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 What is the shear uncorrected stress of a spring?

1. First of all, what is "shear stress"?

Shear stress is the stress that acts parallel to a surface inside an object to cause it to slide. Shear is the action of pinching an object.

It is explained in the figure below.

 When force is applied in the direction of the blue arrow to cut the material, the material repels as it is not dislocated, and force is generated in the direction of the white arrow. This force is called "shear stress".

The "shear stress" that occurs when twisting is called "torsional stress". "Torsional stress" is a type of "shear stress".

"Shear stress" occurs in "compression springs" and "tension springs".

2. Meaning of "unmodified"

"Unfixed" means "fixed".

What is the difference between "uncorrected" and "corrected"?

The design stress of a spring is the "calculated" shear stress experienced by the spring.

It is calculated under the following conditions.

① The same value of shear stress is generated all around the material.

→Actually, when the spring is coiled, the stress inside and outside is not the same.

② Use springs statically.

→ "Statically" means that there is almost no load fluctuation in the usage state of the spring, or 1000 times or less even if there is a repeated load. . 1000 times or more is not assumed.

The "calculated" value in the "preconditions" of ① and ② is the "uncorrected" shear stress.

It is a numerical value that is purely calculated. If you apply it to the formula, you can calculate it naturally.

If the spring is used dynamically (more than 1000 times), modify the stress.

How much should be corrected is generally corrected using Wahl's formula

> Spring shear stress correction factor(Japanese Page) 

3. About Allowable Shear Stress Diagram

The following diagram shows the relationship between spring wire diameter and allowable shear stress.

This is a diagram that often appears when designing a spring.

A few notes about this diagram:

① This figure is a graph of the calculated "uncorrected shear stress" for each material. You can read the numbers from the graph, but it's more accurate to calculate.

② This diagram is for a "compression spring". There is a difference between a "tension spring" and a "torsion spring".

③ The "uncorrected shear stress" at the maximum test force is the "allowable shear stress" in the figure.

④ Materials not shown in the diagram are subject to agreement between the parties concerned.

4. For tension springs

For tension springs, it is scaled smaller than the "shear uncorrected stress" for compression springs.

In this case, it is not called "correction stress". It is the "uncorrected shear stress" of the "tension spring".

The reason why it is necessary to set the numerical value smaller than that of the compression spring is as follows.

① Tension springs may be used without heat treatment (no tempering).

② Generally, the hook part has a large stress.

For tension springs, multiply the stress for compression springs by the following ratio:

① For cold-formed springs "uncorrected shear stress" of compression springs x 80%

② For hot-formed springs: Uncorrected shear stress of compression springs x 67%

In the case of a torsion spring, it is "bending stress" instead of "shear stress", so it is a completely different figure.

Related item(Japanese Page)

＞Spring design "Spring design procedure 7 points"

＞Spring design "Five points for spring material selection"

> Spring design "Five points of compression spring design"

> Spring design "Five points of extension spring design"

＞JIS standard for springs

＞Basic spring terms

＞Spring terms (dictionary)

＞What is the maximum test force of a spring?

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