Finite Element Analysis - Poisson's Ratio 0 to 0.49 - on my fillet weld strength test

Hi there
You are a bunch of bright folk who have got amazingly deeply involved
in a lot of things.
I recently did some FEA (Finite Element Analysis modelling) on a real
physical mechanical test I devised for fillet weld strength
formatting link
"Tensile-test rig for beam-configuration fillet-weld samples"
Movie of - 10 seconds - shared on "Dropbox"
formatting link

This was the original FEA I did and that told me an amazing amount;
concurring with what was observed about where the weld breaks / would
be expected to break, etc.
formatting link
"FEA3D : BCFWTT RHS beam top surface around test weld"
The I did an "idiot"(ish) thing - thinking of Aluminum, took the same
FEA model and changed just the material properties, so it was as if
made of Aluminum, and ran the model again.
formatting link
"FEA3D : Aluminium BCFWTT RHS beam around test weld"
Explanation why that is daft on the page.
However; I could have formulated a much better question.
Given the effect of a change in elastic modulus produces a totally
predictable linear-proportional change in the predicted deflection
under the same load...
So that better question would have been:
taking the original model which I did for steels matching and
modelling the real physical test, what is the effect of varying the
Poisson's Ratio on the outcome?
Because that is the one which is difficult, at least for me, to
imagine.
So I did exactly that, and here it is...
formatting link
"FEA3D : BCFWTT RHS by weld - variable Poisson's Ratio"
Lots of pictures of the FEA output.
What do we know?
Hope this is an interesting topic...
Regards,
Rich Smith
Reply to
Richard Smith
Loading thread data ...
Hi there
You are a bunch of bright folk who have got amazingly deeply involved in a lot of things.
----------------------
That one is way beyond me. I took introductory courses in Statics and Materials Science but never got as far as Poisson's Ratio. Then the Army steered me into computer electronics where I stayed.
I was just reading about Prince Charles and his school days and wondered how British higher education compares to American. I've worked with engineers from all over the world and not seen much difference in their abilities, except perhaps that Americans tend to be more hands-on and foreigners more theoretical, or perhaps disdainful of manual labor. For example a project manager for a -very- large company, an EE Ph.D. from India, didn't know that resistors have a tolerance, he expected 8 digit accuracy from an analog computing circuit.
In my experience the engineering professors and students mutually respected each other, it was a pleasant environment although the coursework was difficult. The grad students I shared the lab with on summertime government research projects were always very helpful.
Reply to
Jim Wilkins
I was just reading about Prince Charles ...
----------------
Correction: King Charles III, vive le roi.
Reply to
Jim Wilkins
It isn't.
What I did made the entirety of the FEA solution become a spring. Obeying Hooke's Law.
formatting link
's Law is paraphrased by the equation F=kx
With a FEA model, that "spring" is internally complex - and will reveal the stresses and the strains across the object modelled. But that isn't a necessary perception or issue at this juncture. All that detail available can be a distraction.
That is the point.
A linear-elastic finite element analysis solution is still a "Hookean spring".
All I'd done is alter "k", the spring-constant. Making "k" 1/3 of its previous value. Result - for a given "F", "x" is 3x greater
F=kx <=> x=F/k
By comparing two runs of the same FEA model in the way I did, I found the one-and-only line-of-sight which reduces this "holy grail" method to a simple spring.
I should have foreseen that.
It's a well of sense in an abyss of stupidity, if you will.
But have we all been there, perhaps more than once, on our paths? Do we learn big lessons that way?
I invited a discussion.
There is good reason to accept "driving" a FEA software as like driving a car. You'll benefit from a vague schematic idea of "what goes on under the hood". But even that isn't necessary. The reason is, as an eminent mathematician explained - arriving at the Finite Element method involved it bouncing back and forth between engineers and mathematicians, with no one person fully understanding everything about it at any one time. He said he reckons it's the largest single joint endeavour in human history. So - just start it up, press the pedals and turn the wheel...
But then I am left with another topic, and I haven't seen that simplicity (yet) with that...
Poisson's Ratio is understandable. Let's only think about stretching an object (tension). Let's make it a square cross-section bar. You stretch the bar by pulling it It obey's Hooke's Law, actually. Double the stress, double the extension (within limits - not starting to plastically deform above "yield") If the bar has got longer but is still the same cross-section, it's increased in volume (that would be a Poisson's Ratio of 0 (zero), by the way). That can't be right, can it? Surely the material objects to that? Doesn't it want to stay the same volume? Well, if it did, that would be a Poisson's Ratio of 0.5 That is easy to see. Taking a cube - it has two ends. But four sides. So the sides have to only "come in" half the distance that the cube stretches to keep the volume the same. Think of little stretch - and the new volume is a little thin square at each end. For constant volume that is counterbalanced by four little squares at the sides of half the thickness. But that isn't what happens either. The sides pull-in, but not as much as would give a constant volume. Somewhere in-between...
The effect that would have can be visualised. You know metals show more brittleness when they get thick? When you stretch the big thick constrained object, the metal tries to pull-in transversely - but can't, because all the other metal beside it is trying to do likewise and none can have what they want because they are constrained to a constant dimension - what you could measure with a rule. That means a transverse stress must build-up in response. Which is exactly what happens. Fully dimensionally constrained, that is "plane-strain".
I think my test samples, the beam test, is thin enough that "sideways pull-in" can and does happen. So as it is stretched, the sideways contraction happens.
A spring is essentially one-dimensional (it has length). Most of the time you use the Finite Element method because you want a 2-dimensional or 3-dimensional solution. My impression is the Poisson's Ratio thing stops it being strictly a simple spring. But at any one location on the model, it obeys the laws of a spring. ie. F=kx
I have never worked as an engineer again since coming back from working on the 3rd Bosphorus Bridge project in Turkey in 2015. Where I was credit with making completion of the bridge possible. That separation you talk of between theory and practice seems set into the workplace. As I span theory and practice, I don't fit any pidgeon-hole. The poor sods look at me across the desk and cannot see how their organisation as-is has anywhere I would fit. Constrained spaces... That's why I work as a welder. I have to earn money some way, and it's not a bad life. It makes all the other crazy things possible, such as I decide I want to sail yachts at sea and "just like that" I'm crew on yachts in club races, heeled-over with sea breaking over the bow and all good fun as part of a crew.
Reply to
Richard Smith
Your point about "ivory tower" (Europe / other parts of the world) and "practical" (North America) can be seen in Standards. We have cascades of ISO's - huge paper exercises. Compare ISO welding standards to AWS D1.1 and to API1104. Particularly API1104, "cross-country pipelines", to really bring it into focus. Another thing is ISO's "waffle away" often without ever mentioning the point. Whereas North American "Codes" start with stating what this is all about, everything needing oversight by a knowdgeable engineer, and any property relied upon not mentioned in the "Code" needing to be controlled. The ISO's often invoke huge expense. Again, compare the ISO's when it comes to pipe-welding to API1104. The costs of implementing API1104 are a lot less than for an ISO (? - it looks strongly that way to me). Yet, clear as daylight, you are going to end up with a good reliable pipeline if you follow API1104.
That is a perception I have - what is it you need, how could you get it, and what does it cost? I had one which would have been hilarious if the fellow hadn't turned scarlet and the blood-vessels bulged pulsing on his temples. Medically a bit dangerous, as well as he was a valued colleague. I did do a wind-up too far... Thing is, about three days later, they were realising, somewhat chagrinned, that what they were being pushed towards was exactly what I was saying at the outset. Based on that analysis; what is it that's needed, how could you get it, and what does it cost? It was just the instinct, because I was the novice and they were the highly-regarded experts.
Reply to
Richard Smith
Your point about "ivory tower" (Europe / other parts of the world) and "practical" (North America) can be seen in Standards. We have cascades of ISO's - huge paper exercises.
---------------
I'm convinced that a major goal of government regulation is to create paper-pushing employment for all-thumbs Liberal Arts majors, especially left-leaning ones who despise commerce. In college I was lectured that the only ethical job choices are in academia and government.
Reply to
Jim Wilkins
I do wander whether malaises I see in England / Britain have been due to a political necessity to create "aspirant" "upwardly mobile" "managerial" jobs for the bulk of the population no longer involved in manufacture.
Obviously "our election manifesto is excellent for you" isn't going to ring-true if you and most of your family are unemployed and in rapidly declining circumstances.
So while touting "free enterprise" the bigger reality has been a "conspiracy" to have a significant part of the population in "non-jobs" ultimately paid for by a National balance-of-payments deficit and resultant Government borrowing?
I make you out as being right to be cynical about the "worthiness indexes" you have had put to you.
Rich S
Reply to
Richard Smith
My impression (twisted, not-objective?) here in the UK is there a lot of "robust talking free-market realists" striding around, making their utterances, wearing their suits, driving around the highways in their German limousines, whose entire "wealth" and "success" is funded entirely by the public purse - the National deficit. In effect, what is seen are "empty suits". ??
Reply to
Richard Smith
..... I make you out as being right to be cynical about the "worthiness indexes" you have had put to you.
Rich S
--------------------
I've seen a lot of that, raising relative self-esteem by attempting to debase others', but personally I carved out my own path and frustrated attempts to bin me, as many have told me when they found I didn't fit their assumed stereotype. As a techie I wasn't supposed to know so much of language, history, art and culture, for instance. Engineers have often assigned me to flesh out their initial sketch of complex electronic circuits despite my having no EE degree, or in some cases design it from scratch, such as a 16-bit data acquisition board to plug into a Macintosh when they couldn't buy a suitable one. In the 80's I designed and built my first computer and digital voltmeter, and learned enough programming that my homebrew computer could edit and assemble its own programs. That helped earn me a place on the design team for new projects.
Good luck with your new King. We don't have nearly the grandeur of history that you do, or that I explored in Germany and my sister in Britain and Italy. It's interesting to watch (Lucy Worsley, Blackadder et al.) but I don't think we miss it much.
formatting link
first Wilkins in the Virginia Colony (1619) became a plantation owner, judge and member of the House of Burgesses. I could have been gentry.
I stumbled onto and watched a Revolutionary War battle re-enactment and noticed that as many if not more people chose to play Redcoats.
Reply to
Jim Wilkins
I do wander whether malaises I see in England / Britain have been due to a political necessity to create "aspirant" "upwardly mobile" "managerial" jobs for the bulk of the population no longer involved in manufacture.
Obviously "our election manifesto is excellent for you" isn't going to ring-true if you and most of your family are unemployed and in rapidly declining circumstances.
So while touting "free enterprise" the bigger reality has been a "conspiracy" to have a significant part of the population in "non-jobs" ultimately paid for by a National balance-of-payments deficit and resultant Government borrowing?
I make you out as being right to be cynical about the "worthiness indexes" you have had put to you.
Rich S
-------------
I've seen considerable disdain for productive work, mainly from those who were well educated but couldn't tie shoe laces. I was active in Mensa where everyone was smart but not necessarily any good at manual tasks like steering a canoe, which is so obvious to me that I don't know what to tell someone who can't. I was the only one who could skip a flat stone across water.
Reply to
Jim Wilkins
My impression (twisted, not-objective?) here in the UK is there a lot of "robust talking free-market realists" striding around, making their utterances, wearing their suits, driving around the highways in their German limousines, whose entire "wealth" and "success" is funded entirely by the public purse - the National deficit. In effect, what is seen are "empty suits". ??
-------------------------
One interpretation of the Pareto Principle or 80/20 rule is that 20% of the people, the "Vital Few", do 80% of the necessary work, and support the rest who ideally should stay out of their way, but don't because they need to feel important.
In the US Army at the end of the Vietnam War discipline collapsed because any attempt to punish a non-white became a Racial Incident. Drugs flowed so freely that barracks inspections stopped so the officers wouldn't have to ignore the punchbowls of hashish. Yet the responsible few were enough to keep everything running as smoothly as normal, as I suspect they always had.
That was another case of creating my own path. I had trained to repair very complex communications gear and was on call for repair trips, so I couldn't be assigned to any other task I couldn't drop immediately. I became post photographer, worked with the USO, fixed stuff in the motor pool, went on meet-the-Germans trips such as a tour of their very orderly sewage treatment plant and was the one token NCO at an officers' banquet at Heidelberg Castle, where I danced on the huge wine keg with the Colonel's otherwise ignored wife.
I was designated to attend a seminar on alcohol and drugs that showed their effects on the blood flow in frogs' transparent feet, mainly restricting or stopping the flow through capillaries, as they also do in the brain. It was held at a Kaserne with an emergency airstrip so I could easily be picked up by helo or bush plane for a mission. The other stuckees were privates who could be spared without loss so the lecturer was surprised to meet a chemist who understood his work and asked difficult questions. The government research grants I'd worked on were, um, related. My job was adding a Deuterium tag so MRI could detect where [things] were active.
Reply to
Jim Wilkins
... I stumbled onto and watched a Revolutionary War battle re-enactment and noticed that as many if not more people chose to play Redcoats.
-----------------
formatting link
"Rather than being Anglophiles, the 40th is a group who thinks the best way to honor this country’s history is to present our early military adversaries as the professional, practical, and tough fighting force they were."
Besides, the Redcoats looked better and won more battles. France gained the victory for us, as revenge for losing the Seven Years War.
Reply to
Jim Wilkins
A lot drops into place - the overall background you mention. Sounds good to me.
Thanks for mentioning The Pareto Principle.
Funnily enough, not knowing of that until you mention in now, the exasperated bane of my life during my Doctorate was the perception of the seductive allure of "those results which are 80% as good but only take 20% of the effort". They never said anything exactly that, but that was my sarcastic characterisation of the indispline and lack of strength of character to make the effort and win the commercially valuable goals. Well, as I saw it. Reality - maybe only in research but likely in other endeavours - Nature / "God" will not reveal secrets and inner workings unless you work really really hard and diligently study, observe, work-around, probe and otherwise by the disciplined supplicant on the path to the answer. I ended my Doctorate as a lone effort, with senior people cynical with the humdrum disappointment of life tolerated my crazy drive to get there. And casting me the occasional tiny gift which was the key to a particular door.
Regards, Rich Smith
Reply to
Richard Smith
Or as a friend puts it "Your candle does not burn brighter because you blow out the candles of others" ?
Reply to
Richard Smith
Or as a friend puts it "Your candle does not burn brighter because you blow out the candles of others" ?
------------------
I liked the attitude expressed by a Japanese auto maker (Honda?) on entering the US market that they weren't trying to grab a bigger piece of the pie, they wanted to create a bigger pie.
Reply to
Jim Wilkins
Or as a friend puts it "Your candle does not burn brighter because you blow out the candles of others" ?
-----------------------
Here is a difference between Britain and the US that relates to acquiring a zero-sum mentality:
formatting link
"Grades in UK are often given according to bell curve; if majority get 90 on a test, then 90 = C, only the top 10% will get an A. In US if you get 90% correct on a test you'll receive an A; if everyone received 90% or higher everyone in class can get an A."
The theatre classes I and some friends took as required liberal arts electives were a welcome break from the grind of a science degree because they were graded pass/fail, and everyone who at least attended class passed. When the teacher asked the class a question we techies were usually the first to raise our hands, the actors and dancers rarely said anything. I suppose we had less to lose if we embarrassed ourselves. Also we were used to participating, in the math, physics and chemistry classes many hands would go up. I earned a C in Calculus that was raised to a B for sitting in front and answering questions, right or wrong.
Reply to
Jim Wilkins
"zero-sum" is problematic. Take that view to manufacturing and construction and it's disastrous. The endeavour is doomed from the outset with "zero-summers" in charge and influencing events. I think that was the difference with my work on the 3rd Bosphorus Bridge project in Turkey 2015. I interacted with people, even if they were with different parties whre the realtionship was strained - that just made the steps very small but always pointing in the right direction - and coaxed everyone along with a vision of a way out of their pain. But most "solutions" - a lot of heads came together for most of those, and of the exceptions it was still in the main two or more heads. Some conversations were in closed-door rooms with top representatives of the parties, with all agreeing that what was said in this room stayed in this room - and some very senior people had some very rough things put to them... What I did running between parties and linking them where by common interest and being different parts of the one solution to that issue or aspect was credited with making the completion of thwe bridge possible.
You remind me of "the zero sum trap" - might work for the service economy so long as you have a financial perpetual motion machine - but you can never run a manufacturing economy that way.
Reply to
Richard Smith
I think grades should have two parts - an absolute correctness depth of knowledge grade and a percentile of the year. Thus "A-62" is "A" for correctness, while the "60" says they were at the 62% of that year.
Reply to
Richard Smith
"zero-sum" is problematic. Take that view to manufacturing and construction and it's disastrous. The endeavour is doomed from the outset with "zero-summers" in charge and influencing events. I think that was the difference with my work on the 3rd Bosphorus Bridge project in Turkey 2015. I interacted with people, even if they were with different parties whre the realtionship was strained - that just made the steps very small but always pointing in the right direction - and coaxed everyone along with a vision of a way out of their pain. But most "solutions" - a lot of heads came together for most of those, and of the exceptions it was still in the main two or more heads. Some conversations were in closed-door rooms with top representatives of the parties, with all agreeing that what was said in this room stayed in this room - and some very senior people had some very rough things put to them... What I did running between parties and linking them where by common interest and being different parts of the one solution to that issue or aspect was credited with making the completion of thwe bridge possible.
You remind me of "the zero sum trap" - might work for the service economy so long as you have a financial perpetual motion machine - but you can never run a manufacturing economy that way.
---------------- Zero-sum assumes people are unable to create anything new and valuable, which may be true of those who believe it.
formatting link
"Work was temporarily halted in July 2013, after it became evident that the site was mislocated, ..."
formatting link
Are you able to reveal any (non-personnel) engineering aspects of what you contributed to bridge completion?
Reply to
Jim Wilkins
Having been in the US education system up till 1982 when I graduated from high school then moved back to the UK I think the comparison of the education standards is not easy as I don't recall the US having any basic standardised tests other than SAT. In the UK at the time there were O levels, now GCSE, and A levels, my US high school diploma was considered equivalent to O levels so//I was effectively 2 years behind where I would have been if educated in the UK. The fact I normally took the more higher level courses in maths, chemistry, physics etc made no difference as there was no way to show what was covered to compare. I know at least one of my US teachers graded on a bell curve and I wasn't always popular for getting high marks as it skewed others downwards.
Reply to
David Billington

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.