EDX Introduction to Steel 101

I completed an EDX course Introduction to steel earlier this week, taught by Mark Miodownik. The course is self-paced, and the total time needed to work through the material is around 2-3 hours.

I completed the course in 1 session, you could split up the course into smaller portions, if you can spend 20 minutes at a time.

I think this short course is an OK introduction to steel, and to the EDX technology. The course can be viewed as an enhanced lecture, since at the end of each short segment there is a little interactivity, in the form of some multiple choice questions or interactive graphics.

The material is really simplified, the major take homes are; the importance of steel, that it’s a versatile material, why it is the ultimate engineering material, what sort of things control the properties.

The course is quite short for such a large subject matter, so of course it’s rather simplified. I think in a few areas it is too simplified and might be misleading. An example of my concern would be the explanation of how quenching effects the microstructure, nothing about martensite phase is mentioned, only that quenching “freezes in the structure”. The approach is rather like the simplifications that take place in teaching physics were you find out at each level that everything you were taught to date, so I hope people watching the video would be motivated to study further about steels or metals.

Anyway these people seem happy:

So well done to Mark Miodownik and Tenaris for this innovation.

Dyanamic test austempered ductile iron

Drs Dawid Myszka, A. Wieczorek and Tadeusz Cybula from the Warsaw University of Technology, Poland investigated the influence of microstructure on the dynamic mechanical properties of austempered ductile iron using Taylor impact testing. Austempered dictile iron means it’s a cast iron, so has graphite particles in a matrix heat treated to become bainite!. Taylor impact testing means you fire cylinders of the material at an immovable object and see how the material gets squished.

Deforming Austempered Ductile Iron

Shattering Austempered Ductile Iron

The heavily deformed volume which faced the impact has resulted in hardening and in transformation to martensite — both hardness and magnetic measurements have been used. Hardening was due to mostly strain induced austenite-to-martensite transformation, and also due to cold-work.

References
D. Myszka, L. Cybula and A. Wievzorek
Influence of heat treatment conditions on microstructure and mechanical properties of austempered ductile iron after dynamic deformation test
Archives of Metallurgy and Materials
V59, Issue 3, 2014

DOI:10.2478/amm-2014-0204

Running on Straight Rails

Boffins in Austria have been studying railway tracks to better understand the residual stresses that result from straightening them during processing.

Roller straightening is the final step in production of the rails, after hot rolling is performed at around 1000&degree;C cooling (presumably with water spray) results in curvature of the rails. This varies depending on the rail geometry and cooling conditions.
Untitled

Results from finite element modelling, and measurement of stresses using the contour method and neutron diffraction were compared. The model matches the trends of the measurements in the vertical plane (possibly the mode important since it has the largest residual stresses). In the paper comparison of neutron results for triaxial stresses shows there are residual stresses in the plane perpendicular to the vertical through the rail tool, although these were not predicted by the FEM model.

Residual Stresses

Residual Stresses along vertical symmetry axis

References

  1. http://phys.org/news/2015-01-rails-straight.html#nRlv
  2. R. Kaiser, M. Stefenelli, T. Hatzenbichler, T. Antretter, J. Keckes and B. Buchmayr (2014) “Experimental characterization and modelling of triaxial residual stresses in straightened railway rails,” The Journal of Strain Analysis for Engineering Design, 1-9 DOI: 10.1177/0309324714560040

Metal working machines

Hebo machines have posted a nice video showing various machines for cold forming steel.

Completely unrelated, this is beautiful machine too, desktop injection moulding:

Use of science-babble in No Highway in the Sky

In No Highway in the Sky some science babble is used to explain the nature of fatigue. The explanation given depends on quantum mechanics and the metal becoming crystallised. It seems this science babble is used to avoid any controversy about the actual mechanism of fatigue. Since the author was an aircraft designer he could easy have become familiar with the contemporaneous explanation. Since the details are a topic of enquiry, inserting something outlandish is probably a very clever thing to do, it prevents inserting information which will mislead specialists and it doesn’t spoil the story for anyone else.

James Stewart in No Highway in the Sky

James Stewart in No Highway in the Sky

 

The outlandish explanation also fits well with the main characters fascination with topics such as the  mathematics of the ancient pyramids, part of the plot is that those with higher authority attempt to discredit him as a nut. They don’t want to believe there is a problem with the planes.

 

There is deeper point which is interesting to explore — it’s not necessary for the mechanism of fatigue to be known to have a predictive theory. It would be quite possible to predict the fatigue failure from the assumption that there is some form of damage accumulation. The mention of quantum mechanics probably means the hero was familiar with the statistics of stochastic effects. Another plot point in the story is that the damage to the material cannot be seen by observation, so that inspection of the aircraft puts the main characters explanation into doubt.

 

The failure of an aircraft by fatigue occurs by nucleation and growth of a crack. Since aluminium can be quite a tough material the size of the crack which can be tolerated before failure can be very large. Modern aircraft can be designed so that cracks can be detected by routine inspection before they reach a size which would cause failure.

No Highway in the Sky

‘No Highway’ is a book dramatising fatigue in metals, the story was made into the movie ‘No Highway in the Sky’ staring Jimmy Stewart. This is the only movie I know which is about metal fatigue. The book was published in 1948, and the movie appeared in 1951.

The author Nevil Shute Norway, was a pioneer aircraft designer. The story centres around Theodore Honey, a middle-aged widower and boffin at the Royal Aircraft Establishment Farnborough (site of much fundamental work on aircraft and fatigue).

Theodore is sent to investigate a previous air crash, but he realises that his theory applies to the plane he is travelling on, which he forces to land. After inspection of the aircraft on land, the much annoyed pilot is ready to take-off again, leaving Theodore Honey behind. However, Theodore’s conviction in his theory leads him to ground the plane by retracting the landing-gear. Everyone is left perplexed by his actions, except the air-stewardess and an actress aboard the plane who Theodore had convinced.

Therefore, go forth, companion: when you find
No Highway more, no track, all being blind,
The way to go shall glimmer in the mind.

Interestingly the book, in which a new airliner design being subject to mechanical failure due to metal fatigue, came before the failures of the de Havilland Comet airliner just six years later (1954).

James Stewart in No Highway in the Sky

James Stewart in No Highway in the Sky

As well as the book “No Highway” and the movie, there is also the radio play made by CBS. The radio play also stars Jimmy Stewart and Marlene Dietrich.

Part 1

Part 2

Part 3

Part 4

Part 5

Part 6

Making a welded Damascus Knife

John Neeman Tools have posted a beautiful video of manufacturing a welded Damascus patterned knife.

5 layers of 3 different steels were forge-welded, folded, and forged. With each step being repeated 8 times. This produces a patterned with 320 layers. Finally twisting and forging the steel produces a more complex pattern.

Just checking the number of layers, I get their total to be different. My calculation of the number of layers is 5 × 28 = 1280, that is 4 times more than claimed (320 layers should be the result of folding 6 times (6 folds 5 × 26).

With 1280 folds, if we assume the thickness of the knife is 2 mm, that means each layer is 1.6 μm, 320 folds would be 6 μm layers. These are both lower than what can be resolved using the naked eye. It’s very close to the wavelength of visble light — if the metal were folded one more time, or the final thickness of the knife is less than 1 mm you would be there.