How to tell if a spring is fatigue, creep or degrade?

In summary, the conversation discussed conducting a spring endurance test and how the spring constant changes with continued cycles. It was mentioned that factors such as extreme temperatures and corrosive environments can affect the spring's initial set, but the principal failure due to cycling fatigue is usually fracturing of the wire in one of the coils. It was also mentioned that for critical applications, presetting is a standard step during the spring manufacturing process. The question of whether the spring constant remains the same after fatigue failure or if it fluctuates was raised, and it was noted that the variance in spring performance during testing is likely due to the testing fixture and recording rather than the spring itself.
  • #1
Travis T
18
2
I'm doing some spring endurance test.

If the spring is exceeding its cycles limit and causes fatigue failure, how normally the spring constant changes? For example, after the expected limit cycles (lets say 2million load-unload cycles), will the spring constant gradually decreases? or fluctuated as the cycles continue (after 2million)?

In simple words, how the spring constant changes (with cycles continue) if a spring is fatigue, creep or degraded? How to determine if a spring steel is degrading?

(Please assume everything is in ideal condition, as there are many factors might affect the result)
 
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  • #2
What research have you done on this subject ?

There is a large amount of easily found information on the internet relating to spring technology .
 
  • #3
simple
take a new unused spring and measure the height
next find out how much weight it takes to compress it one inch
find out how much weight to compress two inch
now you have the bench marks of new spring
do same tests on cycled spring
 
  • #4
If you referring to wire coil compression springs, these will principally only lose their initial set (free length and spring rate) if they are exposed to extreme temperatures that can anneal the material or to an environment that is corrosive to their material.
The principal failure of this type of spring due to cycling fatigue is fracturing of the wire in one of the coils not loss of spring rate or free length; but extremely rapid cycling over an extended period can result in internal heating of the spring wire that can result in a loss of spring rate and free length.

For critical applications, presetting (compressing the spring through its full travel for a few cycles) is a standard step during the spring manufacturing process.
 
  • #5
JBA said:
If you referring to wire coil compression springs, these will principally only lose their initial set (free length and spring rate) if they are exposed to extreme temperatures that can anneal the material or to an environment that is corrosive to their material.
The principal failure of this type of spring due to cycling fatigue is fracturing of the wire in one of the coils not loss of spring rate or free length; but extremely rapid cycling over an extended period can result in internal heating of the spring wire that can result in a loss of spring rate and free length.

For critical applications, presetting (compressing the spring through its full travel for a few cycles) is a standard step during the spring manufacturing process.

Thanks and appreciates!

It is a spring steel (compression), in high and rapid load-unload cycles (100ms per cycle and 2million cycles) and spring constant (k) is to be tested for each 100k cycles. (assume environment is ideal)

Since its load-unload, fatigue failure which causes fracture in the material itself might occurred. So, does it means spring constant should remained even fatigue failure occurred or ...? If internal heating exists, does the spring constant would have observable decreases?

Will spring constant fluctuates through cycles... or perhaps it is just the tolerance of data recording?
 

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  • #6
First, if I understand what you have asked about a chance in spring constant after fracture that would not make any since the spring is now in two broken parts and spring constant is dependent upon the spring's total number of coils.

With sufficient internal haeting some portion of the spring could approach the annealing temperature of the spring alloy and this would result in a softening and loss of temper in the spring wire so there would be a corresponding loss of spring constant and could result in permanent deformation of coil in that region.

Quality manufactured compression springs are very consistent and repeatable in their performance, so I would expect any variances during testing to be related to the testing fixture and recording not to a variance in the spring itself.

While having said all of the above, there is no such thing as a perfectly manufactured spring so there can be some variance in the finished free length, spring constant and fatigue life between test samples of springs manufactured to the same design and specifications.
 
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Likes Travis T

Related to How to tell if a spring is fatigue, creep or degrade?

1. How can I determine if a spring is experiencing fatigue?

To determine if a spring is experiencing fatigue, you can conduct a fatigue test in which the spring is subjected to repeated cycles of loading and unloading. If the spring shows a decrease in performance or stiffness over time, it is likely experiencing fatigue.

2. What are the signs of creep in a spring?

Creep in a spring is characterized by a gradual increase in deformation or displacement over time when subjected to a constant load. This can be observed through measurements of the spring's length or deflection.

3. How can I tell if a spring is degrading?

A spring that is degrading will exhibit a decrease in performance, stiffness, or load-bearing capacity over time without a significant change in external factors. This can be determined through regular testing and monitoring of the spring's performance.

4. Can a spring experience more than one type of failure?

Yes, a spring can experience multiple types of failure simultaneously. For example, a spring may experience both fatigue and creep if it is subjected to repeated loading at a constant load over a long period of time.

5. What factors can contribute to spring failure?

There are several factors that can contribute to spring failure, including improper design, material defects, overloading, exposure to extreme temperatures or corrosive environments, and inadequate maintenance or testing. It is important to consider all potential factors when evaluating the cause of spring failure.

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