Announcement

Collapse
No announcement yet.

Rod ends, tie rod ends, nuts and bolts etc...

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Rod ends, tie rod ends, nuts and bolts etc...

    I was just contemplating things we take for granted, or gospel, or maybe even just plain old "well it's always been done that way", and figured I should share some engineering experience with breaking things for a living that I used to do. And how that relates to the topic line.

    Since I joined about a year ago, I have seen some discussions relating to how things go together, and how they may break. I've got a few observations regarding a lot of things we use that is beyond the intended design. For example: old Ford tie rod ends, the 11/16 threaded ones, that are used for split wishbones. The same logic applies to spherical rod ends.

    Consider this: in the original application, tie rod ends and spherical rod ends (Heims for ease of typing), were designed for push-pull situations. Yes the stud on a tie rod end is in bending as well as shear, but that is a good safety valve to let the stud bend if the tire hit a pot hole or kerb. The body of the tie rod end was not intended to take bending loads however. Actual Ford tie rod ends were made from good steel alloys, but that doesn't make that much difference when applying a bending load. So we take the wishbones or hairpins and what happens?

    The threaded part ends up in bending as well as taking end loads and shear loads. The same is true for Heim joints: they were invented by the Germans for Aircraft use to control moving wing surfaces, allowing some rotation on the stud, whereas the clevis that formerly was used tended to bind on the pivot bolts.

    We found out about them from a recovered German fighter plane that the English were able to dissassemble and analyze. The Rose company in England started making them for the British aircraft industry, and they shared the design with us during the runup to WW2. By the way clevises fall in this same category, not originally intended to absorb bending loads.

    So you say "Dave G, what's yer point?" Just that we should thank the engineer who specced the originals to have a decent safety factor for the intended usage. I tend to go over sizewhen using these, like using the Ford truck 3/4-16 thread tie rod end, part number something like ES150 I think. The stud is larger, and the threaded body is much larger. Meaning when I use it in an application it wasn't designed for, that there will be a little more margin of safety before failure.

    As an aside, the place to keep an eye on for fatigue cracks to start is at the point where the threads just exit whatever it is threaded into. This is the junction point between the bung welded into a split bone for instance and a locknut if used, or right at the end of the threaded bung where the male thread exits the female thread. The root of threads are the highest stressed part of a fastener, and in bending is a good (well bad for us!) place for a crack to start and propagate over time. And since we tend to use a lot of the vehicles we build with these adaptations in a spirited manner and seasonal, there is also the potential for stress corrosion cracking, which can lower the failure stress limit to a fraction of the ultimate strength of the part.

    Concerning bolts thru Heims, double shear is preferable if you can design bracketry to accomodate it. Single shear puts the boltin both shear and bending, whereas double shear is pure shear. Shear strength is typically 1/2 of ultimate strength, so a bolt with a 90,000 psi ultimate strength can handle approximately 45,000 psi in shear. To determine the actual load, or force it can handle, we need to know the actual cross sectional area of the bolt where its in shear. So if part of the threads are in the shear zone use the root diameter for calculating the stressed area, otherwise its the area of the bolt body.

    An example of the area of a bolt is a 1/2 inch bolt has a cross sectional area of 0.196 square inches, and assuming a bolt ultimate strenght of say 180,000 psi ( a really good bolt) the shear strength is about 90,000 psi, resulting in a load of about 17,670 pounds in shear per shear zone, or for double shear, approximately 35,000 pounds of load. But I'm going to throw a monkey wrench in the works.

    Most materials are load rate sensitive, meaning under impact loading they fail at lower stress levels. In Applied Mechanics terms this is called dynamic fracture toughness. Also, many materials (steel can be one) also have a transition temperature, where above that temperature failure tends to be ductile, and below failure tends to be brittle. Anyone who rode or raced snowmobiles back in the late 60s-early 70s may have experienced this, with odd things breaking unexpectedly, like springs, motor mount bolts.

    I could go on forever, but I won't. Ask Dan, I used to have diarrhea of the brain frequently when we were bench racing... It comes from having the "Knack"

    So please ask me questions if interested, as a retired mechanical engineer with both a graduate degree in Applied Mechanics and a lot of experience in Failure, it helps keep my mind active.

    Thanks for taking this for what its worth...

  • #2
    Short Answer..........
    The Silver Bridge Failure, Mount Pleasant, WV
    The Dog Bone Link failed most of what you have described .

    I'm No Engineer !!!
    Just a Observer'r .......that When BAD THINGS HAPPEN
    and you Find Out Why......Don't Do That AGAIN........
    But I'm not totally curable ........I still Ride Motorcycles....LOL

    Comment


    • #3
      Of course the whole field of Applied Mechanics got a good kick in the rear during WW2 when the Liberty ships started breaking in half in the North Atlantic in fridgid waters. I believe the WV bridge was a material selection choice also.

      The Liberty ships were welded structures and made from inexpensive steels. And they had square cut by flame cutting, deck openings for getting cargo into the hold. So there was a "Perfect Storm" (I hate that phrase, but it's appropriate here) of factors that came together to cause these failures.

      1-transition temperature of the steel was around 70 degrees F. North Atlantic waters were in the mid 30s F.
      2-Square cut hatches: the smaller the radius the greater the stress concentration, and a square cut corner is considered a very tight radius.
      3-Flame cut: how many of us have flame cut a piece of steel and then needed to drill a hole thru that flame hardened surface? How many drill bits did we break? Yeah, that steel at the surface of the cut is very hard, AND brittle.
      4-Welded structure. Prior to the Liberty ships most large ships were rivited together. So what you ask? It is a crack stopper! Yes the rivet holes can crack and tear out, but the crack canot jump to the next plate. With a welded structure, the two plates are fused into 1. The crack can run thru the weld into the next plate, and if it is also stressed cold and brittle, the crack will continue running, at the speed of sound for the steel. That's really fast. Dan would like his S10 to run that fast!

      Ok I'll stop now, I'm getting boring!. Now you can see why I really liked Big Bang Theory...

      Comment


      • #4
        So if I read this correctly, bigger bolts are always better... oh and stay away from cold (not going to happen ;) )

        I'm not a fan of heims, dirt is their enemy (not just that but the Chinese are the natural enemy of heims because their QC is so abysmal that you cannot rely on them - and before you 'but' me, outside of a careful review of Aircraft Spruce, find US or German-made heims). Heims are great for non-load situations, but for a bearing surface, poly (or aluminum for those who like chattering teeth) are far better options.

        Using tie rod ends for suspension pivots - most times, the biggest problem that I see with using them is they're bolted into sheet steel. Even with big washers, that looks to me as the biggest potential failure point.

        Welding.... There's a Titanic problem with rivets. While I agree that steel will fracture linearly along the heat affected zone, all the cool kids use steel plates, which have a natural crack-stop at every corner weld. I've never seen a ship with a full-length plate. Also, while rivets are fantastic for Leo's wood sailboat (Bangsail if you haven't seen it on the main page) because technology, welding and material science for metal has gotten so much better that I'm not sure it follows that a rivet is better in any metal application....

        Dan needs a rocket, that would solve biggest issue (and be a nice German solution to a German problem).
        Last edited by SuperBuickGuy; May 11, 2021, 01:34 AM.
        Doing it all wrong since 1966

        Comment


        • #5
          Originally posted by SuperBuickGuy View Post
          So if I read this correctly, bigger bolts are always better... oh and stay away from cold (not going to happen ;) )

          I'm not a fan of heims, dirt is their enemy (not just that but the Chinese are the natural enemy of heims because their QC is so abysmal that you cannot rely on them - and before you 'but' me, outside of a careful review of Aircraft Spruce, find US or German-made heims). Heims are great for non-load situations, but for a bearing surface, poly (or aluminum for those who like chattering teeth) are far better options.

          Using tie rod ends for suspension pivots - most times, the biggest problem that I see with using them is they're bolted into sheet steel. Even with big washers, that looks to me as the biggest potential failure point.

          Welding.... There's a Titanic problem with rivets. While I agree that steel will fracture linearly along the heat affected zone, all the cool kids use steel plates, which have a natural crack-stop at every corner weld. I've never seen a ship with a full-length plate. Also, while rivets are fantastic for Leo's wood sailboat (Bangsail if you haven't seen it on the main page) because technology, welding and material science for metal has gotten so much better that I'm not sure it follows that a rivet is better in any metal application....

          Dan needs a rocket, that would solve biggest issue (and be a nice German solution to a German problem).
          I agree with the Heim comments. Also the cold, just stating a concept to keep in mind should a failureoccur that seems odd. I prefer US made as well. Also this ISan area where you get what you pay for, i.e. don't buy the $10 endsfor high horsepower rear suspension. The $20 same size one even made by the same company probably (not always...) is the better choice. Having said that, a Caveat: If you are in doubt, ask an expert. Also, there are listings available from quality manufacturers that will list the load capacity for all their rod ends, including usually the reduction in bending loads, as well as the load sideways that plls the ball out of the rod end. I've seen listings that show that loading can be as little as 5 to 10 % of the load capacity. This is the reason to always either usedouble shear, or at least put a large washer on the outside of the rod end to prevent its falling off.

          And I think we could engineer a rocket motor for Dan using hydrazineand red fuming nitric acid. So ok it's a little dangerous to handle, and there is a possibility of an uncontrolled conflagration ($10 word for BOOOM!). I have the nozzle out in the gagage just need the chemicals, a pair of metering pumps, and someone crazy enough to put it all together. Sounds like Dan...

          Comment


          • #6
            Missed the bigger bolt comment. Depends on what you are referring to per application. Sometimes a smaller bolt can be an advantage, as it will fail saving a lot of stuff that is more expensive. And sometimes a lower grade bolt can also be advantageous, as in that case it will bend and not fail, allowing maintenance of control toget you offthe track and into the pits.

            I learned this early with the modifieds. I tended to use grade 8 bolts everywhere (available thru work cheap ). But an old timer clued me into thesafety valve idea in the drag link. Those big old right fronts sticking out there when sliding up into someone else had a lot of leverage on the whole system. And with the drag link on the left front, we lost a couple of drag links back to the center steering boxes when the bolts broke instead of bending. Went to a grade 2 bolt and never lost the drag link in an incident again. Bent plenty of the Grade 2 bolts, but they were also available at work.

            And if you were referring to something entirely different regarding bigger bolts, well then...

            Comment


            • #7
              Grade #2....Shear Pins ? !!!

              Comment


              • #8
                Originally posted by Captain View Post
                Grade #2....Shear Pins ? !!!
                That's the idea. At the time we all thought BIGGER. So the steering linkage had 5/8 and 3/4 inch rod ends. Really strong and really expensive at the time. A grade 2 bolt was cheap, and bent before it broke. Which brings to mind the stress-strain curve for steels.

                All low alloy steels, from 1010 mild steel to 4130 chromium-molibdenum steel have the same approximate Young's Modulus of Elasticity of of around 30x10^6 psi. It varies a little bit but for engineers, this is the number used for most calculations (hey we're lazy, and determining the exact number for every alloy would be time consuming, expensive and tedious... you know like engineers).

                The differences are in the ultimate tensile strength, which can be ~50,000 psi for mild steels to 250,000 psi give or take for alloy steels in the quenched condition (altho it would be extremely brittle). The key difference is % elongation, the amount of "stretch" it will experience before breaking catastrophically.

                Mild steels in a normalized condition can have an elongation of up to ~38%, whereas heat-treated but not tempered alloy steels can have an elongation of as low as only 2 to 3 % before failure. We've all seen pictures of NASCAR stock cars after a bad crash and the car is all bent and twisted, but it held together. NASCAR only allows mild steel for its entire chassis/roll cage structure for this exact reason. Bending uses up a lot of energy and keeps the driver alive.

                We've also seen pictures of NHRA fuelers after they have been in some bad accidents, where the car broke all apart. Different theory at work, get rid of the heavy parts and reduce the energy available to keep the central structure intact, saving the driver. These chassis take a lot of abuse, they just break up during the really bad $h!t. Tubes will be deformed around the welds on the stock car after the crash, where the welds in certain areas are expected to fail during the crash in the fueler to shed parts.

                Recent advances in alloying and finishing have made super alloys that have higher ultimate strengths and also higher elongation %. As an example I have a bolt that was made from a cobalt alloy steel, that has an extremely high ultimate strength (290,000 psi), and has an elongation of in the 25% range. This bolt was used to hold the engines in jet airplanes, replacing the previous bolts that were thought to be the cause of engines falling out of airplanes in the 80s. Back then working at Battelle in Columbus OH where I broke things for a living, I had a contract to break 21 of these bolts in various ways in groups of 3, to get them to pass FAA certification. I broke more test fixtures than bolts in ultimate tensile tests, until I redesigned the fixtures entirely. And the fixtures were made from 4340 steel heat treated and tempered. The test machine had a totalload cappacity of 1 million pounds force, and when a fixture or bolt broke, it sounded like a canon going off, and the machine jumped (BTW it was 2 stories tall and fastened to about a 100 ton concrete/steel base).

                Now for the rest of the story: It cost just under $400 in 1986-87 dollars. I don't even want to guess what it would sell for today.

                Comment


                • #9
                  Just to lay a groundwork for later.... my wife is a mechanical engineer who can also tell you the number of jackhammer blows it took to dethread a screw from someone's spinal implant.*

                  Of course, just because she's a mechanical engineer doesn't mean I should trust her answer. If I was stupid and answered the question about whether or not the jeans made her look fat (it's not the jeans), then I can almost promise the life-saving calculation will more likely be a life-ending one...

                  *graphic backstory. She developed a spinal implant that avoided the need to fuse disks together in a spine. In America, it's easier to test on humans then it is on monkeys - but still expensive - so most developers of such things use Romanians and Salvadorians. This particular test subject, a Romanian, decided he felt good enough with his implant to go back to work operating a jackhammer.... it took a week for all the screws holding his spine in place to back out (through the skin) and collapse (taking him with it). The 'good' news in all of that is they did fuse his spine and he didn't lose his mobility.... but seriously, I ignore medical advice with aplomb but I can now see why American monkeys are not longer test subjects - they wouldn't be jackhammering and fully testing the device.
                  Last edited by SuperBuickGuy; May 12, 2021, 01:26 PM.
                  Doing it all wrong since 1966

                  Comment


                  • #10
                    Originally posted by dave.g.in.gansevoort View Post
                    Missed the bigger bolt comment. Depends on what you are referring to per application. Sometimes a smaller bolt can be an advantage, as it will fail saving a lot of stuff that is more expensive. And sometimes a lower grade bolt can also be advantageous, as in that case it will bend and not fail, allowing maintenance of control toget you offthe track and into the pits.
                    I've always thought it'd be a good test to see the variance in non-rated bolts or even Chinesium bolts. I have some head studs that are chinesium. I didn't use them because one failed at 90 ft. lbs. Fractured (guessing here) because it was over-hardened.

                    Point is, even using a cheaper bolt as a fuse carries the inherent risk that they dumped for 4340 in the melting pot just to clean up the shop. I'm not sure I've ever seen a standard which does a low/high, do graded bolts have an upper fail point? Add to that risk the inadvertent heat treating that sometimes happens to get a stuck bolt loose.....

                    In that vein, what many don't understand is that any heating above room temperature to a bolt does change the properties of the bolt....
                    Last edited by SuperBuickGuy; May 12, 2021, 01:35 PM.
                    Doing it all wrong since 1966

                    Comment


                    • #11
                      Originally posted by SuperBuickGuy View Post

                      I've always thought it'd be a good test to see the variance in non-rated bolts or even Chinesium bolts. I have some head studs that are chinesium. I didn't use them because one failed at 90 ft. lbs. Fractured (guessing here) because it was over-hardened.

                      Point is, even using a cheaper bolt as a fuse carries the inherent risk that they dumped for 4340 in the melting pot just to clean up the shop. I'm not sure I've ever seen a standard which does a low/high, do graded bolts have an upper fail point? Add to that risk the inadvertent heat treating that sometimes happens to get a stuck bolt loose.....

                      In that vein, what many don't understand is that any heating above room temperature to a bolt does change the properties of the bolt....
                      I agree, quality control is the issue and answer. Having said that the "normal" consumer goes into a big box store and buys what takes the least out of his/her pocket. And buying American can be misleading as some companies source in bulk and repackage getting around one of the restrictions to US marketing regulations.

                      I try to use hardware from known US manufacturing companies, but even that is getting harder to guarantee good QC. ARP is probably the best, and proves you get what you pay for. The down side is you need to know exactly what fasteners you need. Aircraft fastener companies that meet FAA requirements is viable, again expensive and not available easily.

                      We used Supertanium (I think that's the name) for years, I don't know if they are still available and the same quality. Premier was good also.

                      I have a lot of fasteners left over from my days in A^2, bought in bulk when building the first Mini in the 90s, but mostly small stuff, under 3/8 inch and all fine thread (damn British water solubile cars...). Good for small stuff, not so much for the Whatever, so I'm in the same boat, looking for a good local source.

                      And the jackhammer story, WOW what else is there to say... I hope my back neverneeds that kind of repair. 'Cuze I know I'd do something stupid too

                      Comment


                      • #12
                        To respond to y'all's speculation on rocket motor mods to Mutt the Race Truck - doesn't meet class requirements. Besides, the safety rules for reaction engines are WAY outta my league. But I appreciate your concern........

                        Dan

                        Comment


                        • #13
                          Originally posted by DanStokes View Post
                          To respond to y'all's speculation on rocket motor mods to Mutt the Race Truck - doesn't meet class requirements. Besides, the safety rules for reaction engines are WAY outta my league. But I appreciate your concern........

                          Dan
                          Safety? I don't remember anyone talking about safety.....
                          Doing it all wrong since 1966

                          Comment


                          • #14
                            My Brain Is Full Now.........
                            I'm going to get another cup of Coffee and Watch Toonies with my Grandson

                            Comment


                            • #15
                              Originally posted by Captain View Post
                              My Brain Is Full Now.........
                              I'm going to get another cup of Coffee and Watch Toonies with my Grandson
                              And I'll have a large iced tea please. I'm going to watch Sci Fi.

                              Comment

                              Working...
                              X