The purpose of the bolts is to effect the clamping force between the disc and hub. It is this clamping force that prevents rotation between the two parts, the bolts are in tension to effect this, there is no shear load. Good information here Bolt Science Web Site
But the rear shock bolts are in shear due to the force placed on it by the shock absorber perpendicular to the tensile load right? I guess the load is within tolerance for an M10 bolt though? Anyone know any better? Thanks
Simple logic applied here...........Wheel is still in motion; disc is trying to stop it.........load applied = torsional.......load of disc against side of bolt = shear.
Info for those using stainless as disc brake bolts..........OEM SS bolts are 10.9 All explained here......and where stainless shouldn't be used..... http://www.volksbolts.com/faq/basics.htm Quote: Any Nut Or Bolt Stamped With A 10:9 Or 12:9 Should Be Replaced With An Identically Rated (Or Higher) Component AND NOT An A2-70 Component. Which is not possible with stainless as can be seen from the table.
Wrong it is the friction between the disc and hub effected by the clamping force of the bolts that prevents rotation. Further the tension applied to the bolt is ultimately limited by the weakest material in this case the aluminium hub, the threads of which will strip before the UTS of the bolt is reached
Read below.......... Hi Alan The best stainless steel bolt generally available is A4-80 which has a yield strength of 600 MPa, a 10.9 has a yield strength of 940 MPa. Essentially if the joint was designed for a 10.9, a stainless steel fastener will be down on strength and hence the structural integrity of the joint would be dubious. Normally joints are designed for friction grip which rely upon the clamp force created by tightening the bolt. The joint carries the shear by friction between the joint plates rather than shear going through the bolt. I hope that this helps. Best regards Bill Eccles Engineering Specialist Bolt Science Limited Tel +44 1257 411503 Fax +44 1257 411650 Bolt Science Web Site Or in other words because a stainless bolt hasn't got the required tensile strength, the shear is on the bolt.
I don't agree with the letter from Bill Eccles. in my experience (30 years as an aircraft structures and stress engineer for Airbus, Boeing and Virgin Atlantic), I have designed countless structural joints attached by mechanical fasteners (ti bolts, Ally rivets etc). The primary load in the disc bolts is shear, the load is transferred by the bolts, NOT by friction between the disc and hub. It is true that there is a small amount of tensile preload in the bolt but that is small in comparison to the shear. The preload is to prevent the bolt loosening and fretting between the two components and to stop the disc falling off. It is negligible and thus not normally considered when analysing this type of joint. Imagine if the bolt had no head on it and we were not worried about the practicalities of the real world - in a lab experiment say: if the wheel were rotated in a horizontal plane with the disc sitting on it on six "studs" without nuts - if a force were applied to the disc akin to a brake calliper, the wheel would stop. No friction between disc and hub - all load would be shear through the studs. if I am not correct, I would advise all of you to never fly on an aeroplane ever again as myself and all my colleagues must have been doing it wrong for years. R
OK Please yourself.........You have enough evidence from your own referenced expert to tell you not to use stainless bolts in brake discs......... ..........if you want to kill yourself, that's fine by me, but don't go leading others down the same path. AL Did I forget to mention that I am a qualified structural and civil engineer?
OK.......this help you understand? Al If they don't have the right strength and are not tightened correctly then joint movement can occur. Failure could be by fatigue, wear, self-loosening of the fastener or direct shear failure. The joint would need to be assessed to come up with a view of the likely failure mode. I have no problems with a quote so long it is how I have put it verbatim. Bill Bill Eccles Engineering Specialist Bolt Science Limited Tel +44 1257 411503 Fax +44 1257 411650 Bolt Science Web Site
Yawn..... Again you are missing the point, quote: "not tightened correctly then joint movement can occur". Then shear failure should be considered. I'll point out that the OEM bolts I've seen so far are unstamped dubious grade steel, very soft in fact. Furthermore it is well documented that some manufacturers use 6mm bolts, some stainless etc. I'm not worried....................
That's good then......... You can argue it out with the Bolt Science Website.......I assume you have read what he said........ But as you like quotes, here it is again. "Essentially if the joint was designed for a 10.9, a stainless steel fastener will be down on strength and hence the structural integrity of the joint would be dubious" FFS how many times do you need to see it?
But your 10.9 bolt is screwed into aluminium which will strip way before the tensile strength of the bolt is reached.
I love it when leading technical experts provide opinions on technical points ... and totally disagree with one another. This is what usually happens in any kind of court case involving expert witnesses - each party can always find an expert to endorse any given opinion. Ultimately laymen or juries have to make up their own minds which expert to believe.
But as you obviously haven't read the technical details, the bolt if it is stainless, isn't effing 10.9......
