Nice to meet you. I designed an extension spring (SWP-B) within the allowable value and operated it 1 million times, but the specified load dropped by about 1% before and after the processing process. Since the JIS tolerance is ± 8%, I think it is in a negligible range, but is this phenomenon usually happen?
Thank you for writing to us, TETSU! Actually, there is a possibility that some load loss may occur due to working stress and heat treatment during manufacturing. In addition, there is a possibility that this is caused by the initial permanent deformation!
Thank you very much. What is the reason for the initial permanent deformation? (Strictly speaking, is it because the stress-strain curve is not linear?)
Hello TETSU! If the stress-strain curve exceeds the elastic limit, it may not be linear. Also, in a high-temperature environment, when certain stress is applied to the material for a long time, the strain is large at the beginning, but the strain gradually decreases and eventually disappears. This often happens to springs. Even at room temperature, the phenomenon is more likely to occur, though not as much as at high temperatures.
