Stress Analysis on Disc Spring

[Mleo11]

Anyone has experience with flexures (thin annular plate, with an etched design) that acts as a spring? The flexure is used as a centering guide and provides a spring load.

I am not sure on how to approach a stress analysis.

Any input would greatly be appreciated.

 

[israelkk]

I too could not find a closed formulation for such a spring.

You could write a computer program to analyze such a spring as a combination of curved cantilever springs in parallel. In this case the spring see torsion in addition to bending. Using this approach you can and check many design options systematically and come to the best or optimized spring with respect to the number of arms and strip thickness.

Another way is to use FEA analysis. This will be more time consuming mainly because you will need to check many design options.

Combining both approaches will give an optimized and accurate solution.

 

[TVP]

If I understand your application properly, you should be able to find some formulas for calculating forces, deflections, etc. in Roark's Formulas for Stress and Strain, specifically chapter 11 on Flat Plates. These types of spring elements are commonly analyzed using finite element models.

 

[Mleo11]

Thanks guys for the input.

I have been looking at the formulas for annular plates on Roarks. However, what throws me off is the spiral etching between the OD and the ID. Do I need to analyze that as a separate beam? My company has yet invested in an FEA package.

 

[israelkk]

Roark's doesn't have formulation for spiral like etched arm integrated in circular plate with an inner hole. Can you give more information such as:
1. What will be the use of this spring
2. what range of forces and deflection you are looking for
3. Life cycle
4. Materials (environmental conditions)
5. Will you use one spring or two as an elastic bearing too
5. Dimension constraints (maximum outside diameter, Minimum inside diameter, etc.)

http://www.webspawner.com/users/israelkk/

 

[Mleo11]

Unit is a bipropellant space component designed with no sliding parts. The flat spring, which is identified as a flexure, it has an OD (3/4"), ID (1/4"), and in between there is an etched spiral type design that frees up some of the stiffness of the flat spring. The flexure is clamped on the OD and the ID at assembly. It is used to guide a pin onto a seat and provide a load (less than 2 lbs)that adds back force to the seat . Life cycles are specked out to be 10XE6 and tolerances are pretty tight. There are a few flexures in the design with one other prodiving a different etch configuration.

 

[israelkk]

I assume you are reffering to spring close to this:

http://www.webspawner.com/users/israelkk/

 

[Mleo11]

Sorry I did not get your pic.

 

[israelkk]

I tried but it didn't work

 

[israelkk]

Try to see the file here:

http://www.yourfilelink.com/get.php?fid=4080

 

[israelkk]

You can see a picture of similar spring on page 2 of

http://www.globalcooling.com/pdfs/9_appofstirling.pdf

 

[Mleo11]

Hello,

Yes, the flexure spring is similar to our design.

The attached link illustrates a sketch of the design.

http://www.yourfilelink.com/get.php?fid=5591

 

[israelkk]

I do not understand the logic behind such an arrangement for a flexure disk spring. It is not symmetrical and will give side force and movement too. The springs at

http://www.globalcooling.com/pdfs/9_appofstirling.pdf

http://www.yourfilelink.com/get.php?fid=4080

Are symmetrical and do not produce side movement.

 

[israelkk]

One more thing, the design in

http://www.yourfilelink.com/get.php?fid=5591

is stiffer than the other two which are more logically editable to reach the desired spring properties.

 

[Mleo11]

Actaully it is symetrical, the sketch is poorly drawn. there are three symetrical bands. First band starts at 30 Deg. and ends 300 deg. The hole pattern is an old design sorry about that.

http://www.yourfilelink.com/get.php?fid=5613

 

[israelkk]

This design is not symmetrical too. See the area circled by the red circle. It appears only once on the disc.

http://www.yourfilelink.com/get.php?fid=5668

The beam between the the red circle and the green circle is wider on the middle and narrower on both sides. This is not a good design, you want the beam to be wider on one side and narrower on the other-side to get the largest deflection and the a given force.

 

[Mleo11]

It is not symmetrical because it is an undimensioned hand drawn sketch. All three bands are 120 deg. apart and start start at a radius (.160) from the center. This has not been drawn onto a Solid Works model, I am having difficulty drawing the spiral design.

There is a clamping land on the OD and ID. The the spiral band start and end on between the clamping surface.

 

[israelkk]

Mleo11:

How much deflection is needed at the 2lb load?
Is the 2lb load is needed form one flexure spring or from two (1lb each)?
Will the spring be loaded (deflected) only in one direction or both directions from free position?

http://www.webspawner.com/users/israelkk/

 

[Mleo11]

Hello:

Deflection is what we are analyzing as well as stresses.

Installed the flexure is under .007" deflection. the spring force is 1.5 lbs and the two flexures are overcoming the spring force. The flexures are moving in both directions when the open/close poles are actuated.

 

[israelkk]

I am a little bit confused.

What is the largest deflection that a flexure deflect?
How much force one flexure should give at that deflection?