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Old 02-14-2001, 07:46 PM   #1
Faraz
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Question Titanium Strut Tower bars $300?

We at TRi are thinking about making Titanium Front and Rear Strut Tower bars. These will be the step up from our aluminum front and rear strut tower bars (the rear bar, and contest winner will be released on Saturday).
The only hold up is the cost: about $300. Is there any interest in Titanium Strut Tower Bars at that price? If we get about 10-20 people saying that they would think about or definitely buy Strut Tower bars at that price then we will make them. Thanks for all your help!

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Old 02-14-2001, 08:01 PM   #2
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What's the advantage over a regular bar? The price doesn't bother me so much, as it seems like I'd be just throwing away the extra money to have something that sounds cool.
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Old 02-14-2001, 08:21 PM   #3
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What would the wieght difference conpared to the carbon fiber and which is stronger? Also would this work for a WRX?
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Old 02-14-2001, 08:33 PM   #4
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I don't think titanium would be a good material to make a strut bar out of. Yes its light weight and strong, but its also very flexible. I'd think you'd want a strut bar to be as stiff as possible. Aluminum is nice because its also light weight, and very stiff.
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Old 02-14-2001, 08:37 PM   #5
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yeah the price doesnt bother me... just whether or not it will perform as good or better than the current products available. a little more info will be helpful.
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Old 02-14-2001, 08:49 PM   #6
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I'd be all over Ti parts. The only thing is many Aftermarket makers make strut tower bars. I'd be happier if you'd make a different part out of titanium, like a adjustable suspension arm, etc...
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Old 02-15-2001, 06:31 AM   #7
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Titanium is a fair amount heavier and a fair amount stiffer than aluminum.

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Old 02-15-2001, 06:47 AM   #8
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Titanium is actually not stiffer than aluminum. It does tend to flex, which is not a bad thing necessarily, just depends on your application. The advantage of titanium is that it has incredible fatigue resistance, where aluminum has little fatigue resistance. However, aluminum is very stiff, so if it doesn't flex, the low fatigue strength is a non-factor. I don't feel that a titanium strut tower brace would give you any advantage over aluminum, and in fact, might be worse.
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Old 02-15-2001, 06:49 AM   #9
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I'm no metallurgist, but I've heard that titanium is a nightmare to shape or machine. Does TRi tuning have this manufacturing capability in-house?
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Old 02-15-2001, 07:00 AM   #10
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Harrydog - By what measure is aluminum stiffer than titanium?

Jon - You're correct about it being a nightmare but it doesn't necessarily take any specialized equipment, just expertise and training. From what the machinists tell me titanium tends to "smear" when you try to cut it instead of forming a clean chip.

mbs



[This message has been edited by micah (edited February 15, 2001).]
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Old 02-15-2001, 09:47 AM   #11
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I used to have a lot of mettalurgical info when I was heavy into biking. Aluminum has pretty crappy elongation numbers (its brittle) and pretty crappy fatigue resistance. It has a very low density, lighter than titanium, although to make it strong you need to use much more material.

Titanium has similar eleongation, tensile stregnth and fatihue limits as steel. It eats machine tools and welds must be very clean (no oxy contamination).

Steel is much maligned but probrably still is the most useful structural material. Its elongation, tensile stregnth and fatigues resistance blow aluminum away. The main drawbacks are its weight and the fact that it corrodes.

Heat treating does not change a materials basic properties but rather pushes them around a bit to offer a better compromise for a specific situation. Ie you can make it harder, but now it is more brittle.

BTW, strut tower bars on a road car, hold your front end geometry in corners through tension, not compression. It is only under bumpy conditions that the bar has to resist compression and twisting.

FWIW, I have gotten rid of my Aluminum bikes (Cannondales) in favor of Steel (Colnago, Cinelli & Basso road bikes and a Kona Hardtail mountain bike) They ride sooo much better (and they can be repaired).

If I were buying a strut tower bar (i'm not) my materials choice would be 1. Steel, 2. Ti (too expensive) 3. Aluminum (junk metal, but will probrably last 7-10 years, 4. CF (I don't trust glued joints)

I am not an engineer, just really into this stuff.
That's way more than .02
Tim
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Old 02-15-2001, 10:02 AM   #12
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Boxerman - informative post. Good point about steel. Two things most people don't know:

a) Steel is the stiffest, strongest structural metal we know of. The only thing we have stronger is on a very tiny scale, like carbon nanotubes that are on the order of 1,000 times stronger than steel.

b) The more times you bend a metal the weaker it gets (fatigue). Some metals have a limit to this (endurance limit), ie the weakening effect drops off and the thing pretty much stops fatiguing. Steel has an endurance limit. Aluminum _does not_. So the next time you're in an airplane, watch the [aluminum] wings flexing up and down ever so slightly... if they keep flexing eventually those suckers are gonna snap! (That's why the plane is inspected so carefully, and they will take it out of service before the wings ever break off. Don't worry.).

cheers
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Old 02-15-2001, 10:27 AM   #13
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The choice of material is important..

But also is the design. Without seeing one..and getting some results (testing), I wouldnt throw 300 bucks at something.

Have you got a prototype ?

J.
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Old 02-15-2001, 10:31 AM   #14
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Actually Aluminum does stress harden. I just got done doing a lab with 6061-T6 aluminum this past Tues. As long as you don't go past a materials yeild stress point, it will return back to it's original condition and strength (within a percentage). It's when you start going over the yield stress point that elongation occurs and plastic deformation starts. Slight bending will harden a material, thus making it more brittle and easier to break. When you take a paperclip and bend the curved parts a bunch, you stress harden it, thus making it brittle and easier to break.

Stiffness and strength are to be taken under the condition the part is used too. Cast iron is extremely stong when under compression and has a really high yeild stress. Once there though, VERY little extra force can ba applied before the UTS is reached and the part will explode.

So--I think the reason we see AL used in strut tower bars is that it is relatively cheap, lightweight, and will not corrode. I would be upset if the bars I put in rusted in a few weeks. So despite giving up some strength, AL is a good compromise of the properties we need.
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Old 02-15-2001, 10:59 AM   #15
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>>within a percentage<<

Yah, but it's that <1% that becomes pretty important when you flex it back and forth a couple hundred thousand times!

Agreed though, I don't think fatigue is a huge issue with strut tower bars, that's more of a theoretical conversation in this context.

cheers
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Old 02-15-2001, 11:24 AM   #16
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Titanium is an interesting metal, and often overrated and misunderstood. Pure Ti is actually reactive, and at room temperature reacts with O2 in the air to form an TiO2 coating on the surface which is great for corrosion resistance. However, it must be alloyed to be a real high-strength material.

What is most beneficial to Ti Alloys is the strength-weight ratio, hence the use as connecting rods in mega buck high-hp cars.

A general Ti alloy has the following properties:
Tensile strength: 110-130 ksi
Modulus of elasticity 15,000-17,000 ksi.
Specific weight: 280 lb/ft3.

Compare this with Aluminum alloys (e.g. 6061-T6
Tensile strength: 40-60 ksi
Modulus of elasticity: 10,000 ksi.
Specific Weight: 170 lb/ft3

Compared with Steel alloys:
Tensile Strength: 40-100 ksi
Modulus of elasticity: 28,000-30,000 ksi
Specific Weight: 490 lb/ft3

Hopefully this helps explain the differences. Steel is by far the strongest material, but it is also the heaviest. Ti is relatively strong in comparison, and weighs about half as much. Al is less than 1/2 the weight, but is much weaker.

Ovearll, I'd say a Ti alloy bar would be great, but they are quite costly, and I doubt these bars ever see stresses beyond the Aluminum range, so it would be way overkill. It would have a certain cool factor though.

Dave
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Old 02-15-2001, 11:57 AM   #17
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It would be very tempting to me, just because of the "cool" factor.

In the end it would still depend on comparing it with another Al and CF bar to see what kind of difference it can make.

Philip


[Edit: decided to cancel out my thoughts on the debate, since I skipped my materials class a lot]

[This message has been edited by Philip (edited February 15, 2001).]
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Old 02-15-2001, 01:07 PM   #18
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I know Carbon Fiber isn't a metal...but where would a CF strut bar fit into this group?
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Old 02-15-2001, 01:41 PM   #19
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By working the tubes and playing with diameters and wall thickness you can engineer all the stiffness you could ever want into a strut bar. I don't recall the math but bending stiffness squares as radius doubles or something like that. If you want more stiffness you make the tubes diameter bigger. Better engineering will alter the shape of the tube to orient stiffness and compliance in directions that are best suited to the application.

People think Al is stiff (bicycles) because bike makers use incredibly over sized tubes on AL bikes. Given tubes of equal diameter and wall thickness, I believe Ti and Steel are both stiffer than aluminum.

CF itself is very strong in tension (I think stronger than the above metals). CF is nothing but speghetti strands of carbon suspendended in an matrix of resin. Like rope, if you pull on CF, it is very strong but if you push on it you are testing the stregnth of the resin and not the actual carbon fibers (CF isn't very strong in compression). Also most CF applications glue to CF tubes to aluminum joints with aerospace epoxies. These epoxies can be effected by heat and chemicals. Lastly if CF and an aluminum joint come in contact with each other, an electrical reaction will occur that will corrode the aluminum joint leading to failure.

You might also be surprised how little weight is saved going from steel to aluminum, since steel requires less material for the desired stregnth and stiffness.

Tim
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Old 02-15-2001, 01:56 PM   #20
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Micah, what are you talking about. I know from experience that aluminium is stiffer than titanium. Titatium will flex and absorb shock. Aluminum won't and if it does it will break. That won't be a problem with a strut bar though, because the forces will never be to much. You won't get any more performance from a Ti bar(and maybe worse). All you'll be doing is paying double the price for the ability to say you have a ti bar.
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Old 02-15-2001, 03:58 PM   #21
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Eby - No disrespect intended but perhaps the titanium part you experienced was built more flimsy than the aluminum part. Indeed if you wanted the titanium part to be just as light as the aluminum, you would have to use less metal, because titanium is much denser.

However. The way metal stiffness is measured is modulus of elasticity. What this number (E) measures is, when I put a certain stress on a metal, how much does it bend. And this number is higher for titanium (see Catfish's post. Also www.matls.com). The overall amount the metal can take before is fails is the tensile strength, and this is also higher for Ti.

I agree on your main point; a Ti bar would be a little tiny bit of "r|ce" in this application, considering the cost (though still really cool). However titanium really is stiffer.

cheers
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Old 02-15-2001, 04:30 PM   #22
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I'm glad at least one person agrees with the known properties of materials as explained several times in this post. Another website besides the one Micah mentioned is www.matweb.com, if you care to disagree with known values further.

As far as CF (or FRP Fiber Reinforced Plastics) properties are concerned, they are comparable in regards to strength and their modulus to steel at ~1/5 of the weight IN THE FIBER DIRECTION ONLY. The reason all CF parts look like a checkerboard is because they are trying to give strength in both the "X" and "Y" direction to make the material more suitable.

Just to compare these properties to some known metals, look below: These are just generic numbers, but they give you a general idea. Different alloys and type and weave of CF can alter these properties somewhat.

FRP Carbon Fiber
Specific Gravity: 1.55
Tensile Strength: 220,000 lb/in2
Elastic Modulus: 20 x 10^6 lb/in2

Alloy Steel
Specific Gravity: 7.87
Tensile Strength: 500,000 lb/in2
Elastic Modulus: 30 x 10^6 lb/in2

Alloy Aluminum
Specific Gravity: 2.70
Tensile Strength: 60,000 lb/in2
Elastic Modulus: 10 x 10^6 lb/in2

Some terms....
Specific Gravity - The density of a material expressed relative to the density of water. It is a ratio, and therefore unitless.

Tensile Strength - The ability of a material to stretch without breaking. The number listed is the Ultimate Yield Strength at which the material failed.

Modulus of Elasticity - A measure of the inherent STIFFNESS of a material. Higher values indicate a STIFFER material. The higher number means the material can RESIST deformation with higher loads being applied to it.

So, with all the above information, we can conclude that these materials are stiff in ascending (weakest to strongest) order below:

Al (alloy) - 10 x 10^6 lb/in2
Ti (alloy) - 17 x 10^6 lb/in2
CF (FRP) - 20 x 10^6 lb/in2
Steel (alloy) - 30 x 10^6 lb/in2

This means that a Ti bar will be stiffer than a Al bar, if the amount of material weighed the same, but you could also make a Ti bar just as strong as an Al bar while using approximately 1/2 the material due to it's almost 2X stronger modulus properties.

And Eby, I think you're confusing the ability of a material to resist deformation with ultimate strength. The reason the Ti flexes and absorbs shock is BECAUSE of it's high modulus of elasticity. The reason the Aluminum fails is because it cannot endure that kind of load because it's modulus is nearly 1/2 that of Ti.

Hope that clears it all up.

Dave

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Old 02-15-2001, 04:53 PM   #23
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Well actually I'm just comparing how an object made of titanium would compare to an object made of aluminum. In equal amounts I agree that the titanium would be stiffer, but two objects made of different materials(if done correctly) wouldn't contain the same amount of material. There would be more aluminum than titanium, thus it would be stiffer. My experience comes from mountain bikes. Aluminum is know for its harsh ride qualities, while steel and titanium are much smoother because they flex and absorb schock more. So I guess a strut bar made of titanium could be stiffer, but it would have to be much heavier.
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Old 02-15-2001, 04:54 PM   #24
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Titanium is 43% less dense than steel, but just as strong. The fun part of it is that it must be welded in a pure argon environment or oxygen will work its way into the weld and weaken it. They can also make springs out of titanium. The ZO6's muffler is made of Titanium.
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Old 02-15-2001, 05:47 PM   #25
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An aluminum mountain bike must be made very stiff, otherwise it would not last very long. Steel and titanium both can be designed to flex and if kept within their limits, can do so almost indefinitely (titanium has even greater fatigue resistance than steel). In a bike, some flexing is a good thing. In a strut tower brace, flexing is a bad thing. So, whether the strut tower brace is made from aluminum, steel or titanium, it would need to be designed to be stiff. Stiff is stiff. You wouldn't be gaining anything by going with titanium but you'd be paying alot more for it. Really, the very best design for a strut tower brace is probably one with a 3 point attachment (you know, triangulation and all that).
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