What are residual stresses?

Residual stresses are like invisible tension inside something that’s already been made.

Imagine you're playing with a rubber band. You stretch it really tight and then let go, it snaps back to its normal size, right? Now imagine the rubber band is part of a toy car. If you keep stretching it every time you play, eventually it might feel tight even when it’s not being used. That's kind of like residual stresses, tension that stays inside something after it has been shaped or made.

When things are heated up and then cooled down quickly, like when you bake a cake and let it cool too fast, the inside might still be warm while the outside is already cold. This can make the cake feel tight on the outside and loose on the inside, just like residual stresses in materials.

Or think of building with blocks: if you press them together really hard and then take your hands away, they might stay a little squeezed even when you're not touching them anymore. That's residual stress at work!