Quote:
Originally Posted by olddog
specific gravity listed in engineering toolbox is
aluminum 2.7
steel ----- 7.8
titanium 4.5
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Although I did not mention steel, your point and data appear to be the same as I had indicated — and I agree with both.
Quote:
Originally Posted by olddog
Tensile Modulus - Young's Modulus or Modulus of Elasticity - is a measure of stiffness of an elastic material. It is used to describe the elastic properties of objects like wires, rods or columns when they are stretched or compressed.
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Although I did not address this attribute your representation is again correct.
Quote:
Originally Posted by olddog
Yield strength (you have bent it past the point it will spring back to it original shape).
aluminum 95
steel ----- 345
titanium 730
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The explanation is correct but the actual numbers are alloy dependent and the high strength super steels vastly outperform the best aluminum and or titanium alloys.
Quote:
Originally Posted by olddog
So we have been loose with terms. Aluminum is not stronger than steel. Steel is stronger, but much heavier. When both materials are made to the same strength level, aluminum is lighter but must be bigger to achieve that. So pound for pound aluminum is stronger than steel. Now fuzzily, I remember, something about, even though two beams , one aluminum the other steel, is at the same yield strength, the aluminum beam will flex more at a given load than the steel beam. I believe the engineer told me that if deflection is the critical factor steel is better.
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This engineer may have been related to the engineers that determined factually and absolutely that 160 mph was the highest speed attainable by wheel driven vehicles in a quarter mile.
When we play fast and loose with this type of information it is possible to send the uninitiated or uninformed down a painful and potentially destructive path. It is not fair to them. They have a right to know the facts and if they choose poorly then, they are big boys and that is their choice.
Connecting rod beam deflection is the #1 connecting rod issue in supercharged alcohol and/or nitromethane fueled engines. A deflection in any given power cycle is followed by mechanical failure in the next. The resistance to beam deflection because of the beam section / girth of the forged aluminum rod is what makes it the universal choice for these high powered large displacement methanol and nitro fueled engines.
Quote:
Originally Posted by olddog
Titanium is stronger than steel (about twice) and half the weight. It is twice as heavy as aluminum, but 7 times stronger. Lb for lb, titanium is stronger than steel and totally blows aluminum out of the water. The US government didn't spend millions of dollars building aircraft out of titanium in stead of the much cheaper aluminum because they wanted to waste money. It has its advantages.
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This is again alloy dependent. It possible to find low grade steels that are not as strong as high grade titanium alloys. However when you are looking for the ultimate strength and toughness, like for example in a crankshaft, you will find no titanium cranks at any price in blown alcohol or nitromethane engines — because they are not as strong or durable.
You will find ultra pure electric arc vacuum remelt 4340 steels that carry various marketing names like Kryptonite®, M300 etc. The absolute strongest steel currently used for these cranks is the Timken® 4330V alloy steel which will almost but not quite double the service life of the best 4340 steels.
Quote:
Originally Posted by olddog
There are many other factors that must be considered. The experts are saying that because aluminum is more flexible than steel, it can act like a shock absorber in certain critical extreme condition for engine rods, which allow it to not fail where steel rods would fail. I expect kind of like a building too strong to flex will not withstand an earth quake where a less strong, more flexible, building will stand.
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The compressive strength qualities and relative cushioning effect that aluminum rods provide is important if you detonate the engine. Absent the detonation this quality brings no real benefits to the table.
Experts tend to be a dime a dozen with the occasional sale for even less. I have never met an expert that actually ran the rod materials he promoted as being the best, in these types of engines. Bill Miller is the current exception to that rule. It costs a lot of money when you experience a failure in one of these engines and the so called experts want no part of that risk.
Interestingly the alcohol and fuel racers all use high strength super steels for their cranks and high strength aluminum alloys for their rods. Sometimes the rods are forged sometimes billet plate. Most often they are forged and they tend to be Miller's. In general the forgings provide better strength, toughness and service life and the billet pieces provide greater ability to be tailored to special dimensions and or applications.
Ed