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HuntBikeWheels HuntBikeWheels's article
May 10, 2018 at 19:34
May 10, 2018
Hunt Launches Range Of MTB Wheelsets
@vinay: Just to further this with some more information from John (Peter and my Father and our Chartered Materials Engineer here at HUNT. The Fatigue life of 6069 is also significantly superior to 6061 at approx +60%. Research Gate has some excellent information if you want to search it but the link and charts may not work on here, I'll try the link anyway. https://www.researchgate.net/publication/250335394_The_new_aluminum_alloy_AA_6069 "The yield strength of 6069 T6 is 490 MPa as opposed to 6061 T6 at 290 MPa. It still has an elongation (a measure of ductility) of 10-22% depending on the extrusion process. This is similar to 6061 T6. Anything over 10% is pretty ductile. The link above is a chart showing the fatigue cycles to failure of 6069 and 6061, both in the T6 condition. It is in a weak salt solution, so probably quite good for winter riding. It shows that 6069 is almost twice as good as 6061. Your correspondent is right in most of what he says and it is true that some yielding will blunt the crack tip and reduce stress and hence crack growth. This is why you do not want materials with very low ductility, they just crack really quickly, however 6069 does not suffer low ductility and as Pete says the higher Ultimate Tensile Strength actually reduces this issue too in other ways." I hope this helps Vinay and I hope this helps, please do let us know as these discussions opens our understanding further too which is really cool, Tom Marchment HUNT | TheRiderFirm
HuntBikeWheels HuntBikeWheels's article
May 9, 2018 at 22:34
May 9, 2018
Hunt Launches Range Of MTB Wheelsets
@vinay: You raise some really great questions, so we reached out to Hunt co-founder Pete to see what he said. Here is a short summary of what he said to your response: The ovalizing at the crack tip is a very good point, and that is why higher ductility (which normally means lower UTS) materials will have better fatigue resistance relative to their strength. However, having a higher overall strength helps vs fatigue in two other ways: At the tip of the crack itself, the material is still stronger, so the benefits of ovalizing the crack tip are somewhat offset by the higher yield strength of the material itself. If you are using the same shape, thickness and extrusion dimension, you will get less overall deflection under stress, (because stiffness is usually higher in materials with higher UTS and lower ductility) and that means less local stress at the point of the crack. So if you are an aircraft engineer trying to achieve your design spec strength at minimum weight gain in a stiff material like 70xx series then you will have problems with fatigue that you need to solve. But if you are designing for fatigue resistance you can achieve better performance with slightly over-engineered shape and a high strength alloy at the same weight as 6061. This actually is very good for MTB because you then also have a very high UTS on top of that for protection against really big hits. Lastly, it is worth mentioning that the drop off in fatigue life for 6061 to 6069 is much less of an issue than it is going from a 60xx to a 70xx series alloy. Thank you again and I hope this helps.
HuntBikeWheels HuntBikeWheels's article
May 8, 2018 at 21:12
May 8, 2018
Hunt Launches Range Of MTB Wheelsets
accidental reply, soz.
HuntBikeWheels HuntBikeWheels's article
May 8, 2018 at 21:12
May 8, 2018
Hunt Launches Range Of MTB Wheelsets
@vinay: Hi Vinay, You know your stuff and yield strength is key. I have discussed this in depth with my father John (Chartered Materials Engineer and works here at HUNT | TheRiderFirm) when selecting the materials. UTS (Ultimate Tensile Strength) and yield strength are closely related in alloys and if I recall the details correctly when failure on bending occurs it is the extension side of the material that is passing it’s upper yield limit and so is under tension hence UTS is the figure we used but as you say we could change this out for yield strength, and the numbers/%ages would compare higher for 6069 in the same way to approximately the same % as well. However I have to admit this is reaching the edge of my knowledge, but please do come back to me with any further questions and I can refer my father and brother Pete (also co-founder her at HUNT and materials science graduate from Cambridge University) with some more details on the material differences. Thanks again as feedback, questions and understanding from riders is key to us to a better job, Cheers, Tom Marchment HUNT | TheRiderFirm.
HuntBikeWheels HuntBikeWheels's article
May 8, 2018 at 21:11
May 8, 2018
Hunt Launches Range Of MTB Wheelsets
Hi Core559, we really appreciate any questions or feedback so thank you. You’re absolutely right several companies do indeed use 6069 (490MPa UTS Ultimate Tensile Strength) including Stan’s for their high end rims, in their S1 rims they use 6061 (290MPa UTS). I think Race Face use 6061 for most of their alloy rims but I could well be wrong. 6061 is a great material that is regularly used in very high end aerospace applications, however it’s lower UTS and yield strengths do mean you need to use greater mass to achieve the same comparative strength, and this is fine and we actually use 6061 in our 4Season Road and Gravel rims where ultimate performance is not as important as the balance of competitive pricing for a wheel used primarily as winter/training wheelset and often replaced with carbon wheels when summer comes round. Whereas for MTB we felt that, as MTBers ourselves, we never change our wheels from one season to the next and so wanted the highest spec/strength/weight combination to give us the best performance year round if that makes sense? So we specced thick sidewalls (not the thickest but close) but we did spec the highest strength material in 6069 and this equals one of, if not the, strongest Enduro specific rims available (as far as our material strength:wall thickness calculations and checking/measurements of other rims goes). Thank you again and I hope this helps. Enjoy the trails, Tom Marchment HUNT | TheRiderFirm
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