Oh ok, I understand the difference from those definitions.
My revision guide has a slightly different definition for yield point which says that the yield point is the point after which there is a large increase in strain for a small increase in stress. If there is also no increase in load force, does this mean the cross-sectional area decreases just before the yield point for the stress to increase?
Also, can anybody show me where a yield point is on a stress-strain curve?
Thanks