Leaderboard


Popular Content

Showing content with the highest reputation since 05/21/2017 in all areas

  1. 19 points
    Selection of material is an important aspect for manufacturing industries . The quality of product is highly depends upon its material properties. These properties are used to distinguish materials from each other. For Example: A harder material is used to make tools.A ductile material is used to draw wires. So the knowledge of mechanical properties of material is desirable for any mechanical student or for any person belongs to mechanical industries. This post brings top 18 mechanical properties. Mechanical properties of material: There are mainly two types of materials. First one is metal and other one is non metals. Metals are classified into two types : Ferrous metals and Non-ferrous metals. Ferrous metals mainly consist iron with comparatively small addition of other materials. It includes iron and its alloy such as cast iron, steel, HSS etc. Ferrous metals are widely used in mechanical industries for its various advantages. Nonferrous metals contain little or no iron. It includes aluminum, magnesium, copper, zinc etc. Most Mechanical properties are associated with metals. These are #1. Strength: The ability of material to withstand load without failure is known as strength. If a material can bear more load, it means it has more strength. Strength of any material mainly depends on type of loading and deformation before fracture. According to loading types, strength can be classified into three types. a. Tensile strength: b. Compressive strength: 3. Shear strength: According to the deformation before fracture, strength can be classified into three types. a. Elastic strength: b. Yield strength: c. Ultimate strength: #2. Homogeneity: If a material has same properties throughout its geometry, known as homogeneous material and the property is known as homogeneity. It is an ideal situation but practically no material is homogeneous. #3. Isotropy: A material which has same elastic properties along its all loading direction known as isotropic material. #4. Anisotropy: A material which exhibits different elastic properties in different loading direction known as an-isotropic material. #5. Elasticity: If a material regain its original dimension after removal of load, it is known as elastic material and the property by virtue of which it regains its original shape is known as elasticity. Every material possess some elasticity. It is measure as the ratio of stress to strain under elastic limit. #6. Plasticity: The ability of material to undergo some degree of permanent deformation without failure after removal of load is known as plasticity. This property is used for shaping material by metal working. It is mainly depends on temperature and elastic strength of material. #7. Ductility: Ductility is a property by virtue of which metal can be drawn into wires. It can also define as a property which permits permanent deformation before fracture under tensile loading. The amount of permanent deformation (measure in percentage elongation) decides either the material is ductile or not. Percentage elongation = (Final Gauge Length – Original Gauge Length )*100/ Original Gauge Length If the percentage elongation is greater than 5% in a gauge length 50 mm, the material is ductile and if it less than 5% it is not. #8. Brittleness: Brittleness is a property by virtue of which, a material will fail under loading without significant change in dimension. Glass and cast iron are well known brittle materials. #9. Stiffness: The ability of material to resist elastic deformation or deflection during loading, known as stiffness. A material which offers small change in dimension during loading is more stiffer. For example steel is stiffer than aluminum. #10. Hardness: The property of a material to resist penetration is known as hardness. It is an ability to resist scratching, abrasion or cutting. It is also define as an ability to resist fracture under point loading. #11. Toughness: Toughness is defined as an ability to withstand with plastic or elastic deformation without failure. It is defined as the amount of energy absorbed before actual fracture. #12. Malleability: A property by virtue of which a metal can flatten into thin sheets, known as malleability. It is also define as a property which permits plastic deformation under compression loading. #13. Machinability: A property by virtue of which a material can be cut easily. #14. Damping: The ability of metal to dissipate the energy of vibration or cyclic stress is called damping. Cast iron has good damping property, that’s why most of machines body made by cast iron. #15. Creep: The slow and progressive change in dimension of a material under influence of its safe working stress for long time is known as creep. Creep is mainly depend on time and temperature. The maximum amount of stress under which a material withstand during infinite time is known as creep strength. #16. Resilience: The amount of energy absorb under elastic limit during loading is called resilience. The maximum amount of the energy absorb under elastic limit is called proof resilience. #17. Fatigue Strength: The failure of a work piece under cyclic load or repeated load below its ultimate limit is known as fatigue. The maximum amount of cyclic load which a work piece can bear for infinite number of cycle is called fatigue strength. Fatigue strength is also depend on work piece shape, geometry, surface finish etc. #18. Embrittlement: The loss of ductility of a metal caused by physical or chemical changes, which make it brittle, is called embrittlement.
  2. 6 points
    saurabhjain

    Types of Welding

    Welding is a process of joining similar and dissimilar metals or other material by application of heat with or without application of pressure and addition of filler material. It is used as permanent fasteners. Welding is essential process of every manufacturing industries. In fact, the future of any new metal may depend on how far it would lend itself to fabrication by welding. The weldability has been defined as the capacity of being welded into inseparable joints having specified properties such as definite weld strength proper structure. The weldability of any metal depends on five major factors. These are melting point, thermal conductivity, thermal expansion, surface condition, and change in microstructure. Types of welding: Basically welding may be classified into three types. 1. Plastic welding: In plastic welding or pressure welding process, the pieces of metal to be joined are heated to a plastic state and then forced together by external pressure. These welding are also known as liquid-solid welding process. This procedure is used in forge welding and resistance welding. 2. Fusion welding: In the fusion welding or no pressure welding process, the material at the joint is heated to a molten state and allowed to solidify. These welding are also known as liquid state welding process. This includes gas welding, arc welding, thermite welding etc. 3. Cold welding: In this welding process, the joints are produced without application of heat, but by applying pressure which results diffusion or inter-surface molecular fusion of the parts to be joined. It is also known as solid state welding process. This process is mainly used for welding nonferrous sheet metal, particularly aluminum and its alloys. This includes ultrasonic welding, friction welding, Explosive welding etc. 4 Main Welding Processes: 1. Arc Welding (Fusion Welding): In this type of welding process, weld metal melted from the edges to be joined and allow to solidifies from the liquid state and usually below the recrystallization temperature without any applied deformation. Arc welding is most extensively employed method of joining metal parts by fusion. In this welding the arc column is generated between an anode, which is the positive pole of power supply, and the cathode, the negative pole. When these two conductors of an electric circuit are brought together and separated for a small distance such that the current continues to flow through a path of ionized particles called plasma, an electric arc is formed. This ionized gas column acts as a high resistance conductor that enables more ions to flow from the anode to the cathode. Heat is generated as the ions strike the cathode. This heat used as melting of metal to be joined or melting the filler metal which further used as joining material of welding metal. The electrode is either consumable or non-consumable as per welding requirement. The temperature at the center of the arc being 6000 OC to 7000OC 2. Gas Welding: The gas welding is done by burning of combustible gas with air or oxygen in a concentrated flame of high temperature. As with other welding methods, the purpose of the flame is to heat and melt the parent metal and filler rod of a joint. It can weld most common materials 3. Gas Metal arc welding (MIG): This welding is also known as metal inert gas welding. In this type of welding a metal rod is used as one electrode, while the work being welded is used as another electrode. It is a gas shielded metal arc welding which uses the high heat of an electric arc between a continuously fed, consumable electrode wire and the material to be welded. Metal is transferred through protected arc column to the work. In this process the wire is fed continuously from a reel through a gun to constant surface imparts a current upon the wire. In this welding the welding area is flooded with a gas which will not combine with the metal. The rate of flow gas is sufficient to keep the oxygen of the air away from the hot metal surface while welding is being done. 4. Gas Tungsten Arc Welding (TIG): This welding is also known as tungsten inert gas welding is similar to the MIG in that is uses the gases for shielding. This arc welding process uses the intense heat of an electric arc between a no consumable tungsten electrode and the material to be welded. In this process the electrode is not consumable during welding process and gas is used to protect the weld area form atmospheric air.
  3. 4 points
    The purpose for a governor on at CI engine is the same as the purpose for a governor on any machine: to maintain constant speed under varying load conditions. DrD
  4. 4 points
    To allow slip and creep chain drive is used over belt or rope drive. To get accurate rotational timing a chain drive is best replacement for belt drive. Pro's of chain drive over belt drive 1) It can be used for accurate rotational timing thus used in I.C. Engines as timing chain. 2) There is no loss of energy in the form of heat because no slip and creep occurs. 3) Better service than belt drive. Con's of chain drive over belt or rope drive 1) Initial cost is more than belt drive system 2) Require proper lubrication for smooth functioning. 3) Not silent as belt drive in absence of lubrication. 4) Catches rust easily.
  5. 3 points
    Pre-heat is required for the following reasons: (1) It lowers the cooling rate in the weld metal and base metal, producing a more ductile metallurgical structure with greater resistant to cracking. (2) The slower cooling rate provides an opportunity for any hydrogen that may be present to diffuse out harmlessly without causing cracking. (3) It reduces the shrinkage stresses in the weld and adjacent base metal, which is especially important in highly restrained joints. (4) It raises some steels above the temperature at which brittle fracture would occur in fabrication. Post heating is required to remove further residual stresses present in the weld pool after heat treatment process also. If post heating is not done, then residual stresses develops as cracks and propagates throughout, resulting in the failure of the material. Also Preheat/Post weld heat treatment can be used to help ensure specific mechanical properties, such as notch and toughness.
  6. 3 points
    Following are the reasonable points that conclude the high torque and efficiency of diesel engine. Diesel engine uses simple mechanism for combustion unlike in gasoline engine. Removal of ignition system not only makes the mechanism simpler but also reduces the risk of improper combustion due to damage in ignition system. In short burning of the fuel is easy and always accessible. This results in higher efficiency diesel engine. Diesel fuel is a heavier hydrocarbon in which carbon and hydrogen are strongly bonded with each other. And when energy is supplied in form of heat it gets explode releasing much higher energy then gasoline. In short diesel fuel has higher energy density then gasoline which results in huge explosion. One more factor for higher efficiency in diesel engine is its property of lubrication. Although all fuel has property of lubrication but diesel fuel has much higher lubrication then gasoline fuel. The compression ratio is much higher in diesel as compared to gasoline because in diesel engine air is alone compressed inside the cylinder and it’s a known fact that gas easily compresses then liquid. This is not so in gasoline engine because air-fuel mixture is compressed inside the cylinder. This higher compression gives higher heat and simultaneously higher torque. We can’t use Carnot cycle to get 100% efficiency but can use its principle to attain maximize efficiency. In diesel engine heat is added at constant pressure which results in higher utilization of heat energy to get maximize work output. These were the advantageous features of diesel engine but it has some demerits as well like it releases highly toxic gases, noisy, higher maintenance cost and starting problem (now starting problem is eliminated by using a bulb nearby to the cylinder) to heat the engine before ignition. And it is costlierthan gasoline engine but with optimum operation and good maintenance resolve all these problems.
  7. 3 points
    Lisho Thomas

    Why tyres are made black in color?

    Tyres are mixture of various rubbers with carbon black added. Carbon black improves traction and wear resistance of pure rubber. Another reason is that black color has higher absorption capability by which the tyre of any vehicle becomes adhesive to road
  8. 3 points
    Ohh god.. No one is able to give right answer. All are copying from other sources.. Let’s discuss it with an example of bicycle. In bicycle while operation the power from pedal is transmitted to small flywheel present in the rear tyre. This flywheel locks in one direction so that power can be transmitted from pedal to rear wheel not from rear wheel to pedal. In order to conserve the kinetic energy of the bicycle. Same thing happens in vehicles. In normal conventional gear box when we release our accelerator pedal the kinetic energy of vehicle deploys as it is transmitted back to engine from wheels until we disengage the clutch. Thus an overdrive in an automatic transmission locks in one direction while transmitting power from engine to the wheels and rotates freely on reverse transmission of power from wheel to engine. This conserves the kinetic energy of vehicle for useful movement.
  9. 3 points
    saurabhjain

    Difference between pump and compressor

    Basically a Pump is used for liquid or fluid to transform it to a much high pressure head while a Compressor is used for gases to transform from low to a much high pressure. From Mechanical Engineering point of view liquid is incompressible so Compressor cannot be used for liquid substances. Posted by AbdulQadir Abba Sheriff on linkedin
  10. 2 points
    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
  11. 2 points
    Lapping is process in which two surfaces are rubbed together for achieving superior quality surface finish the process is used where the sealing surfaces subject to extreme pressure are assembled without the gasket material(pure metal to metal contact). The process is done with abrasive material between the lapping surfaces. The abrasive material could be carborundum/diamond paste or it could be in the form of oil or liquid polish. Example: the assembly of a nozzle in a fuel injector of an IC engine. Honing Is done for making smooth surface slight rough so that the lubricating oil is adher to the sliding surface and thus by provide a lubrication film to prevent boundary lubrication between sliding surface. The process is carried out with honning tool and with a controlled rpm and the linear motion of the tool. Example:cylinder liners are honed internally.
  12. 2 points
    DrD

    Rocket Homework Problem

    Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, #38 Machinery Dynamics Research, 2017 Rocket Homework Problem Introduction Most engineers find problems involving rockets to be exciting. There is something about a rocket that fires our imagination, whether we think of going to the moon or one of the planets, or simply of shooting down an incoming missile. The subject of this post involves a rocket on a mobile launcher. The rocket is intended to be transported in a horizontal position, but it must be elevated in order to be fired. Both positions are shown in the accompanying figure. Read the attached PDF for more on this problem. RocketHWProblem.pdf Addendum: One reader has posted a proposed solution for this problem as a comment. It was not my intent that solutions be posted in the comments at all. I only want solutions sent to me by the personal message system. DO NOT POST YOUR SOLUTION IN THE COMMENTS!! Regarding the solution that has been posted, let me say the following: 1. Some of the answers are correct, while others are not. Do not be misled into following this solution because there are errors therein. 2. Even where the results are correct, there are a number of methods that I would not recommend using. Thus again, I say to all other readers, do not follow this solution, but work it out for yourself. 3. Be sure to document your solution, so that if someone else were to ask how you obtained a particular result, you would be able to explain it in a clear and reasonable manner.
  13. 2 points
    What useful information are obtained from tensile test of ductile material You can answer this question. You can like the best answer. You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus
  14. 2 points
    Vinay Paul

    Why diesel Engine don't have spark plug?

    We don't use a spark plug in a diesel engine because after compression stroke in diesel engine the temperature of air inside engine cylinder rises to 600°C and pressure rises to 35 bar. When the diesel is sprayed in the engine cylinder in form of the mist due to high temperature in the cylinder the diesel which is sprayed as mist catches fire due to the high temperature. So we don't need a spark plug in diesel engines. Thank you.
  15. 2 points
    A pipe is measured by Nominal Pipe Size (NPS) per Inch and Schedule number ( Thickness of pipe ) and tube is measures by Outside Diameter (OD) and BWG number ( Thickness of Tube) . The common Pipes size as ANSI are produced from size 1/8" to 48". Pipes are used for mass. fluid and gas transfer in different industrial. Tubes are manufactured from size 1/32" to 12". Tubes are used for heat transfer in Heat exchanges,boilers,vessels and also in fire burners ( size 2" and more) and as instruments tubes and also accessories tools in Turbines and Compressors.
  16. 2 points
    Amit2007

    What is priming & why it is done ?

    During priming of a pump, its impeller is fully submerged in the liquid (say water) to remove any air trap (any kind of cavity that can lead to pressure drop), vapors, etc. This is important because lower density fluid produces a head rise proportional to the ratio of its density to the liquid to be pumped. If the pump is placed above the liquid's upper surface, then suction line has a cavity that does not allow proper suction. To avoid this, priming is necessary. This is for centrifugal pumps and not for positive displacement pumps.
  17. 2 points
    It could be that I'm going blind but I didn't see the word 'better' in any part of the question!
  18. 2 points
    ABS- it allows the brakes to be applied while maintaining a tractive contact with the road. it does not allow the wheels to be stopped a once. if it was stopped at once due to inertia(because of the speed with which it comes), the vehicles skids. it is more prominent in low friction surfaces like on ice, wet road etc. In ABS the wheels are not stopped at once. It grips the disc mounted on the wheel. the disc is pressed and released with a gap of nanoseconds. thus the driver do not actually feel it. It increases the braking distance. EBD- It is an electronic device that is mounted on the vehicle, that actually varies the amount of braking force on each wheel depending upon the road conditions. if one wheel is on a high friction surface less braking force is required on that wheel. thus by sensing the road conditions the amount of brake force is varied.
  19. 2 points
    clutch is a device use to engage or disengage the shaft of the gearbox to the shaft of wheel, while coupling is used to joint two shaft permanantely or temporary,...
  20. 2 points
    The Temperature required for combustion is higher for diesel and the spark plug is not enough to produce the temperature. Even, if it is used, it causes pre-ignition and knocking, which is not preferable. That's why it has higher compression ratio of 14-22, which is pretty much compared to petrol engines of compression ratio 5-8. Thus, there is no point of using spark plugs in not only diesel engines but also in CI engines,which may use biodiesel, kerosene, etc.
  21. 2 points
    Arvind Laad Head Engineering at Creative Ashtech Power Projects Private Limited This diagram is used to find the nature of flow of viscous slurry- whether it is laminar or turbulent. It is also used to derive the coefficient of friction in such cases in order to work out the pressure drop in these pipelines & thus fix the slurry pump parameters.
  22. 2 points
    Forging is stronger for a number of reasons, not least due to the internal stresses of the forged material bolsterring the crystaline structure and running along the shape of the forged item - effectively work hardening. Cast items are generally more brittle (due to high carbon steel being used predominantly to aid the liquid metal flow) and also the precipitation of the Carbon along the crystal walls in the material structure. (I cannot remember the correct nomenclature off hand (I recall "martensitic is in there somewhere), so, with regret, that's the best i can do on this at the moment!!!)