Stress solver advice

[mark smith]

Hi All
I have recently been doing some analysis of some photo etched small flat spring designs made of 301 stainless steel see attached images. The material thickness is ~0.5mm to give an idea of scale.
My analysis was to find the deflection verses force for the centre section so I could produce a design with the required force at the required deflection. In the actual application the part is permanently deformed i.e. certain areas are permanently stretched, so for large deformations I didn't expect my analysis to be accurate even though I used a strain dependant young's modulus? On having some parts made, I measured the spring rate at small deflection and was surprised to find that the spring rate was only about 1/3 that Elmer reported ;-(
Q: is this problem a geometric non-linear one which Elmer's StressSolver is unsuitable for?

Are problems of this type, preferably with large deformation and a non-linear material model, beyond the scope of Elmer & if so can anyone recommend any other open source or low cost commercial software that might be suited?

Thanks in advance and best regards
mark