Stainless cracking. Metalurgists, puzzel this one

[s/v Jedi]

Originally Posted by seandepagnier

Why do you keep repeating "bronze" when it is one of the worst possible things you can bolt to aluminum? Then posting chatgpt bot results that anyone can use for free when we should all know by now that a lot of the stuff that it says is wrong or misleading.

The obvious answer is titanium with some kind of grease as well as replacing all isolation delrin etc.

It isn’t and it isn’t. Like I posted again and again, you must insulate dissimilar metals so you never do what you describe.
And chatgpt isn’t a bot and you can’t get what I posted for free. It is a shame that people are so brainwashed against new tools still after this has happened so many times in the past. CAD software was once ridiculed too.
You must realize that everything it answered on my queries, within the context I provided is 100% true and scientifically proven. Truth isn’t a count of opinions.

[s/v Jedi]

Originally Posted by dlj

Hahahaha, too bad you prefer to have such a confrontational relationship with me.

I want no relationship with you at all. I already listed why I countered you with data supporting my recommendations and also explained why your style of discussion is so unproductive. (repeatedly coming up with new angles after been shown wrong. First it’s just my opinion, then after showing data, it’s because I list arguments for submerged instead if splash zone, then after showing it is for splash zone as well, it is because of carbon fiber, even though this wasn’t mentioned at all and now I show the facts with carbon fiber involved too, it is down to ad hominem, criticizing ChatGPT and now me instead of demonstrating the facts presented are wrong. You can’t because they are correct, not wrong.)

What does need repeating is that my recommendations early in the thread were correct, i.e. stainless steel is not a good choice.

The best solution to the problem is using titanium and insulating washer-bushings between dissimilar metals as well as between metals and carbon fiber.

Don’t use stainless steel in oxygen starved applications when you can’t guarantee it stays dry.

[dlj]

Originally Posted by notoldbilbo

I'm one of 'the other people reading this' with acute interest. I'd like to 'add some context' and seek some Guru Guidance, if I may.

I'm looking to bolt a pair of 95mm titanium pad eyes onto the quarters of my 40 y.o. boat, from which to hang a JSD. According to Don Jordan's teachings, I can expect a Maximum Wave Strike to impart a very occasional ~6000lbf/26700kn 'thump'. Much more than that, and I'll need a 'Beam me up, Scottie' badge.

The question has been reinforcing 'adequately' the unknown grp layup of about 10-12mm locally, to cope. I've queried this before and our good friend Zonker was kind enough to advise, wisely, that I ignore the 'known unknown' of the original layup and add sufficient multi-layers of biaxial carbon cloth inside. I'm happy to do that in my cack-handed way and live ( or die ) with the result.

Or... I could use many more layers of biaxial glasscloth. Example in pic below.

I plan to use a 132mm x 3mm bronze plate as 'plate washer' on the inside, giving an interesting 'stew' for the metallurgists among us. The bolts are 4 x M12 BUMAX 88 ISO10642. Their heads and the titanium will be in the 'splash zone'. The inner threaded ends, in contact with the carbon cloth and bronze plate, will not.

The question now is how best to mitigate the risks of corrosion outlined by s/v Jedi in #85 above. Would Tefgel and butyl tape likely suffice? Epoxy?

Then there is the vexed question of 'Preload'....

I agree with Zonker on using carbon fiber reinforcement - you should ask him how best to isolate your fasteners going through the carbon fiber - he's an expert in this subject.

Why not use titanium fasteners instead of that 316?

Preload - I'd recommend you download MIL-HDBK-60 - that will give you a lot of information to start with. If that doesn't help you, the standard role of thumb (does require some equipment and time) is to test the same kind of bolts you are going to use, measure the amount of torque required to break them, then you tension the bolts in your fixture to about 50% to 60% of that torque.

A question I have for you - how are you attaching the drogue to those plates?

dj

[thinwater]

Originally Posted by s/v Jedi

And about this happening when carbon fiber is involved:

When stainless steel bolts in a structure with carbon fiber-reinforced fiberglass fail more frequently compared to those in fiberglass-only structures, it often points to issues related to **galvanic corrosion**. Here's why this happens:

### **Galvanic Corrosion Between Carbon Fiber and Stainless Steel**

1. **Electrochemical Potential Difference:**
- Carbon fiber, especially when used in reinforced composites, is electrically conductive. In a wet or moist environment, such as the splash zone, this conductivity can create a galvanic cell if carbon fiber is in contact with stainless steel.
- Stainless steel and carbon fiber have significantly different electrochemical potentials. In the presence of an electrolyte (like seawater or even moist air), the carbon fiber can act as a cathode and the stainless steel as an anode. This leads to accelerated corrosion of the stainless steel, especially at the anode, where material loss occurs.

2. **Accelerated Corrosion Rates:**
- The splash zone's environment—with its frequent wetting and drying cycles, high chloride concentrations, and ample oxygen—can exacerbate galvanic corrosion. The more noble carbon fiber material can cause the less noble stainless steel to corrode more quickly, particularly at points where the stainless steel is in direct contact with or close proximity to the carbon fiber.

3. **Localized Corrosion and Mechanical Weakening:**
- The result of galvanic corrosion in this context is often localized pitting or crevice corrosion at the points of contact. This localized attack can significantly weaken the stainless steel, leading to premature failure such as the heads of bolts falling off.

### **Mitigation Strategies:**

1. **Isolate Materials:**
- To prevent galvanic corrosion, it’s crucial to electrically isolate the stainless steel from the carbon fiber. This can be done using non-conductive barriers, such as gaskets or washers made from insulating materials, to break the electrical path.

2. **Material Selection:**
- Consider using more galvanically compatible materials with carbon fiber, such as titanium or high-nickel alloys, which are less susceptible to galvanic corrosion in contact with carbon fiber.

3. **Coatings and Treatments:**
- Protective coatings on stainless steel bolts can provide a barrier to electrolytes, reducing the risk of galvanic corrosion. However, care must be taken to ensure the coatings are intact and effective in the challenging environment of the splash zone.

4. **Regular Inspection and Maintenance:**
- Regular inspection for signs of corrosion and maintenance to replace affected components can help mitigate the risk of catastrophic failure.

**Conclusion:**
The increased frequency of stainless steel bolt failures in structures incorporating carbon fiber-reinforced fiberglass compared to fiberglass-only structures is primarily due to galvanic corrosion. The conductive nature of carbon fiber exacerbates corrosion when in contact with metals like stainless steel, especially in aggressive environments such as the splash zone. Mitigating this issue requires careful consideration of materials, isolation techniques, and protective measures.

Thank you for several good posts.


I should add that this is one of the reasons I am not a fan of DIYs using carbon for reinforcements, using the logic that it must be better.



* Carbon is many times stiffer than glass, but only about 20% stronger by volume, which is usually what matters. As for needing stiffness to spread the load ... yes and usually no. If you build up more layers of glass it will be stiffer (goes up with the cube of thickness) an did you really want materials of different stiffness working together? They don't work together, anymore than you could reinforce chain by adding a nylon rope next to it. The carbon will carry all of the load and the glass will do very little. In my experience, carbon works best for structures where it is used by itself and the stresses are well understood. Randomly adding it to glass laminates can just make things worse.

* The galvanic issues that have been presented. They are serious. The JSD mounting was an excellent example.



* Carbon is not known for toughness; it tends to shatter because it cannot give as far. Much of the time people want to reinforce with carbon the damage was caused by shock loading or impact. What you need is greater glass thickness spread over an area. Not that simple, of course, but slapping in a few carbon cloths is not going to help.

[notoldbilbo]

Originally Posted by dlj

Why not use titanium fasteners instead of that 316?

Preload - I'd recommend you download MIL-HDBK-60 - [ THANKS - WILL DO! ]
A question I have for you - how are you attaching the drogue to those plates?

I've looked, and they'd cost - with nuts 'n washers - just shy of £500 here. That's a lot of beer tokens. I already own the M12 BUMAX bolts....

The Harken Special pad-eyes have just emerged from my box of 'bits and bobs'. What else could I possibly use them for, but this...?

As for 'method of attachment', see pic. Yes, I agree they'll be plenty strong enough. As for chafe, I have antichafe sleeves fitted - and spares!

[dlj]

Pricely little buggers aren't they...

Very nice attachment to those padeyes!

dj

[notoldbilbo]

FWIW, although I've spliced several smaller ones myself, I had my 'primary' JSD soft shackles made by a pro. I've now discovered that they're 'cheap as chips' as vehicle recovery devices from AliExpress - although someone might want to bench-test a couple.




I'm sure they do the $US equivalent for 'your' region.

[dlj]

Originally Posted by notoldbilbo

FWIW, although I've spliced several smaller ones myself, I had my 'primary' JSD soft shackles made by a pro. I've now discovered that they're 'cheap as chips' as vehicle recovery devices from AliExpress - although someone might want to bench-test a couple.




I'm sure they do the $US equivalent for 'your' region.

Wow! That's a great find! Yes, some bench testing may be a good idea, but these soft shackles are just amazing.

I'll have to check these out.

dj

[Jammer]

I like to buy Amsteel from trustworthy suppliers and tie my own soft shackles. That way I get exactly what I want (length, diameter, color, etc) and I can be reasonably confident that the materials and workmanship are good.