I have designed a stamped sheetmetal battery contact (leaf spring) made from 0.2mm Phosphor Bronze. My beam Length is 7mm, width is 1mm and thickness is 0.2mm. I ran through all the calculations using 2mm deflection value and 2N load, and resultant stress is 1266MPA. I have confirmed this value both with hand calcs and also using spring designer software.

According to my data this stress value is 171% of MIN Tensile Strength (107KSI/738MPA).

In my mind, this means that the spring should have plastic deformation and therefore set when it is deflected. It is not and fundamentally I cannot understand why.

Any thoughts?

this is not the first spring I have designed and in all my previous designs I have never been so greatly above TS value and still not see deformation.