crane arm (small provocation)

[omegaquadroerre]

Hello everyone
I would like to ask you a question that led me to discuss with my client animatedly. :angry:

so we'll have two arms of cranes. same size and same loads in the free end.
my client claims that if I carry out the arm in "good steel" the arm is lower. so the more steel is of less quality flet, indeed as he says "the arm is straight".:tongue:

What do you think?:finger:

 

[AlbertoC]

from any integration of the elastic line, e.g.http://digilander.libero.it/carlopala/matecost/lesifora.htmSo the only thing you can discuss is the value of and:http: / / www.sportpro.it / techniques / saggi / telaio.htm # tabella% 20dei% 20material
ciao

 

[gerod]

quoto alberto c.
there is a formula and the variables are those....
Tell your client to inform you.
Let us discuss the definition of goodness and yield!
Hi.

 

[omegaquadroerre]

He thinks that there are good steels that are more rigid.
and he was seriously convinced. ...
How do we engineers convince these people?

 

[cacciatorino]

He thinks that there are good steels that are more rigid.
and he was seriously convinced. ...
How do we engineers convince these people?

experience counts, the engineer must understand why one has certain ideas and interpret them.
In this case I think he was talking, perhaps unconsciously, about residual deformations. the most 'good steel, while being equally rigid, supports a larger epsilon before deforming permanently. That's why I think your client means that the crane made with good steel resists more, i.e. supports a greater load without bending.

in general the concepts of deformation and rigidity are little known by the "praticons" (maximum respect for practicals, ovvimanete).

Bye.

 

[thor105]

He thinks that there are good steels that are more rigid.
and he was seriously convinced. ...
How do we engineers convince these people?

a way could be to realize two small arms of the crane in scale, made with the two different steels, load them with equal loads and show them the difference of deformation. if it is not a complete imbecile you should realize how things are actually.
if it persists in its beliefs, you should arm as the customer wants, and protect yourself by writing a technical report in which you recommend the use of steel with more young module and writing that, however, by choice of the customer, you make it with another material. made also sign a sheet in which the customer claims to want to use another steel. At that point you did your job and the problems are all his.

 

[omegaquadroerre]

That's why I think your client means that the crane made with good steel can resist more, which means it supports a greater load without bending... .

Bye.

Look, you're getting confused, too.
the crane made with a more durable steel (for example a domex instead of a fexxx) resists to a greater load (major scrum) but consequently flet more (episilon greater).
Don't you think?

 

[cacciatorino]

Look, you're getting confused, too.
the crane made with a more durable steel (for example a domex instead of a fexxx) resists to a greater load (major scrum) but consequently flet more (episilon greater).
Don't you think?

Yes, I know very well, when I say "without bending" I mean, in the workshop language, not to undergo permanent deformations.
then, for example the crane made of fe360 remains permanently bent if you use it to pull up 200 kg, the crane made of fe510 maybe not.
It is obvious that if both uses to pull up 100 kg, they suffer the same inflection.

What I wanted to say is that until you stay in the elastic limit of the poorest material you have no problem, but if the applied load makes you exceed the threshold, then the difference between two steels could be seen and how. I think that's what your client was trying to tell you, maybe without having the theoretical training that would allow his speech to be clearer.

 

[omegaquadroerre]

he meant that good steel fletes less
as if the domex had a younger module larger than the fi360.
That's crazy.

This speech of steel stiffness is not trivial.
In fact, high-strength steel is often used to lighten sections at equal resistance. see cranes and trucks.
but as the module of young is equal for all steels, decreasing sections, also decrease in inertia moments resulting in increased bending! ! !
eh eh then we have allegered the structure (saving weight and money), we used an expensive steel (and here you have to see if the game has been worth the candle), but in the end the pushes increase (and the workshop is inca....za)
moral?
Let's leave engineer work to engineers! No?

greetings

 

[cacciatorino]

he meant that good steel fletes less
as if the domex had a younger module larger than the fi360.
That's crazy.

moral?
Let's leave engineer work to engineers! No?

the engineer must interpret the wishes of his client (as any other worker).

What was your client's ultimate wish? raising the same weight with a lighter crane? or raise the same weight with a minor deformation?
from what your client wants descends if you gave him the right or wrong answer, the theory only serves when you're in the office doing your accounts, not to relate to customers.

 

[omegaquadroerre]

wanted to raise the same weight with less deformation. . . .
The theory needs more than that!
the problem is that there are strong customers of their experience (and their money) that
They don't accept anyone's theory.
There are no modules of young people holding.
If he is 100% convinced that he solves his problem by changing steel you tell him?? ? ?
What are you doing? ? ?
thor105 says to do as he says and then let him sign a little paper.. .
Okay, you can stay there once.
But if that happens again?
for example on a spring (says that the spring made in good steel is more rigid than a made in fe360... to that country the concepts of precarious and rigidity of a spring)
as you see the problem is not recently.
and also large companies managed by "praticons" there are many, unfortunately.
How would you rule?
Hi.

 

[thor105]

Look, you're getting confused, too.
the crane made with a more durable steel (for example a domex instead of a fexxx) resists to a greater load (major scrum) but consequently flet more (episilon greater).
Don't you think?

It doesn't seem to me. Since you were talking at equal loads (and I would say sections a priori, otherwise it is not even worth discussing the thing), a more rigid steel is deformed, otherwise it would be like saying that at equal force applied between two springs it is more shortened than the rigid one (to meet an absurd in the definition of rigidity).
it can also have the situation of two steels that have the same deformation to yield, but quite different tensions (so one bears greater loads) and dependence as known is precisely due to the module of young.

 

[thor105]

wanted to raise the same weight with less deformation. . . .
The theory needs more than that!
the problem is that there are strong customers of their experience (and their money) that
They don't accept anyone's theory.
There are no modules of young people holding.
If he is 100% convinced that he solves his problem by changing steel you tell him?? ? ?
What are you doing? ? ?
thor105 says to do as he says and then let him sign a little paper.. .
Okay, you can stay there once.
But if that happens again?
for example on a spring (says that the spring made in good steel is more rigid than a made in fe360... to that country the concepts of precarious and rigidity of a spring)
as you see the problem is not recently.
and also large companies managed by "praticons" there are many, unfortunately.
How would you rule?
Hi.

to sign the card to the customer, it is not to be "praticons", but it is a way to secure even the company from any complaints, keeping also the corporate quality requirements.
in a perfect world for many choices we would trust numbers and probably there would be no need for us engineers (mathematic and physical), but fortunately (otherwise I would not have a job) we live in an imperfect world and therefore the work of the engineer also consists in meeting the needs of the customer, but not failing to report before if a choice is made not too good.
by making him sign a paper show that you did the job you expected from you, but that by choice of the customer was done otherwise.
for how they taught me the engineer must be above all "practical".

 

[stevie]

this is a classic of conceptual errors that can be done in mechanical design, unfortunately also widespread among many "technicians".
the intuitive idea is:

"use a steel with superior mechanical properties, and therefore also the rigidity of the artifact must be superior"

but here we collide substantially with a fact that many neglect. . .
despite the engineering of the materials has made giant steps regarding the yielding and breaking load passing from the first alloys of steel able to withstand a few tens of kg/mmq coming to the modern maraging steels from 2 quintals to mmq, little or nothing could be done regarding the elastic module and. we are on the 200 gpa and from there does not escape, the influence of the elements of alloy is substantially negligible.
or material changes, and the choice is in fact obligated on composite materials (carbon fibres in primes), or it intervenes on the geometry of the sections used.
As far as the customer is concerned, I am not surprised by the general improvisation that pervades the sector by now.

 

[omegaquadroerre]

this is a classic of conceptual errors that can be done in mechanical design, unfortunately also widespread among many "technicians".
the intuitive idea is:

"use a steel with superior mechanical properties, and therefore also the rigidity of the artifact must be superior"

but here we collide substantially with a fact that many neglect. . .
despite the engineering of the materials has made giant steps regarding the yielding and breaking load passing from the first alloys of steel able to withstand a few tens of kg/mmq coming to the modern maraging steels from 2 quintals to mmq, little or nothing could be done regarding the elastic module and. we are on the 200 gpa and from there does not escape, the influence of the elements of alloy is substantially negligible.
or material changes, and the choice is in fact obligated on composite materials (carbon fibres in primes), or it intervenes on the geometry of the sections used.
As far as the customer is concerned, I am not surprised by the general improvisation that pervades the sector by now.

Good boy!
That's what I was trying to say from the beginning!
compliments for the clear synthesis.

 

[cacciatorino]

Good boy!
That's what I was trying to say from the beginning!
compliments for the clear synthesis.

Look, we all agreed on this from the beginning, I was just trying to offer you a different point of view.

Otherwise it seems that we make trivial mistakes that then someone else corrects us, I add this only for precision.

 

[Filippo_]

build the arm of a crane with high-strength steels means less weight to lift and consequently you have a greater load capacity even if the maximum bending would be greater.