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    Coil Spring Stiffness

    A coil spring is made by winding a wire around a cylinder. Here we consider a tension/extension or compression spring.

    coil spring.PNG

    In the simplest case the spring has linear deformation curve (Hooke's law), so we can calculate the constant stiffness coefficient (N/m):

    k=G⋅d48⋅D3⋅nk = \frac{G\cdot d^4}{8\cdot D^3 \cdot n}

    Where G - shear modulus, d = wire diameter, D - spring coil (measured by coil center line), n - number of coils. For spring steel the typical shear modulus value is 78.5 GPa.