[bigfngun]

What is the difference in tensile strength between titanium and the various HY metals like HY-80/100/130.
I know for example HY100 means a steel that can withstand 100,000 pounds per square inch.

[ABNredleg]

bigfngun, on Sat 21 Jun 2008 2026, said:

What is the difference in tensile strength between titanium and the various HY metals like HY-80/100/130.
I know for example HY100 means a steel that can withstand 100,000 pounds per square inch.

Sierra class used alloy 48-OT3V, which had a yield strength of 6,000 kg/cm2. (I've had several glasses of wine this evening so someone else will have to do the conversion. :P)

[DesertFox]

ABNredleg, on Sat 21 Jun 2008 2100, said:

Sierra class used alloy 48-OT3V, which had a yield strength of 6,000 kg/cm2. (I've had several glasses of wine this evening so someone else will have to do the conversion. :P)

6000 kilogram/centimeter² = 85340.05984 pound/inch²

[bigfngun]

DesertFox, on Sat 21 Jun 2008 2106, said:

6000 kilogram/centimeter² = 85340.05984 pound/inch²

That's about what I came up with (BTW I also just got a copy of Cold War Submarines)So wouldn't HY100/130 be better?

[ABNredleg]

bigfngun, on Sat 21 Jun 2008 2127, said:

That's about what I came up with (BTW I also just got a copy of Cold War Submarines)So wouldn't HY100/130 be better?

Crush strength is only one factor in selecting hull materials. Titanium has lower weight, so a titanium hull of the same displacement as a steel hull will have a greater crush depth (assuming the tensile strength is the same). Titanium is also non-magnetic, which lowers the subs signature, and resistant to corrosion, which lowers maintenance costs. On the other hand, it can be difficult to weld, although the Soviets got pretty good at it.

This post has been edited by ABNredleg: 21 June 2008 - 2110 PM

[bigfngun]

ABNredleg, on Sat 21 Jun 2008 2150, said:

Crush strength is only one factor in selecting hull materials. Titanium has lower weight, so a titanium hull of the same displacement as a steel hull will have a greater crush depth (assuming the tensile strength is the same). Titanium is also non-magnetic, which lowers the subs signature, and resistant to corrosion, which lowers maintenance costs. On the other hand, it can be difficult to wield, although the Soviets got pretty good at it.

So, let me get this straight. A hull of titianium of the same displacement as say Hy-100 will have the same crush strength? According to the other post it has a tensile strength of ~80kpsi about the same as HY80 so why the greater diving depth?

[DesertFox]

My understanding is that steel is more flexible that titanium and has advantages of flexing instead of of breaking. The F-14 had a part made out of titanium in the prototype which broke which was later made from stainless for this reason.

[JOE BRENNAN]

To restate post 4 with numerical example, weight is the big difference. Titanium is roughly 60% (depending what exactly is being compared) as dense as steel. I've seen a bit higher quotes for strength of the 'Sierra' alloy on Russian websites, ~100ksi yield (70-72kg/mm^2): anyway 85-100ksi titanium is roughly equivalent to 140-170ksi steel of the same weight.

In an application like a deep diving sub there's a big knock-on effect to the design of using more weight of material to achieve the same strength. Say the Ti and steel are both 100ksi. The hull of a steel sub the same size and strength has to be much heavier, but then it doesn't have the same reserve buoyancy so has to be made bigger, which makes it weigh still more, in a negative design spiral the result of which is an otherwise balanced design of combat sub made using 100ksi steel just can't achieve nearly the same design depth as one made using titanium.

On 'flexbility', titanium has a lower modulus of elasticity than steel, about 1/2. So again if the two design strengths were the same the members of the Ti structure would be around the same size (ie volume), but weigh a lot less and the whole structure would flex around twice as much under a given load. The latter is no advantage, but it's apparently acceptable for other design purposes in a submarine pressure hull. In some structural applications though stiffness is critical, eg. the machinery foundations in a ship aren't even of high strength steel, there's no point, the critical requirement is the structure deflect as little as possible under a give load (which is what stiffness is), not how much load it can take before permanently deforming (or coming within some specificed distance of such a condition, which is what strength is).

Joe

[Jason L]

Quote

My understanding is that steel is more flexible that titanium and has advantages of flexing instead of of breaking.

Depends dramatically on the exact structural alloy used.

Quote

On 'flexbility', titanium has a lower modulus of elasticity than steel, about 1/2. So again if the two design strengths were the same the members of the Ti structure would be around the same size (ie volume), but weigh a lot less and the whole structure would flex around twice as much under a given load.

Elastic modulus does not equate directly with stiffness - its linearly related but the actual structure (ie the exact geometry of the cross sections, etc) are equally important. Its possible you end up with a structure that is as stiff AND as strong by changing materials.

[JOE BRENNAN]

Jason L, on Sun 22 Jun 2008 0419, said:

Elastic modulus does not equate directly with stiffness - its linearly related but the actual structure (ie the exact geometry of the cross sections, etc) are equally important. Its possible you end up with a structure that is as stiff AND as strong by changing materials.

In the example I gave (on purpose) the strength of the two materials is assumed equal, which is realistic in case of Hy-100 v the higher quotes of strength of Sierra class Ti alloy. Hence the structural members would be the same size, and structural stiffness would directly equate to modulus of elasticity. You're perhaps thinking of aluminum v steel structures where the aluminum being both less much less dense and less strong must have more area, and that area can be deployed in larger cross sections, so the overall stiffness of the steel structure, in for example bending, isn't necessarily as much greater than the Al one as the modulus of elasticity is. However even in steel v AL stiffness is still directly related to MoE in case of pure tension or compression. You're bringing up a point which is correct where it applies, but doesn't apply to the example I gave.

Joe

This post has been edited by JOE BRENNAN: 22 June 2008 - 1038 AM

[Jason L]

Well assuming the members are the same size, then yes the stiffness would be almost exactly half. Even for the axial compression/tension though its linearly related to the product of crossectional area and modulus of elasticity.

[Gunguy]

Anyne know who makes the HY 130 steel? Is there a website on it? Also, anyone know the comparison of HY130 to armored plate steel as used on our latest armor packages for our vehicles etc?

This post has been edited by Gunguy: 23 June 2008 - 0947 AM