Yield in Material
Yield in Material
(OP)
Good Morning Everyone,
I am working on some beam deflection problems for work. I am calculating not just if the outer surface of the material is going to yield or not but exactly how deep the yield penetrates the material. Is there a standard practice percentage that yield can go into the material before the percentage of material not in yield can no longer snap the other back?
Thank you,
RMX
I am working on some beam deflection problems for work. I am calculating not just if the outer surface of the material is going to yield or not but exactly how deep the yield penetrates the material. Is there a standard practice percentage that yield can go into the material before the percentage of material not in yield can no longer snap the other back?
Thank you,
RMX





RE: Yield in Material
Permanent deformation will occur when the elastic limit is exceeded. It is the lowest stress at which permanent deformation can be measured. Most metals have a linear stress-strain relationship up to the yield point.
http://www
RE: Yield in Material
RE: Yield in Material
RE: Yield in Material
RE: Yield in Material
Tobalcane
"If you avoid failure, you also avoid success."
RE: Yield in Material
Also, look at the same link with a "15" at then end. I don't think there is a "standard percentage" like you are after.
RE: Yield in Material
The part that has yielded may lead to crack formation or corrosion intrusion.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Yield in Material
ITstuff - The part I am currently dealing with is a simple plastic component that will flex around a snap feature and snap in behind it to create a positive snap. Therefore, cracks or compromised material is non-important as this material will only see a compressive load. That is why I have been asking about an industry standard but it seems there really isn't one. I can see that if this was a metal component that compromisation would be much more critical but in my specific case it is not all that important.
Thank you all for your inputs. Let me know if any of you have any more thoughts!
RE: Yield in Material
Designing Plastic Parts for Assembly, 6th Edition
http://
Joining of Plastics: Handbook for Designers and Engineers, 3rd edition
http
RE: Yield in Material
sigma(bending)=Mc/I where you vary c from 0 to the outer surface and find where sigma(bending)>= the yield stress?
Dan
RE: Yield in Material
However, let's say that you could magically determine that every part of the material is exactly the same. The next problem is that it would be shape-dependent.
Next, if you say that you only have a certain part of the material in yield, you have to remember that once you yield the material, if you're talking about steel or aluminum, you have made the material stronger, per strain hardening. So now you have a deformed portion of the beam, which is stronger than the remainder of the beam in a location where the rest of the beam does not have much ability to "spring" it back to where it was originally.
You're looking at something that is quite similar to welding distortion. The bad news is that if you ran a weld bead on the outside fiber of your beam, perpendicular to its axis, you will see exactly what will happen, which is that it is going to distort permanently. If you are talking about trying to figure how little over yield you can go without permanent distortion, the answer is going to be "not very much."
Engineering is not the science behind building. It is the science behind not building.
RE: Yield in Material
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Yield in Material
DanStro - Yes, that is one of the ways that you determine the maximum depth that the yield has penetrated the material. But my question is how much depth by percentage is allowed before the beam has been permanetely deformed.
RE: Yield in Material
RE: Yield in Material
Tobalcane
"If you avoid failure, you also avoid success."
RE: Yield in Material
RE: Yield in Material
RE: Yield in Material
if you want to go beyond that cozzone is a good method for determining the plastic bending strength of a section.
RE: Yield in Material
RE: Yield in Material
Yes I agree with you on the discrepancy between theory and practice, but you asked a theoretical question and you will get a theoretical answer. However, unless you have actually put strain gauges on the product and captured real data, pure observation of the product not breaking is still speculations of what the real stress are. You said that you have springs 10x the ultimate strength on the outer surface and still meet over a million cycles. Did you have strain gauges on the actual springs and found that it in deed in fact reached 10x its Su? If you have, more power to you. However, most of the time with analysis (theoretical) is to get you in the ball park of what is really going on with probably +/- 10% to 20% error. All in all it is just math. Not until you actually test it under real conditions you will know the real characteristics. That is why once you get real data; you can correlate or correct your analysis so that on the next iteration, your error will be less.
Tobalcane
"If you avoid failure, you also avoid success."
RE: Yield in Material
RE: Yield in Material
RE: Yield in Material
RE: Yield in Material
Mate sorry you are, "I am apparently not in a good mood by not getting a definitive answer". But consider, researching the subject before posting, provide all the information up front, and determine what you are really asking. What if you started with: I am trying to conduct a linear analysis of the extreme fiber stress of a delrin (or whatever it is) symmetrical section plastic part, flexing around a snap feature (uploaded drawing). The part will only be used once. The desire is to have the part......
See link at:
http://www.eng-tips.com/viewthread.cfm?qid=256804
Cheers
Boo1
RE: Yield in Material