NUISANCE: I beleive they are the same, although yield stress is the more common term. At any rate yield stess is usually used. Bear in mind not to use the yield stress alone, use a theory of failure such as the Maximum Shear Theory.
Yield Stress: "The lowest stress at which extension of the tensile test piece increases with increase in load"
Yield Strength: "The stress at which a material exhibits a specified deviation from proportionality of stress and strain."
tbh I thought that it was the yield stress that is used. But when I look up the mechanical properties that I'm using it rarely gives me the yield stress but instead the Yield Strength.
I really don’t know how to gain the yield stress when I am given the yield strength.
With regards to your suggestion of using "Maximum Shear Theory". Thanks I'll have a look at this.
I really do wonder what my degree in Mech Eng was for. I'm a recent graduate, and I'm finding that I wasn't taught all I needed know in mech eng
Your definition of yield stress doesn't seem to make sense, as any increase in load will result in an increase of extension. I suspect you missed a word.
You will often find that similar words and phrases are used colloqually, and that the usage is often imprecise, and understood differently by different people. When it is important to attempt to ensure that everyone is on the same page, you should clarify your usage by including a precise definition, or citing an accepted text or standard.
Nope, school doesn't teach you all that you need to know. In fact, you'll never know all that you need to know. The important skill to learn is how to identify when you don't know something so that you can ask questions rather than make guesses.
Hi Nuisance
What component are you trying to design its important because you should include a safety factor whish maybe governed by a design code or specification.
Yield stress and yield strength are the same thing as earlier posts have indicated.
Normally, the specification for the steel will show the yield stress OR the yield point, and you use whichever one you have. Normally, a steel specification, such as ASTM A36, will require a minimum yield strength, IE, it will specify which one is measured, and no one checks the other one.
And, in many cases, if you're designing to some standard or code, allowable stress is specified. In those cases, you don't fool with theories of failure, just maximum tensile or compressive or shear stress.
Yield strength is a property of the material. Just as ultimate strength, fatigue strength etc. are. Stress, on the other hand, is the result of a load or force being applied to that material. There is no such thing as yield stress. It is only stress and you must design your gadget so that the stress does not exceed the yield strength (or ultimate strength or fatigue strength, depending on the intent of the design) of the material. Yield strength (sometimes refered to as yield point) is the the highest stess that the material will withstand and still retain its elastic properties. That is to say, it will return to its original shape when the load is removed. This yield point is sometimes refered to as the proportinal limit or elastic limit of the material. The design should always be accompanied by a factor of safety unless you want it to yield for some reason. The safety factor used is dependent upon the manner of loading and can be found in the form of recommendations in most engineering handbooks.
You may have been dozing when it was taught, but yield stress is the level of stress when the material transitions from elastic to plastic deformation, or in the case of brittle materials to failure. As mentioned above, you must include a safety factor which provides adequate margins of safety for the particular operation. This becomes complex and a lot depends upon things like loading regimes, redundant load paths, and the criticality of results of failure. If you look at whether or not weight, flexibility, cost, and other considerations are important, most engineers will design "hell for strong".
