iMechanica - Puzzle: What caused this failure? - Comments

Re: what material is this?

Biswajit Banerjee — Sat, 19 Jul 2008 02:06:09 -0400

Linhua,

There is no attachment. Just the two images that you see in the post.

-- Biswajit

what material is this?

Lianhua Ma — Thu, 17 Jul 2008 00:53:42 -0400

I can not see the attachment, can you upload again?

Re: Puzzle - Ajit's guess

Biswajit Banerjee — Wed, 16 Jul 2008 22:55:53 -0400

Ajit,

You analysis is amost absolutely correct. The bottom picture doesn't have any glue on it - that's what the surface looks like just after it's cut (before joining). The ridges are gone in the failed specimen precisely because of dissolution. I took the photographs while testing a light microscope that can (supposedly) magnify to 40x. But given the vibrations in our lab only around 25x is possible.

I took the unfailed picture at a higher magnification to give you an indication of the material. What do you think it is?

-- Biswajit

Michael, You're spot on

Biswajit Banerjee — Wed, 16 Jul 2008 22:50:42 -0400

Michael,

You're spot on about the torsion bit. But I'll leave the experiment with ovine lactic fluid to you and then we can compare images on iMechanica.

-- Biswajit

Re: Oreo

Biswajit Banerjee — Wed, 16 Jul 2008 22:48:55 -0400

Chad,

I assure you that the next time it'll be an Oreo. That thought had never crossed my mind.

-- Biswajit

Re: Puzzle

Biswajit Banerjee — Wed, 16 Jul 2008 22:48:11 -0400

Mike,

I was hoping that some of the younger members of iMechanica would give it a shot before I provided more details.

The failed image has been magnified 6 times, the unfailed one 16 times (my mistake).

The joint is not a weld and the material is not a metal. The unfailed material does not have cracks - those are ridges generated during the cutting process.

-- Biswajit

Wow, Ajit's analysis is very good,I am inclined to accept it!

Mike Ciavarella — Wed, 16 Jul 2008 00:43:23 -0400

michele ciavarella
www.micheleciavarella.it

That seems reasonable.

Mike Graham — Tue, 15 Jul 2008 14:39:20 -0400

I think this is spot on. You can see telltale signs of the torsional failure of the bond between the alternating organic materials. My guess from the failure pattern is that the outer shell was twisted fast, causing a relatively clean failure of the binder. Perhaps this was some sort of preperation for a chemical treatment in a bath of ovine lactic fluid?

Re: Puzzle - My Guess

Ajit R. Jadhav — Tue, 15 Jul 2008 13:51:45 -0400

I will do as best as this flaky Drupal and Internet connection allow me to do.

I bet it's a polymer glue and that the failure occurred in torsion (of a rotating rod), sure, but that primarily this happened because the actual cross section failed short of the required strength in torsion.

In the top picture, the circles appearing in the grayish background are due to air entrapment or perhaps, even gas release during polymer setting. The whitish patches in the center is the glue material fractured suddenly in shear. However, it may carry inclusions like crud or dust particles. The glue in the bottom also shows sudden brittle mode fracture. The bottom picture shows the glue applied with a brush, just before the two parts are axially pressed together.

I would bet that the rod material itself was non-polymeric---otherwise, one would expect dissolution of surface layers, and no gas release of this nature.

A reasonable guess would be that either wood or ceramic or metal (likelihood in that order) rods were joined using a synthetic glue, e.g., two parts of the axis of a motor or a hairdrier or a turbine or so, and that the joint failed due to above reason.

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No mention of scale, material, whether it's a micro/meso/macro-graph, method of preparation of micrograph... And what else do you expect?

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I also felt initially that it could be fatigue. But, fatigue, it's not. There are no progressions characteristics of beach marks. Plus, typically, fatigue cracks grow from only one dominant point on the circumference. Here, the top picture shows a lot of shear walls. So, sure, it's a sudden and brittle failure. But not involving fatigue even in its history. (Plus, the top bubbles are not stretched in one direction, and are too big. So, they can't be dimples. They have to be gas bubbles. My best guess is air entrapment during mixing of the base and the hardner.

Up to you, Biswajit.

My guess is that it's an Oreo.

Chad Landis — Tue, 15 Jul 2008 10:08:11 -0400

Not even close huh?

for sure failure under torsion --- but

Mike Ciavarella — Tue, 15 Jul 2008 08:51:40 -0400

but I am unsure about fatigue, I do not see clearly beach marks

plus what are these buttered circles? corrosion?

tell us more about it. What do you mean joint? Which type of joining? Welding?

Also what are the scales, they seem different in the two pictures?

What is the material -- looks a metal. Why the second 'unfailed' seems neverthless to have cracks?

Many more details for a reasonable descprition are needed to raise the case!

Puzzle: What caused this failure?

Biswajit Banerjee — Tue, 15 Jul 2008 02:23:37 -0400

Here's a puzzle for our readers. The following image is of the surface of a failed joint followed by a picture of the joint (not the same one but a similar one) before joining. What material is it? What caused the failure? All manner of speculation is welcome.

Failed joint

Unfailed joint