What's the Stress in a Spring?

Dunno, but it will be very floppy.
Can't you calculate the properties of the 'first' spring and then model a 'material' to simulate these properties (or just use the numbers) to model the 'final' spring?
I'd assume there would be very little stress in the first spring.

Or maybe you can just calculate the total lengthe of wire and ....errr....maybe I should quit while I'm behind...
Sorry if the above is bonkers
Del _{(note to self ... engage brain before posting)}

Could you give a clearer explanation of what you think?

Have you tried working with a spring manufacturer? I've had good luck in the past with them making custom springs.

Here's one site www.leespring.com

I appreciate all the responses and will look at different materials. I should clarify that this is a spring manufactured by winding a small diameter, tightly wound spring onto a mandrel to form a larger spring with an open pitch. This larger spring has a diameter approximately 10X of the smaller spring.

I used spring theory to calculate the theoretical spring constant and torsional spring stress of the smaller spring. I was then able to predict the larger spring's torsional yield stress based upon the actual tensile strength of the smaller spring.

To determine theoretical spring constant, I need the following values: Rigidity Modulus (G), mean spring diameter and number of active coils. For the smaller spring, I derived G from Poisson's Ratio and Young's Modulus. How do I derive G for the larger spring using the mechanical properties of the smaller spring? I could then plug this into the equation along with N and D for the larger spring.

Another question I have is how do I predict the ultimate tensile strength of the smaller spring? The Spring Theory equations apply to the torsional stress and the value predicts at what point the spring will yield and have permanent set. But spring theory doesn't predict the UTS. For example, the smaller spring should theoretically yield at .01lb, which it does on the tensile tester. But it has an experimental tensile strength of .16lb. From mechanics, torsional stress is 0.577 X yield tensile strength and yield tensile strength is 0.75 X UTS (for steel). By this convention, the theoretical spring torsional yield strength of 0.01lb would produce a theoretical yield tensile strength of 0.017lb and a theoretical ultimate tensile strength of 0.023lb. The theoretical spring UTS of 0.023lb is only 15% of the experimental spring UTS.

how do I predict the ultimate tensile strength of the smaller spring?
You don't...you look up the material or measure it