The yield stress should be between the elastic limit and the ultimate stress  hence, you can use the 0.2% offset method and the yield stress and the ultimate stress point are not thesame.

You should use Point A from 0.2% offset method as the yielding point and Point B is actually ultimate tensile strength for your test.

Ultimate tensile strength can be a yielding point for a very hard and brittle material where material shows higher modulus and fails without showing much of plasticity.

Hope it helps!

What is your problem? No problem.  You have point  A  as proof stress (based on o.2% off-set method) and point  B  as the tensile strength (ultimate point)

Good Luck

Dear Hsu

The yielding point is a point after which the stress strain curve deviates the hooks law i.e. Stress and strain deviates from linearity.

That is the reason we take offset point 0.2% and draw a parallel line. The point that deviates is your yielding point.

In your case, its POINT A is yield point.

Yes after yield point your stress can either increase or decrease depending on material properties.

For your second question :

Yeilding point and Ultimate tensile strength(UTS) can be same. However, it is possible in highly brittle materials like ceramics.

In your case, it is a polymer, which is quite ductile in nature. So in your case the UTS and yield point are different and well distinguished. So POINT B is UTS.

Hope it helps

Regards

Santosh