Strong Steel wire but an elastic spring? Why?

[tlfx1996]

The steel wire can withstand strong tensile stress, but when the steel wire is being coiled into a spring it can be an elastic spring. Why is this? Can this be proven mathematically?

 

[rcgldr]

How much resistance will that strong steel wire provide against a twisting motion, opposing torques applied to opposite ends of the wire, which is most of the relative deformation in the case of a spring?

 

[tlfx1996]

I'm sorry, can you explain your answer straight away. Ii'm not sure of the answer. thx

 

[256bits]

A straight rod will have some resistance to being twisted or having a torque applied to it. There will be a stress and strain asscociated with the amount of twist.

Now coil up the rod into the shape of a coiled spring. If a force is put on the spring, the rod, or rather a cross section through a part of the coiled rod, even though coiled up, can be analyzed for the stress and strain in the same manner as the straight rod experiences a torque.

For a coiled spring loaded axially,
http://www.codecogs.com/library/engineering/materials/springs.php
http://nptel.iitm.ac.in/courses/Web...ials/lects & picts/image/lect20/lecture20.htm

When they say shear and bending can be neglected, they mean a pure axial load, so no sideways force or a moment is to be applied to the spring.