Any metallurgists in here that could tell me why this broke?

[Endacy]

Here is a picture of 'something' which I broke a little while ago, or more specifically it broke during use at a stress level far below what it should be designed to cope with. Is it possible to give an idea of the reason for failure from the way the metal has broken and the structure left? It was being twisted a the time and it is designed to be twisted! I'll let you all know what it is later and the story surrounding it - it's vaguely interesting...

Cheers!
James

 

[snowcat]

im asumeing its cast.

 

[Endacy]

Hmm, i'm not sure. I didn't think it was to be honest but then again maybe that was the problem! How can I tell?

 

[Hitch]

Sometimes these things do break, especially if they have been given too much physical many times before.
What is it, a bit of half shaft or something?

 

[snowcat]

spark test, chip test looking at the structure it looks like cast but stress fractures can look like that with lcms, the botom of the pic looks like it has an old flaw in it. if its lcms its proberbly a case of age and metal fatigue.

 

[Drains]

I sometimes work at a place which has a vertical mill that was a Taiwanese(?) copy of a Japanese original. Bits of it break unexpectedly, usually because the mettalurgy of the parts isn't up to scratch. Your pic looks like the kind of thing we see.... eg badly manufactured copies of components.

Big grain structure in your broken bit. Looks cast and a bit weak.

I think a bit more info would make a diagnosis easier though. Come on, what is it???

Si

 

[scarecrow]

Looks more like granite to me
also looks like it has been underwater for a while
cant wait to find out what it is

 

[Endacy]

That's some quick replies!

It is a steering relay for a series Land Rover, see this pics - it's the cylinder thing on the left with the two arms on it top and bottom.

Here's the vaguely interesting story:

My original siezed up years ago so I replaced it with an unknown but brand new one I got for £5 at a 4x4 autojumble from someone who never used it. A few months later I reversed up a kerb and the central shaft twisted meaning the top and bottom are were no longer at 90° to each other. Curious.

Cue me purchasing another brand new one, albeit a pattern part, from a large parts dealer (~£40). It's this one. I suspected the shaft was twisting whenever the steering took a knock and was going to replace it anyway. It failed like this when I went round a roundabout at 11.30pm. I lost steering, went over a kerb and ended up perpendicular to the road blocking two lanes. A short amount of thinking later I decided 'I can't fix this right now' so I called the breakdown company and the police. The police kindly parked behind me with their blue lights on and let me sit in their car. Recovery were there in just over 30 minutes. The police had to shut the road briefly so the recovery truck could pick it up!

I suspect there a lot of these patern parts out there and I also suspect that the shaft was twisting and work hardening, it then failed. This one has a brand name on the bolts and I intend to contact them to see if they made it, or just the bolts! They might want to see this. I think simondrains is right on the money here.

scarecrow: It's sat around for a while and the surfaces have rusted a bit and got a bit grubby, hence the underwater look.

I now have a genuine Land Rover one (which my local dealer ordered for me on a Friday especially to be delivered Saturday morning so I could be mobile by Monday), this was £75.

Oh and if anyone would like to see, here's my truck:

 

[Drains]

Have you considered taking it back to the parts dealer and accusing them of trying to kill you? "Fit for Purpose" is a phrase that comes to mind....

lol, I thought you'd called the Police to report some daylight robbery!

Si

 

[scarecrow]

That's a nice looking Land Rover Endacy. I presume that shaft should be made from a good-quality steel doesn't look like steel in the picture looks more like cast just thank you're lucky stars it didn't break on the highway.

Let me know if you ever break the tow rope you could tow an articulated lorry with that rope

 

[Endacy]

I did actually contact the supplier and similar phrases they gave me some credit as a goodwill gesture. Given the part was 1.5-2 year old that was quite good of them. They weren't interested in having it back because they said it had never happened before, just seems odd that I bent one previously.

The police were fine too (about the fact I was blocking the road ) they said they were having a quiet night and that was the most exciting incident so far.

 

[rtbcomp]

Scarey. Does the manuacturer's name suggest that the part was made in Britain?

 

[Alex]

And now you know why I dont like cast metals.

Instead of cast metals :

Forged - like alloy wheels

or preferably CNC machined from a solid block of whatever metal, Stainless is nice.

 

[rtbcomp]

I can't believe anyone would make a component like that out of cast, there's a lot of torque going through that shaft.

 

[TechnicAl]

Im a metallurgist and like most "ists" its impossible to get an straight answer out of me.
Firstly its very difficult to see via a photo on the net and I have little perception of size.

It looks like a good fracture in that there doesnt appear to be any defects, the grains size looks small which is good and there are no shiny bits that point to fatigue.
I dont think its cast so it must be wrought. Wrought products can be directional, the better ones are manufactured in such a way to eliminate directionality.
Therefore it suggests that the fracture has occured across the weaker direction or that the material is weaker than required.

Im guessing but I would expect the original LR part to be forged from some sort of alloy steel. This is probably formed out of some rolled mild steel.

 

[migmag]

Interesting one this endacy maybe this could be put in the catastrophic engine failure thread??

Well its pretty catastrophic when ya steering goes aint it?

 

[Alex]

Actually I thought it could be quite fun.

 

[migmag]

catastrophic to your undercrackers at least.


Unless your a propper welder in which comando is the only way to go..........

 

[Wozzaaah]

I'm glad I wasn't commando when that wire cup brush caught me in the groin! That would have been an interesting photo for Nuts or Zoo though.

 

[malcolm]

I wondered whether the bits on the outer 1mm on the left and right sides of the failure might have been fatigue cracks. Being on the left and right only could suggest bending forces had some influence as well.

The failure is right at the end of a set of splines, so maybe the machining was badly thought out leaving a sharp internal corner which could have helped initiate cracks.

Complete loss of steering through catastrophic failure is normally something that steering parts are designed to avoid. Land Rover have probably put a lot of thought into that bit. Hope the aftermarket suppliers haven't re-engineered it ever so slightly to make it cheaper to make.