Question:
I was wondering if anyone can give me a proper definition of yield
stress?
The thing that is confusing me is if yield stress is the same as the
yield point yield point? My current understanding of yield stress is
it's the range at which a material have elstic properties whereby the
material would return to its original shape even if a force is
applied. However I believe that if I answered a exam question like
this it would not be correct as I have not applied stress part into
it.
Answer:
Yield stress is the point where plastic deformation of the structure
begins to happen. Beyond the yield stress, the part of the structure
which yields will not return to its orginal shape.
Some materials return to their original size if stressed below some
limit value, and remain stretched if stressed over that limit.
Steel is usually considered this way.
Other materials do not have a clearly defined knee beyond which they
yield, so an arbitrary low level of yield is taken as a measure of
their yield point. Aluminum alloys are often specified (and stressed
to) the 0.1% yield value.
On the stress strain curve of a ductile material below the yield point is the elastic range where stress is proportional to strain. Beyond the yield point stress is no longer proportional to strain and enters the plastic range. At this point and above deformation will not return to its original shape and stress tends to redistribute to other points in the material. This a property of a material such as steel that has ductility.
