The stiffness of a element is the amount of load required to produce a unit displacement of a metal bellows or other elastic element, usually expressed as "K". If the elastic behavior of the element is nonlinear, the stiffness is no longer constant, but varies with the increase of load. General engineering bellows type elastic elements, stiffness tolerance can be limited to +/-50%. The stiffness of bellows is divided into axial stiffness, bending stiffness, torsional stiffness and so on. In the application of bellows, most of the force is axial load and the displacement is linear displacement.

I、main design and calculation methods for the axial stiffness of bellows:

1、Calculation of bellows stiffness by energy method

2、The empirical formula is used to calculate the bellows stiffness

3、Numerical calculation of bellows stiffness

4、EJMA standard stiffness calculation method

5、TOYO method for calculating stiffness

6、KELLOGG stiffness method

II、Main research methods of bellows:

1、Perturbation method

2、Initial parameter method of numerical integration

3、Integral equation method

4、Perturbation finite element method

III、The main bellows stress calculation:

1、Numerical calculation of bellows stress

2、EJMA stress calculation method

IV、Calculation of effective area of main bellows:

1、The concept of effective area and the change of effective area

2、The volume effective area of the bellows

3、Calculation of the effective area of bellows

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