I cant remember off the top of my head what colour you're calipers are Baz, but going by your sig image they look silver.

If that's the case, I'm pretty sure they'd have turned extremely golden if there was that much of a binding problem and that amount of heat going through them?

Yeah i`ve never had any problems with brakes binding,calipers are silver and haven`t been refurbed as far as I can tell .

Baz

I'ts possible but I would have thought unlikely, you have to remember that smalls items such as a brake caliper get hot quick and where as large things such as the wheel have a large thermal mass and hence are slow to heat.

I have not seen the wheels and may be talking complete crap, but as a betting man I would think the following most likely:

Someone heated the wheels using oxy/gas to straighten them out, followed by powder coating to hide the marks caused by the torch.

I feel slightly embarassed in having caused all this panic when it seems to be just down to a dodgy job with my wheels .

Baz

I'm just guessing, still could be a material defect effecting all Coupes

Well I need to put my mind at ease, so im going to X-ray the buggers anyway. Mine have been refurbed but not powder coated so I don't imagine the heat process is the same. Although as you say perhaps its a defect in the wheel design or material.

don't be embarrassed - you never know, your alert *might* just prevent someone from thinking a bent Coupe wheel is repairable and thus you might have saved their lives

or, as mentioned, you may simply be the first of a series of future failures that we need to be ready for

X-ray or eddy current might be better, I'll ask my Level 3 tomorrow.

Alternately, microhardness will tell you if the alloy has lost some strength and may be cheaper. (only leave v. tiny marks)

Baz totally agree with Nigel, it was great you let everyone know

Eddy current testing is definately a no go on an alloy wheel. This method is only used for ferrous alloys - wheels are non-ferrous.
Micro hardness testing is no good for defect detection either and will not detect a strength loss in the alloy due to the limited surface area and loading used on the test.
Only 3 ways to check for cracks in a casting (which an alloy wheel is);
1. X-ray, high energy type (this is the most reliable).
2. Ultrasonic - can be difficult to interpret the results of this on components of unusual geometry.
3. Simple method - take the wheel off, take the tyre off, give it a slight tap (AND I MEAN SLIGHT!) and if the casting is sound then it should give a clear bell like ring - if you get a dull clank then there is a crack present.
But I must point out that this last method won't detect a casting flaw such as dendritic shrinkage or inclusions which can act as internal stress raisers and lead to crack propagation under loading or cyclic stress.
X-ray is the only way to be sure.

Sorry for the metallurgy lecture, but I wouldn't want anyone putting their faith in any test result when the wrong test method has been used.

Paul

Sorry Paul, I wouldn’t normally do this, but as this is such as serious issue I’m going to have to.

Short post:
From your post you have either mixed up eddy currently and magnetic particle, or don’t know the coupe wheels are aluminium alloys not steel.

For aluminium alloys always use eddy current for surface breaking cracks, possibly dye pen although might have problems with lacquer, possible x-ray but check with a fully qualified NDT engineer (I’m not)

Long post:

1. Eddy current IS the default choice for non ferritic materials such as copper, aluminium etc. You can do on steel but you need specialised probes. X-ray is used to flaw defect alloy wheels during production, but eddy current is the most popular post production test and is used everyday in the aircraft industry for checking alloy wheels. Eddy current is the most sensitive NDT you can perform on aluminium looking for surface breaking cracks test post production. The main requirements for eddy current are that the material is conductive and due to the permeability non ferritic.

2. You are also mistaken about the use of x-rays. High energy x-ray should only be used for dense materials such as concrete, high density steel, nickel based alloys. If you use high energy x-rays on aluminium alloys unless the thickness substantial you will over expose the film (no more than 80kV should be used to x-ray aluminium). X-ray is a volumetric technique more suited to detecting voids rather than cracks as you have to shoot across the crack to see it. If you get the wrong angle you can’t see it (a bit like looking at the side of a pin compared with looking at a pin end on).

3. Finally hardness IS a strength measurement, and is used all the time as the standard method to confirm heat treatment by sections unless you either produce test pieces or hack up the item to do tensile testing,. You are right in that it measures a small area and so a large number of measurements are required but it puts a small load over a small area (load over area = stress), which can be related to the strength as an estimate eg pages 99-100 this book.
http://books.google.com/books?id=5uRIb3e...a2xVmQ#PPA99,M1

Strictly speaking you should be doing Brinell hardness on aluminium alloys but you will end up with little dents all over the place, hence Microhardness as it has a smaller size, you are right though it’s not the best way as you may only measure the surface

This is going off topic and if you want to debate the merits of NDT techniques I suggest we move to chat.

Always check with a qualified NDT engineer before proceeding (I am not) but for people wanting to get their aluminium alloys checked use eddy current possibly in conjunction with x-ray (don’t use x-ray on its own. Or possibly a hardness check although its not a fantastic method unless you want to take section from your wheel (ie cutting up a perfectly wheel to say “yep that was fine”).

Sorry for banging on but this is a potentially serious issue.

No problems mate, there is always a difference of opinion when 2 metallugists put their heads together
There is an old saying "There is no such thing as a one handed metallurgist because on the one hand it could be this but on the other hand it could be ..." You get the drift

Just to clarify things;

1. Yes I am fully aware that wheels are aluminium and that eddy current is one of the prefered test methods for these alloys, it's just that eddy current is less reliable on cast alloys due to the inherent defects which occur during the casting process.

2. I agree with what you say about X-rays if you are using a film cartridge set up, but most modern foundry facilities now use Real Time X-ray which uses a robot arm to move the casting through the X-ray field and so are more likely to detect a crack.

3. I have no issue with using a hardness test to detect strength loss, it was just the use of a micro hardness test, Brinell 10/3000 is the prefered method on castings.

Now to get back on topic - looking at the photo of surface 2 there appears to be a a casting defect present which could be initiation site of the failure, but I must stress that it is difficult to work from photo's and that nothing beats having the sample in front of you.

Paul

Long post alert!! Deep breath

I have just discussed this matter with my NDT section and they have suggested the following process for inspecting automotive aluminium alloy wheels. These guys are fully qualified level III NDT engineers with 30+ years each aerospace and automotive experience.

1. Remove tyre
2. Vapour degrease
3. Dye penetrant testing to detect surface breaking defects
4. Eddy current testing on suspect areas – also can be used as a conductivity test to check loss of heat treatment although this requires different set up
5. For Baz they suggest having done the above you also real-time x-ray failed wheels and compare with your rear wheels.

I have asked if they would be willing do the job and they are too busy at the moment, but they said they would be prepared to organise it with an approved NDT alloy wheel test house.

I asked about prices and they reckoned it would cost £50 min per wheel, but thought £70 more likely. Too make it cheaper (nearer £50) they suggested dropping the conductivity test and preparing the wheels yourselves, i.e. removing the tyres, cleaning etc.

So if anyone is unsure of their wheels and want them testing and Fiat aren’t interested, I suggest setting up a group buy and getting them done. I am not willing to organise the group buy as I don’t want to get involved with money, but I would be willing to make sure this work is done properly by competent NDT engineers to a proper approved process.

Baz, I may be able to get your wheels done for small price possibly FOC. If you don’t have any luck with Fiat. We have a vapour degreaser, dye pen, eddy current and an extremely large real time x-ray with robotic fixtures. The guys were quite interested in having a look at your wheel from a voyeuristic point of view and I think I could persuade them to have a look at the complete set for interest and amusement (NDT humour – don’t ask we have a room full of unusual casting defects). The only issue would be you’d have to get them to Stevenage and back at your expense/ hassle.

Metalman for your interest, the inspection of aircraft alloy wheels requires the mandatory use of eddy current inspection followed by recommended low energy realtime x-ray, although not essential after 300 hours. Aircraft wheels are normally pressure cast aluminium alloys, or machined wrought.

Amazingly, FIAT Customer Support hasn't called back yet - they will be getting a not-very-gentle reminder later this week.

I will be asking them to contribute (or pay in entirity) the costs of having the wheels inspected.

If we can get the wheels inspected as part of an interest to look at a genuine (rather than forced) automotive failure, then that's great.

My guess is that we should have at least three of the wheels inspected - the fully-failed one, the other front with the cracks and one of the rears.

Im not amazed to be honest. Im sure they will be thinking along the lines that the failed wheels are 10 years old and have probably suffered a major trauma of some sort and then been repaired to a poor standard and have now failed further down the line(on a similar note i have now had 2 of my Team Dynamics Pro Race wheels fracture/crack and Rimstock are just not really intersed in my complaint).
I really dont think they will be interested unless this starts hapening on regular basis and people threaten court action against them - or are you going to prove me wrong Fiat???

Perhaps you should tell them you are going to tell Watchdog. They would love that!

Nigel,

I was suggesting NDT for Baz if he wanted to validate the reuse the rear set and for anyone else with simialaer concerns. Personally, I'd just buy a full set off carl it I were Baz, as it will take ages to sort with fiat and there probably is something wrong with them.

Not much point looking at Baz's if they are not intended for use, unless to develop technique. Destructive testing and fractography would yeild more answers.

Interestingly in my discussions with the NDT lads yesterday, they told me that aircraft wheels have a fuse in usually set to 250°C. If the fuse goes, the wheels have to be scrapepd and re-heat treated.

Of course this could be down to a basic material defect as alloy wheels are notouriously full of porosity and inclusions etc. - in some ways I hope it is as then the ball is in fiats court.

Hey I just got a set of these 1.2s ? How long have you had them before they cracked. If mine were to crack without me doing something stupid Id moan my ass off until they would replace them. Thats terrible if they are not helping you.

+1
I didn't like that at all (ProRace1.2 for almost 2months now)

V.

I have ProRace1s and they've been refurbed at least twice.

Thay have also been driven harder than most Coupe wheels will ever get to experience

I`ve got a set of wheels on my car (provided by Sparkyman as I waited a week on carlt to tell me if I could get a set of LE`s he had only to tell me that one of them was badly buckled ) . I`m not planning to use my old back wheels but I was just gonna keep them by as emergency spares (and only use them on the back if needed).

Baz

Mine are now exactly 4 years old. They have done approx 25,000 miles. The first one cracked approx Jan 2007 and the second in September 2007 when i was in Italy - well when i say they cracked on these dates, what i mean is that this was the point when all of a sudden i started to lose tyre pressure, although i suspect the failure had occurred well before this. They have both now been repaired. I dont really do all this picture hosting business, but can email a photo of one of the cracked wheels for you to host if you like Nigel so others can see?
I spoke to Rimstock who manufacture them and they dont seem at all concerned and will only investigate if i pay for the tests to be done to find out if its a manufacture fault or not....

also, if you do remember to remove the tyres, DO NOT put them on a normal tyre removal machine, you'll totally alter the current state of the alloy, i'm afraid its a knife & snips !