Outer Limits 4x4 Board

i remember that quote by bill aka frakenrover. at the time i thought, what the??? must be a typo. is this possible for an axle to twist 700 degrees and is there any benifit over an axle that wouldn't twist as far but be stronger? i know this is a bit vague. but imo these axles twisting that much would have to compromise in end strength?
serg

I doubt Bill (frankenrover) knows how far the axle twists under load.

What he and others have done was to mark straight lines along the length of new axles. When the axles were removed later it was clear that they had twisted and pics were posted on pirate.

The twisting that was shown by the lines is permanent deformation.

John (redrover) calculated in his above post, that a typical stock axle would start to yield at about 18 deg of twist.

Most mechanical properties of steels are determined from standardised tension tests. When low strength steels are tested in a tensile testing machine the stretch is proportional to the load until the yield point.

At the yield point they continue to stretch with no increase in the load and in some cases the load drops.

Then they start to work harden and the load has to be increased further to continue stretching. The rate of stretching is now greater than it was before yield and the rate continues to increase until the test piece breaks.

Typical elongation before breaking is about 20% of the original length.

If the load is released before the yield point, the test piece will return to its original length. After yield, there will some permanent deformation - it will only spring back approximately the amount that it stretched at yield.

High strength steels are different.

They do not have a characteristic yield point. Because of this, we assume (for design purposes) that yield occurs when the elongation is 0.2%.

They are not as ductile as low strength steels - less elongation (but a much higher load is required). Elongation for EN26 is 14%.

It is rare to conduct a torsion test on steels as we know the relationships between torsion and tension for most purposes.

So an axle from low strength steel may suffer a large permanent twist before it breaks. But it would not be as strong as a similar axle from heat treated 4340, EN26 or hytuf that would not reach the yield point (0.2% offset) at loads that break the low strength ones.

so the tensile tests are only based on elongation and not twist ???

Yes, that is what "tensile" means (stress in tension). Torsion produces shear stress. The shear stress to produce yield is general 75% the stress required to produce yield be tension.

Very interesting tech Bush65 and Red 90. If either of you were commisioned to design an optimum replacement rear 24 spline axle for a Rover without using prohibitively expensive exotic alloys, anything up to Hytuf would be permissable, How would you design and heat treat it ?
Bill.

daddylonglegs wrote:Very interesting tech Bush65 and Red 90. If either of you were commisioned to design an optimum replacement rear 24 spline axle for a Rover without using prohibitively expensive exotic alloys, anything up to Hytuf would be permissable, How would you design and heat treat it ?
Bill.

Material: Hytuff

Design: Not much to design because of the constraints (splines at both ends and the length are fixed). Just pay attention to reducing the stress raisers to improve fatigue life - run the splines beyond where the side gear and flange fit and a large radius at the change in section. Neck the axle down between the splines to improve the resiliance.

Heat treatment: From my data sheets. Heat to 870 deg C and hold until uniform and quench in oil. While still warm from hardening, temper at 250 to 300 deg C for 2 hours.