# How to find stiffness using load versus defelection curve?

1. Feb 25, 2009

### perfectz

I know that stiffness is load per unit deflection. I have the load versus deflection curve for a steel plate. Is it possible for me to find the stiffness of the plate?
Thank you.

2. Feb 25, 2009

You could translate it into a stress strain curve and the slope in the elastic zone is the E-modulus. If you have the geometry.

3. Feb 25, 2009

### minger

By definition the stiffness would be the slope of the line at any given point. However, due to nonlinearities, your line is probably not linear. You could simply take the initial slope of line.

4. Feb 25, 2009

yes of course

5. Feb 25, 2009

### perfectz

THank you...

6. Feb 28, 2009

### Dr.D

The stiffness value you want depends somewhat on your purpose for finding the stiffness, particularly if the load-deflection relation is nonlinear.

For many purposes, it is useful to define an average stiffness that represents the average slope over some working deflection range, whatever is appropriate to the situation appropriate to your problem. This would be the slope of a chord to the load-deflection curve, rather than the slope at a point. Obviously it will not be exactly correct at more than one point (the mean value point), but it will be somewhat close over the whole range.