TR2/3/3A Aluminum one time use stretch bolts

[sp53]

Aluminum one time use stretch bolts, is that true they can only be used once?

Thanks steve

 

[bobhustead]

All bolts are stretch bolts. The ability of a bolt to hold tension is called, I recall from college physics, is its "Young's modulus." This is the ability to absorb distortion and still return to its original shape on a molecular level. In any use that really needs this question to be answered, aluminum "stretch" bolts can be used zero times. Holding hinges on your screen door is one thing. Holding anything that vibrates, rotates, wants to move, etc. is another thing.
Bob

 

[CJD]

Technically, you are referring to stretch past yield bolts. They are very common on modern engines, and yes, only one use and they get tossed.

Just a little refresher on metal behavior, any time you put a load on a bolt, it stretches. Up to its yield strength, it acts like a spring. Double the load and it stretches twice as much. But as long as you stay below the yield strength, it will return to its original length when the load is removed. All the bolts on our TR's are reusable indefinitely, so long as they don't get damaged or corrode.

Many modern engines use bolts that are torqued past there yield strength, but not past their ultimate strength. Ultimate is when they snap. When you remove these bolts, they are permanently stretched longer than when they were installed. They use them because they hold better with highly stressed parts.

Most of the bolts in car engines are steel alloy. Aviation does use actual aluminum bolts. They should never be re-used for a different reason. Aluminum has a limited fatigue life, so you cannot risk re-using an aluminum bolt. Aluminum bolts really have little use in cars, since most people don't inspect cars like planes are inspected. If you use an aluminum bolt long enough it will snap.

 

[DrEntropy]

All bolts are stretch bolts. The ability of a bolt to hold tension is called, I recall from college physics, is its "Young's modulus." This is the ability to absorb distortion and still return to its original shape on a molecular level. In any use that really needs this question to be answered, aluminum "stretch" bolts can be used zero times. Holding hinges on your screen door is one thing. Holding anything that vibrates, rotates, wants to move, etc. is another thing.
Bob

And VOLUMES have been written annually to explain why: ASTM/SAE for one.

 

[sp53]

Thanks you guys my son will be impressed and I am always impressed about the support and the time people on this forum will take to help, very cool. In my surrounding area, I could not find any information on how and why. I am not sure if mechanics at repair shops take a chance with the aluminum, but I would guess for most shade tree guys, they take a chance.

Thank you Steve

 

[PC]

Where aluminum bolts can be used and re-used is in applications where very light weight is important but thread loading is very, very minimal.

Racing bicycle chainring bolts are usually aluminum. They're used in groups, spreading load over multiple bolts and the load isn't on the threads but on the outer body of the nut. And That loading is shear on the body. There's almost no tension load on the threads.

 

[Popeye]

Far off from Triumph, but BMW uses (single-use) Al bolts on some bits. I believe it has to do with galvanic corrosion and a magnesium block, but smarter minds than me should chime in.

I never reused them - if Bentley said to replace, I did so. The cost of the bolts was dwarfed by whatever bit I was replacing, not to mention the cost of failure. I always ordered new bolts when doing repair work. (I've since sold the car )

 

[DrEntropy]

Aluminum has its place, engineers design things accordingly. Lightweight, ductile, different grades for different applications.

As mentioned at other times, my father was the head of Destructive and Non-Destructive Testing for a steel company which furnished the stainless tubing for Electric Boat in Connecticut (among other things, like: bearing stock for Timken and AC Delco). Tensile and Charpy testing were among the things I was "home schooled" on. Always had an ASTM/SAE set of books available. Dad jokingly would say his primary job for the company was "making scrap."