ME6503 Design of Machine Elements 2 marks with answers

ANNA UNIVERSITY,CHENNAI

REGULATION 2013

DEPARTMENT OF MECHANICAL ENGINEERING

SUBJECT CODE:ME 6503

SUBJECT NAME:DESIGN OF MACHINE ELEMENTS

UNIT I    STEADY STRESSES AND VARIABLE STRESSES IN MACHINE MEMBERS 

Introduction to the design process - factors influencing machine design, selection of materials based on mechanical properties - Preferred numbers, fits and tolerances – Direct, Bending and torsional stress equations – Impact and shock loading – calculation of principle stresses for various load combinations, eccentric loading – curved beams – crane hook and ‘C’ frame- Factor of safety - theories of failure – Design based on strength and stiffness – stress concentration – Design for variable loading.

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PART-A ( Two Marks)

    1.What are the various phases of design process?

    i.Recognition of need. 

    ii.Definition of problem

    iii.Synthesis 

    iv.Analysis and optimization 

    v.Evaluation

    vi.Presentation

   2.Define stress concentration and stress concentration factor.

 Stress concentration is the increase in local stresses at points of rapid change in cross section or discontinuities.  Stress concentration factor is the ratio of maximum stress at critical section to the nominal stress.

3..What are the factors to be considered in the selection of materials for a machine element?

       i.Required material properties

       ii.Manufacturing ease 

       iii.Material availability 

       iv.Cost

4. What is principle stress and principle plane?

      A plane which has no shear stress is called principle plane the corresponding stress is called principle stress.

   5.Write the torsion equation.

. 

                T/J = CØ/L = Fs/R 

          T – Torque  J -   Polar moment of intertia  C-   Rigidity modulus  Ø – Angle of twist  

          L –   Length of the shaft  Fs – Shear stress  R -   Radius of the shaft  

   6.Write the bending equation.

      M/I = E/R = Fs/Y.        

         M –  Bending moment         

         I  -    Moment of intertia 

        E -   Youngs modulus 

        R -   Radius of the shaft 

        Fs – Shear stress 

        Y  -  Distance from neutral axis  

  7.Define: Factor of safety

      The ratio between maximum stresses to working stress is known as factor of safety.

Factor of safety =    Maximum stress / Working stress

   8.What are the types of variable stresses?

        a.Completely reversed or cyclic stresses 

        b.Fluctuating stresses 

        c.Repeated stresses

   9.Distinguish between brittle fracture and ductile fracture.

    In brittle fracture, crack growth is up to a small depth of the material.  In ductile fracture large amount of plastic deformation is present to a higher depth.

10.Explain size factor in endurance strength.

Size factor is used to consider the effect of the size on endurance strength.  A large size object will have more defects compared to a small one.  So,endurance strength is reduced.

  If  K is the size factor, 

Actual endurance strength = Theoretical endurance limit x K 

11.What are various theories of failure?

      i.Maximum principal stress theory. 

      ii.Maximum shear stress theory. 

      iii.Maximum principal strain theory.

    12..List out the factors involved in arriving at factor of         safety. 

      i.material properties 

     ii.nature of loads 

     iii.presence of localized stresses

     iv.mode of failures 

   13.Explain notch sensitivity and State the relation between     stress concentration factor, fatigue stress concentration          factor and notch sensitivity.

Notch sensitivity (q) is the degree to which the theoretical effect of stress concentration is actually reached.

The relation is, Kf  = 1 + q (Kt-1)

14.What are the factors that effect notch sensitivity?

 i.Material 

 ii.Notch radius 

 iii.Size of component 

 iv.Type of loading 

 v.Grain Structure            

15.Define Ductility

It is the property of the material enabling it to be drawn into wire, with the application of tensile force. It must be both strong and plastic. It is usually measured in terms of percentage elongation and reduction in area. (Examples) Ni, Al, Cu

  

 16.Define fatigue 

         

   When a material is subjected to repeated stress, it fails at stresses  below the yield point stress; such type of failure of the  material is called fatigue.

  17.What are preferred Numbers.

    Preferred numbers are the standard guidelines for choosing exact     product dimensions within a given set of constraints and It is      denoted as R. It helps to minimize the number of that need to be       manufactured an element.

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