Problem with water jet being material usage, with an oddly shaped object like a shepherd's hook stake, you'd have a difficult time nesting a bunch of these together closely, unless you change the geometry of the stake. Even with good nesting, you'd lose a fair bit of material, which (material cost) was one of your primary "pros" listed for this.

very true.

"You're not taking into account the moduli of the materials, which really makes a large difference in a calculation such as this, if I'm thinking about it correctly."

titanium has a higher modulus than aluminum, so given the same size beam, an aluminum one will bend more than a titanium one under the same load

however, aluminum is lighter than titanium. so, in theory your beam can be made of thicker aluminum. this added thickness will make it bend less under the load and it will be on par with the titanium beam from the first example.

so you have a modulus vs. density comparison for some given beam shape. funny enough, steel, titanium, aluminum, and magnesium are all kind of equal to one another in that comparison.

the trick to the above scenario comes down to volume. a magnesium beam that supports a given weight while only bending a certain amount is significantly larger than a steel beam that weighs the same and bends the same under the load.

here is where carbon fiber is a winner. it has a high modulus and a low density compared to those metals.

of course we are talking about tent stakes here where modulus isn't really important due to the application. the stakes are being axially loaded when driven in. strength of the material will be more critical. strength can be increased for a given material by certain treatments and alloys. 7075 is very strong aluminum. still bends as easily as the other aluminums out there but it takes more force to deform it permanently. titanium is even stronger than that. titanium is harder too so given the same shape the titanium will hold it's point better.

but here come the old weight thing again. more aluminum could be used to change the shape to make it more resistive to deforming

now I'm just babbling on... but usually innmy line of work it comes down to more than just a couple parameters to determine the optimal material for a given application

one thing that titanium has over other materials is that it is very resistive to corrosion and it maintains it's strength better at higher temperatures. neither of these usually comes into play in the backpacking community soni kind of think of it as a gimmicky marketing material in most outdoor sport applications

Lawson

I'm not saying you cant bend it, I'm saying without doing it properly(raw-to-aged), it will fail at the bend at some point. The initial bend will create a "craze" mark/s on/just below the surface. The craze mark will grow with each load cycle, with the craze growing into cresent moon shaped "beach marks", that slowly penetrate into the shaft until it breaks. The break will be spiral/semi spiral, or beach mark through the shaft 90 to the axis, this is text book. Aerospace gear and control boxes utilize allot of 7000 series aluminum because of its strength. While bicycle frames for example tend to be 6000 series or other aluminum alloys because they handle load cycling better than 7000 series aluminum. I have built quite a few of both. The stakes could have some potential, but like was mentioned earlier, go with a nail type head, or go with a reduced diameter, just below the drive end, with a cord attachment.

> Look at carbon fiber. On paper it would make a seriously awesome tent stake until you drive it in hard soil and it shatters.

They apparently don't shatter

Dustin Snyder was also making these but he's removed all his posts until later - perhaps so people don't take his ideas?

Hi Josh,

I am not sure I agree with you. Grade 5 titanium has a higher bend radius then 7075-T6 aluminum.

Lawson:

Your strength comparison calculations are not using the right engineering criteria for design. Your engineer friend is using axial stress as the criteria, but you must also perform a buckling analysis, which is the failure mode that a tent stake is most likely to experience (it will bend long before it will break). In buckling, the elastic modulus is a critical factor. I've performed a buckling analysis using the diameters you've given, and the aluminum stake can resist a buckling force (like from a hammer pounding on it) 53% higher than the titanium stake. Also, as another person mentioned, the weight difference is marginal for the two designs (less than 1%).

That being said, my personal preference is for Ti stakes because they withstand the impact of hammer blows better. Aluminum stakes get all distorted where they are hammered, and this can lead to the top of the stake breaking off while hammering due to a phenomenon known as stress concentration.

I'd be happy to email you a pdf of my buckling analysis if you'd like. If so, PM me.

Regards,
Scott

it is tent stakes were talking about here ???

7075-T6 i believe is used in climbing equipment ... and i dont believe any of the forces use for staking even nasty heavy weight vampires would ever exceed that for climbing ...

IMO its all academic, itll all be plenty strong for staking purposes

I tested the CF stakes I had made, for initial strength by driving them into a hard gravel driveway along with a easton stake, and a ground hog. At the point the aluminum stakes started to bend, the carbon fiber stakes were still fine. I did this in several locations. I personally, feel that if the stake will perform to where a high quality aluminum stake will deform that is sufficient. I'm sure you could shatter it at some point if you really wanted to, but this point would be above the point where other high quality stakes would have already deformed. For the record, The Vargo ti stakes will deform about the same, a steel nail stake will deform at some point as well, as will a durapeg (not a popular stake around here).

"7075-T6 i believe is used in climbing equipment ... and i dont believe any of the forces use for staking even nasty heavy weight vampires would ever exceed that for climbing ..."

this isn't really saying much, because force by itself is meaningless. It's stress that matters and when critical stresses of a given material are exceeded. this is the combined result of force, shape, and material properties.

I could support the weight of a building on a pad of paper. so given your example, paper is capable of supporting loads much higher than what a tent stake will see. but how well is that paper tent stake going to hold up.

people use aluminum all the time ... i cant really see stakes pulling being more "forceful" than taking a lead fall on a biner or small alum chock

now someone said whacking a stake n hard gravel with a rock can bend it (alum and titanium) ... absolutely ... but then i suggest that if the ground is that hard and you find big enough rocks to whack it, you anchor with the rocks instead ... unless yr carrying a hammer anyways =P

i would say that a lot of these fancy materials save a marginal amount of weight ... and while it is theoretically stronger, the reality is that it wont be enough to make all that much of a difference

but we do get to use those fancy words that sound so cool, and i feel so much better paying those exclusive prices ;)

hmmmmm

MSR ground hogs are usually around 2.00 a piece.I wouldn't consider those exclusive. Most of the stakes, except ti nails etc are in the same ballpark. Not sure where stakes get exclusive prices , unless you usually use plastic walmart stakes.

ground hogs are alum ...

http://www.rei.com/category/4500663

the prices for alum are quite a bit cheaper than those fancy titanium ones ... which i believe was the point of this thread ;)

Hi Scott,

Thanks for running a buckling analysis on this.. I will say though, I am a bit confused. It appears like you said the aluminum has 53% more buckling resistance then the titanium, but the titanium handles buckling stress better due to its resistance to stress concentration. So besides stress concentration would the aluminum stakes actually be stronger or do a better job of resisting buckling like I first proposed? If so this is great news.. According to my calculations a 7" long .156" diameter 7075-T6 Aluminum hook stake would weight 6.76 grams while a 7" long .125" diameter 6-4 Titanium hook stake would weigh 7.23 grams. That's a 7% weight reduction for something thats stronger, weighs less and costs half as much.

Thanks again,
Lawson

Edited by Mountainfitter on 06/24/2011 13:53:57 MDT.

Lawson

You dont have to agree with me, I can tell you exactly where it will fail, no numbers, no computers. I'm just saying, I'd avoid putting a hook in them. Years ago when I built aluminum bike frames, I used to bet our "engineer" where the frames would fail, I always won. Got any money?

Kevin

Those carbon stakes are brilliant!

"I am a bit confused. It appears like you said the aluminum has 53% more buckling resistance then the titanium, but the titanium handles buckling stress better due to its resistance to stress concentration. So besides stress concentration would the aluminum stakes actually be stronger or do a better job of resisting buckling like I first proposed?"

The buckling and the stress concentration are two different issues. The aluminum will not buckle until a load is applied that is 53% higher than the load at which the titanium will buckle. So, yes, the aluminum is significantly stronger when it comes to buckling. The stress concentration applies when looking at the hook end of the stake. When you hammer aluminum, it deforms more than titanium due to the ductility. As most UL backpackers use rocks to hammer their stakes, the deformation is very jagged. These jagged marks concentrate stress in the material. In other words, it is possible for the hook to snap off due to the stress concentration in these jagged marks. So, in this respect, the titanium is more durable.

"According to my calculations a 7" long .156" diameter 7075-T6 Aluminum hook stake would weight 6.76 grams while a 7" long .125" diameter 6-4 Titanium hook stake would weigh 7.23 grams. That's a 7% weight reduction for something thats stronger, weighs less and costs half as much. "

I get 6.20g for the aluminum and 6.24g for the titanium - virtually no difference. That's based on diameters of 1.56 in for aluminum and 1.25 for titanium and densities of .102 lb/cu. in. for aluminum and .160 lb/cu. in. for titanium.

Regards,
Scott

The carbon ones look a lot like yours don't they ?

Fact is though, they work. Look, in a WFR class I took the instructor said, all bleeding stops ..eventually, well all stakes break at some point , eventually. May as well go with the lightest, best holding ones you can and know there will be some attrition.



FWIW, I was originally trying to work out some other stakes with Lawson, but alas , they fell through.

Kevin

Thanks for the reply Scott. The hook part takes an extra inch of rod. So they are actually 8" long before bending. I probably entered the density of the aluminum wrong and is the reason I keep getting 7% but either way the aluminum is lighter (1%) and stronger (53%) so this is good news. Maybe instead of a replacement, the aluminum stakes can be a cheaper alternative to the titanium ones. Now the tricky part is finding the stuff... Thanks again :)

Yes, putting a hook into the end of the wire will either crack the wire or severely weaken it, and that applies to most any metal and most any alloy (copper, Nitinol, etc excepted).

Also, a hook at the top end makes the stake bend when being hammered into the soil. The load tends to hit off-axis. This can lead to buckling and failure.

So why use a hook AT ALL?

Why not press-fit a small Aluminium cap onto the main wire stake instead. You can hand-press on or hammer on the larger area, it will hold the guy rope onto the stake well enough, and you can use it to extract the stake as well. Being totally straight there is neither weakening due to bending, nor buckling when hammering (gently).

Hum ... must make up a few myself and test the idea.

Cheers