Phatman

As a materials science and engineering major graduating in less than a month, I love these discussions. Its the shape of the tube, not the actual material in this case. That's why there are more jobs out there for mechanical engineers than materials engineers. The mechanical engineers compensated for the shortcomings of aluminum by making sure that it never flexed enough to cause significant fatiguing. They did this with giant tubes.

I think we should get into the precipitate hardening properties of copper aluminum alloys vs copper, magnesium zinc alloys. Or perhaps how the Hall-Petch relation applies to the grain refining effect of niobium in high strength steel.

Phatman

PS...is anyone out there looking to hire an entry level materials engineer in the next few months or so?

cyccommute 

You have it backwards. Look here. A lower Young's modulus (aka elastic modulus) means that the material is more elastic. Rubber has a Young's modulus of 0.1 GPa, aluminum has one of 69 Gpa and steel has one of 190 GPa. I certainly wouldn't call rubber nonelastic. The rubber doesn't resist deformation. Hit it with a hammer and it will spring back. Hit a piece of steel with a hammer and it will deform permanently. But it takes much more force to deform it.

Nightshade

Steel "rings" while aluminum doesn't. That "ringing" damps vibration by converting it to mechanical
energy which disapates the pulses of the vibration. Sure, you can't hear the ringing but if you put a
vibration probe on the frame while riding you can see it in orders of amplitude.

capsicum

Also not quite right.

Elasticity is the ability to deform or stretch under load and return to it original shape when unloaded.
Modulus is the stiffness for a given size, specific modulus is the modulus divided by the specific gravity.

cyccommute 

From Wikipedia

modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically (i.e., non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of its stress-strain curve in the elastic deformation region:



where λ (lambda) is the elastic modulus; stress is the force causing the deformation divided by the area to which the force is applied; and strain is the ratio of the change caused by the stress to the original state of the object. If stress is measured in pascals, since strain is a unitless ratio, then the units of λ are pascals as well.

I'll agree that elasticity is the tendency of a substance to return to its original form after deformation. However, there is nothing in the above definition that would be related to the size of the object being tested.

The Webster's definition is

Main Entry:
mod·u·lus
Pronunciation:
\ˈmä-jə-ləs\
Function:
noun
Inflected Form(s):
plural mod·u·li
Etymology:
New Latin, from Latin, small measure
Date:
1753

1 a: the factor by which a logarithm of a number to one base is multiplied to obtain the logarithm of the number to a new base b: absolute value 2 c (1): the number (as a positive integer) or other mathematical entity (as a polynomial) in a congruence that divides the difference of the two congruent members without leaving a remainder — compare residue b (2): the number of different numbers used in a system of modular arithmetic
2: a constant or coefficient that expresses usually numerically the degree to which a body or substance possesses a particular property ([such] as elasticity)


In this case, definition 2 would be the most appropriate. The elastic modulus could also be stated as the elastic coefficient.

cyccommute 

I believe you have hit the nail (steel one) on the head.

Booger1

What do you mean it doesn't ring,what is that suppose to mean?You've never seen aluminum wind chimes? If it's some kind of shape that should ring and doesn't,I'd be looking for a crack!Hanging a crankshaft,hitting it with a hammer is a great way to pretest for cracks.Good if it rings,you better be looking closely for cracks if it doesn't.Dead soft aluminum won't "ring" as well as tempered will,but it will ring unless it's cracked or has some casting flaw in it.Get an aluminum tube,cut off a piece,hang it from a string,hit it,it will ring.You can probably get lead to ring if you try hard enough.The only metal I can think of off the top off my head that won't ring is mercury,it probably will if you can get it cold enough.You can get water vapor to ring if you freeze it in the shape of a bell.You can probably get all kinds of things to ring if you can get them in a solid enough state to do so.

I do stress relieving at work on all types of metals with vibration and sound waves.Harmonics is one of the main reasons it works.

deraltekluge

Racing car frames (pure racing, specially constructed racing cars that aren't constrained by rules) use carbon fiber these days.

capsicum

Generally an aluminium-honeycomb cored carbon-fiber/epoxy composite sandwich, based monocock chassis. Non repairable, but if made right it absorbs a lot of impact in a crash and it's close to the lightest stiffest fanciest thing out there. (Burt Rutan's Voyager airplane was made very similarly. Went non stop round the world, without refueling.)

cachehiker

I'm an electrical engineer who simply evaluates a lot of motors, vibration, and audible noise, as well as the dampening associated with them so excuse me if I'm wrong but doesn't plastic deformation imply more hysterisis?

Yes, there a modulus of elasticity established for aluminum. However, there is, more or less, enough hysteresis that "below the yield point" is a vague concept when you're dealing with aluminum. When you design a bike frame with it, you have to limit the yield to where the hysterisis doesn't result in metal fatigue within a reasonable lifespan.

Below the yield point works well when you're working with steel. You therefore design around low cycle fatigue instead of high cycle fatigue.

There are a lot of riders out here wishing I was real ****ing slow on my double butted Reynolds 631 frame.

Robert Foster

I once went fishing out by San Clemente Island. We dropped anchor and I must have cast out bait for an hour with out a bite. So we decided to troll for Yellowtail. Even when they were running we didn't get as many bites as this. I have to wonder what kind of saddle material the OPs professor says is best? Sorry I just felt we were getting off the track here. The question was if the professor was correct or did we get the correct statement made by that professor. Neither matters if the OP is taking a test, the answer is always what the professor said in class.

Retro Grouch 

The OP's original question indicated he was taking an "Advanced Materials Science" course. I wonder what they teach in the "Introductory Materials Science" course.

CdCf

I agree completely!

I couldn't tell different frames and frame materials apart if my life depended on it, and I dare say that most people are seriously deluding themselves, either consciously or subconsciously.