laser welded sst tubing

[clee]

I need a method of estimating joint strengths on laser welded stainless tubing assy's. The joints are overlaped [telescoping] and laser welded at the exposed end of the larger tube. material is 304 and tubing is hypodermic sizes, in the range of .013 - .06"OD with walls from .002 - .01"
Any pointers or info sources would be appreciated

 

[tld23]

Clee,
The joint strength will depend on what is being measured. There are three main loading modes

1) Tension - pulling one tube out of the other
2) Torsion - twisting along the tube axis
3) Bending - loading normal to the tube axis

You may want to assess all three modes or combinations of them. I assume you are using an austenitic grade (such as 304). The good news is that SS is generally easy to weld - but pick a weldable grade. The welds should be tough yet ductile and so the classic von Mises criteria will be appropriate. You will have to do some simple calculations to work out the stresses in the parent sections and the welds. For the welds use the throat area. Consider any loss in strength due to the welding. These simple calcs will give a good estimate of the load to first yielding, calculating the ultimate strength will take a bit more effort.
Post again if things are more complex than I have appreciated. TERRY

 

[clee]

tld23, thanks for your reply.
The loading I'm most interested in is in tension along the axis of the tubes. I'm assuming the primary, or most significant mode within the joint will be shear. The material is 304, and I am working with the assembly house to estimate weld dimensions to obtain throat values.
Would you consider the straight 304 [as opposed to 304L] a good choice for welding?
I think my biggest unknown is how to estimate material strength loss resulting from the welding process. I have read that laser welding tends to produce clean and therefore relatively strong welds, but I have not yet found any factors to apply to material strength in the weld.
Any additional thoughts would be helpful.
Thanks
Chris