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Metal matrix??(6 posts)

Metal matrix??Spiderman
May 13, 2001 10:02 PM
what exactly is a metal matrix? is it an alloy in the tubes? or just one metal for the tubes and another for the lugs? Specialized claims its M4 pro is "Manipulated Alloy." what exactly is that? is it the same as metal matrix? Thanks in advance for any thoughts/info.
re: Metal matrix??DrD
May 14, 2001 5:05 AM
Ok - think of a carbon fiber composite - in that you have carbon fibers in an epoxy (or other polymer) matrix - a metal matrix composite is similar to that, except that the reinforcement is generally not fiber - in fact, if you were to have a pile of the reinforcement in front of you, you would think it were a pile of grey dirt - the reinforcement is very small in size, because of what it does/how it strengthens an alloy. In addition, the volume fraction of reinforcement in a metal matrix material is much much less than something like a CF composite. Common reinforcement materials for aluminum are things like silicon carbide and alumina - I am not certain which Specialized uses, but for the sake of this description, it is irrelevant. So - a metal matrix composite material is a metal which has a uniform, fine dispersion of the reinforcing particles mixed into it - the reinforcement can do a number of things - without getting into the metallurgy too much, let it suffice to say that the reinforcement can refine the internal structure of the metal, as well as make permanent deformation (i.e., in bike terms, a dent) more difficult.

The big difference between a polymer composite like CF and a metal matrix is the scale over which the reinforcement operates - in the case of a carbon fiber material, your reinforcement directly alters the properties of the materials, and is load bearing in nature (so things like the direction the fibers go is very important) - in a metal matrix composite, the reinforment alters the strength through changes at the microstructural level - orientation is not important (though the size of the reinforcement is - I won't get into that here, though).

So that's a pretty rough/basic explanation...
re: Metal matrix??Spiderman
May 14, 2001 7:52 AM
thank you for your in depth answer. Are metal matrix rides considered harsh like alu. or soft like steel or c/f? Do they last long?
re: Metal matrix??DrD
May 14, 2001 4:47 PM
Consider it to be an aluminum alloy (which it is) with a bit higher yield strength.

How long a frame lasts, and how it rides has less to do with the material it's made from than it does from the frame geometry and tubing diameter (e.g., large diameter tubing is going to be stiffer than one with a narrow diameter, poorly designed/welded joints are more likely to crack than good ones, etc.). The Specialized frames seem to have a pretty good reputation, but I have never ridden one so I can't really offer much advice on them in that respect.

You can't really make the statement that all steel frames are soft, etc. - in the steel frame case, there are alot of frames which have pencil-thin chainstays, and they tend to be a bit flexy for larger riders - however, there are also some with beefier stays, which are as stiff (or stiffer) than anything else out there...
Metal matrix failuresBrian N
May 14, 2001 8:58 PM
I'm in a slightly interesting position to answer the question about the frame durability. two falls ago I TA'd a failure analysis class in which I had the students study failed bicycle parts (made my grading infinitely more interesting!!!) that people submitted to me for a free analysis. One of the people gave me a old S-works road frame of the metal matrix composite material. The frame was broken in a head on collision in which the oncoming driver made a left turn without looking (have we all had this happen at one point or another???). The combined speed was approx 35 mph. Naturally, the frame broke like most would. What was interesting was that instead of bending and breaking in one or two joints, the frame shattered almost like glass at almost all the major tubing intersections. Upon microscopic examination, it was found that the cracking followed the ceramic particles in the tubing at the weld/tube interfaces. You see, the weld was a standard aluminum alloy filler metal (without ceramic particles) so that there was a steep difference in properties (i.e. strength) at the tube/weld junction. This is where the frame cracked, and the crack followed the interfaces between the ceramic and aluminum. Another twist: I had a very similar accident at similar speeds on my old Allez Comp (the lugged steel version). My bike came through with the slightest crimp (no aligment problems) in the downtube at the "z" in specialized. I weigh 190 lbs too, which is more than the other rider. That two very similar bikes (besides frame materials) went through the same accident with drastically different results is intriguing in the least. I want to state that these results mean nothing statistically (i.e. both could have been a fluke), but the metallurgical examination of the broken M2 bike doesn't lie. Their increased stiffness/strength DOES come at a price. However, under normal riding conditions (i.e. not getting hit by cars!) their benefits most likely outweigh their detractions! They do make some very light bikes, I would just be aware of their toughness.

-Brian
I busted onemike mcmahon
May 14, 2001 9:30 PM
In '96, I bought a metal matrix mountain bike frame from Griffen. Four months later it snapped in two at where the top tube and down tube meet the head tube. I was just bottoming out on a hill I rode on a regular basis: no abuse or anything out of the ordinary. I weigh about 180 (probably closer to 175 at the time). The good news is that Griffen replaced it with a newer version of the same frame that has held up nicely. It is light and rides well; although I have a harder time distinguishing frame material riding characteristics on mtbs. Also, I don't know the material differences between the Specialized and the Griffen. Just my MM story.