Testing On Stress Relaxation And Lifetime Analysis Of Miniature Tension Springs And Torsion Springs

Stress relaxation is one of the main forms of failures for the spring. Stressrelaxation is not easy to be observed and is often ignored, but it may be result in veryserious damage. Because of wide applications and importance of spring material andelastic element applications, in-depth investigation of the variation of the stressrelaxation, and finding effective preventive measures become an important issue forthe basis of theoretical research in materials science and engineering.In this paper, we studied stress relaxation behavior of the tension spring in thepressure relay at100°C, using the traditional cycle operations and continuous testingmethods. The experimental results show that due to the existence of the error inhandling process and the measurement repeatability is poor, the traditional cyclemeasurement fails to reveal the true relaxation law. The continuous stress method oftesting can discover the stress relaxation rule of the tension spring. The stressrelaxation curve of tension spring and the relaxation rate-time curve is similar to thatof the compression spring, which shows two distinct linear stages.In order to study the law of stress relaxation about the torsion spring and achieveaccurate prediction of the actual life of the torsion spring in service, we designed ahigh-temperature electronic relaxation testing machine for torsion spring. The devicecan test the stress relaxation curve below300°C such as torque-time, twist angle–time, torque-twist angle relations continuously and accurately. The paper alsoinvestigated the stress relaxation of QBe2torsion spring in120~220°C with thedevice. The results show that the stress relaxation ratio of the torsion spring wouldincrease as the temperature increasing. Stress relaxation kinetics is linear in thecoordinate system of the relaxation rate-logarithmic time. The relationship of therelaxation rate-time can be expressed with the formula of Ts/Ts0=A+Blnt and theactivation energy Q is estimated as0.248eV by the Arrhenius calculation. Logarithmof relaxation rate-reciprocal of temperature curve of the torsion stress is linear,indicating that it is viable to predict the stress relaxation lifetime of the torsion springstored at room temperature by a temperature acceleration test.