Could you please tell me how to calculate the service life of S-shaped springs that are used repeatedly (twisted) for car seats, etc.?
Mr. Nakatani, the design method and calculation method for springs for cars’ seats are different for each spring, such as zigzag springs, foamed wire springs, etc.
If it is an S-shaped spring used repeatedly, I think it might be a zigzag spring. The basic specifications are material diameter: d, pitch: p (twice the loop radius r), and torque bar length: 2l.
A typical example of calculating the basic planar shape of a zigzag spring is as follows.
Tensile spring constant: k = longitudinal elastic coefficient × π × d ^ 4/64 × number of peaks ((2/3) × l ^ 3 + r (π × l ^ 2 + 4lr + (π / 2) r ^ 2))
Maximum bending stress: σ = 32 × load (l + r) / π × d ^ 3)
In addition, there are calculation formulas according to various conditions such as equivalent bending rigidity and seats’ load-deflection, but not all can be described here and I am sorry for that. (Reference: Japan’s Spring Society “Spring” 3rd edition)
Recently, it seems that there are many springs with complicated shapes, and it may not be possible to deal with them with the basic formulas. How about using the finite element method as well?
