I'm a mechanical engineer working in the defense industry. I do a lot of calculation work on fasteners used in critical applications. As a result, I'm a total torque spec nerd when working on my own cars. You guys nailed a lot of the science. Only thing missing was mention of thread shear during the overview of failure modes, but maybe that's too much. Seeing the 'Donut take' on something I do professionally was awesome! Such a great video!
One question, the max torque of a bolt is designed after its yield strength Rp0.2 or after its fracture toughness Kic due to the sharp edges and stress concentration?
@@Dozav7 Bingo! Commercially available fasteners are normally designed so that that threads won't shear before the fastener body/shank fails, but it can happen in certain applications/contexts (for example, inadequate thread engagement on a stud).
They also seemed to miss the thread pitch affecting the leverage of the torque on the bolt stretch too, but you know I guess they don't wanna get too involved with it for a quick yourube video.
Why did I pay $50k a year for 5 years to learn this same stuff I could've learned on Donut 😭 I love this show but I'm getting increasingly irritated lol
Had a broken 3/4" torque wrench in school and we were trying to torque U-bolts on a semi. When we realized that something was wrong, no one believed that we had a "broken" torque wrench and said that we just weren't there yet. Ended up stretching the bolt to the point where it snapped in half and sounded like a shotgun blast.
@@blvckskull7954 well yeah but for steels it’s gonna follow Young’s modulus. They also got the overload plastic deformation bit wrong cause it will come back a bit but not completely to original length haha
Great video explaining a critical lesson! Something I was taught in my undergrad machine design course is that most of the loading (>90%) on the threads is handled by the first three threads making contact on the nut.
Hey I’m supper into cars and a rookie mechanic. Your videos have inspired me to try and get my ASE! My older sister just sent me the book so now I’m studying as much as I can and just landed an amazing apprenticeship at a really good shop! Thank you Donut!
I used to build brake assemblies for an auto manufacturer. The assembly included the knuckle, hubs/bearings, disks(rotors), calipers, pads, abs sensors, control arms, etc. They took it seriously. EVERYTHING that touched the floor was to be thrown away. Bolts, clips, and even finished goods. They didn't want dust anywhere near those parts until they were fully assembled to the vehicle.
@@JeffLocke1 I actually haven't seen arp bolts anywhere for a Genesis Coupe. But for a set of 12, it's $36. I'm pretty sure arp bolts would be more, but it's time for me at this point.
What engineering and physics? This is sub-highschool grade physics at best. What exactly are you praising other than knowing a shocking amount of people don't have a high school education?
Genuinely thanks for the clip. A few mechanics seemed to miss this part of the apprenticeship. Rattle-gunned-to-death wheel nuts have been a big problem in my world. 👍👍
You can also break a torque wrench when you max it out and let it keep going. Technically torque wrenches need to be calibrated to be accurate. 6-18 months. Calibrating it though is usually a test more than anything.
Interestingly the elastic/plastic/ deformation related to tensile strength is the same science we apply to human anatomy relative to ligaments, tendons, muscles and fascia etc to explain/ prevent neuromusculoskeletal injury.
As an Aviation Technician this warms my heart to see. I watched a video before changing the control arms on my Sunfire. The guy in the video said "just tighten it as hard as you can. You don't want this to come loose." I corrected him in the comment section and got blasted by people for it 😄.
I work for a fasteners company, and those types of studs are no joke. They are used in the oil and mining industry, and man, just reading through their spec sheets is insane.
Thank the gods for this channel. I’ve been binging y’all’s videos for a few weeks now and it’s so much good car content with plenty of entertainment factor to boot. Thanks guys
Being one of the few mechanical engineers in the comment section, one thing that they didn't mention is WHY there is a torque specification. Torque specifications are required to produce a given preload in the bolt. Bolt preload for static loading prevents joint separation and yielding of the bolt and bolt preload for dynamic loading prevents fatigue and reduces the alternating stresses in cyclic loading. It's important to have this preload to effectively reduce the forces on the bolt and bolted members as well.
I do structural testing of aerospace hardware. We had a steel test structure that had some 2" high strength bolts intended to be torqued close to yield. During install we broke one. Turns out the bolt coating and lube we were using had a much lower K factor than what was thought. So our torque resulted in more tension than we thought and overloaded the bolts. Fun fact: some of the bolts on RS25 rocket engine are tightened with the use of an extensionometer to precisely measure the exact stretch created in the fastener.
3:23 Did you know engineers purposefully get head bolts into the elastic range? It allows for that stretch on purpose. That’s why you are required to replace head bolts with new head bolts when you reinstall it.
I was rebuilding an engine many years ago and accidently used the torque spec for fastener listed below the fastener I was working on. I was supposed to torque my rod bolts to 10-pounds but wound up torqueing them to 100-pounds. I torqued several this way and didn't realize the error until the threads ripped out of one of the bolts as I was tightening it. Thankfully, a new set of rod bolts was not that expensive, and my local engine shop was able to get them the next day.
Did something like this once me and my dad impacted the bolt then manually with a breaker heated with rose bud until after all that then we realized it is a brush hog and was tightening smart I know
All I see in my head is that scene from Community where Chang's destroying Jeff's car and Jeff comes out and he's like "you're wearing safety goggles while destroying my car?!" And Chang responds "Safety first!"
The tensile load in a bolt is directly proportional to the torque applied to said bolt. The constant of proportionality depends on the thread pitch, mean thread diameter, and coefficient of friction. Torque figures on bolts are almost always specified when the bolt is clean and dry, so that a known relationship between torque and tensile load will apply. If a lubricant is used on the threads, then that throws a lot of uncertainty into the torque-clamp load relationship. If a bolt is overtorqued, it may still be useable. One way to tell for sure is if you can still spin a hex nut all the way up and down the threads with little to no resistance.
Just to add a bit of science: when torquing beyond yield into a plastic deformation the material will still return the amount of energy stored in the elastic deformation: see snapping a rubber band. It snaps, but it also releases all the elastic energy stored in the stretched elastic.
I just took this in college and I feel so happy that I actually know that! Also the graph region is elastic, elastic plastic, plastic It’s 3 regions not 2
Reminds me of breaking a bolt in a skateboard truck. You take the math and plug in your variables: how tight you want your trucks, your height to weight ratio, the height of the bank your dropping off, & the amount of weight you're exerting as you fly down and land from point A to point B. Voilà!
FUN FACT: On a CH-47D helicopter the PC links are torqued to 400 to 660 IN LBS it has a castle nut you have to line a cotter pin up in the key way. You can go to 660 three times before replacing the hardware. But you have to change the castle nut Everytime you removed the torqued nut after flight.
not only is the area of the bolt doubled but the radius of the bolt is increased so the torque you put on the bolt corresponds to less force. clamping force is roughly a function of radius, thread pitch, and torque applied
Finally!!! As an engineer I’m tired of hearing mechanics say “I don’t need a torque wrench. Ive been doing this for years. I know it is torqued to spec by feel”.
Time is money, on new vehicles there's not a lot of room to work let alone get a torque wrench in there. Want to know how to find out if someone is an engineer? They'll tell you
A cool thing about bolts/pins is some are meant to be crushed. I work with pins with threads on each end with opposite rotation from one another and by torquing the nuts you squeeze the center, expanding a Teflon piece in the center to make sure it doesn’t move in case a bit falls off. That being said we also step up the torque to keep it centered
I tried out Omegle one day and a girl asked if my dad was divorced because he has a F-150. But she has a Toyota Tundra, now I might be wrong but to me it seems like her parents bought that truck since she looks in her teens.
3:30 after the material experiences plastic deformation, it will still have some elastic deformation that will reverse or 'snap back' when the load is released but your stress/strain curve will be shifted by the amount of the plastic deformation.
It would have been good to see a talk on stretch gauging bolts when individual fastener integrity is absolutely critical. Usually rod bolts but there's others too. While a torque spec and angle is good for most usage, a stretch value lets you check individual fasteners instead of relying on the assumption that all bolts are identical.
Makes sense!! I was replacing a diff cover when I first started wrenching, left a small amount of silicone on the tip, shaped with what seemed to me as no effort.... haven't done it since
In germany we have saying coming from a movie which is: Nach Fest kommt ab! Which translates to: After tight comes loose (Because the bolt or the threats or what ever snaps)
I tighten down 1 inch lug bolts for a skidded tire. You can tighten them with a 1 inch air gun at 2200 pounds without breaking one. I use the 3/4 Milwaukee to tighten them up now so we don’t stretch them
I think you can achieve those 2200 lbft required to break that 1 inch bolt... You have two options: Option 1: Use a 1 inch impact wrench (the ones used to tighten down truck bolts, there are tools that deliver over 2500lbft). Option 2: Use a torque multiplier (a tool used to torque down truck wheel nuts). I've made half-inch bolts cry with option 1, and broke a truck bolt once with option 2...
Late bolt will shear before normal stress becomes a problem. Tc/J IS formula. Ductile materials like most metals break with shear then stress in applications like this. Also at 45 degrees is the max shear angle to you get a cone shape at end.
