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Tutorial on Helical Springs Stability and spring Buckling

By Prof S S Chauhan, IEC College of Engineering & Technology, Greater Noida
Stability of the spring (Buckling)
Buckling of column is a familiar phenomenon. Buckling of column is a familiar phenomenon. We have noted earlier that a slender member or column subjected to compressive loading will buckle when the load exceeds a critical value. Similarly compression coil springs will buckle when the free length of the spring is larger and the end conditions are not proper to evenly distribute the load all along the circumference of the coil. The coil compression springs will have a tendency to buckle when the deflection (for a given free length) becomes too large. Buckling can be prevented by limiting the deflection of the spring or the free length of the spring.

The behavior can be characterized by using two dimensionless parameters, critical length and critical deflection. Critical deflection can be defined as the ratio of deflection (y) to the free length (Lf) of the spring. The critical length is the ratio of free length (Lf) to mean coil diameter (D) The critical deflection is a function of critical length and has to be below a certain limit. As could be noticed from the figure absolute stability can be ensured if the critical length can be limited below a limit.

Similarly compression coil springs will buckle when the deflection (for a given free length) becomes too large. The condition for absolute stability can be given as:

For steels this can be simplified as:

Where a is a constant related to the nature of support of the ends simply referred as end constant