internally threaded bar verification

[Matteo.R]

Good morning to all, this is my first discussion, I am a master student of aeronautical engineering and I would have a doubt regarding the design of an auction that I have to do for a school project. the rod in question is an aviation duty rod and is loaded with normal effort. to the extremes two terminals with male thread whose nominal diameter is known, as in the exemplifying figure that I attach:my question is: how to proceed in the check on the cross section of the auction that houses the terminal?
if you would like to check a generic central section (where the rod is not threaded, by the way) I would write:
♪[ \frac{N_Z}{A}\leq\ \frac{S_y}{CS} \]where nz is the normal effort acting on the auction, \[ A=\pi \frac{D_1^2-d_1^2}{4} \] is the area of the section (d1,d1 are the external and internal diameters), sy is the yielding voltage of the material and cs is the safety coefficient used. regarding a section in which the internal thread for the housing of the terminal is present, how can I proceed?

 

[New Rider]

Good morning to all, this is my first discussion, I am a master student of aeronautical engineering and I would have a doubt regarding the design of an auction that I have to do for a school project. the rod in question is an aviation duty rod and is loaded with normal effort. to the extremes two terminals with male thread whose nominal diameter is known, as in the exemplifying figure that I attach:View attachment 60671my question is: how to proceed in the check on the cross section of the auction that houses the terminal?
if you would like to check a generic central section (where the rod is not threaded, by the way) I would write:
♪[ \frac{N_Z}{A}\leq\ \frac{S_y}{CS} \]where nz is the normal effort acting on the auction, \[ A=\pi \frac{D_1^2-d_1^2}{4} \] is the area of the section (d1,d1 are the external and internal diameters), sy is the yielding voltage of the material and cs is the safety coefficient used. regarding a section in which the internal thread for the housing of the terminal is present, how can I proceed?

\( \sigma =\frac{f}{ar} \)

 

[Matteo.R]

Thanks for the answer. with ar, however, is the resistant area of the threaded part of the terminal or the threaded circular crown area of the rod?

 

[Fulvio Romano]

Huh? I arrived before @meccanicamg ? ?

Yay! !

with ar means the resistant area of anything threaded. It is not a physically attributable area to something because compared to the thread throat, the thread adds a bit of material and therefore of resistance, but also generates a carving effect that increases tension.

ar is not calculated, it is measured. it leads to break a screw or a mothervite, it divides the applied force for the breaking sigma of the material and comes out ar.

 

[Matteo.R]

I understand, thank you for your help! so since in my case the terminal has a m52 thread, the resistant area is that corresponding to a m52 thread even considering the sole screw on the rod?
Is there a way to dimensional the thickness that must have the rod in the threaded area?

 

[meccanicamg]

a part of formulas and concepts find them in This is post.
Actually the durable area is computed as you can see at the link I put before. you consider the middle diameter and the bottom diameter for the male threads and of course the average diameter and the head diameter for the threaded holes on this crown with n threads you make the traction check and on the ridges.

 

[meccanicamg]

I understand, thank you for your help! so since in my case the terminal has a m52 thread, the resistant area is that corresponding to a m52 thread even considering the sole screw on the rod?
Is there a way to dimensional the thickness that must have the rod in the threaded area?

a catalog m52 has a pitch of 5 mm. I would say that it is not the maximum of life to make the rods to adjust to a big step.... normally it is made to fine step maybe m52x2 or x3 or x4 mm.

brutally to know how big the pipe will be that it has to resist traction it has an internal diameter of 52 and an external diameter y such for which the traction force divided the area of this ring produces a sigma lower than the admissible one.

If you prefer, you can do the reverse formula.

♪[ A=π•\frac{D²-d²}{4} \]
\[ \sigma=\frac{F}{A} \]
\[ \sigma_{ADM}=\frac{Rs}{g} \]

 

[Matteo.R]

Thank you very much!
I confirm that the thread will be at the end step m52x3 as you expected. to dimensional the tube then I will look for the diameter "external" of minimum that guarantees a sigma lower than the admissible one considering the circular ring that has for diameters 52 as inner diameter and as outer diameter. Thank you again!

 

[Betoniera]

Hello everyone
I also greet with mechanicsmg that I intend for his interventions and with which I have already confronted myself sometimes.
in comparison there are often differences for the following 2 reasons
1) I am civil engineer and follow construction regulations
2) I use the method of calculation of the limit states, while here it tends to use the method of admissible tensions.
the comparison is interesting and educational for the differences that are found.
I would not like to confuse you, but the method I show you is suffrage, in every step, by the legislation (dm 17-01-2018 technical norms on construction)
I think that, especially in the aeronautical field, you must strictly refer to a regulation (not necessarily the one I have indicated) and follow it exactly

to understand what I'm saying I send you an example of calculating a simple traction bolt

the problem is identical to your provided that you insert the net area of the section instead of the net area of the bolt.
net area means the net are of the thread, regardless of whether it is internal or external.
but what you need to get used to doing is to quote the normative reference of the formulas you use
for example, in our case, the tensile strength is the one indicated at the point [4.2.66] of ntc.
I point out that that formula considers the rupture voltage and not the yielding voltage.
but that is a calculation to limit states, so the effort nd is not to exercise, but is amplified by 1.5 times.
I don't dilute, but if you want to do the strutturist, you have to chew these topics well (although at first they seem a complication).
Hi.

 

[meccanicamg]

Hello everyone
I also greet with mechanicsmg that I intend for his interventions and with which I have already confronted myself sometimes.
in comparison there are often differences for the following 2 reasons
1) I am civil engineer and follow construction regulations
2) I use the method of calculation of the limit states, while here it tends to use the method of admissible tensions.
the comparison is interesting and educational for the differences that are found.
I would not like to confuse you, but the method I show you is suffrage, in every step, by the legislation (dm 17-01-2018 technical norms on construction)
I think that, especially in the aeronautical field, you must strictly refer to a regulation (not necessarily the one I have indicated) and follow it exactly

to understand what I'm saying I send you an example of calculating a simple traction bolt

the problem is identical to your provided that you insert the net area of the section instead of the net area of the bolt.
net area means the net are of the thread, regardless of whether it is internal or external.
but what you need to get used to doing is to quote the normative reference of the formulas you use
for example, in our case, the tensile strength is the one indicated at the point [4.2.66] of ntc.
I point out that that formula considers the rupture voltage and not the yielding voltage.
but that is a calculation to limit states, so the effort nd is not to exercise, but is amplified by 1.5 times.
I don't dilute, but if you want to do the strutturist, you have to chew these topics well (although at first they seem a complication).
Hi.

Hello betoniera. It is always a pleasure to compare because you can combine and complete methods of analysis and calculation.

In order to deepen this we can find the norm of eurocode 3 i.e. uni en iso 1993-1-8 that we also use when we have to realize a bolted structure. If we have to study some non-standard phenomenon we have to fall back to tensions... of course not being normative about it.
There will certainly be some aeronautical standards that will give strict calculation methods but at school level, in the first approximation I do not see any other solutions.