Strength of welded joint

[Steph123]

Hi,

I'm currently working on a design, and I need to join .5" CS plate with 1.25" x .120" round CRW(DOM) tube. As this is a marriage of aesthetics and structural integrity, my goal is to find a suitable design solution which affords me a seemingly, seamless joint once the welds have been blended in. The tube being used is CRW(DOM)and the plate CS1020. My main concern is not to have a weld that will overly compromise the structural integrity, but it doesn't have to be the optimal choice, as form is my primary concern; it does have to be safe though!

I have attached a dodgey image of the weld area in question from the CAD model. I would run a single pass on both sides of each joint, so effectively there would be 4 welds in total. Is this going to be a strong joint?

Thanks in advance for any advice that can be offered,

Steph

 

[HgTX]

No one here can answer whether it is a "strong" joint because we don't know your loading.

What exactly are you unsure of? You should be able to calculate the strength of those welds.

Hg

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[desertfox]

hi Steph123

We would need to know the type,size and loads the weld is liable to see in service before we could advise you anymore.

Take a look at this site it may help:-

http://gowelding.com/calcs/

 

[Steph123]

I'm not looking for advice on loading, I'm looking for advice on the type of joint, as it's unconventional. One of my contemporaries led me to believe that this type of weld would actually compromise the strength, whereas I considered it would increase the strength.

So again, I'm not looking for numbers, I'm looking for advice on the type of joint being used, where there is a 'slit' or opening machined length-wise in the end of the tube and the plate is positioned and welded in the centre of the opening. I expected an answer somewhere along the lines of, "you will have to heat-treat the area to reduce stresses created during the welding process" or something of that nature.

I guess I'll have to did out some books/reports to find the answer.

Anyway, thanks for trying,

Steph

 

[SnTMan]

Steph123, as I understand the problem, you will essentially have 4 fillet welds with a leg of 0.120 in of some length. Weld metal outside this area will not add much to the joint strength.

Your weld area will be roughly 4*.707*.120 = 0.34 in^2 per inch length. The strength in CS materials will be roughly 60000 psi * 0.34 = 20000 lb/in length. This is based on average stress for the joint in tension only. Other loadings will produce different weld stresses. This is just handbook stuff.

In CS materials you will not likely need to PWHT, and will not gain anything from it.

This type of joint may suit your needs or it may not. You will have to define for yourself "safe", "strong", etc. based on the applicable REQUIREMENTS.

Regards,

Mike

 

[Tmoose]

http://www.prodigalchild.net/Rech4Crp.jpg

http://www.istockphoto.com/file_thumbview_approve/3097140/2/istockphoto_3097140_column_and_beams.jpg

http://www.gdlcycles.com/general/215-9383-Frame-1.jpg

http://www.geekologie.com/2008/01/09/bikeframe.jpg

http://www.gdlcycles.com/general/336-22516-Frame-1.jpg

http://www.richardsachs.com/images/toys/rsdropouts.jpg

http://www.gdlcycles.com/general/326-21299-Frame-1.jpg

http://www.richardsachs.com/images/toys/rsachsbb.jpg

It really does make a difference how high the loads are, and if the loading is pure tension or compression along the axis of the tubular member, or bending in y direction, or the z direction, or maybe whether that hunk of angle iron is applying the load.

 

[Steph123]

Thanks Mike, I appreciate the info.

Thanks Tmoose, a few of those JPEGs were just what I needed to see. The joints are where the stanchions and the upper and lower tubing of a motorcycle frame meet. There are mainly twisting/bending forces to deal with. The angle iron is more a mounting bracket than anything else.

Thanks again,

Steph

 

[MintJulep]

I don't like it at all for a motorcycle frame.

You really can't control the weld very well. If you try to do it as a butt weld you won't know what penetration you really get. If you try do it as a 1/2 bevel you will probably end up with bridging.

At the end of the notch you will have a horrible stress discontinuity, and very likely will have fatigue cracks initiating there.

Note that the bicycle drop-outs linked by Tmoose are brazed, not welded.

I would be inclined to redo your joint by building up your plate to a round that matches the ID of the tube, and then braze.