An as-wound helical compression spring, made of music wire, has a wire size of 0.080in, an outside coil diameter of 10/16 in, a free length of 4in, 22 active coils, and both endssquared and ground. The spring is unpeened. This spring is to be assembled with apreload of 8 lbf and will operate with a maximum load of 22 lbf during use.
(a) Estimate the factor of safety guarding against fatigue failure using a torsionalGerber fatigue failure criterion with Zimmerli data.
(b) Repeat part (a) using the Sines torsional fatigue criterion (steady stress componenthas no effect), with Zimmerli data.
(c) Repeat using a torsional Goodman failure criterion with Zimmerli data.
(d) Estimate the critical frequency of the spring.
Step 1 : Write down input parameters.
Step 2 :Visitcompression spring design for fatigue loading and solve the problem. Results generated by the calculator are as follows.
Step 3 : For the calculation of critical working frequency of the spring, spring rate shall be calculated. Visit rate based compression spring design calculator and calculate spring rate (k). Results generated by the calculator are as follows.
Step 4 : Visit critical frequency of compression springs and solve the problem. Results generated by the calculator are as follows.
The natural frequency of the spring is calculated as 174.4 Hz. According to Ref-1, the cyclic loading frequency shall be minimally 13 times smaller than natural frequency. Based on this information, maximum cyclic loading frequency is calculated as 174.4/13= 13.4 Hz. If the loading frequency is lower than 13.4 Hz, the effect of resonance is negligible and fos values given in Step-2 can be used.
If a spring cannot be designed to have a natural frequency more than 13 times operating frequency, or if thespring is to serve as a vibration damping device, it must utilize one of several methods of energy absorption.