Welding Distortion Explained Part 2: Stresses and Strains

[@tomwagemans1872]

I don't know why this series hasn't got more views? This is something that every welder must see. I'm in night school learning tig welding and find this super interesting!

[@anengineersfindings]

Glad it was helpful!

[@zekecook6586]

good point Tom!

[@belatoth3763]

It is really helpful and comprehensive but requires some concentration. So not for entertaining, just like videos with half naked girls making woodwork :)

[@impactodelsurenterprise2440]

The fact that the three truss presentation could have been done simply in animation, this dude went all out to make a real world model to illustrate the point. Salute!

[@ianludwick1180]

I have been a welder for 25 + years. Tig ,Mig, Arc, and the new lazer welding which is amzing on thin metal. It reduces distortion loads. This was an amazing video. I know how metal moves. Mild, stainless, and aluminium. I did not know the theory behind it. I found ways to counter it through trial and error. Like welding a square frame and keeping it square. Welded parts that shrunk by 12mm. That's a lot of full pen welds on a part that was about 2 metres. This thought me that a lot of what I did was correct. But I had no idea why. And thought me so many ways to counter the work that is not possible to counter distortion on while welding. I massively appreciate these 4 video and will watch them about 20 times each, so the information sticks. Thank you. 💛

[@anengineersfindings]

Many thanks for your interesting comment. It is very rewarding when a welding veteran like yourself finds my video's useful. Sorry for the cheesy video and audio quality, but this was way back when I had no much video experience. ATB, Alex

[@thecommentary21]

Hi, Im an architech, PHD, scientist, astronaut, General, field marshal, admiral, navy seal, special forces, hells angel, secret agent, international financier and just wanted to say I liked your video!

[@anengineersfindings]

Thanks, and given your resumee, be sure that I stand at attention while i write this ;)

[@alamihabiba619]

loL :-))))) thanks both of you!

[@jackhooper5523]

Excellent video the contraption you made is brilliant for illustrating the stresses caused by the localised heat.

[@jmc6940]

Excellent videos, vary professional. The content is invaluable. Your a great teacher thank you for sharing.

[@anengineersfindings]

Thank you Sir, glad you find the content useful.

[@Mike-ud5of]

Thank you for taking the time to share this excellent explanation and demonstration-just like you point out, the discussions I’ve seen on this topic don’t touch on why the material doesn’t just return back to a stress-free/undeformed state. And that question has been bugging me up until I watched this video-so thank you for the explanation and this great series! Your vids appear to be seriously under appreciated on KZbin. Thank you again and please keep up the good work.

[@anengineersfindings]

Many thanks for your kind comment, Mike. Glad if you find my videos helpful. Cheers!

[@MuellerNick]

Excellence part 2. All well explained, good experiments that show the point and nice old and new instruments ... er .. contraptions. :-)

[@bhimapandava7767]

Wow. So far this series is fantastic. Thanks for taking the time for making it. I *really* hope you're motivated to create more videos like them.

[@benz-share9058]

I am starting my 2nd project welding stainless steel (which is more likely to distort than mild steel) and am re-watching this entire series. Your presentation and examples are excellent! In my last stainless steel project I used the TIG torch to do some heat straightening and it worked very well. Thank you very much for the work and thinking you put in this series.

[@tomcren59]

You are a seriously talented educator.

[@anengineersfindings]

Thank you, Sir. Glad you see it that way.

[@stevecanny1583]

Another terrific episode Alex!! :)

[@supercalcium]

Increíble información., aún cuando no logro entender el 100% de la explicación, todo es muy útil. Gracias.

[@banjerism7281]

This is great. Thankyou.

[@zoozolplexOne]

thanks for sharing!!! very useful to me

[@Gottenhimfella]

at 10:02 , you imply that the material should not be able to sustain a compressive stress exceeding the yield strength on the material's data sheet. I thought the data sheet would be unlikely to give a figure for the yield strength in compression? Isn't this usually higher in practice, for metals, that the yield strength in tension, but difficult to quantify because compression failures vary so much in the character of their deformation mode(s)? Fantastic series, wonderfully informative and well explained. I have spent a lifetime being puzzled by distortion outcomes which now seem straightforward. Thank you SO much!

[@anengineersfindings]

Yield-strength in tension and compression is typically pretty equal, as long as we are dealing with a ductile material (since plastic deformation in tension as well as in compression is caused by slipping dislocations). At 10:02 I hesitate a bit because the paper scale I prepared is based on the material's designation "S235" (i.e. having a minimum yield strength of 235 MPa). The material used in the experiment is a bit stronger than that. If the heated material would have yielded at 235 MPa, the strain gauge would show 50% of the yield strain. I wanted to spare the audience this explanation, sorry ;) Thank you very much, glad if you find the content good.

[@Gottenhimfella]

@@anengineersfindings If "Yield-strength in tension and compression is typically pretty equal, as long as we are dealing with a ductile material" I am puzzled why the neutral axis becomes offset from the midplane when the elastic bending limit is exceeded and becomes plastic, as when using a press brake to put bends in steel plate? Is it the rate of yielding (rather than the strength) which differs from the compression side to the tension side, once the yield point is reached?

[@anengineersfindings]

@@Gottenhimfella The compression side of a sheet in a press brake is not loaded uniaxially, while the tension side is (except of the sheet's edges). The compression side is loaded multiaxially because of surface pressure and surface friction between sheet and the punch/top-tool. This causes the compression side to yield differently than the tension side thus shifting the unstrained "fiber" away from the sheet's center. A classic and recommendable book on this subject is "Mechanik des Plastischen Fließens" by H. Lippmann, which maybe available in English (I'm not sure).

[@thomasherbig]

Great!

[@Tachikomaster]

Another great video, than you for in depth explanation. One question that spring to mind, does the real life materials behave like compression springs as in your contraption or like constant force springs?

[@anengineersfindings]

Typical metals used in welding typically behave like springs up to a certain stress, beyond which they yield. This behavior is modeled in "the contraption" via springs AND the frictional element. The contraption is not just an array of springs, this would not suffice to explain the three-bar-truss.

[@Gottenhimfella]

@@anengineersfindings I thought Michal's question was slightly different than the one you answered. I think he was asking if the relationship between load and deflection was the same for coil springs (which he referred to, not quite correctly, as compression springs) as for the trusses of the experiment. To which the answer (if you'll both forgive my presumption) would be yes, there is a linear relationship in both cases, in other words a non-varying ratio between load and deflection throughout the elastic phase for a spring, and for a truss. Constant force springs are not very common, but their resistance to deflection stays relatively unchanged through at least a part of their range of movement.

[@anengineersfindings]

@@GottenhimfellaSurely you can refer to the plastic deformation (i.e. the frictional element) as a "constant force spring", if this helps understandig the process. I didn't use this term because I haven't encountered it that much.

[@jonludwig8233]

Great content👍 thanks. I'm still unclear on how the cooling phase work, what determines the amount of stress imparted from cooling? Is it fair to say that the distance the bar travels during heating is exactly opposite from the distance the bar travels during cooling (in the contraption)?

[@anengineersfindings]

I guess you can say that the bar must travel the same distance back as it was displaced beforehand. You may think of the displacement as the temperature difference in the three trusses, which is zero in the beginning and zwero after cooling. Thanks

[@cembellsteve]

So, you should never weld . Make it a bolted joint. No stress I wonder if the old rivet joints had some stress annalist as deep as this ?

[@beachboardfan9544]

Is there ever an instance where compression and tension displace at different rates?

[@trebushett2079]

Plastic Deformation = Beyond The Limit Of Proportionality

[@thanhnhanhuynhnguyen3652]

Well. I watched the series only one time, but there is a question keep bugging me. In diy cnc making, as i researched, it is recommended to avoid any welding cause it will cause distortions at that moment or over time. Im aware that your strategy will minimize that so is there a way to weld a cnc chassis without worrying about distortion, as the wisdom of no welding in cnc machine is popular? The question come from the fact that you welded your straightedge and it performed well after 2 years Thank you and looking forward to your reply!

[@impactodelsurenterprise2440]

If by welding u mean using hollow sections to weld together into a CNC chassis, then it's best you don't do that at all. Why waste all that effort to produce a sub par machine?

[@thanhnhanhuynhnguyen3652]

@@impactodelsurenterprise2440 Yeah i thought the same but many folks are making their machine that way. I figured that you need grinding process to flatten and level everything. And a good welding technique which prevents internal stress (?) is also needed. Am I right or i still miss something?

[@impactodelsurenterprise2440]

The major problem is rigidity and vibration. There's a reason why majority of machine centers are made out of solid cast iron, mohr coulomb. Even with solid cast irons, you still have to deal with thermal growth. Also when manufactures cast the machine chassis they typically weather it for many years, allowing any residual stress to release itself. If you're making a cnc router for wood, or laser cutter then welded frames would suffice.

[@thanhnhanhuynhnguyen3652]

@@impactodelsurenterprise2440 ahh i see now! Thank you very much for sharing! Much appreciated! I made a wood cncrouter using aluminum extrusion as i believe its much better than welding. Making a cnc co2 laser cut right now using the same material. Will make a mill soon, thanks to your info i will definitely check out other options such as granite surface plate since casting and welding are definitely not an option. I showed me the answer for a question that had stuck in my mind for months. Thank you again and would love to hear more on this subject!

[@thanhnhanhuynhnguyen3652]

@@impactodelsurenterprise2440 and one more question. This channel owner weld a straightedge which worked well for years. Hows the welding didn’t affect the quality of the straightedge? Thank you!

[@NOBOX7]

Crystallization is the reason plastic deformation is not elastic during cooling