Compound Fillets
Compound Fillets
(OP)
I've used compound fillets for packaging and weight reductions in members under tensile load, but does anyone know of any guidelines or sources for using compound fillets under combined tensile and bending moments loads? Essentially I have a T section where the two "arms" of the T support the trunk as it's being pulled (I'm stuck with the configuration so please don't offer suggestions as how to improve the design, I know, I know...). Where the arms meat the trunk there are tensile and bending moments and how the compound fillet is really working isn't obvious to me.





RE: Compound Fillets
Could you clarify the loading configuration please. From the description, are you loading perpendicular to the T section?
Thanks
Jetmaker
RE: Compound Fillets
We always use an elipitical(3 to 1) fillet with the long leg in the direction the force is being applied. Usually the dressing of a fillet is to increae fatigue resistance.
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RE: Compound Fillets
RE: Compound Fillets
Have you considered full penetration bevel welds?
RE: Compound Fillets
RE: Compound Fillets
Borjame, I can only speak of my experience with castings, compound fillets or extended fillet legs are used on the leg were a higher proportion of loading may occur. I do not have the guidlines you are looking for, just posting clarification.
RE: Compound Fillets
Echoing the post by “CWIC”. The object in either is to distribute the stress across the junction or connection favoring the member with the highest stress.
My came from an article comparing different fillets.
Post your question here.
http://www.forging.org/forum/forum.htm
You might also check the ASM Forging and Casting Handbook
www.asminternational.org
These handbooks are expensive but worth it. As mentioned in another post they have a $179 unlimited access fee.
RE: Compound Fillets
Let me first make the following assumption. You are wanting to use a compount fillet for fatigue reasons. Also, the T section is symmetric about the trunk. If this is not correct, please let me know.
The tensile load will cause a peak load to occur along the trunk at the intersection of the fillet tangency. The bending load resulting from the eccentricity of the bolts on the arms will occur midway in the fillet. The 2 will not overlap much. However, under linear-elastic properties assumptions (i.e. loading below yield point), the stresses should superimpose.
I would calculate the bending stress concentration factor for an angle under a bending moment. I believe this is available from ESDU. I would use the tightest radius that you call out for the compound fillet.
Increasing the fillet radius is always a good thing, as this will reduce the stress concentration. Another option is to install a radius filler on the arms to locally stiffen the arms and shift the load line closer to the trunk. I would suggest searching the web for tension clip analysis.
Hope this helps.
jetmaker
RE: Compound Fillets
Also, what is your criterion of failure?
Also, how is the section made - eg if it is an extrusion then you could do some very fancy things with fillet shape.
Cheers
Greg Locock
RE: Compound Fillets
The part is being cast(complexity of overall shape dictates this) but weight is an issue. My two criterion are weight and stress. FEA shows that the high stress point is actually in the fillet runout on the T arm portion which would say to me that there's where I should put the larger radius which is opposite of where you would place it for a simple member in tension. This is where I came to you guys to see if there were any general guidelines associated with this. I want to be sure I'm interpreting the model correctly. If these results don't jive with conventional wisdom the model may be providing bunk answers.
RE: Compound Fillets
Thanks for the added info. By all means, put the large radius towards the T arm. This will increase the material in the bending region, lowering overall stress.
However, as you have access to FEA, it should not be too difficult to do some quick checks to verify this. It seems that you have already undertaken some of this.
Good luck.
jetmaker
RE: Compound Fillets
With a casting you could go to any fancy shape, I'd guess the arms and leg will end up tapered.
Is there any requirement that the top of the T be straight?
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is quite a likely solution.
Cheers
Greg Locock
RE: Compound Fillets
Has anyone got any good sources of data for stress concentrations for compound radii?? I'm only aware of a small amount in Peterson.