Smaller is Stronger

Two foils (Ni and Cu) once bent, sprung back exactly the same.

Metal foils much thinner than a human hair show greater strength than expected.  The picture shows that this strength depends only on the size, not on the material properties of the particular metal.

These two foils are 10 microns thick, one is nickel and the other copper.  They have been annealed to give a large grain size (about 20 microns in both) and bent around the mandrel (the end of which just be seen at the bottom right of the picture.  Once bent, on release, they have sprung back the same amount, indicating that they have the same strength.

This experiment was carried out by Isis de Lavau and Jeremy Jardin, students from the French engineering school CESI, on placement here in September.