Placement Paper

ONGC Short Questions and answers in Mechanical Engineering for practice,Important objective type questions of mechanical engineering frequently asked in all IT and Non IT (PSU) GATE,UPSC,SSC,CAT,all technical engineering written test examinations.

1 What is the difference between isotropic and anisotropic materials?

 Ans If a material exhibits same mechanical properties regardless of loading direction, it is isotropic eg., homogeneous cast materials. Materials lacking this property are anisotropic

2    what are orthotropic materials

It is a special class of anisotropic materials which can be described by giving their properties in three perpendicular direction et wood composites

3    A plain carbon steel has BHN of 180 What are values of R^{c, VHN and ultimate strength?}

^{Ans Rc-RHN/10  18,VHN BHN 180}

^{4    What properties need to be considered for applications calling for following requirement:}

^irigdity

^{strength for no plastic deformation under static load}

^{wear resistance}

^{reliability and safety}

^{Ans Rigidity- elastic modules and yield strength}

^{Strength for no plastic deformation under static loading-yield point}

^{Wear resistance-Hardness}

^{Reliability and safety-Endurance limit and yield point}

^{5     Explain the effects of alloying chromium and nickel in stainless steel.}

^{Addition of nickel and chromium increases the tensile strength and increase in resistance to corrosion takes place.}

^{6    Mention two types of dislocation'}

^{Dislocation refers to a break in the continuity of the lattice. In edge dislocation, one place of atoms gets squeezed out.In screw dislocation the lattice atoms move from their regular ideal positions.}

^{7    What are the principal constituents of brass?}

^{Principal constituents of brass are copper and zinc}

^{8 what is curie point?}

^{Curie point is te temperature at which ferromagnetic materials can no longer be magnetized by outside forces}

^{9 Specific strength of materials is very high when they are in fiber size but lower when they are in bar form-Why?}

^{Crystal structure has ordered, repeating arrangement of atoms, fibers are liable to maintain this and thus have high specific strength. As size increases, the condition of ordered and repeating arrangements cant be guaranteed because of several types of defects and dislocations and thus the specific strength gets lower}

^{10    what is the percentage of carbon in cast iron?}

^2.5%

^{11     Which element is added in steel to increase resistance to corrosion?}

^Chromium

^{12     whether individual component material retain their characteristics or not} 

^Yes

^{13    An elastomer is a polymer when its percentage elongation rate is}

^{Greater than 100%}

^{14    If % elongation of material is more tha  200% it is classed as}

^Rubber

^{15    Why is it that the maximum value which the residual stress can reach is the elastic limit of the material?}

^{A stress in excess of elastic limit with no external force to oppose it will relieve itself by plastic deformation until it reaches the value of the yield stress}

^{16 Why fatigue strength decreases as size of a part increase beyond around 10 mm?}

^{Perfection of material conditions is possible at lower sizes and as size increases, it is not possible to attain uniform structure of the material}

^{17    Distinguish between creep and fatigues}

^{Creep is low and progressive deformation of a material with time under a constant stress at  high temperature application.  Fatigue is the reduced tendency of material to offer resistance to applied stress under repeated or fluctuating loading conditions?}

^{18 While normal carbursing and nitriding surface treatments increase fatigue strength excessive treatment may decrease the fatigue strength Why}

^{Normal carbursing/nitiriding treatments increase volume due to phase transformation at surface and introduce residual compressive surface stress and thus increase the fatigue strength,  By excessive treatment the high compressive stresses are introduced but these are balanced by high internal tensile stresses of equal value and the subsurface fatigue cracks may develop in the regions of high tensile stress and lead to early fatigue failures}

^{19    List at least two factors that promote transition form ductile to brittle fracture}

^{Manner of loading and the rate of loading promote transition from ductile to brittle fracture, A machine member may have ductile failure under static loading but may  fail in brittle fashion when the load is fluctuating Similarly a material may evidence ductile failure under tensile loading at ordinary testing speed but if load is applied at a high velocity then failure may be brittle}

^{20 Which theories of failure are used for (a) ductile material and (b) brittle materials}

^{For ductile materials theories of failure used are maximum shear stress theory, and maximum energy of distortion theory, while for brittle materials theory of maximum principal stress and maximum strain are used}

^{21    what is stellite?}

^{I t is a non ferrous cast alloy containing cobalt chromium and tungsten}

^{22    Car tyres are usually made of} 

^{styrene butadine rubbe}

^{23    What is the structure of pure iron and whether it is soft or hard?}

^{Ferrite and it is soft}

^{24    which elements increase the corrosion resistance of steel?}

^{Chromium and nickel}

^{25    Which rays are produced by cobalt 60 in industrial radiography?}

^{Gamma rays}