Springs are the mechanical parts which have many application in industries. Static and dynamic forces cause relaxation in these parts so that they lose some of their free length and reaction force. Springs constant are very important in airplane and vailway industry since constant and variable forces are applied to them in period time, therefore it is necessary to avoid decreasing in spring constant in this condition. In this research, at first manufactured springs were stress relieved under different temperatures. In the next step constant displacements were applied to stress relieved springs by means of designed fixture. Springs constant changes and rate of these changes during different stages of the test were obtained. Results shownd that the stress relieving at 300 ° C has the best effect on prevention of decreasing in springs constant and free length under static long-term load. پرونده مقاله

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 . پرونده مقاله