ok, these parts were in a rear suspension, the clevis is stainless, and the rod is "hardened" steel, according to the manufacturer. it was in a double shear situation and one of the shear points is at the failure. also the parts have been chromed. I am just looking to confirm my suspicions, and help to prevent others from having a similar failure. thanks
We need 38 Chevy the metallurgist here...I wanna see how he interprets this! In my fascinated ignorant look at this disaster, I see a clear ring...my utterly worthless interpretation is piece of crap steel surface hardened to glass...surface cracked, leaving the ring, then the rest just failed right on through. An issue...why RIGHT THERE on both??? Why not at end of threads?? Did something about the actual use or geometry stress them there somehow??? What did this stuff look like on the car?
What were they used for? Does the OD of the bar get smaller where it broke? Steel and hardened steel will neck down before it fails, cast iron and other cast alloys will just break without necking. You should have someone do a Rockwell test to see what the hardness is. It looks like it could be embrittlement due to the chroming process. See the ring around the part, that is where the base material was penatrated by the solution. That also does NOT look like hardened steel. See how the material looks grainey, it looks more like a cast something or another.
The first thing I'd do is lose the Chrome plating, then look at the set-up, combination of factors those being first on my list! This is both sides or two different times same side?
hydrogen embrittlement. it happens when you chrome hardened steel, and it's only an issue with hardened steel. there is a process to bake the parts afterwards to help reduce the chances of it being a problem. too late in this case!
Ditto on what ray said..Hydrogen Embrittlement. chrome shit loks nice but as far as suspension parts go or parts under alot of stress ..well as some Harley guys put it..chrome dont get ya home.
Still trying to figure out what the application is. Don't look like anything I remember seeing on a hotrod. IRS on a tuner/ricer, and that's why you didn't say? How could and why would that be used in a bending/sheer situation? A rod like that is usually only used in a tension/compression situation.
Gregg, can you Email me some more details about this? maybe a picture of the rods in the car before they broke? Very crystiline break. But what is odd is the case hardening type ring of brighter material around the break line. Because it almost looks like a welded area where a bolt or something was attached to make the rod longer.
From what 38 has said in the past, hydrogen embrittlement only happens to highly toughened steel...I suspect this is something more streetrod, like surface hardened rebar with cast clevises...lots of chrome stuff I suspect fails because custom biker/streetrodder parts are often cheap material, not real good steel improperly plated. HE was first noticed on Navy combat carrier planes when superduper landing gear pieces, plated to resist salt, started failing... I think a big part of this is why fail THERE on both?? What put the stress in the same place in both?? Maybe a geometry problem...or maybe just both were nicked by a vise in the same area at some stage of work.
http://www.duro-chrome.com/docs/article.pdf read the entire article.. also very difficult to get laid if yer DEAD!
I know some people say chrome won,t affect some steels. BULLSHIT chrome on inportant parts is just asking for trouble.
I just went through my book "Understanding How Components Fail" by Donald J. Wulpi- and it looks exactly like the brittle fracture example; origin area, brittle fracture ring, and ductile fracture area cream filling.
It might be me misunderstanding, but I don't see how the rod was in shear stress at the failure point. And, similar to what Dr J said, these parts look to be tension/compression members, so they're not designed to take much in the way of side loads. The angle at the break suggests a tensile failure to some extent, but at less of an angle (~45*) which suggests a 'less ductile/more brittle' material. The base material looks very grainy, so it seems like the wrong material for tension. If the chroming process made it brittle, I think it only effected the penetrated area, therefore reducing the effective diameter of the rod. Ha ha- I'm taking stabs at it from what I can remember from 'learning' about this Shiite. What's the prize? And, "NO FAIR!" if Nosurf wins, he used a reference! Thanks, Kurt
Totally. Embrittlement can affect ANY metal. Looks like poor component design to me. The grain structure isn't too bad for a "medium" hard steel. I don't think a rod that long ought to have shear loads placed upon it, at least not rear suspension type shear loads.
I'm with Bruce on this one. Notice how the parts didn't bend or stretch before they failed? Looks like cheapassed material in the wrong application to me.
In my humblest of humble opinions, I would say two additional things (meaning a combination of the three I will mention.) 1. Under engineering. As with a lot of parts sold as "Street Rod" or "Hot Rod" parts, they are skimpy on the steel. I think they (the manufacturer) things that it's a street car, so they can skimp on the materials. When in fact it will be driven on the street, a monster power plant is usually hanging out the front. The small diameter of the links mixed with the Hydrogen embrittlement, caused part of the failure. 2. Stress. If the clevis end of these links was metal to metal with the axle, that means that the only vibration isolation was the tires. Not a lot there. As all of us have seen on anything Henry Ford produced before Ford discovered rubber in the suspension components, the cars a laced with stress fractures. From suspension components to the frame to the body itself, most early cars suffered from it. One of the many reasons we try not to use metal to metal rear suspension components unless the car is intended for racing only, or it's just not going to be driven that much.
From my humble knowledge is that if you need shiny suspension parts you can nickel plate them, but you cannot chrome them. Case in point, Penske did this on his indy cars for years.
I just looked at a front axle done with Electroless Nickel and then scotch-brited to dull it a bit. Looks fantastic.
Nickel is as bad as chrome for embrittlement. It's the procees, not the metal that generates the hydrogen. The reason nickle was allowed on race cars at indy, and not chrome, chromed parts are difficult to magnaflux, as chrome masks the cracks.
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