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  • DrD

    #20 -- A Question of Stability (Revised)

    By DrD

    Mechanics Corner
        A Journal of Applied Mechanics and Mathematics by DrD, #20
        © Machinery Dynamics Research, 2015
    A Question of Stability Introduction     The word stability in its several forms is widely used in nontechnical communication. A person whose life it highly consistent from day to day is said to have a stable life. When the political situation in a particular area appears to be unlikely to change, it is said to be stable. A person who is well balanced and unlikely to be easily provoked to anger is said to be a stable person. When the medical condition of a sick or injured person ceases to get worse, the person is said to be stabilized. A company on the verge of bankruptcy is said to be an unstable company. But what does the word stability mean in a technical context? Each of the foregoing examples hints at the technical meaning without really being explicit about it.   A factor g = accel of gravity was missing in the potential energy expression. That is now corrected.
  • saurabhjain

    Calling Mechanical Engineers to collaborate on Twitter

    By saurabhjain

    If you are a mechanical engineering professional and have a twitter account .. we invite you in our mechanical engineering  campaign to collaborate on twitter.. Retweet the following status on Look forward for your presence. Regards Mechanical Engineeirng forum
  • DrD

    A Question for Readers

    By DrD

    Many of you have asked me various questions, so now it is my turn. Let me lay a bit of background first, and then the questions.   I have had some conversations recently with JAG (one of the other writers here at ME Forums) regarding the choice of software for 3D modeling and analysis. JAG has made some excellent suggestions, specifically a cloud based program called Onshape. Unfortunately, for reasons that are unclear, my computer cannot run Onshape; I have worked with their help people for several hours, all to no avail. JAG recommends this in part because there is a "free version for the hobbyist" and a relatively inexpensive "full version for the professional." That is pretty attractive, but since I can't run it, I'm stuck.   I gather that virtually all engineering colleges these days are teaching some sort of 3D modeling and analysis software, but that raises a few questions in my mind. 1. If your college teaches brandX 3D software, what will you do when you go to work for a small company that cannot afford anything more than 2D drafting (simple CAD), with no analysis capability at all? How will you do your job then? You probably have your own pocket calculator, but will you have your own copy of ANSYS or Pro-E? 2. What software does your school teach (every students should have an answer to this question, so I expect lots of replies on this one!)? 3. If you have used software extensively for analysis of engineering problems (beam deflections, stress analysis, fluid flow, heat transfer, etc), are you confident  that you will be able to work all of those problems if there is no such software available to you on the job?   I might add, as sort of a postscript, most of you know that I am older than dirt (I just had another birthday, so the situation is even worse!), so I tend to look at things from an elderly perspective. One of my great fears as a working engineer was "What will happen when I'm ask to do something that I don't know how to do?" It happened more than once, and it usually resulted in a flurry of intense research to come up to speed on whatever topic was involved. I could usually do that because I have a pretty good library, and I knew how to use a university library as well. But in terms of software, I was always concerned that I had no FEA program, so how could I do problems that others were doing by FEA? I have come up with some interesting work-arounds, including writing my own FEA for some problems, but I never wanted to be dependent on software that I could not afford to own. So, back to my questions about: How are you going to buy your own copy of ANSYS? DrD

Our community blogs

  1. I recall many years ago first hearing the term Over Engineered. It rang a sour note but I had not given it much thought. I still hear this said today about older equipment. For instance the DC Generators at Pratt Institute in Brooklyn NY have been in operation for over 100 years. I had the opportunity a few years ago to visit my alma mater. To my surprise and delight the Chief Engineer who provided the tour of the facility to my class in about 1977 was still on the job as was the equipment. But I digress.

    Over Engineered is often brought up when speaking about 1950’s vintage American automobiles. “They don’t build them like that anymore”. They don’t build them like that anymore because they don’t design like they use to.

    When I worked in the auto industry in the late 70’s and early 80’s engineering was in good part “seat of the pants” designing. A lot less analysis than one would expect. Two-D CAD was just getting introduced. There was extensive testing before production. What a lack of analysis left unknown, testing –often brutal testing- would reveal.

    If a component broke it was made stronger by adding more material or eliminating tight radii or other stress concentration features. Whether the rest of the system was just good enough or 10 times stronger than needed was an unknown. Over time components that never failed were targets for cost reduction. This also was not as analytical as it is likely today.

    Getting back to the subject of this blog, I would offer that the "weaker" a device is, the more it was engineered. Weaker, because it is designed closer to the expected loads. This of course is aside from shoddy design work.  For greater strength the addition of material will usually achieve this. For an item like the generators at Pratt added weight can also help with vibration. The penalties are the onetime cost of added material and greater shipment weight. Adding more material globally to a system such as a rocket, aircraft and to today’s automobile is forbidden. This requires much move engineering.

    I hope I have provided a better understanding of the term Over Engineered and realize it is really a misleading expression. Equipment back then was Over Designed because the factors of ignorance were much greater just a few decades ago.

  2. You know that diesel engine is the most appropriate choice of the engineers when it comes to drive heavy automobile like trucks, aircraft, ships etc. But what makes it so torque, is it the engine design, working cycle or something else. Please share your  deep analysis to answer this questions




    Seminars have always been an important aspect of education. It's an opportunity to either gain knowledge on an unknown topic or develop ideas regarding something you already know.It's a place where you meet highly skilled persons and get to know their recent researches.You should attend at least a couple of seminars annually to keep yourself updated about the advancements taking place in your field. I've seen many people who keep avoiding seminars, although interested, just because they have never attended a seminar before. If this is your case, then I've only one thing to say "There's always a first time." Until and unless you attend a seminar, how can you overcome the fright?




    Attending a seminar for the first time does not mean that you'll feel low or less confident than others. Here are a few tips that can make you seminar-ready. Here are a few tips that can help you get through a seminar and actually learn from it.


    1. Know the Topic

    Usually there are no prerequisites to attend a seminar but ideally you should know something about the seminar you're going to attend.First know the topic, yes the topic. I've seen a lot of people coming for a seminar and asking what the topic is! Know the meaning of each term related to the topic, like definitions, some dates, names of some important people in that field, etc. If you still have some time and energy left, know who the speaker is and his background. You can look for his area of study, some research works, etc. So now that you know what you need to know, I'll suggest you some ways by which you can know it.( I just hope I didn't confuse you. Oops, I did! )

    Now-a-days you can literally find everything on the web,sometimes even the details you need about the speaker from his research works. Now that you have the basic knowledge of the topic, you can consult the faculties if you feel like. You can find lot of details online but only after talking to the profs you get to know which information is relevant for the seminar you're going to attend.Knowing more never goes in vain, but off course you wouldn't like to clog your mind with so many points. If you feel it hard to remember all the points, you can make short notes and take it with you to the seminar. Just make sure your focus is on the speaker as soon as the seminar starts and not on these notes.


    2. A proper attire

    it's never mandatory to wear formals for attending a seminar but avoid fancy dresses. Remember you're in the professional world, dress up like that. If you like make-ups go for it, but keep it light and simple. Just make sure you're comfortable with your look. In most of the cases, dressing up properly makes people feel confident.


      3. Non-verbal communication

    People can communicate a lot of things even without uttering a single word, through their body gestures, eye movement, etc. ere lies the importance of non-verbal communication. You can put a smile on you face just to show that you're there to learn and not to oppose the idea the speaker is going to present. Nodding your head sometimes during the speech can also communicate a lot about you. It means you're listening and understanding the topic as well.


      4. Be attentive

    It's not important to understand each and every part of the speech but at least you should get the essence of the speech. Just remember that the seminars are designed to provide you with a usable content on a variety of relevant subjects and keep you updated with the latest advancements in your field. So, try to gain as much knowledge as possible.


      5. Asking Questions

    It's the best way to get you ideas about the topic reviewed by an experienced person, you'll get to know if you're on the right track. Speakers also encourage questions and it's a way of learning on their part too. But whenever you ask a question, make sure you know exactly what you need to know clearly. Frame the question in your mind first, you certainly don't want to stumble while asking.
    At this moment, I certainly don't want to demotivate you, just remember that silence is better than asking "silly questions".



    So the next time you're going for a seminar, you already now what to do and how to do!


                       Happy "Seminar-ing" !


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    What is a BUE?

    BUEs are built-up edges formed due to the accumulation of work-piece material against the rake face of the tool.

    How are BUE formed?

    During machining, the upper layer of the work-piece metal experiences a large shear force as it comes in contact with the tool-tip and an amount of the metal gets welded to the tool-tip. This is due to work hardening of the metal layer. The metal adhered to the tool becomes so hard that it is difficult to remove.


      Why are BUE formed?

    BUE formation is common under a few conditions which are :
    1. Low cutting speed 
    2. Work hardeneability of work piece material
    3. High feed rate
    4. Low rake angle
    5. Lack of cutting fluid
    6. Large depth of cut

    In which materials is it observed easily?

    BUE formation is usually noticed in alloys such as Steel rather in pure metals.It is also observed in soft materials like soft pure Alumunium, hot rolled low carbon steel.

    What are the effects of BUE?

    There are a few basic effects caused by the BUE formation like :
    • Change in tool geometry
    • Change in rake steepness
    • Reduction in contact area between the chip and the cutting tool.

    What are the advantages of BUE?

    BUE formation can have a few advantages on the cutting tool and ease of machining like :
    • Slight increase in tool life
    • Reduction in power demand.

    What are the disadvantages of BUE?

    The count of disadvantages is actually more than the advantages it has on the machining process.
    • Poor surface finish 
    • Problems in dimensional control of the process
    • Leads to flank wear (damaging the flank face) 



    How can the BUE formation be prevented?

     BUE formation is a common machining problem but there's a soluion to every problem.Here are a few prevention steps to reduce BUE formation
    • Increasing cutting speed
    • Use of cemented carbide tool in place of HSS tool
    • Introduction of free machining materials ( loaded or resulphurized steel)
    • Application of an appropriate lubricant at low cutting speed


    P.S. - Suggestions are always welcomed.

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    When two links (or elements) in a machine are in contact with each other, they form a pair. When the relative motion between these two links is completely or partially constrained, then the links are said to form a kinematic pair.
    In simple words, a kinematic pair or simply a pair is a joint of two links having relative motion between them. 

    Material Science and Engineering (1).jpg

    Kinematic pairs can be classified on the basis of:


    1) Nature of contact between the pairing elements 

    (a) Lower pair – surface or area contact between the members of the pair

    There are 6 types of lower pairs

    I. Revolute pair (R)
    II. Prismatic pair (P)
    III. Screw or helix pair (H)
    IV. Cylindrical pair (C)
    V. Spherical or globular pair (G)
    VI. Planar pair or Ebony (E)  


    Types of Lower pair


    (b) Higher pair – point or line contact between the members of the pair 
    Examples of line contact  
    I. Tooth gears 
    II. Ball and roller bearings 
    III. Wheel rolling on a surface    

     gear-a04.jpg   spherical_roller_bearing.jpg   wheel-contact-with-road-rolling-friction


    Examples of point contact  
    I. Cam and follower pair      



    (c) Wrapping pair – similar to higher pair, but there are multiple point contacts, one body wraps over the other, comprises of belts, chains, etc.

    Examples – A belt driven pulley      



    2) Nature of mechanical constraint 

    (a) Form or Self closed pair – the contact between the two bodies is maintained by geometric form
    Examples – Screw pair (lower pair)    



    (b) Forced closed pair – the contact between the two bodies is maintained by application of external force
    Examples – Ball and roller bearings       


    (c) Open pair – links are not help together mechanically, contact due to the force gravity or some spring action.
    Examples – Cam and follower pair

    3) Nature of relative motion of one link to the other in the pair 

    (a) Sliding pair – sliding motion
    Examples – Rectangular rod in a rectangular hole in a prism  


    (b) Turning pair – turning or revolving motion
    Examples – Circular shaft revolving inside a bearing  

    (c) Rolling pair – rolling motion
    Examples – Ball and roller bearings    


    (d) Screw or Helical pair – both turning and sliding motion
    Examples – Lead screw and nut of a lathe  


    (e) Spherical pair – one link is in the form of a sphere and can turn inside a fixed link
    Examples – Ball and socket joint


    P.S. ~ Suggestions are always welcomed.
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    Turbines are machines which convert fluid energy to mechanical energy. When the fluid used is water, they are called hydraulic turbines. 
    Hydraulic turbines may be classified on the basis of four characteristics :
    Material Science and Engineering (1).jpg
    • On the basis of the type of energy at the turbine inlet
    Impulse turbine
    • total head of the incoming fluid is converted in to a large velocity head at the exit of the supply nozzle ( entire available energy of the water is converted in to kinetic energy.)
    • water entering the runner of a reaction turbine has only kinetic energy
    • the rotation of runner or rotor (rotating part of the turbine) is due to impulse action
    • Flow regulation is possible without loss
    • Unit is installed above the tailrace
    • Casing has no hydraulic function to perform, because the jet is unconfined and is at atmospheric pressure. Thus, casing serves only to prevent splashing of water.
    • It is not essential that the wheel should run full and air has free access to the buckets.

    eg - Pelton wheel turbine ( efficient with a large head and lower flow rate.)

    Reaction or Pressure turbine
    • the penstock pipe feeds water to a row of fixed blades through casing that convert a part of the pressure energy into kinetic energy before water enters the runner
    • water entering the runner of a reaction turbine has both pressure energy and kinetic energy
    • the rotation of runner or rotor (rotating part of the turbine) is partly due to impulse action and partly due to change in pressure over the runner blades
    • Water leaving the turbine is still left with some energy (pressure energy and kinetic energy) 
    • It is not possible to regulate the flow without loss
    • Unit is entirely submerged in water below the tailrace
    • Casing is absolutely necessary, because the pressure at inlet to the turbine is much higher than the pressure at outlet. Unit has to be sealed from atmospheric pressure.
    • Water completely fills the vane passage.

     eg - Francis and Kaplan turbines ( efficient with medium to low heads and high flow rates )

    • On the basis of the direction of flow through the runner
    Tangential flow turbine

    Direction of flow is along the tangent of the runner

     eg - Pelton wheel turbine.

    pelton turbine.gif
    Radial flow turbine

    Direction of flow is in radial direction

    • radially inwards or centripetal type, eg- old Francis turbine
    • radially outwards or centrifugal type, eg -Fourneyron turbine
    Stay_guide_vanes.png       Reaction.gif
    Axial flow turbine
    • Direction of flow is parallel to that of the axis of rotation of the runner
    • the shaft of the turbine is vertical, lower end of the shaft is made larger which is known as hub (acts as runner)


    eg - Propeller turbine ( vanes are fixed to the hub and they are not adjustable )

           Kaplan turbine (vanes on hub are adjustable )



    Mixed flow turbine
    • Water flows through the runner in the radial direction but leaves in a direction parallel to the axis of rotation of the runner

     eg- Modern Francis turbine.

    borgwarner-efr-7163-turbo-3-content-11.j     bD24ct.gif
    • On the basis of the head at the turbine inlet

    High head turbine

    • net head varies from 150m to 2000m or even more
    • small quantity of water required

    eg -: Pelton wheel turbine.


    Medium head turbine

    • net head varies from 30m to 150m
    • moderate quantity of water required

    eg -: Francis turbine.

    Low head turbine

    • net head less than 30m
    • large quantity of water required

    eg -: Kaplan turbine.

    • On the basis of the  specific speed of the turbine

    Before getting into this type, one should know what the specific speed of a turbine is. It defined as, the speed of a geometrically similar turbine that would develop unit power when working under a unit head (1m head).


    Low specific speed turbine

    • specific speed is less than 50. (varying from 10 to 35 for single jet and up to 50 for double jet ) 

    eg -: Pelton wheel turbine.


    Medium specific speed turbine

    • specific speed varies from 50 to 250

    eg -: Francis turbine


    High specific speed turbine

    • specific speed more than 250

    eg -: Kaplan turbine

    P.S. ~ Suggestions are always welcomed. 
    7 hours, 59 minutes ago
  4.     Mechanics Corner
        A Journal of Applied Mechanics & Mathematics by DrD, #33
        © Machinery Dynamics Research, 2016

    Advanced Polynomial Curve Fitting

        The use of polynomials to fit engineering data is a common engineering practice. In school, we learn that "A data set consisting of n data points ((x_{i},y_{i}), i=1,2,3,…n) can be exactly fitted with a polynomial of degree n-1. Thus three data points can be fitted exactly with a quadratic expression, four data points can be fitted exactly with a cubic expression, and so on. If this approach is pursued much further, something ugly appears: while a polynomial of degree n-1 will pass exactly through n data points, for large values of n, it will oscillate wildly in between the data points. Since one of the most common reason for using a polynomial fit in the first place is for interpolation -- to be able to estimate a function value at locations between the known data points -- this wild oscillation is devastating. It is at this point that least squares fitting is usually introduced to give an approximate fit using a much lower order polynomial. A different approach is employed here.


  5. good morning
    Someone could tell me what the name of this mechanism or how can I find a way to design it.
    It is a shaft that moves in a straight line vertically and along the way makes a 180 ° worst shaft never leaves his line of action .
    these links you can see the operation of the mechanism 



    Thank you

    Imagenes del giro.docx




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    Hi guys, can someone here help me to understand this better, explain in a teoretical way to understand Chvorinov's Rule and Bernoulli`s equation?

    Not just in a simple way, but deeper, can someone here do that, or knows how?


    Thanks in advance!!!!

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    Robotics brings together several very different engineering areas and skills. There are various types of robot such as humanoid robot, mobile robots, remotely operated vehicles, modern autonomous robots etc. This survey paper advocates the operation of a robotic car (remotely operated vehicle) that is controlled by a mobile phone (communicate on a large scale over a large distance even from different cities). The person makes a call to the mobile phone placed in the car. In the case of a call, if any one of the button is pressed, a tone equivalent to the button pressed is heard at the other end of the call. This tone is known as DTMF (Dual Tone Multiple Frequency). The car recognizes this DTMF tone with the help of the phone stacked in the car. The received tone is processed by the Arduino microcontroller. The microcontroller is programmed to acquire a decision for any given input and outputs its decision to motor drivers in order to drive the motors in the forward direction or backward direction or left or right direction. The mobile phone that makes a call to cell phone stacked in the car act as a remote.

    27_Shahul Gasnikhal__Economical Robotic Vacuum cleaner.pdf


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    3D printing technology is attracting every science and technology enthusiast whether it is a mechanical, civil, architecture, electrical, manufacturing or medical application. Everybody is interested in creating models, prototype using 3D printing technology. It’s not a technology but a 3D printing evolution. The pace at which this industry is growing and the novelty that 3D printing has introduced, it is predicted that additive manufacturing will affect almost all the fields of daily life including trade and commerce in near future.




    Checkout these Affordable & High Performance 3d Kits From Stuffmaker

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    Dileep Duvvuri
    Latest Entry

    all mechanical engineers blog

  6. With so much scientific tools, why do designs fail?

    Why the unsinkable Titanic sank? Why did the thoroughly tested Columbia space shuttle burned out on return? Why Toyota had to call back thousands of cars designed by expert engineers?

    Design might fails because somebody made a stupid mistake in his calculations, like in the old joke about the bridge that fell down because the engineer forgot to multiply by two. It might happen, but it is extremely rare. Most design failures happen because one specific mode of failure was never checked against, because it was never identified as risky.

    The sad truth is that we cannot design anything to work. We can only try to find out if a certain design might fail in a certain specific way. This is one reason why we cannot send computers to design things. They are excellent in optimizations, when we tell them what parameter to optimize and for what mode of failure.

    The Tacoma narrows bridge collapsed in 1940 because nobody thought that wind might arouse resonant vibrations in the bridge. It was OK for what it was designed for: for static loads. No computer would have suggested another mode of failure.

    The Titanic sank because nobody asked what happens if the ship scratch its side on an iceberg. Had it been thought, maybe the designers would have ordered that it would be better to throw the engines to full back and bump into the iceberg head on! It would have been damaged badly, but it would not sink.

    If only the designers of the Columbia would have only thought of the possibility of losing their thermal shield bricks on launch, the Columbia would have still be in service today. For a fact, once they identified the problem, they had no big difficulty to fix it.

    The philosopher of science, Karl Popper, said that in order to be scientific a claim must be "falsifiable". Moreover, he suggested that a claim cannot be proved by repeating experiments with positive results. No matter how many times it passes a test, there is always a chance that one more test will prove it wrong. To prove a theory requires infinite number of successful tests. One failure is enough to disprove it.

    So it is in our world of design. The failures described, all have shown that these designs were not perfect. They had errors embedded in them. And these errors are all the result of not being able to foresee the single mode of failure that could go wrong. No scientific calculation can help against an unidentified mode of failure.

    What is the lesson to be learned? Be paranoid! Always look around searching for the mode of failure you might have missed.

    I like to call rules by names. The name I gave this rule is "the law of the wild west".

    It goes as follows:

    The guy who kills you will be the one hiding behind the bush, that you failed to notice

    titanic sinking.jpg

  7. Why is BHINGHAM PLASTIC not a fluid?

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    What  is the significance of RMS (root mean square speed) in mechanical engineering?(in application point of view)

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    these are logos of the most famous factories of cars in the world.



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    What will happen if we condense the exhaust gas of coal gasification after passing through the gas Generator and then feed it to water treatment plant and then drain that water to the ground or reuse it. Can this be possible? No exhaust gas or reduced exhaust gas issue to environment.

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    Hello friends,

    If any body have JIS standard please share.

    I need JIS standard for Forging, Machining,Casting,Sheetmetal, Plastic & rubber.

  8. What is the basic difference between Shaft and axle in automobile..?

    looking for some valid and good answer. Hope you can do this.

  9. Crystalline semiconductors such as silicon can catch photons and convert their energy into electron flows. New research shows that a little stretching could give one of silicon's lesser-known cousins its own place in the sun.

    Nature loves crystals. Salt, snowflakes and quartz are three examples of crystals – materials characterized by the lattice-like arrangement of their atoms and molecules.

    Industry loves crystals, too. Electronics are based on a special family of crystals known as semiconductors, most famously silicon.

    To make semiconductors useful, engineers must tweak their crystalline lattice in subtle ways to start and stop the flow of electrons.

    Semiconductor engineers must know precisely how much energy it takes to move electrons in a crystal lattice.

    This energy measure is the band gap. Semiconductor materials such as silicon, gallium arsenide and germanium each have a band gap unique to their crystalline lattice. This energy measure helps determine which material is best for which electronic task.

    Now an interdisciplinary team at Stanford has made a semiconductor crystal with a variable band gap. Among other potential uses, this variable semiconductor could lead to solar cells that absorb more energy from the sun by being sensitive to a broader spectrum of light.


    A colorized image, enlarged 100,000 times, shows an ultrathin layer of molybdenum disulfide stretched over the peaks and valleys of part of an electronic device. Just 3 atoms thick, this semiconductor material is stretched in ways to enhance its electronic potential to catch solar energy.

    The material itself is not new. Molybdenum disulfide, or MoS2, is a rocky crystal, like quartz, that is refined for use as a catalyst and a lubricant.

    But in Nature Communications, Stanford mechanical engineer Xiaolin Zheng and physicist Hari Manoharan proved that MoS2 has some useful and unique electronic properties that derive from how this crystal forms its lattice.

    Molybdenum disulfide is what scientists call a monolayer: A molybdenum atom links to two sulfurs in a triangular lattice that repeats sideways like a sheet of paper. The rock found in nature consists of many such monolayers stacked like a ream of paper. Each MoS2 monolayer has semiconductor potential.

    "From a mechanical engineering standpoint, monolayer MoS2 is fascinating because its lattice can be greatly stretched without breaking," said Zheng, an associate professor.

    By stretching the lattice, the Stanford researchers were able to shift the atoms in the monolayer. Those shifts changed the energy required to move electrons. Stretching the monolayer made MoS2 something new to science and potentially useful in electronics: an artificial crystal with a variable band gap.

    "With a single, atomically thin semiconductor material we can get a wide range of band gaps," Manoharan said. "We think this will have broad ramifications in sensing, solar power and other electronics."

    Scientists have been fascinated with monolayers since the Nobel Prize-winning discovery of graphene, a lattice made from a single layer of carbon atoms laid flat like a sheet of paper.

    In 2012, nuclear and materials scientists at Massachusetts Institute of Technology devised a theory that involved the semiconductor potential of monolayer MoS2. With any semiconductor, engineers must tweak its lattice in some way to switch electron flows on and off. With silicon, the tweak involves introducing slight chemical impurities into the lattice.

    In their simulation, the MIT researchers tweaked MoS2 by stretching its lattice. Using virtual pins, they poked a monolayer to create nanoscopic funnels, stretching the lattice and, theoretically, altering MoS2's band gap.

    Band gap measures how much energy it takes to move an electron. The simulation suggested the funnel would strain the lattice the most at the point of the pin, creating a variety of band gaps from the bottom to the top of the monolayer.

    The MIT researchers theorized that the funnel would be a great solar energy collector, capturing more sunlight across a wide swath of energy frequencies.

    When Stanford postdoctoral scholar Hong Li joined the Department of Mechanical Engineering in 2013, he brought this idea to Zheng. She led the Stanford team that ended up proving all of this by literally standing the MIT theory on its head.

    Instead of poking down with imaginary pins, the Stanford team stretched the MoS2 lattice by thrusting up from below. They did this – for real rather than in simulation – by creating an artificial landscape of hills and valleys underneath the monolayer.

    They created this artificial landscape on a silicon chip, a material they chose not for its electronic properties, but because engineers know how to sculpt it in exquisite detail. They etched hills and valleys onto the silicon. Then they bathed their nanoscape with an industrial fluid and laid a monolayer of MoS2 on top.

    Evaporation did the rest, pulling the semiconductor lattice down into the valleys and stretching it over the hills.

    Alex Contryman, a PhD student in applied physics in Manoharan's lab, used scanning tunneling microscopy to determine the positions of the atoms in this artificial crystal. He also measured the variable band gap that resulted from straining the lattice this way.

    The MIT theorists and specialists from Rice University and Texas A&M University contributed to the Nature Communications paper.

    Team members believe this experiment sets the stage for further innovation on artificial crystals.

    "One of the most exciting things about our process is that is scalable," Zheng said. "From an industrial standpoint, MoS2 is cheap to make."

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    Atomic Number : 13

    Density (20oC) : 2.70 g/cm3

    Atomic Weight : 26.98

    Melting point : 660o C

    Boiling point : 2467o C


    Aluminum finds use as a deoxidizer, grain refiner, nitride former and alloying agent in steels. Its ability to scavenge nitrogen led to its widespread use in drawing quality steels, especially for automotive applications. Since aluminum is so often added to high quality steels.

    Metallic aluminum is the most common addition agent. It is sold in the form of notch bars, or stick, and as shot, cones, small ingots, chopped wire, “hockey pucks”, briquettes and other convenient forms such as coiled machine fed wire. These standard products are supplied in bulk or packaged in bags or drums. Purity for deoxidation grades is usually over 95%, the major tramp elements being zinc, tin, copper, magnesium, lead and manganese. Coiled aluminum wire is normally made to 99% minimum specification.
    Ferroaluminum, a dense and highly efficient aluminum addition, contains 30-40% Al. It is supplied in lump form, 8 in. x 4 in., 5 in. x 2 in., 5 in. x D, and 2 in. x D, and nominal 12 lb. and 25 lb. pigs, packed in drums and pallet boxes.

    Aluminum has a weak effect on hardenability (it is never added for this purpose) and, because of its grain refining properties, actually detracts from deep hardening. Heat treatable steels made to fine grain practice require slightly extra alloying to counteract this phenomenon. Aluminum is, however, a ferrite former and promotes graphitization during long-term holding at elevated temperatures. It also enhances creep, probably because of its grain refining property. Aluminum, therefore, should not be used in Cr-Mo or Cr-Mo-V steels specified for boiler or high temperature pressure vessel applications. Perversely, aluminum is otherwise beneficial to such materials since it reduces scaling through the formation of a more tightly adhering oxide film, particularly if chromium is present as well.


    Beyond its important functions in deoxidation and grain size control, aluminum has several applications as an alloying agent. Nitriding steels, such as the Nitralloy family, contain up to 1.5% Al to produce a case with hardness as high as 1100 VHN (70 RC). The outer layer of this case must, however, be removed by grinding to prevent spalling in service. The oxidation (scaling) resistance imparted by aluminum is exploited in some stainless steels and various high temperature alloys. Precipitation hardening stainless steels (17/7 PH, 15/7 PH, etc.) make use of aluminum’s ability to form strength-inducing particles of intermetallic compounds. Aluminum is found in many superalloys for the same reason.

    Aluminum combines very readily with nitrogen, and this effect has important commercial uses. Aluminum killed deep drawing steels will be nonaging since AlN is extremely stable. Such steels will not exhibit stretcher strains (Lüder’s lines) or a yield point, even after prolonged holding after cold rolling. Aluminum is also added to nitriding steels for its ability to form an extremely hard case.

    Aluminum is an important addition to some HSLA steels, and AlN was the first nitride used to control grain size in normalised and heat treated steels. Again, Al removes nitrogen from solution and provides grain refinement. Both of these effects promote high toughness, especially at low temperatures.

    Mention should be made of the effect of aluminum on nonmetallic inclusions, since these will always be present in AK steel. Because aluminum is among the strongest deoxidizers known, it can combine with, and partially or totally reduce, any other oxides present in steel. The subject is quite complex and depends not only on aluminum, but also on oxygen, nitrogen, sulfur, manganese, silicon, and calcium contents. For ordinary steels, however, the pattern is generally as follows: unkilled steels will contain oxides of iron, manganese and silicon, to the extent they are present. Steels deoxidized with silicon and aluminum will contain complex inclusions containing silica, alumina and manganese and iron oxides. As aluminum is increased, it gradually replaces silicon in the inclusions, and the principal inclusions in aluminum killed steels will be alumina and iron-manganese aluminates. Calcium-aluminum deoxidized steels will contain calcium aluminates, the composition and properties of which will depend on oxygen content (see Calcium). The residual Al
    2O3 in a ladle aluminum deoxidized steel will usually be in the range of 0.015-0.020%. This alumina range will be present regardless of the amount of aluminum used for deoxidation. It is assumed that the remaining alumina of iron aluminate is slagged off.

    Aluminum also has a profound effect on the structure of sulfide inclusions. The three basic types of sulfides present in steels have been designated as Type I (fine, randomly distributed spheroids, usually oxysulfides), Type II (intergranular chains which are most harmful to mechanical properties) and Type III (large, globular particles with complex, multiphase structures). Incomplete deoxidation with aluminum results in Type I inclusions; complete, but not excessive deoxidation produces Type II inclusions, while excessive aluminum addition leads to the formation of the Type III particles.

    High aluminum contents also promote the generation of interdendritic alumina galaxies, which can impair machinability. Aluminum is added in some stainless grades to improve machinability.

    Aluminum as alumina in calcium aluminate slags has found extensive use as slag conditioners at LMF stations. These are used to remove sulfur and inclusions, to lower costs of dolomitic lime, fluorspar, aluminum and calcium carbide additions, to protect the refractory lining, and to improve castability. Applications include both aluminum- and silicon-killed steels.

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