50 Amp receptacle in barn with 50 Amp 240 Service?

I did this and kept my job "Tensile-test rig for beam-configuration fillet-weld samples" Movie of - 10 seconds - shared on "Dropbox"

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Wow, dramatic, and your test rig works very well.

Is that sudden brittle fracture typical of welds in tension? I thought it was better to have a joint plastically deform somewhat and distribute any localized stresses before fracturing.

It is sudden fracture with no warning. Reason had to make the rig - sudden elastic energy release at full load. Unfair to do to a shop press. But brittle - not really. The fracture surface looks like "microvoid coalescence". The fracture looks to be a shear in line with the applied stress, so sudden fracture but ductile fracture mode??

I can see where you are going with your question about the overall joint, but the good solution has a different logic. You are thinking that virtue is in the joint be able to and actually plastically deforming. The good solution is totally different. Given the strength you see is way higher than expected. There is no sign of the yield stress manifesting - neither the plate steel nor the weld metal has its yield stress show. This makes no literal sense, but - the sudden fracture is at stress about the same as the rated "Ultimate Tensile Strength". You see around 560MPa with S355 steel (355MPa yield) welded with G3Si1 (ER70S-6) GMAW welding wire. Why I can't see how this makes sense that the strength you see matches the UTS is that the UTS is obtained in uniaxial tensile test of a long cylindrical sample and there is plastic necking - with UTS being breaking-force/*original*-area. The break area is much smaller than the original cross section in relation to which the yield stress manifests.

Anyway, long digression into mechanistic detail. Seeing a very high stress at the joint before anything happens, it follows that you can protect the joint(s) by ensuring that the sections you are joining would have general yielded at a lower stress than would break the joints :-)

So for many structures you check that distributed general beam bending

- the tabulated or easy-to-calculate "Euler-Bernoulli" plastic yield load - is less by a satisfactory margin than the sudden break strength of the fillet welds.

As I said - I think if you do that you fully protect the joints with their high strength but sudden breaking behaviour.

There's two things I see that I didn't explain well

• "microvoid coalescence" is the classic fracture mode of a *ductile* material in overload.

• as the fillet weld strength is very high, it is easy to ensure the fillet welded joint is significantly stronger than the sections it is joining.

Iterating again, using more fancy terms : given fillet welds break by sudden fracture at a very high stress - and you want to avoid any sudden fracture - it is easy to arrive at a safe structure by ensuring that the structural loadings which make the sections (I-beams, Rectangular Hollow Sections, etc.) bend by plastic yielding are significantly lower than the structural loadings which if passed to the fillet weld joints would make then break. The reason this is easy to ensure by design is that the fillet weld strength you see is so high in relation to the yield stress behaviour of the sections being joined. So the strength of the fillet welds easily well-overmatches the section's plastic deformation limited load-bearing capacity. Yet another round of explaining - what you'd see with such a "safe structure" on increasing load beyond anything sustainable is that the long sections begin to bend while the welded joints seem unchanged and not involved.

It is sudden fracture with no warning. Reason had to make the rig - sudden elastic energy release at full load. Unfair to do to a shop press. But brittle - not really. The fracture surface looks like "microvoid coalescence". The fracture looks to be a shear in line with the applied stress, so sudden fracture but ductile fracture mode??

I can see where you are going with your question about the overall joint, but the good solution has a different logic. You are thinking that virtue is in the joint be able to and actually plastically deforming. The good solution is totally different. Given the strength you see is way higher than expected. There is no sign of the yield stress manifesting - neither the plate steel nor the weld metal has its yield stress show. This makes no literal sense, but - the sudden fracture is at stress about the same as the rated "Ultimate Tensile Strength". You see around 560MPa with S355 steel (355MPa yield) welded with G3Si1 (ER70S-6) GMAW welding wire. Why I can't see how this makes sense that the strength you see matches the UTS is that the UTS is obtained in uniaxial tensile test of a long cylindrical sample and there is plastic necking - with UTS being breaking-force/*original*-area. The break area is much smaller than the original cross section in relation to which the yield stress manifests.

Anyway, long digression into mechanistic detail. Seeing a very high stress at the joint before anything happens, it follows that you can protect the joint(s) by ensuring that the sections you are joining would have general yielded at a lower stress than would break the joints :-)

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That 16' portable overhead gantry track I built last spring was designed so the center splice would be somewhat stronger than the 4" channel iron, by having a higher moment of inertia. As expected the first sign of overload was the channels twisting, and I added bolts and spacers connecting their webs until the deflection was satisfactory. It held the 2100 pound log without the central support legs but as a precaution I left them in and walked them over the grounded log to move it from the storage to the sawmill side.

The splice bolts were fitted with only a few thousandths of clearance,

The project met its design goal of lifting 2000 Lbs and moving it 16', using components I could carry through the woods to a log or rock and erect on site by myself. 2000# is the rating of the trolley, I think the track could hold 3000 with the center supported. I moved the load with a long rope in case I was wrong.

When I was in school I had a part time factory job at which I operated a Tinius Olsen tensile strength tester.

I suppose the difference between a UTS test and your rig is that the tester doesn't have much stored energy so plastic deformation reduces the stress, while on yours it remains high. Yours represents actual service better.

There's two things I see that I didn't explain well

• "microvoid coalescence" is the classic fracture mode of a *ductile* material in overload.

• as the fillet weld strength is very high, it is easy to ensure the fillet welded joint is significantly stronger than the sections it is joining.

Iterating again, using more fancy terms : given fillet welds break by sudden fracture at a very high stress - and you want to avoid any sudden fracture - it is easy to arrive at a safe structure by ensuring that the structural loadings which make the sections (I-beams, Rectangular Hollow Sections, etc.) bend by plastic yielding are significantly lower than the structural loadings which if passed to the fillet weld joints would make then break. The reason this is easy to ensure by design is that the fillet weld strength you see is so high in relation to the yield stress behaviour of the sections being joined. So the strength of the fillet welds easily well-overmatches the section's plastic deformation limited load-bearing capacity. Yet another round of explaining - what you'd see with such a "safe structure" on increasing load beyond anything sustainable is that the long sections begin to bend while the welded joints seem unchanged and not involved.

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I take that to mean that the sections would have permanently deformed and would be in the region between yield and UTS, gaining strength by work-hardening when the weld snaps.

I had to straighten some of my used 4" x 8' channel iron. One piece with slightly smaller dimensions than the rest didn't change at the deflection calculated for A36 steel and may have been A50. I had to bow it by over a foot to straighten it. While it was loaded I didn't get close enough to take measurements.

:-)

Some technologists for a steelworks explained about this to me. With very accurate control of the steelmaking process, they only just meet the specification yield stress. Resulting in steel which is lovely to work with in the workshop. Punches, shears, drills, presumably press-brakes, etc. perfectly.

Cheaper steels drawn in when steel price is high often seem to have a hardness and yield above the specified minimum. The punch bangs, etc.

Might seem paradoxical, but you can't use the steel above the design loads relating to its nominal yield stress, so every advantage is gained in the workshop and no advantage is lost in service with just meeting specified yield. I know from beam bending tests on good quality Structural Hollow Section that the actual yield stress of eg. an S355 (50 grade) steel is such a tiny bit above that nominal 355MPa.

For a good quality steel with a higher strength - you'd get it with good means which cost a bit more than a lower yield steel, like having more manganese while keeping carbon content low, so you still just meet specification yield and you still have a steel which is love to work with in the workshop.

As I understand it.

Some technologists for a steelworks explained about this to me. With very accurate control of the steelmaking process, they only just meet the specification yield stress. Resulting in steel which is lovely to work with in the workshop. Punches, shears, drills, presumably press-brakes, etc. perfectly.

Cheaper steels drawn in when steel price is high often seem to have a hardness and yield above the specified minimum. The punch bangs, etc. ...

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There is an old process to salvage steel that has inadvertently become difficult to machine cleanly from random heating called "water anneal". The steel is heated red, allowed to air-cool until the glow disappears, then quenched in water. I've used it to soften flame and plasma cut edges that dulled a bandsaw blade. It seems to improve the machining of steel that tears out in chunks instead of shearing smoothly, such as hardware store cold rolled rod and bar.

In the blacksmithing class I learned that hardened steel can be annealed with good control in a toaster oven by leaving it in for an hour or so. It may not reach the oxide color of a brief temper. The smith tempers his custom knives in a similar industrial oven. They would be difficult to heat evenly otherwise.

My interest, which I haven't fully succeeded at yet, is a knife with a durable edge and fileable wood saw teeth on the back. I converted a recip saw blade from rip to crosscut teeth, made a handle and ground a knife edge on the back, but it doesn't hold the knife edge for long. It does cut wood quickly and I've also used it on aluminum, to help the tech repair a CAD design computer when the new power supply wouldn't fit the space from the old one. He was amused by the mountain-man aspect of fixing high tech with a handmade knife.

I haven't tried this yet, it seems like something that should be learned from a master rather than by trial and error. Maybe I should take the smith's knife making class.

As a kid I practiced building a wattle shelter in the woods using a knife, ball of string and plastic drop cloth. It was immediately obvious that a pruning saw would be the better tool to cut withes.