When you try to bend a metal spoon, initially you might find it's a bit hard, but once it starts to deform, the resistance is reduced. Why is that?
A metal material yields after a certain amount of deformation. The yield point/surface is the threshold of plasticity. It's an abstract concept that we need to define in simulating metal plasticity.
In this lesson, we discuss the definition of yield point/surface.
Here are the accompanying handout slides for this lesson.