Re: what is the strenght-weight ratio of titanum compared to other steels e.t.c

Strength to weight ratios generally refer to the tensile strength of a 
material divided by the density of the material.  This strength divided by 
density is called "specific strength."  Along the same line, thermal 
conductivity of a material divided by density is called "specific thermal 
conductivity."

Specific strength of a material can be used to determine whether one 
material is better than another in a weight sensitive application.  Since 
you are in engineering, you would like some numbers.  Also, you won't mind 
converting from english units to SI units (a lot of information in the 
literature is still in english units.)

So lets consider a few examples of specific strength.
Example 1.  Structural steel has a strength of about 20,000 pounds per 
square inch (psi) and a density of about 0.25 pounds per cubic inch.  When 
you divide 20,000 by 0.25, you get 80,000 with the units being inches.  In 
this case, bigger numbers are better or higher specific strength.
Example 2.  Aircraft aluminum with a strength of 70,000 psi and a density 
of 0.1 pounds per cubic inch.  70,000 divided by 0.1 is 700,000 inches.  
Therefore, aircraft aluminum has a much higher specific strength than 
structural steel.  So building an airplane out of aluminum is better than 
building it out of structural steel.
Example 3.  Steel piano wire has a strength of about 450,000, with a 
density again of about 0.25 pounds per cubic inch.  450,000 divided by 0.25 
is 1,800,000 inches.  So piano wire is quite a bit better than aluminum, 
but it is tough making airplane wings out of those little wires.
Example 4.  Graphite fiber comes in a wide range of strengths (just like 
steel).  Lets use a high strength variety with a tensile strength of about 
700,000 psi and a density of 0.073 pounds per cubic inch.  Specific 
strength: about 9,600,000.  So, rather than spending time trying to figure 
out how to make airplane wings out of steel wires, why not spend your time 
and effort figuring out how to make wings out of these little, fine 
graphite fibers.

With respect to titanium, titanium is available in several levels of 
strength, like steel.  It has half the density of steel, however.  
Therefore, titanium as a general rule has about twice the specific strength 
of steel.  And of course, there are many issues which determine which 
material to use besides specific strength.  Temperature resistance, 
stiffness and cost are usually as important as strength, depending upon the 
application.

So, good question, and good luck in your engineering efforts.