Material that generates / emits heat when flexed/struck (similar to piezo) without breaking down?

Question

for an application where a small amount of warmth is needed, and electrical or other power sources are unavailable... could simple flexing / working of the material generate a small amount of heat, without destroying the material over time.

Answer 1

If you keep flexing it often, it strain hardens and then fractures at the place of flexture. A radioactive powered battery or a chemical generator may be other options.