Help with metal strengths

Can someone elaborate on Yield and tensile strength of metals and how they are measured? For instance, I'm searching McMaster Carr for various ideas and types of metals and question the strength ratings.

When the stats indicate 35,000 yield strength, is that per inch, per foot, per yard, etc? What happens when I cut it down? I'm also comparing a flat stock aluminum at 1/4" thick x 2" wide to a 2" wide(base) x 1" high(leg) x 1/4" thick and a 1/8" thick aluminum channel. The 1/8" thick channel has the same yield strength as the flat stock. Is it due to the

1/8" difference in thickness? Would a 1/4" thick channel have a greater yield? Does that have anything to do with flexibility?

My objective is to weld pieces of aluminum into this shape .......

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which I already did with the 2" x 1/4" aluminum I mentioned. Through trial and error, I learned it flexes too much for my need. Therefore, I need stronger and less flexing(preferably none). I choose aluminum due to it's lightweight, but if necessary, then I will use steel or something else anyone may want to suggest. Overall, I assume channel or even rectangular tube would be more ideal to eliminate flex and provide more strength but I need to stay at 1/4" thickness and 2" width.

All help appreciated.

Thank you

Reply to
Meanie
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I wanted to add, as I search the McMaster Carr website for those various metals, I'm seeing the same yield strength for many different metals comparing the same type of layout which adds to my confusion.

Thanks again.

Reply to
Meanie

Per square inch of cross-sectional area.

How are you cutting it? Yield strength tells you how much tensile load you can put on it before it takes a permanent "set." In other words, it's the elastic limit. At any level of stress below that, the steel will spring back like a rubber band.

It doesn't matter how long or short the piece is. What matters is its cross-sectional area perpendicular to the load you're applying to it.

Tensile strength is the value of the load you can apply before the metal breaks. It's higher than the yield strength, but sometimes it's very close.

BTW, these values are measured with tensile-testing machines, which are lab equipment. Instron is the best-known brand. They clamp each end of a test sample and pull on the ends. 'Sounds simple, but they cost a bundle.

It has nothing to do with flexibility (stiffness). The yield and tensile strengths depend only on the material, the temperature, and, for all practical purposes, the total cross-sectional area of the material.

I'm hoping someone else will answer that last one. I'm pooped for the day. d8-)

Reply to
Ed Huntress

You're probably looking at the *per square inch* material strength, which is the same for different sections. What matters is the area of a cross-section of that material section -- like L-channels, round rods, etch.

Cut across them and measure the area of the cut.

Reply to
Ed Huntress

Hmm, I was the startup engineer on Post-IT notepads 30 years ago. We used and instron to measure the adhesive strength at a target of 80 grams peeling a one inch wide polyester strip off. Instron must have a WIDE range of load cells.

Karl

Reply to
Karl Townsend

Oh, yeah. Instron makes a machine to test the strength of just about anything you can think of.

The ahrd part in many cases is figuring out how to clamp the material. With wood, for example, it's hard not to wind up testing the along-the-grain shear strength, or the strength of cross-grain compression, when you want to test the strength of linear tension.

Reply to
Ed Huntress

There should be units. The units should be of pressure -- PSI or Pascals.

You are probably seeing the yield strength of the METAL, not of the PART. Yield strength (in PSI) is a property of the stuff the part is made out of. The strength at which the part will deform or break will be in units of force (pounds or Newtons) and is a function of the material and the part geometry.

You're looking for stiffness, not ultimate strength. Stiffness of a material is called Young's modulus. It's also in PSI, and you'll have to look up just what it means -- but a higher Young's modulus means a stiffer part.

If you're pulling on it where you say "Fig 2", and it's pulling on something where you say "Fig 1", then between the 210 degree bends it's going to be all floppy, no matter what. You're putting a bending stress on it that's strongest at your "Fig 2" point, and flat strap just doesn't resist bending well. If you could substitute bigger material (tubing or bar) for the cross piece up to the bend, and just use thin strap to the ends, then you'd be a lot better.

Reply to
Tim Wescott
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You're dead on. The "fig 2" is where an adapter/mount is attached for a very small trailer. The "fig 1" is where the drawbar attaches to an axle. After my test run, the area in "fig 2" is bending inward, most likely from inertia when braking, but overall, I realize the stop and go will apply the most pressure in that area and soon break.

When you say bigger material, are you indicating an aluminum channel or rectangular tube will work much better? This is my thought due to the supporting sides/legs which I am hoping will eliminate the flexing and strengthen that "fig 2" area.

Thank you

Reply to
Meanie

I can't really envision exactly what you're trying to show here -- what/how does a "drawbar attach to an axle"??? If the circle/"adapter" at 2 is intended to be a location for ball hitch and you're pulling at that point and (whew, lot's of and's) it's a top-view, either weld a good chunk of angle on the flat or fill in the open area on the behind side with flat plate (assuming you don't want anything on the top).

What size/material is hard to say w/o any weights at all so I won't even try to guess on that part...

Reply to
dpb

Making the frame as close to a triangle as possible (in other words, reducing the 5-1/2" & 8" dimensions) will increase the stiffness. Assuming the loads are all in the plane of the drawing, laying the bar flat will make the frame *much* stiffer; 64x if I did the mental arithmetic right. And switching to steel will make it 3x stiffer (and

3x heavier).
Reply to
Ned Simmons

One thing you need to remember when deciding between steel and aluminum. If steel flexes, but does not bend bast it's elastic limit, there is little or no "fatigue" introduced, but if aluminum moves AT ALL it is building up "fatique" damage and will soon break. For a trailer hitch you do not want ANY flex if it is aluminum, and more important, you do not want aluminum if there is any possibility of movement/bending. Also, welding aluminum structures where repetitive stresses are expected is a job for an EXPERT with engineering knowlege as well as welding ability. I was not able to access the diagram - will try later - but from the description so far I'm thinking you should be using square steel tubing with fish-plates or gussets welded to the angle joints

Reply to
clare

Would be a lot easier if we knew what this contraption is supposed to do, and what it is supposes to attach to. I finally got the diagram to open.

I'm assuming the two ends (diagram 1) are drilled and an axle/pivot/pin runs through it and the framework you are building is somehow supported at the "rear" (diagram 2) to keep it from dropping, and there is a pivot(ball or pin) connecting it to the drawbar of theis "lightweight trailer".

If it doesn't pivot at "diagram 1) and is not supported at "diagram 2" you have a lot of other problems. What fits inside the frame that requires it to be that shape??? If anything??.

We REALLY need more information to give you any kind of usefull input.

Reply to
clare

Can't do that. The "drawbar" encases the rear wheel of a motorcycle. It's width(two ends of fig 1)is the exact distance of the rear wheel axle and the depth is about 3" from the back of the tire. Therefore, I cannot make it smaller without interfering with the movement of the tire.

Obviously, there is another drawing displaying fig 1 and fig 2. Fig 1 is a hole which fits over the axle and locked in with a bushing and pin enabling it to pivot on the axle. Fig 2 is a flat plate welded to the drawbar. The trailer has a two piece coupling and one side is bolted to the flat plate. The other is obviously on the trailer's tongue. It can be detached with the removal of a hitch bolt/pin and separated from the drawbar.

Reply to
Meanie

You are correct in your guess. It pivots at the end of fig 1 and attached at fig 2.

As explained to Ned above......(cut and paste)

The "drawbar" in the drawing, encases the rear wheel of a motorcycle. It's width(two ends of fig 1)is the exact distance of the rear wheel axle and the depth is about 3" from the back of the tire. Therefore, I cannot make it smaller without interfering with the movement of the tire.

Obviously, there is another drawing displaying fig 1 and fig 2. Fig 1 is a hole which fits over the axle and locked in with a bushing and pin enabling it to pivot on the axle. Fig 2 is a flat plate welded to the drawbar. The trailer has a two piece coupling and one side is bolted to the flat plate. The other is obviously on the trailer's tongue. It can be detached with the removal of a hitch bolt/pin and separated from the drawbar.

Reply to
Meanie

To help anyone get a clearer picture, here are two photos of the drawbar hook-up on the bike and trailer.

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Reply to
Meanie

I suspected that was what you were working on. The "drawbar" pivots on the rear axle of the bike, and the trailer pivots on a pin - with no support at the back of the hitch. NO WAY would I attempt to do it that way - particularly with aluminum. You WILL lose the trailer, and you could very likely cause a serious accident when that happens.

There are lots of well engineered bike hitches readily available - and some for not much more than it would cost you in materials. Look at the Kuryakyn line - most models are less than $300 and they are a VERY well designed and built hitch. KhromeWerks, HitchDoc, Bushtec and custoncruiserchrome all make decent units as well - but I'd be taking a close look at the Kuryakyn - best value for money.

Reply to
clare

5/16X2" 4140 bent, not welded would mabee work - but not be light. 1/4" MIGHT even work, I'd gusset the back angles. What provision are you making for leaning the bike???.

Another option would be a side pivot hitch, with the hitch of the trailer attached to one side instead of the center, with a bend in towards the center to allow you to make right turns. Ball hitch bolted to the rear bike axle. Like a bicycle trailer.(look at the Burley Nomad as an example) or the CTS (Thule) system -

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gives you an idea ov what I'm talking about, but still using a pin. (as does Burley)

The 4140 is going to cost you at least half the price of a Kuryakyn hitch. Whan make model and year is the bike??

Reply to
clare

Not sure what you mean "no support at back of the hitch" but it's a similar design as this

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and many of these

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I do not want a permanent hitch. I want something removable. I like to keep the lines of my bike clean and only use the trailer on long trips, otherwise, I can assure you, I would have had any of those retailers on it.

Reply to
Meanie

It's a single wheel trailer. It leans with the bike.

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02 Kawasaki Mean Streak
Reply to
Meanie

BTW, none of those retailers/manufacturers make a hitch for my bike. There are a few (less than a handful) who can custom make a permanent hitch. The single wheel manufacturers also custom make them with two options of a permanent or the axle hook-up which is where I obtained the idea.

Reply to
Meanie

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