Get value from a nonlinear stiffness graph

[korper]

I have got a nonlinear graph for a nonlinear spring on the paper. Is that possible to scan it and transfer to a recognizable table for the phy. properties of the spring? Matlab can do so?
or, The only way is to select dozens of point and cauculate the Stiffness by them with certain algorithm?

 

[brad]

Your statement seems to presume that there is a single value for the stiffness of the nonlinear spring. For a linear spring, there is one value of stiffness; however the very definition of a nonlinear spring is one in which the stiffness varies with displacement.

Typically nonlinear stiffnesses are handled either in a piece-wise linear fashion (which would require 'picking the points'), or they are described using a discrete equation which is then curve-fit to the existing data (generally using a least-squares fit).

I have in the past scanned in nonlinear curves, then utilized cad software to extract a curve which is then discretized in many different points. These points can then be fed into any math processor (matlab, mathcad--even excel) and then curve-fit utilizing appropriate assumptions.
Brad

 

[korper]

I have in the past scanned in nonlinear curves, then utilized cad software to extract a curve which is then
^^^^^^^^^^same to my case^^^^^^^^, But what is the software and How to discretize to points. Do U mean raster to vector conversion? Is there any other simple way?

Anyway thanks!