Anchors - Bigger is Better ?

[Andrew Troup]

Originally Posted by DumnMad

Bent shank - thats how the shank should fail if overloaded. Higher tensile steel is more brittle - over 500MPa not allowed in building - less able to take cyclic loading and second bend can break without warning.

High strength has its place but if the shaft bends don't continue to use it.

+1 ! .

[JonJo]

[QUOTE=DumnMad;1211975 Higher tensile steel is more brittle - over 500MPa not allowed in building - less able to take cyclic loading.

High strength has its place but if the shaft bends don't continue to use it.[/QUOTE]

Odd really but ASTM 514, MPa yield of 690 min, is specifically recommended and used as the columns in high rise buildings, they allow considerable weight savings - which apparently becomes important the higher the building. Also used in cranes and bridges.

Anyone ever heard of a genuine Rocna, Supreme, Excel (of which there are now thousands in use) bending, let alone snapping?

My thought is - if ASTM 514 snapped it would make a prime forum thread and there has been nothing in Cruisers Forum, Anything Sailing, Sailing Anarchy, Trawler Forum, YBW etc - so along with the mythical scare campaign - how about an image.

[JonJo]

Andrew,

I quoted Dumn - he said not allowed to use in building unless less than 500 MPa - its his quote not mine. Maybe he needs to clarify which buildings ASTM 514 is not allowed.

All anchors can bend, I would not recommend anyone bending and then straighening and re-using it. In the grand scheme of things anchors are not that expensive and trying to 'retrieve' one seems silly. I suspect it might be quite difficult to straighten ASTM 514 in any case

I'm still interested has anyone bent a ASTM 514 shank - has anyone ever heard of one snapping?

[Delfin]

Originally Posted by DumnMad

Bent shank - thats how the shank should fail if overloaded. Higher tensile steel is more brittle - over 500MPa not allowed in building - less able to take cyclic loading and second bend can break without warning.

High strength has its place but if the shaft bends don't continue to use it.

I believe that is simply incorrect. The elongation before break of mPA 800 steel is 26% and that of A36 mild steel is 20 - 23%. The reality is that high tensile steel is less likely to break than mild steel because it will bend more before breaking. If one has the choice between purchasing an anchor with a shank of mild steel vs. a shank of high tensile steel of the same thickness, pick the high tensile steel if staying put at anchor makes sense to you.

Bisalloy 80

Mild Steel

[DumnMad]

I'll spell it out for you.
Modern buildings have a failure mode where yielding(plastic deformation) is built into the design for energy absorption. Not allowed over 500MPa in these zones.

[Andrew Troup]

Delfin

You're right to say "high tensile steel is less likely to break than mild steel because it will bend more before breaking."

It almost goes without saying. The elastic limit is higher: this means it can bend a lot further before it starts even to yield. The elongation before break you refer to includes elastic strain as well as subsequent plastic strain.

The point I thought DM was making, and with which I agree, is that once it DOES yield, high tensile material is generally no longer fit for service.

This is chiefly because the ductile to brittle transformation is now more likely at normal temperatures, and typically too likely. The properties of HT materials change much more radically after plastic strain (in other words, loads which exceed the elastic limit) than the properties of mild steel typically do.

This is why, when you bend steel wire, you can bend and rebend soft wire repeatedly before it will snap. With HT fencing wire, it's much harder to bend, but a couple of 180 bends will cause it to snap like a carrot.

JonJo: as soon as I had posted I realised I had not checked the exact wording in the post you were responding to, and realised you were not perpetrating a non-sequitur, as I had suggested. I deleted my post immediately, but you must have received an email through being subscribed.

I humbly apologise and withdraw.

[Delfin]

Originally Posted by Andrew Troup

Delfin

You're right to say "high tensile steel is less likely to break than mild steel because it will bend more before breaking."

It almost goes without saying. The elastic limit is higher: this means it can bend a lot further before it starts even to yield. The elongation before break you refer to includes elastic strain as well as subsequent plastic strain.

The point I thought DM was making, and with which I agree, is that once it DOES yield, high tensile material is generally no longer fit for service.

This is chiefly because the ductile to brittle transformation is now more likely at normal temperatures, and typically too likely. The properties of HT materials change much more radically after plastic strain (in other words, loads which exceed the elastic limit) than the properties of mild steel typically do.

This is why, when you bend steel wire, you can bend and rebend soft wire repeatedly before it will snap. With HT fencing wire, it's much harder to bend, but a couple of 180 bends will cause it to snap like a carrot.

Sorry, but this is still incorrect. The term "Elongation at Break" means the degree to which the material will stretch before breaking, either with a straight pull (how it is measured for specs) or in a bend. Because A36 has a LOWER % of elongation it will break BEFORE the High Tensile steel breaks. In addition, the force required to bend the HT steel is significantly higher. This is why, contrary to the previous comment, HT steel like Bisalloy 80 is PREFERRED for high rise buildings, not barred.

Data should mean something, shouldn't it?

[Andrew Troup]

Delfin

I don't think you even read my post. You are challenging things I didn't say, or about which I said the opposite of what you seem to think I said.

[Delfin]

Originally Posted by Andrew Troup

Delfin

I don't think you even read my post. You are challenging things I didn't say, or about which I said the opposite of what you seem to think I said.

I read this:

Originally Posted by Andrew Troup

The point I thought DM was making, and with which I agree, is that once it DOES yield, high tensile material is generally no longer fit for service.

I merely pointed out the obvious from the data. Both A36 and HT will break. HT will break after more force is applied and after more deflection has occurred than is required to break A36. You also wrote that when HT yields by breaking it is generally no longer fit for service. Well yes, just as A36 would be unfit for service after it breaks with less effort.

If you are agreeing with DM that a broken anchor is not fit for service whatever it is made of, well, that makes three of us.

The point is that Bisalloy is a superior product based on the DATA than A36 because of its physical characteristics, regardless of your experience with bending wire.

[Weyalan]

I'm no expert, but if your anchor is experiencing loading that causes non-recoverable deformation, I reckon you need a bigger (i.e. stronger) anchor. The classic graph of elastic deformation / elastoplastic deformation / plastic deformation / failure is not as consistent in the real world as it is in the text books.

[DumnMad]

We are talking about " metal fatigue", google it; You can straighten mild steel and continue to use it safely, but once high tensile steel is bent its ductility is virtually stuffed.
If the anchor with a bent shank is high tensile steel then chuck it. If its mild steel, or grade 500E say, then straighten it, keep it in reserve & get one with a thicker shank. BIB

[JonJo]

Originally Posted by Andrew Troup

JonJo: as soon as I had posted I realised I had not checked the exact wording in the post you were responding to, and realised you were not perpetrating a non-sequitur, as I had suggested. I deleted my post immediately, but you must have received an email through being subscribed.

I humbly apologise and withdraw.

My fault, I should have checked your post was 'posted' - but I was on the run.

Its refreshing to see courtesy, no offense taken

Jonathan

[JonJo]

Isn't the debate academic, there is no evidence of bent ASTM 514 shanks (I'm sure it has occurred but I'm guessing owners have kept quiet as they would damage more than the shank and almost the only way to bend an ASTM 514 shank is through stupidity (or that chance in 1,000,000 accident and anchor makers will keep that quiet). Most brand name modern anchors are now made with shanks greater than 500 MPa and the only ones made with 'mild steel (whatever that means) are copies and probably do not work too well as anchors anyway. Consequently if your shank bends the anchor is probably rubbish (and has poor holding), straighten it and it will bend again (and it will still have poor holding) - so the advise for any bent anchor (and stainless ought to come into the mix) ought be - dump it (for a variety of reasons) and get another. And I see little reason to buy a bigger poor holding anchor with a mild steel shank - it will still have poor holding and will probably still bend (though less frequently). So I'd suggest BIB, as in 'Better is Better'!!

Now that should all bring a smile to the anchor makers!

The only redeeming feature I can think of mild steel is that you can probably bend it back relatively easily. I suspect the only way to straighten ASTM 514 (or anything approaching that specification) is in a metal press, not that common off the beaten track.

Jonathan

[Delfin]

Originally Posted by DumnMad

We are talking about " metal fatigue", google it; You can straighten mild steel and continue to use it safely, but once high tensile steel is bent its ductility is virtually stuffed.
If the anchor with a bent shank is high tensile steel then chuck it. If its mild steel, or grade 500E say, then straighten it, keep it in reserve & get one with a thicker shank. BIB

I'm not trying to pick a fight, DM, but everything you write is 180 degrees opposite of reality. High strength steels have higher resistance to metal fatigue and can withstand more cyclic loading than mild steels. That is why high strength steels are superior for tall buildings - they can withstand more swaying without failure than mild steels. The reason is because HT steels are less likely to develop fracturing along grain faces in part because the grains are smaller. From a paper on the subject: "ASTM A 440 has a yield strength of about 345 MPa (50 psi); the other steel (tested) is a proprietary grade hardened and tempered to a yield strength of about 750 MPa (110 ksi). Under long-life fatigue conditions, the higher-strength steel can accommodate higher strain amplitudes for any specified number of cycles; such strains are elastic. Thus, stress and strain are proportional, and it is apparent that the higher-strength steel has a higher fatigue limit."

I think you may be confusing hardened carbon steel with the ASTM A514 steel like Bisalloy, which has LESS carbon in it than mild steel. But no one that I know of makes an anchor shank of high carbon steel.

[Andrew Troup]

Delfin

I might have been wrong in guessing you hadn't read my post; it appears you simply misunderstood the thrust.

I'm not sure it's profitable continuing further with you on this, because you don't appear to understand the terminology, and perhaps even the basic concepts, well enough to land any punches.

What disheartens me is that you seem to have a strength of conviction which is out of step with the degree of understanding.

On the off-chance, I'll try once to explain what I'm driving at, and hope that if you have no appetite for it, somebody else might.

You wrote:
<<You also wrote that when HT yields by breaking it is generally no longer fit for service. Well yes, just as A36 would be unfit for service after it breaks with less effort.>>

Well no, I didn't write that. Please re-read. The words in bold are supplied by your imagination, and indicate a lack of basic appreciation of how metals respond to loads.

Yielding is not breaking. Yielding happens when the metal is stretched or bent past the elastic limit, and the word has this specific and exclusive meaning in all engineering and 'strength of materials' discussions throughout the English-speaking world.

Once a material is loaded past the elastic limit and starts to "yield", plastic * deformation begins.

This "plastic" portion of the deformation persists when the load is released. Up to that point there are no dimensional changes, in fact NO permanent changes, except a few which might be detectable at a micro or nano scale: eg discontinuities at the level of crystalline or sub-crystalline structure will migrate, and tiny cracks might propagate further.

(the latter being the mechanism of fatigue, which is relevant to the discussion, but my argument to date does not touch on, unlike DM's).

*(which doesn't stand for 'post-elastic, but in this context it might as well)

So what I am saying is that, once it has changed dimensionally in a permanent way, a high tensile steel undergoes a change in properties: it becomes stronger, which is good, and less ductile (more brittle) which is bad. In crude terms, it gains strength at the expense of toughness, once it is stretched or bent.

Mild steel does this to a much reduced degree, which is why it is generally OK to straighten a mild steel anchor shank and carry on using it. You might even get away with doing this twice, if it's not severely bent.

Mild steel is a very tough material indeed from the start, in the precise engineering sense of the word "tough". In crude terms, toughness measures the amount of energy a material can absorb after yielding and before breaking.

It's particularly relevant in the case under discussion, where the shank, by bending, realigns with the load and reduces the bending stresses considerably.

This doesn't make a mild steel shank better, or worse, than an HT shank. It makes it different.

And it makes it a Good Thing, to my way of thinking, that more people do not follow JonJo's suggestion and use smaller, NewGen anchors.

It seems to me that might not be a winning strategy in a small subset of possible scenarios, which might involve the anchor shank being permanently bent one way, then the other.