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Old 17-03-2016, 15:45   #16
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Re: Titanium hardware

Excellent information! Thank you.
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Old 17-03-2016, 18:10   #17
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Re: Titanium hardware

Quote:
Originally Posted by Stumble View Post
Len,

I wouldn't use a titanium shackles for anchor chain unless you are also using titanium chain. There is no advantage to having a shackle substantially stronger than the chain it's attached to. Just use a shackle rated for the chain you have.
Stumble,
I've a few questions & thoughts on using Titanium for anchor shackles, if you'd be so kind.
The precursor to my queries, being a bit of a read, such that those new to materials, engineering, & metal failure modes, can grasp understand what I'm asking & why.

Regarding Titanium anchor shackles. I'd first want to do some more study on them, but there IS a Big temptation to use them in that application, for me at least.
The reason being, that even when you buy a premium HT (high tensile) galvanized shackle for your ground tackle, which has a theoretical breaking strength of several times more than your G4/G43 chain. In severe storms (read hurricane strength), shackles seem to often be one part of the ground tackle system, which fail.

And they do so, because the pin in the shackle, which passes through the end of the chain, is unsupported for almost all of it's length.
Now were the hole in the chain large enough so that you could insert a compression sleeve overtop of the shackle's cross pin. And the crosspin were actually a cross bolt, as in some HT Crosby variants.
So, then, after doing this, you torqued the cross bolt down to the proper spec for it's size, & inserted a safety wire.
Then the cross bolt (pin) would be being stressed in a different mode than is a simple cross pin.
One where it is/would be able to exercise a much greater percentage of it's theoretical/published strength because of this.

For when the pin in a shackle passes through a link of chain, all of the load on the shackle's cross pin, bears exclusively on the tiny section of metal which contacts the rounded over profile of the inside of the chain's link.
So, then, the bending moment, & strain on the shackle's pin are huge, due to this point loading.

Also, if one looks at how the strengths of shackles are rated. Such numbers are arrived at with a specified percentage of the cross pin being supported by the material which it's shackled though. And said percentage of the shackle's cross pin/bolt which is supported, is a large fraction of the gap which it is spanning.
Which, in the test, the pin passes through a straight hole, in a thick piece of metal. So that the load on the shackle pin is spread fairly equally across far more/most of the cross pin's length.
Thus rendering it significantly stronger than in a scenario where it passes through a link of chain.

Basically, in the test, the shackle's pin passes through a straight hole through a piece of metal, which is then pulled upon in order to load things up in order to conduct the testing (measurement).
So that the load exerted on the shackle's pin, is spread out over a FAR greater area, than is the case when it's slotted through a piece of anchor chain. And there's far less unsupported length of the pin, available to bend.

Or to simplify things, which is easier to bend?
- A 1/4" piece of steel stock, resting atop a flat, 1/2" wide, unbendable rail.
- A 1/4" piece of steel stock, resting atop a 1/2" diameter, round, unbendable rail.

Obviously the one on top of the round surface is easier to bend. And that, more or less, is what the cross pin of an anchor shackle is subject to where it passes through a link of chain.

And with steel, in order to get it to bend. Generally speaking, load wise. You've already exceeded 1/2 of the metal's ultimate strength.
So from there, it's load carrying ability goes downhill rapidly. And if the steel in such a scenario is an anchor shackle...

Most of this information, was distilled in another thread on here, which had to do with the performance of a Fortress anchor during a hurricane. And what, in the survivor's account worked, & what failed.
With inputs from Fortress anchors, & some other industry experts, on some of the why's behind same.
Not that the majority of the shackles failed, necessarily. But of those which survived for inspection, many were significantly deformed. With the attendent loss of strength that accompanies such.

Thus my interest in Titanium shackles for anchoring. Assuming that they're of the proper grade of alloy, & they're well manufactured. As well as their not being subject to being too brittle for the job. Either due to the nature of the material, their manufacturing process, or from work hardening/cycling.

Thoughts?
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Old 17-03-2016, 19:09   #18
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Re: Titanium hardware

This really is a question that needs to be addressed to an engineer not an attorney btw.... My take follows.

A titanium shackle is going to cause galvanic issues on the chain and the anchor. So long as you keep a very close eye on the galvanizing of the rest of the parts it may be fine. The upside is that you can always cut away a few links of chain without an issue if the damage starts becoming a concern.

On the anchor I am not sure. You could add a small anode to the anchor perhaps, or use spray on galvanizing from time to time.

But I am just guessing I don't have any reports of titanium anchor shackles being used. Want to be the experiment?
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Old 18-03-2016, 02:05   #19
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Re: Titanium hardware

I hear what you're saying. Incluing the bit about professions.
My concerns aren't about corrosion, which, for the most part you can see. But about the strength & fatigue life of the shackles. Particularly because, as a sailor (USN) I cut my teeth in the days when the Soviets were developing & fielding several classes of submarines built out of Titanium.
And the brittleness of the material was one of it's big sticking points in their performance/service life. Albeit, it/they was being repeatedly cycled to rediculous depths & pressures (loadings), so, yeah, that played a role in the metal's performance as well, but...

When one adds that kind of reputation to what the flex life of stainless is like. And that much which is done with titanium is still "semi-experimental". It gives me pause.
So, given that you sound like an expert on it, I threw the question out there.

Though, Yep, sounds like a question to be fielded by the shackle's makers. Including scaring up copies of engineering reports, etc. As, obviously there are much stronger metals out there than the alloys used in HT shackles. But the question is, are they well suited for the application.
Then, too, there's the KISS solution. Upsizing one's ground tackle system.
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Old 18-03-2016, 08:03   #20
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Re: Titanium hardware

Keep the concept of titanium being 'brittle' in context. It comes up pretty often, but it's a little deceptive. In engineering circles 'brittle' has to do with the delta between the UYS and UTS as a function of the UTS. Brittle I these circles really doesn't mean the same as what normal people mean when they talk about it.

To clarify let's take an example using 6061 alumnium. With a yield of 8ksi and a tensile of 18ksi, we have a delta of 10ksi. As a function of the UTS this delta is huge (over 50%). Now let's look at G5 titanium... With a UYS of 128ksi and a UTS of 138ksi the delta is exactly the same 10ksi, but as a fraction of the UTS is relatively small (less than 10%).

Keep in mind those titanium space frame eye glasses you can tie in knots. Those are also generally made from G2 titanium, which is also a brittle metal. So how is it that a brittle metal can be tied in a knot without being permanently ruined? It's because the glasses have never been pushed past the UYS and has a relatively low Youngs Modulus. Combine a high UTS and low YM and you get a metal that can flex under very high loads but returns to it original shape (which is part of why Ti makes extraordinarily good springs).

This is also why G9 was created. Because the UYS is lower is makes G9 tubing far easier to bend, and has less spring back, than G5 does, while retaining very high strength.

Btw Ti also has a knuckle in its s/n curve, meaning at loads below a given threshold it doesn't suffer fatigue damage. The Ti subs were not just stressed, they were pushed amazingly hard. This knuckle in G5 occurres at 74ksi, which means the subs were subjected to hundreds of thousands of cycle loads at levels beyond the UTS of stainless.
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Old 18-03-2016, 17:25   #21
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Re: Titanium hardware

My Morgan 27 uses stainless chain plates bolted through the deck with carriage bolts. I was thinking about replacing the stainless carriage bolts with titanium carriage bolts from Allied Titanium. Any problems with titanium in that application?

I would love to have the chain plates made out of titanium but doubt the fabrication cost would be practical.
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