Choosing the Right Yield Stress

Do i have to take for each section of thickness a different yield stess ? Can anybody help me please ?Yes and no. If you are looking for the Y of the material then no. If you are doing a comparison of the component then yes.

I am sorry but i dont understand you. I know the mises stress of this disc/plate and now i want to check if the stresses are above the yield stress limit. And for various thicknesses/diameters there are different yield stress given, that's my problem. Do i have to calculate with a yield stress of 650 MPa for the lower part and 750Mpa for the thinner areas ?

Not if it is the same material. The Y of a given material will change slightly from one T to another T but the graph of Y will always be close for a given material despite the T change.

We always graph out the Y on different thicknesses of the same material due to code requirements and its fairly consistent.

However if you are testing the Y for design purpose then the unit has to be tested as a whole and not section by section.

Yes, the part consists of one material.Does this mean that i have to use a yield stress of 650MPa for the hole part because the thickest area is 52mm thick ?

No! The material strength is not related to the thickness. The strength of the part is related to the thickness.

With a second look it seems the datasheet specifies different delivery options for the same material (!?) and if it is the data sheet for your material you probably have to chose what the raw material size is and then you use the stress given for this.

Seems odd that the stress is size dependent.

As per my post (#11) below, since this is a heat treated material with a Quenching cycle, the cooling rate of the material is affected by the bulk mass of the material. As a result, a thicker plate or larger diameter bar will cool slower than thinner or smaller diameter one; and, the cooling time affects the phase change and internal structure of the material; which; in turn determines the finished properties of the material.

If you would like to see and learn more, I recommend you go to the below website. It has a straightforward more detailed discussion on this subject.

https://en.wikipedia.org/wiki/Quenching

I sincerely hope this is homework, and that you are not being paid to work this out.

It's like saying "I just bought a new car. Can someone tell me how to drive it?"

GA Yield stress is yield stress for any given grade of material no matter what the thickness, at least that's what I recall from my schooling. I have designed a lot of things in my life time(most without the use of modern technology, i.e., computers) using this fact, and none have failed yet.

ok thanks, i got it now

There one comment that I have to make regarding the the yield stress table listing, while it may be inferred, I think, for clarity, the two material entries should be titled respectfully by "Bar Diameter" and "Plate Thickness".

Apart from that, it concerns me that we really don't know how dogge92 intends to use this information, i.e., for analysis a part that is going to be machined from supplied heat treated bar or he is trying to apply it to a part to be heat treated after being machined.

To expand on my first post, this is a heat treated quenched and tempered material and, due to the effect on cooling rates during quenching, assuming Dogge92's parts are to be machined from bar, the bar diameter to be used for machining each part determines the appropriate yield strength to apply in that part's design analysis, regardless of the finished dimension(s) of the part.

Thank you