That's what I've seen/heard. Steel and titanium -should- have infinite fatigue life below some stress level, other metals don't. However poor detail design and machining, rough surface finish, and imperfections in the material can magnify the local stress level enough to start an unexpected failure.
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Not fatigue, but a "minor" detail change:
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cross-section of the one-piece rod was adequate to support everything but the threads were only strong enough to hold one level.
I would note that the chain used is not common hardware store chain and also that they no longer use the standard lever type load binders (boomers) and now use ratchet & screw type which is much less likely to pop open and is much safer to tighten and loosen. Young truckers don't even know what a snipe is. While heavy haul truckers still do use chain for securing machinery, most loads are now secured with nylon straps which are much lighter and easier and safer to handle and less likely to damage loads. IMHO light weight ratchet straps are a wonderful developement and have just about eliminated my need for chain.
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On my jobsites, nylon slings have just about replaced wire rope slings for most rigging. Some older iron workers still like small wire rope slings for chokers but most jobs use nylon as it is lighter and easier to use and inspect and is often much stronger.
A double wraped nylon choker or barrel hitch is very secure. I especially like the endless loop or grommet slings as they are easy to use and last longer as they do not place most of the wear in the eye as is usual in double eye slings that are used as chokers without a shackle. A double thickness 1-2" flat nylon grommet sling or even better a small kevlar or polyester core round-sling is IMHO much superior and handier than any other kind of wire or fiber rope or chain, unless heat or sharp edges are involved.
We still use wire rope for heavy main rigging but even there nylon and kevlar is becoming much more common because it is lighter and much stronger and easier to use and handle.
Recent (?) variant I've seen on steel delivery trucks - short lengths of chain wrapped around the load, pumped up tight by fabric ratchet-straps on each side. These are special for the job, with one end made to go onto the cleats along the lorry bed underedge and the other end with a "hook" to slot into / pick-up the chain. Security and simplicity of fabric ratchet-straps with cut-resistance of chain.
I object to that. We had a hardware and autoparts store for 20 years and we never had a "common" grade of chain. We stocked grade 30 and grade 70. Grade 30 (seemed to hold up better to being dragged) is what most of the farmers bought, and grade 70 (have to cut it with an abrasive blade or a hydraulic cutter) is what the truckers bought. We also had matching grades of hardware in stock. I never heard of grade 43 back then, but that is what Harbor Fright claims their chain is last time I looked.
I really liked those old snap binders. Very quick to engage and very easy to get a feel for how much tension you had on the chain by how hard it was to swing the cheater bar. I was taught three rules for using them by my dad.
Always use the right size chain binder for the chain you are using
Always use a cheater bar.
Always use your slack chain to wrap the binder so its less likely to pop open.
Not a chain specific rule.
Always check your load at every stop. (This applies to any load.)
Never had an accident with chain. Neither did my dad. He hauled for a little while. Even hauled two truck loads of stone for London Bridge.
You know its funny. I have a couple ratcheting binders and I hate them. I use them for hauling my scissor lifts or tractor to job sites. Well maybe not hate, but close. Its hard to find the snap binders anymore unless you go looking for them. Even on the ratcheting binders old habits are hard to kill. After its snug enough to make me happy I swing the handle around to hit the deck and wrap my slack chain around it to hold it in place. LOL.
... AND... I still see trucks from time to time with a whole array of different size snap over chain binders hanging from the back of the cab. Well, as recently as a couple years ago. I don't go around checking trucks. LOL. I suspect there may some state specific regs and some industry specific standards.
Hi - good direction pointers - thanks. Got to work in this direction.
Especially as have "Design of Welded Structures" coming up in Welding Engineering course
Are there any good suggestions as to how I might really put in some milage on this topic? It's the one I feel I really need to make progress on if I am to make this year pay.
If you're interested in shipbuilding history, look at the myriad failures, some spectacular, in the old Liberty Ships of WW2. Those are interesting from both a design / engineering perspective and a welding / metallurgy perspective.
Also look at this Wikipedia listing- it may help:
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It should at least provide some jumping-off material that may spark your interest.
What amazed me about the Liberty Ships failures was two things: the cause and the fix. Figuring out that the spacings of the waves either supported the whole ship by both ends or in the middle, and welding a long strap along the side fixed it elegantly simply.
the severe failure during construction when the hull was fully supported. In researching RMS Titanic I found that cold embrittlement from sulfur wasn't known until the 1920's or considered in ship steel until the
1940's. Before that if the steel behaved well in the hot rolling mill it was considered good enough. Ships built to standard commercial practices didn't fail often and when they did the evidence was lost. In Titanic's case the testimony of 2nd Officer Lightoller on the stern that the hull didn't break was accepted versus that of the engine room greaser on the funnel platform that it did, directly below him.
The sagging and hogging strains ships experience at sea have been known at least since ancient Egypt, where they used rope to strap the ends together.
The liberty ship based in SFO harbor - forget the name - was inspected for use and was taken by a group of faithful ex-liberty ship sailors from San Francisco - to Normandy. I want to say they did it for the 50th but I also recall they went dead in the water and were stuck in Panama until a engine part could get to them.
There is an interesting History Channel show about them and the design issues.
These guys were for the most part beyond wanting to go ashore. Likely they trotted out chess boards and enjoyed life awaiting the seas of the North Atlantic.
Mart>> The liberty ship based in SFO harbor - forget the name -
Yep, square corners on structures that must bear stresses aren't cool. In the welding workmanship and Visual Test training we're taught that any re-entrant angle less than 90 degrees is automatically reject as either a sharp irregularity or overlap when it comes to welding.
In our apprenticeship it is pounded into us that any truly square opening is subjected to intense stresses at the corners (stress risers) because forces cannot flow smoothly through the joints. If a joint is designed to be square, you can bet that there is a gusset involved that will help carry / distribute stresses through the structure.
Often the weld design will call for a full penny bevel joint with a fillet reinforcement. That fillet serves as the gusset to distribute the stresses.
Coping beams (slicing the flanges off for a short distance at the end(s) so the beam will interesect sdieways against another beam)
One shop I worked in - the oxy-acet. torch worked best at around 25psi (1~1/2Bar). Clean cuts faster than when at 70psi (4~1/2Bar). But boss' order - 70psi all the time. Well, when they used to cope beams there'd often be vertical slots over an inch deep beyond the depth of the coping, as the oxygen jet chewed down the web.
When coped I'd slice the flange (no extra cut depth) then bring the torch to the side (which you have to do anyway) and round my transition from "along" to "up".
One of the things I was amazed at when learning to weld was that a tip had a broad range of thicknesses it would cut, depending on O2 pressure, and that the acet stayed at one figure, in my case, I like 4. And then to see that you could cut cleanly an inch from the tip with a lot of O2 was like shooting a machine gun.
Why anyone would flatly insist on a 70 psi figure baffles me. Regulating it would use less O2, and in the case of overcutting something, avoid damage that could have been prevented. Kerf formation and slag formation/removal had to be a factor, too. But then, I have known engineers and supervisors who were "hardassed", and it was "My way or the highway" kind of guys. Some were right, and after you learned, you understood. Some were wrong, and you either did it your own way when they left and suffered the consequences, or they moved along soon. Or you just kept doing it the same old way and messing stuff up.
You gotta be a good Indian to be a good Chief, and sometimes you just gotta be a good Indian, and do what the Chief tells you to do. Even though you know he's wrong.
I like working in my own shop and being the Chief Chief. ;-)
Steve
Heart surgery pending? Read up and prepare. Learn how to care for a friend.
Wider conversation. I learned a lot in my time working in FabCo's. Hiding my academic qualifications and getting stuck into work in these places taught me a thousand times as much engineering as I had ever learned previously passing through my academic / scientific work.
Some people explained very wise things to me where I was working. Other times I made a mental note of things I was seeing and asked about them at the Welding and Joining Society - good to be a member of a professional society.
Setting any oxy-acetylene cutting torch is actually very much more difficult to learn than setting up an oxy-acetylene cutting torch, I found.
It took a long time "for the penny to drop".
I ignore the gauges - even if they are were (i) there and (ii) still worked
Step 1
with no flame, no acetylene, no preheat-flame oxygen:
Squeeze the cutting oxygen lever fully and direct the oxygen jet against your finger, which is about 10mm (3/3in) from the nozzle. Visualise whether the propulsion would clear the kerf - adjust pressure accordingly.
Step 2
Set the preheat flame - no cutting oxygen at present
Open the acetylene and look at the acetylene-only flame. Visualise whether the amount of acetylene gives the correct amount of preheat.
If you can visualise better with the "neutral" flame, by all means, look at that - but I find the acetylene-only flame easier to judge for soon-to-be preheat power.
Step 3
Bring the preheat flame to neutral then squeeze the oxygen lever fully "on" and re-adjust the preheat flame to be burning slightly oxidising side of neutral (flame strictly neutral isn't so crucial for cutting - nothing which remains after the cut was ever molten - hence you cannot deteriorate the properties of the finished component). Why slightly oxidising? Well - you want "definitely not carburising" and with the torch chewing up oxygen for cutting at a much greater rate and that can knock your preheat flame off-tune during the cut, better to be a bit oxidising to start with...
Important point in understanding Step 2 and certainly all of step 3 - what is preheat...
Preheat is what keeps the stable cut running. It brings the steel under the cutting oxygen jet to the burn temperature of steel in the pure oxygen jet. For your stable ongoing precision cut. That's why we set the final adjustment of the preheat flame with the oxygen lever squeezed - because that is the circumstance where the preheat flame has to be running true.
Your initial ignition of the cut - at an edge or a restart - you don't adjust for that. Reason - you can take as little or as much time applying the preheat flame only, no cutting oxygen, to reach ignition temperature. And nothing is molten, so there is no quality issue. So you do not figure anything of the initial ignition in torch setting - it isn't critical. Whereas cutting jet force and the running preheat are critical - they are what you set.
Get this right and you can get clean cuts with sharp edges top and bottom.
In fact, you become someone who can "fab. on site". That is - they can have the steel (beams & columns, plate steel) delivered to site and you make up the steel structurals on-site to what is measured. Fab. as in steel fabrication. Useful for deformed buildings, ad-hoc requirements, ...
If anyone reckons this advice is good I'll try to put up a website with sketched pix of this and other oxy-acet techniques.
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