Effect of speed on fatigue life?
Effect of speed on fatigue life?
(OP)
Spring: about 5 in dia x 9 in tall barrel style coil spring using about .5 in wire. Fully compresed height is roughly 1.5 in.
Fatigue test: cycle spring from almost compressed height to about 4 in height at some rate until it breaks.
Question: How does that rate affect the life of the spring?
Fatigue test: cycle spring from almost compressed height to about 4 in height at some rate until it breaks.
Question: How does that rate affect the life of the spring?





RE: Effect of speed on fatigue life?
RE: Effect of speed on fatigue life?
RE: Effect of speed on fatigue life?
I know that it doesn't actually operate near the resonant frequency, but I was thinking about cycle testing as fast as 5 or 6 Hz. What does resonating actually do to the spring? I'm guessing inertial forces would add to the spring force pushing on whatever the spring is hooked up to. But how does that affect fatigue life of the spring?
OK, are there some numbers to crunch to figure out the resonant frequency? Or should I hit it with a hammer and time the wobbles?
RE: Effect of speed on fatigue life?
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RE: Effect of speed on fatigue life?
RE: Effect of speed on fatigue life?
Let me put it another way.
If four identical springs are compared before & after a life cycle test:
# action result
1 sits relaxed no change
2 sits compressed loses force
3 cycles quickly loses some force, fatigues
4 cycles slowy loses more force, fatigues differently?
RE: Effect of speed on fatigue life?
The force reduce can be a result result of a relaxation or simply because the stress was (higher than the yield shear stress where the spring actually gone into the plastic zone and yielded. The result is a minor preset (scrag). If this is the case you do not have a sufficient safety factor.
You should calculate the stress at the desired force and compare it to the material yield shear stress. It should not be more than 35% to 50% of the ultimate tensile stress depends on the spring material.
You described the spring as barreled spring, is the gap (pitch) between the coils constant? or it is variable? Is the 5" coil bottoms first or all the coils bottom (touch) each other at the same time when spring is pressed to solid?
What is the type of material the spring is made off?
RE: Effect of speed on fatigue life?
There are 4½ coils total, including the squared-off ends of about ½ coil at the small diameter.
I can live with losing some force.
My goal is to do cycle testing faster without compromising the results. Slower cycling will help the spring last longer? OK. But that means faster cycling will kill it sooner, invalidating my test?
RE: Effect of speed on fatigue life?