Calculation of stress on welds 3

[illustrator15]

Hello,

Could someone please tell me what factors should I consider if I want to calculate stress on the welds mentioned in the attached picture?

There is a 200 kN force on the assembly of bracket and round bar whereas bracket material has a yield strength of 420 N/mm2 & Round bar material has a yield strength of 450 N/mm2.

Thanks

 

[Engdoitbetter]

Due to the various uncertainty which affect welding, usually calculation is performed in a simplified way.
In this case I think you have basically shear stress through the weld circumference which balances the load on the left.
Unfortunately I don't have references regarding the standards which are applicable in this case. I would certainly wait the answer of more experienced engineers than myself.

You can also rely on this site

http://www.roymech.co.uk/Useful_Tables/Form/Weld_strength.html

Hope it helps.

Stefano

 

[London]

A quick check with Working stress design would be something like this:
pi x 54 x 0.707 x 10 x 0.4 x 420 = 201kN
This is assuming the weld is acting in shear, the average diameter if the weld ring is 54mm (conservative) and the weld strength is 420N/mm2. The weld qualification would confirm this.
I have ignored the contribution of the 4mm seal weld on the front

 

[som1973]

Weld stress = load(force)/Weld throat area

weld throat area of circular fillet weld is calculated as follows

= 0.707 x weld throat thickness x PI x diameter of Pin

then compare the calculated weld stress with Permissible stress ( 0.60) (60 %) x Yield strength of Pin)

 

[dik]

RoyalMech is a really good site... Welding info has been provided; yOu may want to add a horizontal bar over the 'V' type weld to indicate a flat surface if necessary.

Dik

 

[illustrator15]

Hi London,

Could you please tell me what 0.4 is in your equation and which filler material you have assumed for the weld strength of 420 N/mm2?

It would be very helpful to me if you explain your equation.

Thanks,

 

[dhengr]

Illustrator:
If your background is what your handle suggests and you want to learn to do engineering like this, you would do well to get some good engineering text books: Engineering Mechanics, Strength of Materials, Machine Design, Welding Engineering. The last one might be some Lincoln Electric books by a guy names Omer W. Blodgett, “Design of Welded Structures” and “Design of Weldments,” and others.

There are a couple errors in the above posts. London says, about the groove weld.... “pi x 54 x 0.707 x 10 x 0.4 x 420 = 201kN,” and that should actually be [(pi x 54)(10)](.4 x 420). The 0.707 does not belong in that equation. The first two terms are the circumference of the throat, the next term is the depth of the throat, and these three terms are the area of the throat. The last two terms are the allowable shear stress based on Fy of the lesser base material. The weld is in shear through the least throat dimension/depth. I believe the .4 comes from some of the steel design codes (for example AISC), and some people use .5 or .577Fy. Som1973 says, about the fillet weld.... “0.707 x weld throat thickness x PI x diameter of Pin,” and that should be (0.707 x fillet weld size)(PI x diameter of Pin). The first two terms are the throat dimension/depth. Actually, the diameter could be increased by 2mm to get to the center of the throat. They are each talking about only one of the welds and both welds should be (can be) considered in your calcs. You guys all seem to look for some cookbook formulas to solve every problem, or set them up that way. Think through these problems and do them one logical step at a time. What is the min. throat dimension/depth? What is the min. throat shear area? This area can be stressed to the max. allow shear stress implying a max. load, or alternatively, (200kN)/(total throat area) = weld shear stress.

Now, as regards your detail: you do not want any weld extending beyond the back pl. back face, see Dik’s comments...., or you will have to grind that down/flat to get a good bolted connection. I would change the back dia. of the pin from 47 to about 41mm, and I would keep the slope about the same on the back pl. bevel but reduce the land to about zero, so that is just a groove weld without the flat bottom. As long as your welder can get into that root to make a good weld, this will save you several weld passes without decreasing the weld strength. And, you want a concave or fairly flat surface on that weld, so the throat may be only 9 or 10mm deep. I would change the front fillet weld from 4 to about 8mm in size. The reason for this change is because that weld is in shear through the throat due to the 200kN load, but it is also in tension due to the way the back/base pl. flexes when the bracket is bolted up and loaded.