dimensive bolt size

[Livio1087]

Hey, guys, I have a question to ask you:
I have to disproportionately measure the pull of a pneumatic cylinder alesaggio 80 stroke 800 mm. the strength that the 4 tie rods must bear is 5030 n.
as a safety coeff I hypothesized that each rod should support the entire load 5030 (coeff sic = 4). pressure is 10 bar.

I find myself having to check hard these blessed unbearable fellows.
http://pneumatica-it.timmer-pneumatik.de/artikel/artbild/maxi/zho-dz1.jpg(to get an idea)

I calculated the precarious by supposing the resistance class of the screw (trailer) was 5.6 i.e. yielding 300mpa and breaking 500.
300=5030/a => a=16.76 and I chose a m6x1 (resistant area 20.1)

I calculated the preload as 0.8*300mpa*20,1=4824n
and then the pair to apply to tighten it. 0.2*4824*6=5788.8nmm

I remember that my professor said to test them hard with the haigh diagram but I remember well... .

or do I use the uni 7670 and impose an admissible sigma of fatigue < current scrum? ? ?


thanks to all



in particular would you tell me a general method to check the links with bolts working as in this case obviously traction?

 

[gerod]

for screws you can use cnr10011 or better Eurocodes.
Eurocodes are similar and also find the screws.
I would use miner.
Hi.

 

[Livio1087]

mines cioè?

 

[Livio1087]

pile of damage? ? ? ?

 

[gerod]

Miner? the miner rule!
If you have the cnr10011 you should have seen it!
Hi.

 

[luigi.paiano]

the reasoning you've done is right!
the calculation to work clearly you do it only and only if the fatigue is there, I think it is not there.
However in general for fatigue calculation bolts can be stressed at traction and cutting.
the calculation is identical to another any material subjected to fatigue, absolutely nothing changes.
However, usually using the criteria to calculate the equivalent stress (e.g. the distortion of energy) this stress equals the stress of precarious clearly corrected by the safety coefficient.
the rule of miner to which it was referred is that of the '' cumulated year'.
In practice, if you have different load cycles (therefore in substance cycles at different stress) you can calculate the cumulated damage as a sum of the ni/ni where the number of cycles at that particular stress is, while the number of cycles that the material can bear at that stress. the material breaks when the summary makes one.

 

[luigi.paiano]

however you have actually sized for static resistance. fatigue assumes that stresses vary over time!

 

[gerod]

for the record the Eurocodes treat the fatigue, even for the vines!