Help - Tensile strength of carbon fiber.

I need some assistance with finding the tensile strength in carbon fiber.

Today I was conducting, what's called a cavity monitor survey.
It's sending a laser down a borehole to measure the size of void at the end of the hole.
Well the instrument is worth $115,000.
I was asked to send it down. 102 meter drill hole. This is done by attaching the camera to carbon fiber rods.
Each rod is 50 mm thick and 1 meter long.

Well today I had the CMS down to 98 meters. Then one of the carbon fiber rods snapped.
Luckily I was able to catch the power cable before it to went plummeting down the borehole.

But now, I have a $115k unit, dangelin by its power cable.
I was able to secure the cable before I came up to surface.
But tomorrow I'm heading back down to try to retrieve it.

I want to know if it's a manufacturer defect or if it was overloaded.

Does anyone know of a website that allows someone to calc. The tensile strength of carbon fiber?

too many variables with cf. composites

weave patterns, epoxy types, vacuum formed vs not. etc, etc...

I'd contact mfg for design limitations.

a reply to: Mandroid7

Ya I've sent them an email as well.
And asked if they have any retrieval tips lol.

One thing I forgot to add to my OP was that the hole has a dip of 86 degrees.
So pretty much vertical.

a reply to: Macenroe82

The rods are 1 meter long. You have to screw the individual rods together ?
That is a lot of work. Is there no way to use a steel cable?

a reply to: Macenroe82

If they know tensile strength of one, you could prob calculate max setup length by taking cam and wire weight and then keep adding weight of each rod to total, until you come to a percentage of max weight. That's you max length.

Visualizing what your talking about the retrieval, I picture a hook retriever on 200 lb fising line and a reel.

If you haven't seen them, they are a spring with a strong line. It would wrap on and slide down the power cord, may have to modify it to bite cable, hooking your pull cord on the side of spring should be enough to lift cam, when u do both at same time.

Sounds like a cool job, you should post a youtube.

a reply to: Macenroe82

its over my head by here you go:

The stiffness of a material is measured by its modulus of elasticity. The modulus of carbon fiber is typically 20 msi (138 Gpa) and its ultimate tensile strength is typically 500 ksi (3.5 Gpa).

a reply to: butcherguy
The rods come in 30 meter lengths. So 30 rods at 1 meter each, with a joint linking each rod together. At the end of the 30 meter length, there is a joint that will hook to the first rod of the next length.

a reply to: Macenroe82

Luckily I was able to catch the power cable before it to went plummeting down the borehole

If you were able to do that, and assuming CF has a tensile strength of 3.5GPa then it's either;

A: It's not an overloading issue.

or

B: You've got forearms like Popeye.

a reply to: Mandroid7
I have a few mining videos on my YouTube channel.
Also have video from My early prototype of my underground drone going into an open stope. It was a lighting test. So there's 2 different lighting set ups. Both with low lumen though. 1 set up was like 300 and the other 500.
My lighting now is 3000 lumen. It's funny when I look back and see how I used to do things vs now.
Also have footage of our pit walls being scaled of loose rock. 3 dudes repelling over the edge with scaling bars.
Video of a 3D model I created of the water management facility I designed.
and so footage of the stupid amount of bears we have on site.
Go to

And then click my user name and my videos will come up.

My question is, what is the weight of the equipment you sent down? I deal with alot of hoisting and rigging of many tons at times. Why are you using carbon fiber rods?

a reply to: DJMSN

Thanks for the effort, I was looking at that earlier.

a reply to: Groot
I'd say close to 370 lbs.

a reply to: Macenroe82

Then 5/16 in. steel cable is plenty of strength.

www.engineeringtoolbox.com...

That sounds like a flaw in the joint that failed. I cant see the rod snapping in half. I make high carbon 7 wire strand. Our smallest is 3/8. It would pull it out no problem. When we have a failure in the field it is usually cause by surface damage, vertical cracks, a poor quality weld, or misoperation the field with a torch.
The carbon fiber should be stronger then steel. Our half inch breaks at over 40,000 lbs, but it does have elasticity, and it streaches right before it breaks. 4.2 mm single wires break at 6000 lbs

a reply to: Macenroe82
HUH? You would have been better off using a steel rod, or aluminum, or even rope or wire rope, or steel or copper rope/tubes. And reading this if its only a messily 370 pounds any would do.

I take it your using carbon fiber rods so you can control it and aim it in different directions while its down there, in which case I sort of get it why your bothering with this. And for some reason you thought since carbon is light it would not add much to the overall weight. Your thinking on it wrong, if anything something more sturdier and heavier will help out when you want to guide the bottom weight of your little 150K sensor instrument.

But really bro. Do they just let anybody play with 115k sensory equipment toys? I am sure you will find a way to use it with all kinds of other equipment. But yes carbon fiber does have a habit of snapping or cracking if there is to much pressure or to bumpy of a ride, so if you twist those rods, or wobble around to much, your better off using rope or long aluminum or steel rods screwed together.

While it may be as strong as steel in some ways without the added weight of steel, or it could easily hold that 370 pound weight, anybody could easily snap it with both hands most likely if its just a bunch of long rods put together its likely to be very brittle. I don't think your problem is a problem tensile strength as in more or less of elasticity under pressure.

Anyways, seems like a none issue to me. I am sure you will figure something out.

a reply to: Macenroe82

Each rod is 50 mm thick and 1 meter long.

Just wondering,

How do you know an individual rod itself snapped instead of failure occurring at whatever junction holds the rods together?

a reply to: Macenroe82 How were the carbon fiber rods attached together. Do they screw together? Is there a torc specification from the manufacturer? That's where the failure happened. They very well may attempt to blame it on you. There was probably an air bubble in the resin on the joint. You would think that even the material would hold suck a small load, afterall, even a power cable is holding it now.

The strength of the joints will be additive, so the most strain is near the top. Is that consistent with what happened? The joints will definitely be the weak spot....unless you say otherwise.

If you had a sample I may know someone who has a tensile lab machine in mu old job. The machine will literally pull that effer apart till it snaps in two and give you a very accurate measurement. I've used it in the past for both metals and different fibers including Kevlar, (hemp twill) rope, but mainly metals used in cable bridge application. People paid us while I worked their to break all kinds of shi* cause we had the machine. I have good friends that still work there if this is something you are interested in lemme know ill make the appropriate calls and get u in touch.

a reply to: galadofwarthethird

Your sort of right.
The rods act as a stabilizer to allow for a fixed Azimuth.
The camera head, once in a void, will start to spin 360 degrees. It spins while it measures the entire area.
It will create an exact profile of the open void.
Once on surface, I import the 3d point cloud into CAD, create a mesh, and bingo, we got a profile of the void.