Name that fracture

By jwright650 (*****)

Date 06-19-2008 19:24

Do you have a picture that is further away so we can get a grasp on what it is that we are looking at?

By CWI555

Date 06-19-2008 19:53

The idea was to get blind response based only on the appearance of the fracture. You are looking at the fracture face. It is a stamped steel product that is now in two parts, the other half of which looks the same. Ductile, brittle etc?

By OBEWAN

Date 06-19-2008 20:10

Based upon the graininess, I vote for brittle. There are no chevron ripples as seen with ductile crack propagation. They say the ripples can disclose the point of origin/direction of propagation.

By GRoberts (***)

Date 06-19-2008 22:24

In the left side of the photo, it looks like the facture is very smooth. That seem fairly brittle for material approximately 1/8" thick. I don't see any significant reduction of area of the vicinity area. There doesn't seem to be much indicating that ductile tearing took place.

By DaveBoyer (*****)

Date 06-20-2008 04:27 Edited 07-07-2008 04:01

Post removed, as I was way off base on this one. Dave

By js55

Date 06-20-2008 14:29

I would first say that I don't think there is enough info to definitively say. I would like to get closer. But as an opinion I see a dull gray appearance on the left where the light isn't shining directly on it that indicates ducility. There are no hard angular shiny facets that indicate brittleness, but I also dont see any evidence of microvoid coelescence either. Again, gotta get closer. And it doesn't appear to be a fracture at all but a sheared part as Dave stated. There seems to be a slight contraction at the bottom and a very slight expansion at the top which would indicate its been smacked.
Thats the best I can do.

By gwg

Date 06-20-2008 15:16

Semantics - a sheared edge is a created fracture surface! Looks like a fracture surface that was in shear - poor quality photo however.

By hogan

Date 06-20-2008 15:19

sheared when stamped

By CWI555

Date 06-22-2008 09:34 Edited 06-22-2008 09:39

The part in question was not smacked. It is off a car, the rear left to be exact. This was a car I was in, therefore I have precognative knowledge in that it wasn't smacked at the time it came appart. I dont know the proper name for the part, but if you picture a front wheel drive with independent rear suspension, this is the rear bar that ties into the body and axil spindle/strut. From what I can see and experienced it simply let go in the fashion you see in the picture. To the far left, you can see the metal scrapped away where it was drug down the highway until the car stopped. (in 2 360's I might add). The car in question had 20k miles on it and no history of damage.

I believe it to be a faulty part, but wanted some independent opinion based on the picture (which is representative of what it looks like) before sending it off to a met lab for analysis.

Thanks for your opinions.

Regards,
Gerald

By rlitman (***)

Date 06-22-2008 13:25

Sounds like a "control arm". Ouch!
So, did the wheel go flying off, or did the corner of the car just drop onto a wheel stuck at a 45 degree angle or so, acting as an anchor (sounds more like that)?
These parts do have very high shear forces on them, balancing the down force from the springs, against the up from the wheels. More so, when the rear is loaded (with passengers, or cargo). Still, it should WAY outlast that, with an unmodified factory suspension (some suspension modifications can also add to the stresses on it).
You might want to check nhtsa.gov for a recall. Car makers have been known to stamp these out of too thin material, and then release a reinforced version after some time. If that is the case, it would be a good idea to replace both sides, assuming the car is salvageable.

By CWI555

Date 06-22-2008 16:18

The wheel just dropped and dragged the car around in circles. I am still unclear how the car didn't flip. The car is in the shop, but of course the dealership and manufacture are insisting it was impact damage. We will see, and yes control arm was the word I couldn't remember. One thing I am sure about, it should not have busted in the manner shown.
I got the "we are the experts, your an idiot" attitude at the dealship. However; when I insisted on having the parts, they resisted. It took a call from an attorney for them to release them to me. They were non to happy with setting up a chain of custody before the parts came off the car either. All in all they seemed rather perturbed that I didn't pay attention to their "expert".

These parts will be in an independent lab by tommorow.

By DaveBoyer (*****)

Date 06-23-2008 03:20 Edited 06-23-2008 03:23

The part LOOKS like it left go all at once, that is why I thought it was the stamped edge of the part. Normally in a fatigue failure there is an area where the fractured edges rubbed against each other before the fracture propagated through the entire part. Generally when the failure occurs over time, there is dirt or rust in the portion that started to fail first.

Tensile failure should show distortion elsewhare in the part and necked thickness at the failure.

Both of these scenerios assume a ductile part. Even heat treated steel parts with mid 30s Rockwell "C" hardness show the progressive failure in a typical fatigue failure.

Unless this fracture is in a weld HAZ, the material is ductile, otherwise it could not have been formed.

Can You post pictures of the other side of the part, and of the pieces in "operating" position?

If You want an opinion from somebody who might be considered an expert in this field send Me a PM and I will try to hook You up with Bob Durand, who was the lab manager at the auto frame plant I worked in.

By CWI555

Date 07-03-2008 10:33

I've gotten the lab results back on this. It was in fact brittle fracture. The car has been repaired now, so I'll get some pictures for you in the operating position. For legal reasons I've been instructed not to pass along the specific data and pictures. When the legal end is settled, I'll pass along the specific data and pictures.

By DaveBoyer (*****)

Date 07-04-2008 06:39

Did You get the fractured parts back?

By CWI555

Date 07-07-2008 10:48

Not yet, Should have them back this week.

By Jim12

Date 06-25-2008 20:53

Here is another contact you may try to get analysis from, but you will need more specifics as he looks at the whole picture not just the fracture as stated by others there could be other issues. This is a very knowledgeable individual as he worked with caterpillar and now owns his own business and instructs failure analysis classes.

Failure Analysis Services, Inc
Darrel Davis
FaServices.com
309-925-7251

By Bonniweldor (**)

Date 07-03-2008 00:22

Of the fracture surface itself, the image resolution is not good enough to make any meaningful assessment, unless one were familiar with a frequency of known similar events.

That said, the lack of macroscopic tensile deformation along the fracture face suggests a brittle failure condition. I would be looking for some sort of fatigue feature to explain how the crack initiated. A metallographc section across crack begin zone and 25% of crack propagation should be enough to characterized if there was a microstructural contribution. Combine compositional and metallographic information to judge state of metal and if it is appropriate for the application. Hardness would corroborate any indication of untempered martensite in the microstructure.