Understanding Spring Lifespan: Insights from a Mechanical Engineering Student

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In summary, the life of a structure under oscillating stress is determined by one of three criteria, with the fatigue limit being a critical factor for steel springs. Other factors must also be considered in real-life situations. It is important to understand this when designing machines.
  • #1
Hydroshock
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So currently I'm in school for Mechanical Engineering, though I got a general question.

I could have sworn that I read in my physics book working up to the point I am now reading that as long as a spring isn't pushed past it's stress point that it should last forever. Though now I have had someone trying to tell me that it would last only so many cycles and wear out over time ? I'd suppose this would be somewhat important to know for sure when designing machines.

If anyone could answer that would be great.

Thanks.
 
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  • #2
If a structure is known to last at least 10e6 cycles, then its life is assumed infinite. The life of a structure under oscillating stress is generally determined by one of three different criteria, the modified Goodman, Elliptical, or ASME (i think?) criteria.

And yes, this is VERY important for any machine design.
 
  • #3
A quick google gave me this link:

http://www.mech.uwa.edu.au/DANotes/springs/fatigue/fatigue.html

Summarizing a little, since most springs are made of steel, they have an endurance or fatigue limit. This is a strength that which below, the part can "theoretically" endure infinite cycles. Aluminum materials typically do not exhibit this limit, but since steels do, there is a stress that which below you can assume infinite cycles (give yourself a good safety factor though).

In real life, one would need to account for other factors which may limit a parts life
 
  • #4
Think of it this way, each stress cycle lowers the maximum allowed stress a lil bit. So after many many cycles, maximum permissible stress ll come near to the operating stress, & failure.
This is just a crude explanation. Read mechanism of fatigue loading from metallurgy book to understand it in a better way.
 

1. What is a spring?

A spring is a mechanical device that is typically made of metal and is designed to store and release energy in the form of movement or force. It is usually in the shape of a coil or spiral and can be stretched or compressed.

2. How do springs work?

When a spring is stretched or compressed, it stores potential energy. This energy is released when the force that is stretching or compressing the spring is removed. The spring then returns to its original shape, releasing the stored energy.

3. What are some common uses for springs?

Springs have a wide range of applications, from simple household items such as pens and mattresses to more complex machinery such as car suspensions and watches. They are also commonly used in industrial settings, such as in valves and pumps.

4. What factors affect the behavior of a spring?

The behavior of a spring is affected by several factors, including its material, size, shape, and the amount of force applied to it. The type of motion, whether it is stretched or compressed, also plays a role in how a spring behaves.

5. What are some safety considerations when working with springs?

When working with springs, it is important to handle them with care as they can exert a significant amount of force. It is also important to wear protective gear, such as gloves and eye protection, to prevent any potential injuries from flying springs or sharp edges. Proper maintenance and regular inspections are also necessary to ensure the safe operation of equipment that uses springs.

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