Study on Sag Test of Hot Coiled Compressive Spring for Suspension

Abstract

The sag of coil spring has usually been estimated by creep test or relaxation test. However, the condition of those tests are not standardized.
The aim of this paper is to present the experimental results which could give some assistance for standardizing the method of sag test. It was realized that the measurement of sag should be made at normal load of coil spring and the appropriate time of test was 96 hours. Experiments were also carried out about the influence of temperature and the correlation between the sag of coil spring and that of those tests.
For estimating the sag-resistance of material, three testing methods, which are torsional-creep method, torsional-relaxation method, and hysteresis loop method, were compared. The conclusion in that the torsional creep method have been reasonable accuracy, and good correlation with the sag of coil spring.