Dangerous designs?

http://www.unb.ca/web/P&P_Centre/engcomp/engcomp.htm
http://www.key-to-metals.com/Article20.htm
http://www.ul.ie/~mst/jeremy/abstract/elements_ac.html

Here are 3 informative short articles I found on the subject, and after reading some about Ti mr. D'Artois may have a point about Ti, but his attitude is a bit irritating to me, maybe the rest of you here have learned to tolerate him.

 

Don't worry, it happens with a lot of people all the time.
We are joined here with a lot of cultures from all around the world and come along just fine. Quite amazing if you look to the evening news
Sometimes you have to look a little closer than skin deep.

 

So on your figures (yes, there is probably a stronger grade of ti alloy) carbon is 4 times stronger and nearly 5 times stiffer. If you compare carbon sandwich to single skin titanium that difference will multiply a few times. With composites you can varry thickness and direction indeffinetely further increasing its advantage.

To build a Volvo 70 the same pannel weight you will have to build it with 1.6 mm titanium skins, not allowing for stringers. Titanium sounds great for cruising yachts, safe and durable, don't see it comming for racing yacht as yet.

 

None of the articles have good figures about alloys of Ti, and the more commercial its use might be come the more money will be thrown into research and more alloys developed for specific uses. Aluminum is crap by itself, but some of the Al alloys out there are hard to beat on cost and specific properties, even by composites.
There is also casting and forging of parts that most composites suffer. Look at F1 racers and see where chasis and suspension pieces end there is a bonded metal piece that joins it with the next part.
What a composite can do in a sandwich to simulate the principle of an I beam, metal alloys can do with the use of honeycombs. How do you fabricate something like this to employ it in a boat?
Cost cost cost! There are great things one can do with unlimited funding for materials, fabrication, and most of all design!
What if the cost of composite boats was to go sky high all of a sudden.
How? They have a short lived life, as mr. D'Artois says, and are not reasonably recyclable. What do we do with millions of hulls made of GRP when they turn to crap? It becomes an environmental issue and we only use so much of polyester putty! Metals can be recycled!

 

The problems with titanium generally are enclosed in its limited availability, its costprice and the toughnes of the metal in the forming and machining process.

Welding is no issue, any professional welder that can weld stainless steel perfectly can also weld titanium.

The present main supply sources for the military type of titanium alloys are Russia and China. Russia, back in the early '90's had such large surplusses of Titanium that prices sank to DM 17,50 per kg in sheet and profile. Thousands of tons have been disposed of meanwhile just like their strategic stocks of aluminium and copper, but that is history now.

The two main alloys, Ti-6Al-4V (IMI318) and Ti-5Mo-5V-2,5Al are commonly used in the process-aerospace industry and for specila applications.

Both are alpha-beta alloys.

Some properties of Ti-6Al-4V are: (AMS 4928F)

Ultimate strength (psi): 160000
Yield strength: 145000
Charpy V-notch impact @ Room temp (ft-lbs) 10500
Viscosity of breaking MPa mm 1/2 : 1160-1420
Shearing strength (psi): 93600
Density (lbs/cu in) : 0.16
Melting point (F) 3200

It is not the most ideal type for sheets, Ti-5Mo-5V has better specs/properties is quite more elastic and is over the whole range superior;

The thermal conductivity of these two titanium alloys is low: 3.73 Stu sq.ft./F/ft

During the testprocesses with several alloys, we learned that it is possible to weld AlMg4,5 direct to Ti-6Al-4V and that testing the strength of the weld, the aluminium broke off after the weld, not at the weldseam.

Forming without pre-heating is very difficult. A 100 tns press could just bend a 3mm sheet: the form memory is incredible. If not preheated small cracks on the surface will occur. At proper preheating by way of electrical oven, surface cracking will not happen.

As to corrosion: The corrosion resistance is second to none: 1/1000mm in 1250 years in polluted seawater;

There are several surface treatments possible : electrolytic polishing and diamond coating under absolute vacuum to give it the highest form of abrasion resistance are the most common. Electrolytic polishing will give a surface that is similar to high polished stainless steel; with the only diffrenec that this look will remain while stainless steel will dull and if not repolished regularly it will rust in a seawater environment.

The reason for the high costs of Titanium is not the natural availability but the very high volumes of electricity required in the manufacturing process.
Just like aluminium but in a tenfold.

It was the only building material available for the construction of the A12 and the SR-71 (thanks for the correction usa2) because of the high temperatures that occur at flying at high mach numbers. Aluminium will melt and could therfore not be used.

As to weight: The panelweight of a Titanium panel will be around 13,5 kgs per sq. meter (w/o reinforcements) A bare hull with reinforcements for a VOR 70
would have an estimated weight of 7000 kgs.

 

http://www.boatdesign.net/forums/showthread.php?p=73253

Here, we can take this discussion about Ti to an other thread in MATERIALS where it might be more appropriate and leave the poor canting keel people alone

 

Went there!