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Thread: Two rod straight joints

  1. #11
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    Quote Originally Posted by Luniz View Post
    Plus: A PIPE is a thing for liquid or gaseous substances to go through, hence it is referenced by its INSIDE Diameter. A TUBE however is a thing made to build structures from.
    And a ROD is a long cylindrical piece of metal with a diameter somewhere between a WIRE (smaller) and a BAR (larger).

    A ROD made out of wood is often called a DOWEL.

    A BAR with a hole running through the middle of it is called a HOLLOW BAR. Since it is referenced by both its inside and outside diameters, it might be called a PUBE!!!???

    Off-road racecar frames are often built out of PIPES. These frames have to carry large loads, and can potentially have very large impacts. So making them out of relatively thick wall, high quality, piping, such as is used in the Petro-Chemical industry, makes a lot of sense. Consider that such PIPES often carry highly toxic or explosive chemicals at extremely high pressures, yet still have to be reliably welded together at their many hundreds of butt joints. (Edit: the internal pressures can exceed the yield stress of mild-steel! Racecar frames are girly-boy stuff... )

    As for the OPs original problem. I suggest you go to your local cafeteria and, ahem, "beg, borrow, or buy" one of their chairs or tables. Should be enough tubing there to finish your frame.

    Z
    Last edited by Z; 12-20-2013 at 07:40 PM.

  2. #12
    What load is this tube carrying? Is it a regulated tube?

    Can you switch to a sleeve over the junction?

    Can you upsize the tube to use a mild steel one? If you have zero spare 4130, how will you confirm that you're using the right filler wire for the mild-to-4130 joints and practice those joints?

    If it's only one tube you need, can you get it from a different supplier at a higher cost?

    As-welded 4130 is about 15% stronger (60* vs 50 ksi yield) than 1018. Additional strength is possible in 4130 with heat treatment, but there is an advantage as-welded. You should be below the endurance limit in normal service and below the yield limit in your anticipated overload conditions, but they've got a saying about actual vs anticipated loads: "That's Racin'!" You'd think we'd test in wide-open lots with well-defined courses away from obstacles, but I managed to drive our 2011 car straight-on into a curb at around 40 MPH two days before Texas Autocross Weekend a few years back. Somehow, it handled better afterwards - with new lower control arms.

    The advantage of 4130 over 10xx for American teams has little to do with material properties and everything to do with Aircraft Spruce stocking 100 sizes of 4130 tubing to ship out on UPS. If you specify that you want manufacturing test papers for one tube in your order you might get certification papers for all of them.

    *on spec sheet - YMMV.
    Charles Kaneb
    Magna International
    FSAE Lincoln Design Judge - Frame/Body/Link judging area. Not a professional vehicle dynamicist.

  3. #13
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    "That's racin" indeed. I follow the mild steel argument but I struggle to agree with it. I have personally seen a fair number of these cars crashed over the years. Side impact with a pole, front impacts with buildings or curbs, rollovers, etc. 5+ examples I can think of right offhand that resulted in real damage. Bad decisions in course layout? Sure. But who hasn't made a bad decision or two. If 4130 has an advantage in crash worthiness I would argue it at least warrants considering. Spending money on safety in racing is usually the best money you can spend. Would we suggest buying the cheapest helmet and say that buying anything else is a waste of money? This is a huge change from my position 10 years ago when I was building cars (when I thought these cars would never hit anything), but when you've seen some scary stuff your opinion tends to change.
    University of Texas 2002 & 2003
    University of Houston 2007

  4. #14
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    All that I can say is that these yellings and sarcastic comments were indeed a good lesson learnt. We do consider the arguments above as correct and makes us consider these flaws in our project. Due to lack of experience we committed this mistake and didn't think so critically as we lack time and everything seems new and complicated. We aim to successfully represent first and learn for the coming years.

    Thanxx

  5. #15
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    Rex that's a heads up for us even though we agree 4130 is a bit unnecessary. Being a first year team lacking experience in building and driving we are definitely worried about impacts and failures. Hence i agree a little extra expenditure would save the money spent to repair the broken bones :P

  6. #16
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    Fair call Raptor, my sincere apologies for yelling. As a long term contributor to these boards I find myself often repeating the same points. It is more the fault of the difficulty in finding info / random scattering of information across these boards - and my lack of patience - than your inexperience. Lesson learnt.
    Geoff Pearson

    RMIT FSAE 02-04
    Monash FSAE 05
    RMIT FSAE 06-07

    Design it. Build it. Break it.

  7. #17
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    Big bird we take yellings as a matter of concern. Shall keep this in mind for the next time. But just a worry will this have a negative impact on the design judging wherein the only reason for the use i can give is the safety.

  8. #18
    I cannot speak for Geoff "Big Bird", (although I bet he will think as I do) but as a design judge in many FSAE / FS competitions I can assure you that any question simple or sophisticated, educated or lees educated, where ever it comes from will never ever create any "pre-judging" in my mind or any other judges/ mind. At the contrary the daring of asking questions (whether the answers in this forum are smooth or brutal) shows the interest of the student and his desire to learn. It will be pleasure to meet you one day at one the competitions and put the name and the face together. At the design event it is your car and your knowledge that will be evaluated, not your forum participation.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  9. #19
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    Hi all,
    Our Main Roll hoop is of mild steel. And the side impact structures are of chromoly 4130 and We used ER70S-2 as filler material for the dissimilar metals. Is it fine to do so?? Or does it fringe any specific rule??

  10. #20
    No Raptor, that's fine. ER70-S2 is the correct filler for mild-steel to mild-steel, milt to 4130, or 4130 to 4130 (unless you are going to heat treat it - then you have some rreading to do.)
    _______________________________________

    Northwestern Formula Racing Alum
    Head Engineer, Frame/Suspension 2006-2009

    My '73 Saab 99 Road Race Build

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