test tensile strength on cast iron screws g25

[meccanicamg]

Thank you so much! If the screw breaks at 100 and the preload at 70, if I apply a force of 70 I go to zero.
from my zero I have available all 100 again before the break right?

No. That's what I told you.

the tightened screw generates a force that compacts the joint of the two plates creating traction on the stem.
if you apply on the plates a force that traction again....you can apply 70 and until then the screw is soft....but you can apply 30 more.

 

[Chris_BRB]

Let us clarify now thank you, but in the formula below if I have to verify that I do not tear my mothervite in the cast iron, how am I to use that of the cast iron not that of the right screw?

 

[meccanicamg]

Let us clarify now thank you, but in the formula below if I have to verify that I do not tear my mothervite in the cast iron, how am I to use that of the cast iron not that of the right screw?

In fact, the norm does not provide for the tearing of the mother-in-law. Therefore use the standard for steel constructions adapted to cast iron or aluminium is completely wrong.

 

[wert]

In an empirical way, they taught me (and in 40 years of design I have always followed this rule) that if the screw is engaged in the mothervite for an adequate length, in case of over-sollecitation will always break the screw, for which the calculations are concentrated only on the screw. always empirically, this is true if you consider a screw length engaged in the madreviti for a length of 1/1,5 times the value of the nominal diameter of the thread, in case of ductile materials. for fragile materials, this ratio must rise to 1.5/2 times the diameter of the thread. for what concerns me, I could check these values on aluminum die castings and indeed, with a screw engaged 1.5 times the diameter, on 10 breaking tests, for 10 times the screw under the head has been torn. to further confirmation of this, just look at the heights of normal dice. . .

 

[Chris_BRB]

thank you so much to both

 

[Chris_BRB]

talking to my colleagues came a further doubt about post #21.

We put two screws, one during the stress in the working condition goes in compression, one in traction.
with the preload the threads are already in traction, so if when then the screw works still goes in traction makes an additional traction effort that goes to sum up to the preload and then you have to sum the labor traction force and the preload force and such sum must be lower than the limit resistance no? (as in the exercise of mechanics mg of the post #11), if instead the vine during the work phase goes in compression should not be added the preload because being the threads in traction, going in compression goes to download the preload already carried out.

I'm sorry, but I find it difficult to understand this passage.

No. That's what I told you.

the tightened screw generates a force that compacts the joint of the two plates creating traction on the stem.
if you apply on the plates a force that traction again....you can apply 70 and until then the screw is soft....but you can apply 30 more.

 

[meccanicamg]

talking to my colleagues came a further doubt about post #21.

We put two screws, one during the stress in the working condition goes in compression, one in traction.
with the preload the threads are already in traction, so if when then the screw works still goes in traction makes an additional traction effort that goes to sum up to the preload and then you have to sum the labor traction force and the preload force and such sum must be lower than the limit resistance no? (as in the exercise of mechanics mg of the post #11), if instead the vine during the work phase goes in compression should not be added the preload because being the threads in traction, going in compression goes to download the preload already carried out.

I'm sorry, but I find it difficult to understand this passage.

I don't know.