Threaded Bar Failure

[Hitch]

Looking at it 3 cans of cider later....

The green is the force exerted on the yolke by the bolt, that pulls the yolke up to bend it.... the compression is the force that is exerted by the yolke, onto the bolt.

It appears that in my diagram i have mixed the two different forces.

 

[wyn]

A couple of pics of the setup in which the threaded bar was used.

The last pic shows the elongation/ failure (when it goes it goes with a bang )

The first two pics shows the bar threaded into the shaft, with the bearing and counter weight having been pushed on.

The jacking cylinder is hollow down the centre so just sits over the threaded bar. The two plates have 20mm holes and spread the load.The plates are the cover plates that bolt on the end of the shaft. the extra bolt welded on the outer plate is the pickup for the speed sensor.

When the bearing is being jacked on double nuts are used on the outer plate

 

[rtbcomp]

The thread won't be in shear. If any bending of the yoke produced a shear it would produce equal and opposite shears on each side of the bolt, thus no resultant force.

After dreaming about this all night, the easiest way to think about it is that the top surface of the bolt thread will be in contact with the bottom surface of the yoke thread, thus pushing the yoke towards the head of the bolt. Pushing produces a compression force.

There will be no force in the bolt above the yoke. (apart from torque as you tighten the bolt, but that's another can of worms!)

 

[TechnicAl]

I think justme has a point. The bolt must be in compression on a puller. Whether its ALL in compression I dont know

 

[Justme]

I think justme has a point. The bolt must be in compression on a puller. Whether its ALL in compression I dont know

I think ALL the bolt in & under the yoke is in compression cos all the threads are pushing the yoke up & the center down creating compression. Ok more compression in the lower parts & less in the upper parts but still compression.


Justme

 

[rtbcomp]

I think ALL the bolt in & under the yoke is in compression cos all the threads are pushing the yoke up & the center down creating compression. Ok more compression in the lower parts & less in the upper parts but still compression.


Justme

That's what I said in post 23, except that the compression force must be the same throughout the length of the rod. If it wasn't it would move due to the resultant force.

Within the yoke this force will be distributed along the length of the threads, thus the force on each thread will be the compression force divided by the number of threads, so the force on each thread will be less, but the compression in the rod the same.

 

[Archie]

Agreed again, rtb, but I still maintain that the compressive force in the bolt transmits to the yoke through the threaded part of the bolt inside the yoke by shear force. Imagining a cross section of the bolt and yoke, all those teeth would be in shear. I'm starting to confuse myself now!

 

[rtbcomp]

In the diagram shear is a horizontal force, all the forces are vertical.

There will be a horizontal component of force on the thread due to the angle of the thread form, on the left of the bolt this will act to the right, on the right it will act to the left, each cancelling the other out, so no resultant force and no shearing action.

 

[Archie]

I think I may have got my threads crossed.....

 

[stormin]

There's is only ONE thread on that bar, it goes from one end to the other.

 

[drivewasher]

There's is only ONE thread on that bar, it goes from one end to the other.

The threaded bar in the pics is obviously in TENSION if your "pushing" that bearing and its carrier onto the shaft the bar is threaded into.
You can see the bar has streched

 

[Weldingartisan]

How about high tensile studding? It is available (though expensive) in 12.9 grade, the same as cap heads. W/A

 

[Mr T]

Sorry to tag onto the end of an existing conversation but this seemed relevant to my problem. Im doing a dissertation based on pulling threaded steel rods out of timber at varying angles to the grain. Im trying to work out the throretical failure of the steel rod. Its 16mm threaded stainless steel (Grade 304) which i believe has a tensile failure of 515MPa. What is the area of a 16mm bar? how much is lost due to the threads? makes thanks

 

[rtbcomp]

Measure the diameter at the root of the thread and apply the formula

A = Pi * R^2

 

[Mr T]

rtbcomp thanks, i don't currently have a bar, need to pick some up in the next week or so was just trying to get a head start with my writing. I was just wondering if anyone knew where it was a standard dimension or varied from manufacturer.

 

[rtbcomp]

rtbcomp thanks, i don't currently have a bar, need to pick some up in the next week or so was just trying to get a head start with my writing. I was just wondering if anyone knew where it was a standard dimension or varied from manufacturer.

Thread dimensions comply with international standards.

Have a look at this thread http://www.mig-welding.co.uk/forum/showthread.php?t=9492

 

[Paul.]

Minor Diameter of an M16 is 14.210mm for the nut (Internal thread) and 13.05 for a bolt (external thread) thats for a medium class of fit.

 

[Mr T]

rtbcomp thats fantastic, many thanks for your help

 

[Mr T]

paul thanks too - now ive not go any excuse to get on with the rest of my dissertation.....

 

[madkayaker]

Careful Mr T this place is very addictive