Elinvar (source code)
= Elinvar
{c}
<Elinvar> names a family of alloys designed to have a small <temperature> coefficient of elastic stiffness over a useful operating range. This addresses a different problem from <Invar>: low thermal expansion does not automatically imply <temperature>-independent <Young's modulus>.<Nobel Lectures, Physics 1901–1921/Invar and Elinvar by Charles-Édouard Guillaume>[Discussion of elastic anomalies, temperature compensation and precision applications]{ref}
For a simple elastic oscillator, $f\propto\sqrt{k/m}$, so a small stiffness change gives $\Delta f/f\simeq\tfrac12\Delta k/k$ at fixed <mass>. An alloy with suitably compensated stiffness can reduce thermal drift in a mechanical frequency standard. Its composition, heat treatment and operating range still matter; the name does not mean exact invariance at every <temperature>.
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