Challenge

[Lunner]

You have two metal shapes, cut from 5mm steel sheet, you need to think of the strongest possible way of attaching the two thinner ends together, hooks will be put through the holes at the end and the joint will eb tensile tested.

It only needs to be strong enough so that the structure itself fails before the join, also needs to be 20mm (about how they are positioned) from the larger section, and as light as possible.

http://www.lunner.co.uk/williamsclio/DSC00060.JPG

Ideas so far are glue, and welding, but no specifics

[arj256]

Could bolt it consistnantly along the thin bit and if you want it really strong, put some sealing compound in as well. If your going really strong lol.
Or could use rivets as well. And even spot weld, but do you want to minimise distortion?
If its for a tensile test then id say a few bolts would be allright as decent bolts can hold a few tonne, just get em small enough not to risk fracturing the thin bit.

[edde]

If costs no problem then stir friction weld the parts together the joints are stronger than a solid block of material. However its costs and difficult to do. We use it at work and it is strong.

The section doesn't look to thick but rivetting it with sealing compount well done will be very strong depending how the material is the material can be weeker. However its a thin secon so you'll probably pull the material first. Round where the joint is your supposed to have about 2.5 times the thickness of the rivet on both sides which is probably impossibly.

I take it junction plates are out the question ie sandwhich it together?

[richy]

gaffer tape ???? pmsl :lol:

[BenR]

if they are spaced that far apart, then are you allowed to use a material to bridge the gap, or must the actual joining method/compound be the bridging material?

[Lunner]

No i just spaced them like it to illistruate the point.

Basically its a uni project, the area of the thin bits to be joined are rectangular sections 5x8mm, and the join can be 80mm long.

You can do literally ANYTHING, but the emphasisis on strength and lightness.

For example you could cut half the material away and create almost a lap joint, so one half fits into the other half, and resembles a section 5x8mm rather then 10x8mm or 5x16mm as you would get if you over lapped them

[stan]

Rivets will be the best bet.

wot tensile force does it have to take? if you know that you can work out the required ammount for a given pin diameter to give a maximum shear....

[Lunner]

Need to work that out, can't remember the tensile strength of steel off the top of my head, but its the structure that has to fil before the joint does, so 40mm^2 of steel.

Thing i was worred about wiht riveting it, the rivets will take the stress easy anough, but if you use say a 3mm rivet that leaves you wiht 2.5mm of steel each side, will this just not fail instead?

[stan]

got u, so its a failure test...and the test piece has to fail before the joint?

if you bond and rivet it (or if the clamping force is great enough), the lap joint effectively becomes one solid section (up to a point). so, so long as the total cross-sectional area at the rivet (i.e twice one side) is greater then the cross-sectional area of the neck, then the neck will fail first. if your smart you can work in stress concentration factors that are applied at the neck.

[Fred]

arc weld the ****er together, job done

[edde]

Need to work that out, can't remember the tensile strength of steel off the top of my head, but its the structure that has to fil before the joint does, so 40mm^2 of steel.

Thing i was worred about wiht riveting it, the rivets will take the stress easy anough, but if you use say a 3mm rivet that leaves you wiht 2.5mm of steel each side, will this just not fail instead?
I'd keep away fron Rivetting such a thin section I had a similar project at uni but our pieces were much thicker so that sort of failure wasn't going to happen (well it wouldn't if people hadn't cheated building them)
What about bending the two pices to make two hook type pieces out of the material and so hook them over each other?
Friction welding is what you want though it looks nice and simple and very very strong.
Or what about drilling a hole in the bit you want to fail? Since all your trying to do is find the strenght of the material if you weeken the material in one point then it will fal there beofre any joint ie rivetting etc.

[Lunner]

arc weld the f*cker together, job done

I'll bring a couple of sections over and you can arc weld it then Fred, and then we'll test the strength of your welding

[Slithers]

arc weld the f*cker together, job done

I agree with fred here a decent weld should be strong as ****.

Also if your allowed to modify the 2 adjoining pieces in anyway so if you can take a channel out of each side of the joint after welding to create an I beam shape cross section, after all shape plays one of the most important parts of a materials strength.

[Lunner]

An I beam section is very good when subjected to a bending force, but for direxct tensile strength amount of material is mor important......stress = force / area, so a larger area wil distribute the force better, meaning a lower stress :D

[Swervin_Mervin]

Wish I could remember my uni teachings!

I'd bond it personally. Rivets alone will fail IMO as they could fold across their centres. Solid pins however, would work very very well if they were a tight fit. Get the pins ever so slightly larger than the holes for them, heat up the plates, bang the pins in and the metal will shrink around them.

[Slithers]

An I beam section is very good when subjected to a bending force, but for direxct tensile strength amount of material is mor important......stress = force / area, so a larger area wil distribute the force better, meaning a lower stress :D

True but the material that is taken away to create the I beam cross section will result in an increased power/weight ratio, which is another factor in your challenge aint it?

Actually you could consider drilling some holes along the centreline through the joint after welding it then maybe welding it round the inside joint of each hole, so you reduce the weight, but are welding it at an internal point increasing the strength of the joint.

[Lunner]

Sounds good to me, my only concerm is the amount of material there.

What i think i will do is cut each section, on a diagnal, so they joint together wiht no over lap, you then have a length of about 90mm (overlap woudl be 80mm) to weld/glue along. This reduces the weight of the piece in the process as well.

Also the rectangular sections at the top can be modified, ie the bottem corners can be removed, althoguh if the piece fails due to modifications that is calssed a s a joint failure