Detachment Test: Ideas?

where is this rod used? is this a connecting rod in an engine?

Nope, not to be used in an engine, it is a medical device

A bend test? Support the ends of a short piece and push it down in the middle with the Instron. More like a peel test.

Thermal cycle(or thermal shock) the rods?

What does the rod do in service?

One final point, years ago I did adhesion tests on some SS plates. We found that wire wheel cleaning was superior to glass beading. I know, I didn't believe it at first.

We needed elastomer-coated aluminum wheels for a robotic microfiche vault years ago. The wheels scooted the microfiche through a scanner. The elastomer was molded around the hubs which were knurled and adhered so well you couldn't pry it off. Knurl your rods if the coating absolutely positively must not shear off.

Knurling is a good idea. Do they make knurling tools that knurl rollers to knurl on diameters as small as 1 cm?

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I knurling isn't feasible, using coarser harder blasting media might also help.

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I realize the OPs question is about testing, but without knowing the in service conditions, it is difficult to make suggestions.

Sure do. Might even find pre-knurled rod stock so they don't have to do themselves.

What I actually need to know is which primer promotes the best adhesion between the metal and the acrylic. The rod (nail) is to be temporarily implanted on long bones. Once implanted, the nail will be mainly subjected to flexing, torsion and scratching

I don't think anybody here can say. I know I can't.

The rods I had in my feet were uncoated. The screws that are still there are, too.

I'd be talking to the players in industry.

Perhaps something along the lines of octyl cyanoacrylate. Surface roughness will still be important.

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Perhaps consider having small slots or small holes cut (laser?) through the rod perpendicular to the axis of symmetry near the ends of the rods. Using PMMA inserts in the holes could insure there is no problem with air inclusion, as long as bonding was sufficient.

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When you are setting up the testing, the rods should probably be tested in a wet condition having been allowed to soak in simulated body fluid at close to body temperature for sufficient time to allow decreases in tensile strength related to moisture uptake.

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If the rod is to be subjected to flexing torsion and scratching in service, it would be a good idea to subject the rod to a combination of each of those things in excess of what might be expected in the body. Repeated torsion and flex tests of pre-scratched material soaked in simulated body fluid at 40 C.

Thank you for your input! for the sake of keeping the OP within readable limits I did not disclose additional details of complementary processes we do on our products when tested.

Polymers to be used in medical implantation are subject to serious, learned research before applying for approval. Then you (may possibly) obtain approval - region by region. All through the development, testing, approval and supply process you must have specialised liability insurance.

I earnestly suggest that anybody who wants to provide a recommendation or suggestion in this thread should make a quick Google search on "plastic implant failure" before you scream and run away from this thread.

PMMA as well as octyl cyanoacrylate are both widely used in a variety of ways inside the body and exhibit good biocompatability. I'm sure the OP is aware that the product will have to pass rigorous evaluation to be accepted....I'm guessing that the interest in testing is related to that knowledge.

Thank you for your input, but my question ONLY refers to the design of an adhesion test of acrylic on a metal rod using a Instron test machine. This should be totally independent from the intended use of the product. Our company has been in this business for about 50 years, and we are doing quite well. We produce under many ISO Norms. Most of our products are FDA and CE approved.

'...my question ONLY refers to the design of an adhesion test of acrylic on a metal rod using a Instron test machine. This should be totally independent from the intended use of the product....'

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It seems like you would want to make sure the test evaluated the piece under conditions that approximate the most extreme likely to be seen in service. As an example, PMMA exhibits a reduction in tensile strength and a shift from ductile to brittle behavior with absorption of water. The certainly seems like something that could affect adhesion.

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Doesn't the value of the test depend highly on the intended use? It seems like a test on a rod that had the coating pre-scored to a depth not likely to be exceeded in service, that was soaked in saline fluid at body temperature for a few days and then repeatedly flexed and twisted, would be much more useful than something that didn't take the intended use into consideration.

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I don't intend this comment with disrespect, this is your court. I would appreciate some insight into why my thinking is off base, if you have a moment to respond.

Never mind. I just read your reply #15 to my earlier comment. It all becomes clear now. Thank you.

Dear "truth", I want to tell you that I really appreciate your input even when you vehemently defend an opinion because this denotes passion and concern for what you are doing. Thank you again!

We use over molding or insert molding for medical devices. Deeper recesses or grooves are designed in the metal part to give mechanical anchorage.

If it is an implant, then extensive validation tests are needed to ensure that there will be no gaps where infections can lodge.

Hi Jim! I already had a couple of tests in mind, and wanted to know if replies to the OP coincided (or not) with my ideas or shed light on a new approach to the problem. I like your idea cause the test you propose does not require to buy or make special tooling for the Instron in order to perform it. To see if it works or not, I will go one step further: I will take a metal block and drill 2 holes in it: one will have a thread to fix it to the machine by means of a screw, and the other one (opposed face) will have a 10MM hole. Instead of peeling the the PMMA midway off the rod, I will peel of the end(s). GA

What i did so far:

I drilled a hole into an aluminium block, peeled all the PMMA from the rod (except a 10 mm wide band). The idea is to push the rod trough the hole and to measure how much force the Instron will make to break the PMMA band off the rod.

This is how I mounted both parts on the machine:

We will start doing some tests later today. Will tell you if it works or not

Hey, thanks for the follow-up pictures and progress update! So few people do that, but I for one, and I suspect many others, really appreciate it.

Yesterday we finally managed to do only two tests: coating 1 vs. no coating.

Results were: Coating 1: 24.98 MPa / No coating: 1.56 MPa. Although the first results are very interesting, we will repeat the tests on 10 samples of each of the 4 different coatings we have in mind and compare them to the same amount of non coated rods.

If these results happen to be statistically significant we will probably use this method as our testing standard.

Thanks for the GA. I get a few nearly good answers but rarely the cherry. You did end up doing what I had envisaged when I said "peel all but about.." I figured you were smart enough to get the gist and do the job the way that suits you best anyhow.

Pleased to see that it worked for you and of course the relative strengths can be compared even if a quantitative figure can't be calculated.

A GA for posting results and pics

Jim