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9/9/2008 11:02 PM
If one looks across job advertisements with some focus towards
materials specifications; one definitely sees that employers and
managers think that non-materials engineers can specify materials.
This also is apparent in the technical and popular literature.
I seen the beginnings of this in my undergraduate degree, where
it wasn't unusual for people in Civil or Mechanical Engineering
were taking an option in Materials Science and Engineering. I am
not suggesting this is a bad thing, however specifying materials
is as big a job as designing the structure. And a Materials
Engineer is not (in general) capable of designing a structure.
The best demonstration that I have that materials specification should
be done by materials science and engineering professionals is
of an extra-terrestrial nature. In the mid 1990's, I got involved with
people trying to start commercial use of Space (in particular, the
Moon). There is lots of literature on this topic on the Internet, so you
can find specific examples on your own.
However, almost without exception (I haven't personally found an
exception), Mechanical and Civil Engineers have been talking about
building steel structures on the Moon for decades. Yes, there are
reasonable, potential sources of iron on the Moon. There is no
carbon! Most alloying elements are missing. Lunar night is
cryogenic, temperatures of -230C are seen. The regions of
permanent shadow near the poles are even colder. The common
steels that Civil and Mechanical Engineers know will not be
available. or even applicable.
Non-materials engineers have never clued in to environmental
conditions, they believe that iron means steel, and that all
steels can be used anywhere, just as if they were on Earth (in
particular, USA and Europe). As such, the only "explorations" in
materials specifications they (MEng, CEng) can do are the minor
perturbations of some existing condition. There is no guarantee
that the existing condition is a global extrema! Furthermore,
there is no way they can jump from their local extrema to some
global extrema. They do not understand materials.
10/29/2008 4:13 PM
[ Again, only lurkers. Hmmm. ]
Are we allowed to mention ASM here? On a quasi regular basis in Advanced Materials and Processes, we see mention of some group of parts replaced by an assembly of much fewer parts. Really, this (probably) should have been done at the initial design phase in most of these situations. Someone made material decisions that in retrospect were not correct.
You can help by posting news articles where either a material, or a means of processing a material has changed from initial specifications. Which only leaves explaining the change. :-)
An ancient decision on materials still persists to this day: the materials that are designed to be machined. Free machining steels are one example, but there are others. Why would we alter materials performance characteristics for the lifetime of any structure, strictly to make it easier to remove some of the outside layer of an object?
Dare I venture out on a thin branch? Even people without a materials science and engineering degree can appreciate can appreciate using materials that are either homogeneous, or minimize gradients in materials change. This is by no means a universal principle; for example, it appears that certain nano-laminated materials can withstand radiation environments better. But any modulation of a material should be planned, and not an accident of construction.
I am not against welding. Foremost it can be a wonderful way of repairing a structure. If some structure fails (prematurely) in service, being able to weld the structure and continue to operate while planning for the replacement of the structure is a wonderful ability. In the past, a person commonly heard that the weld metal was stronger than the parent metal. Wonderful and somewhat irrelevant. What was once a single material, is now 3 materials. The parent material, the weld zone, and the heat affected zone (HAZ). We typically need to make the weld zone different in chemistry in order to attain this "stronger" claim. Which now sets up the possibility of a corrosion couple over a small distance if an electrolyte is present. And while in the past the only property of concern was strength, we now know that toughness, hardness, chemical potential and a host of other properties can come into play. And we are still ignoring the HAZ: it does not experience any change in chemistry as a result of welding, but still sees the thermal event and undergoes micro-structural changes.
I had a brief relationship with a company (mostly mechanical engineers) that felt they needed materials science and engineering input. And they then proceeded to ask me to do things which had little or nothing to do with MSE, and were mostly mechanical engineering. And if they did have a materials question, they would tie my hands by saying I couldn't choose a different material. Relationship? Hah! They never paid anything for my "services". I don't have reserves to pursue litigation.
But back on topic, they wanted to make this horribly complex geometry for something. The engineer in charge (a mechanical engineer, probably an EIT) was of the opinion that all the parts get stamped from a flat sheet of metal, and then everything welded into the final geometry. The idea that bends could be made, instead of cuts and welds was completely foreign. That I brought up some of the theory of planning this sort of activity was felt to be a nuisance at best; CAD could do it all. Bending does impose its own changes on a material, and an optimal design would plan for where a bend was preferred over a cut and weld, if a bend was allowed. No CAD program is going to do this in general, and I suspect none do it in special cases either. (While I don't have a lot of experience with CAD, I have the programming background to write a CAD program.)
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