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To the question, yes, ‘re-annealing’ should not be detrimental. Time/temp prob too low for grain growth, or geometric distortions (unless they are Class 3B threads - maybe). Coating will need to be reapplied, e.g. losing water-of-hydration leaves Zn phosphates as powder. Then H embrittlement...

Also might be covered in SAE AS1290 'Graphic Symbols for Aircraft Hydraulic and Pneu. Systems'

Failures that I’ve seen on axle shafts typically occur at the geometric spline-to-full diameter transition, obviously from stress concentration; flat perpendicular break, not 45-deg. Check FE modeling of having a large and gradual transition. Aforementioned grades all sound like good choices...

The preamble: Al alloys such as 6061 are tempered by first by heating to put all of the alloying elements, (Mn, Si, etc.) into solid solution, then quenching to approx. room temp. The alloy elements won’t do anything on their own for a few millennia or more; however if heat is applied, the...

Agree with all above. Cyclic triaxial compression = no failure. (Except with fissionable materials taken to extreme density :) Anything other than purely hydrostatic would produce resolved shear stresses, maybe dislocations extruding out as mentioned, etc.

Regarding a. and b. – Theoretically, no, not the same. Failure loads are functions of strain rate (and also temperature). Lab tests can range from creep (~10^-6 in/in/sec), to quasi static (~10^-1 /sec), to dynamic (10^2 /sec), hi-speed (e.g., Hopkinson ~10^4 /sec), explosive (10^6 /sec)...

If it was my 1998 and my daily driver, I would smooth out the wheel bead seats as you have already done, paint any exposed metal, and use a tire bead sealant, e.g...

Not unusual for the gov’t (or industry in general) to RE component parts such as the subject heat exchanger. It may have been purchased as ‘Sole Source’ or a ‘Commercial Off-the-Self’ part with no tech data or drawings. Contractors tend to hold back the tech data and make the gov’t pay extra...

I've done something similar in the past. What worked, without going thru calculations for your geometry: Fine diamond knurl on the interfaces; Acme threads (metric equivalent); lube the female thread (keep interface dry); torque for all you're worth; then pins.

Instead of heat treatments, any possibility of sleeving up the bar midlength to decrease the bending stresses? Or a shorter bar? That's if you don't mind not having a weightlifting association spec bar.

Stress/strain relaxation from temperature/time should be accounted for with polymers. When you find a good tension measurement method, you will probably want the comparisons done in the same environment: a climate controlled area with not too much difference in elapsed time. Note nylons are...

If you can go larger than the stated 1/2-inch diameter, try steel tubing slit lengthwise; make wall thickness to suit.

The many degrees of freedom (so to speak) in the processing can take forging into an art. Consider the variables such as the rate of heat loss to the surroundings, geometry of the part, type of material, closed or open dies, strain rate, capital equipment, and economics (where the goal is to...

You may be able to find more sources by searching on 'farm augers' - very commonly used for moving bulk agricultural solids. (Also a dangerous piece of equipment, I might add, if not used with caution.)

Some anecdotal comments: I've always preferred ACME class 2G or 3G thread forms (not sure about a metric equivalent); seems like they are less prone to galling. Also the ability to use lube or anti-seize compound I see as a huge plus. Material-wise, I think your choices are OK, even steel...

As you may be aware, the mechanical props of polymers are temperature and strain rate dependent, so you would also have account for those variables. (Polyurethane is a thermoset, which may lessen those dependencies some.)

Is machining considered cold working? Both points of view that you presented are correct but one would be more correct depending on part use and geometry. What are you are making? If the note that you quoted is found on an ‘engineering’ drawing for something like a large machinery component...

I think you are describing a bi-conic taper (rather than a 2-d wedge) that is being force fit into a cavity with matching internal tapers. And you want a uniform (or close to it) hoop stress thruout. Disregarding any unfortunate and uncontrollable patient ailments (diabetes, osteoporosis...

Anyone mention the olde school solutions: Lock wire nuts (used for aircraft vibration), or castle nuts & cotter pins?

Thread rolling imposes residual stresses (strain hardening). You are asking at what temperature these stresses will start to relax. Depends on the time and temperature, generally going linear with the former and exponential with the latter. Check heat treatment handbooks. You want the...