Machine design Interview Questions & Answers

  1. Question 1. Define Ductility?

    Answer :

    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, (e.g.) Ni, Al, and Cu.

  2. Question 2. Define Fatigue?

    Answer :

    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.

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  4. Question 3. Define Factor Of Safety?

    Answer :

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

    Factor of safety = Maximum stress /Working stress

  5. Question 4. Define Endurance Limit?

    Answer :

    Endurance limit is the maximum value of completely reversed stress that the standard specimen can sustain an infinite number (106) of cycles without failure.

  6. Question 5. What Is Impact Load?

    Answer :

    If the time of load application is less than one third of the lowest natural period of vibration of the part, it is called an impact load.

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  8. Question 6. What Are The Various Phases Of Design Process?

    Answer :

    The various phases of design process are:

    1. Recognition of need.
    2. Definition of problem
    3. Synthesis
    4. Analysis and optimization
    5. Evaluation
    6. Presentation
  9. Question 7. What Are The Different Types Of Loads That Can Act On Machine Components?

    Answer :

    Different loads on machine components are:

    1. Steady load.
    2. Variable load.
    3. Shock load
    4. Impact load.
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  11. Question 8. What Are The Factors Affecting Endurance Strength?

    Answer :

    Factors affecting endurance strength are

    1. Load ii. Surface finish
    2. Size
    3. Temperature
    4. Impact
    5. Reliability
  12. Question 9. What Are The Types Of Variable Stresses?

    Answer :

    Types of variable stresses are:

    1. Completely reversed or cyclic stresses
    2. Fluctuating stresses
    3. Repeated stresses
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  14. Question 10. Differentiate Between Repeated Stress And Reversed Stress?

    Answer :

    Repeated stress refers to a stress varying from zero to a maximum value of same nature.

    Reversed stress of cyclic stress varies from one value of tension to the same value of compression.

  15. Question 11. What Are The Types Of Fracture?

    Answer :

    The two types of fracture are

    1. Ductile fracture
    2. Brittle fracture
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  17. Question 12. Distinguish Between Brittle Fracture And Ductile Fracture?

    Answer :

    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.

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  19. Question 13. Define Stress Concentration And Stress Concentration Factor?

    Answer :

    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.

  20. Question 14. Explain Size Factor In Endurance Strength?

    Answer :

    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, then

    Actual endurance strength = Theoretical endurance limit x K

  21. Question 15. Explain Griffith Theory. (or) State The Condition For Crack Growth?

    Answer :

    A crack can propagate if the energy release rate of crack is greater than crack resistance.

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  23. Question 16. What Are The Modes Of Fracture?

    Answer :

    The different the modes of fractures are:

    1. Mode I (Opening mode) – Displacement is normal to crack surface.
    2. Mode II (Sliding mode) – Displacement is in the plane of the plate.
    3. Mode III (Tearing mode) – Out of plane shear.
  24. Question 17. What Are The Factors To Be Considered In The Selection Of Materials For A Machine Element?

    Answer :

    While selecting a material for a machine element, the following factors are to be considered

    1. Required material properties
    2. Manufacturing ease
    3. Material availability
    4. Cost
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  26. Question 18. What Are Various Theories Of Failure?

    Answer :

    The failure theories are:

    1. Maximum principal stress theory.
    2. Maximum shear stress theory.
    3. Maximum principal strain theory.
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  28. Question 19. List Out The Factors Involved In Arriving At Factor Of Safety?

    Answer :

    The factors involved in arriving at factor of safety are:

    1. Material properties
    2. Nature of loads
    3. Presence of localized stresses
    4. Mode of failures
  29. Question 20. Give Some Methods Of Reducing Stress Concentration?

    Answer :

    Some of the methods are:

    1. Avoiding sharp corners.
    2. Providing fillets.
    3. Use of multiple holes instead of single hole
    4. Undercutting the shoulder parts.
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  31. Question 21. Explain Notch Sensitivity. State The Relation Between Stress Concentration Factor And Notch Sensitivity?

    Answer :

    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)

  32. Question 22. What Are The Factors That Affect Notch Sensitivity?

    Answer :

    The factors effecting notch sensitivity are:

    1. Material
    2. Notch radius
    3. Size of component
    4. Type of loading
    5. Grain Structure
  33. Question 23. What Is The Use Of Goodman & Soderberg Diagrams?

    Answer :

    They are used to solve the problems of variable stresses.

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  35. Question 24. Define Mach Inability?

    Answer :

    It is the property of the material, which refers to a relative ease with which a material can be cut. It is measured in a number of ways such as comparing the tool life for cutting different material.

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  37. Question 25. What Is An S-n Curve?

    Answer :

    N curve has fatigue stress on ‘Y’ axis and number of loading cycles in ‘X’ axis. It is used to find the fatigue stress value corresponding to a given number of cycles.

  38. Question 26. What Is Curved Beam?

    Answer :

    In curved beam the neutral axis does not coincide with the centroidal axis.

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  40. Question 27. Give Some Example For Curved Beam?

    Answer :

    C frame, crane hook.

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  42. Question 28. What Is Principle Stress And Principle Plane?

    Answer :

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

  43. Question 29. Write The Bending Equation?

    Answer :

    The bending moment equation is, M/I = f/y= E/R,


    M – Bending moment (M is in N-mm)
    I – Moment of inertia about centroidal axis (I is in mm⁴)
    f – Bending Stress (f is in N/mm²)
    y – Distance from neutral axis (y is in mm)
    E – Young’s modulus (E is in N/mm²)
    R – Radius of curvature (R is in mm)

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  45. Question 30. Write The Torsion Equation?

    Answer :

    The torsional equation is, T/J = q/r = GӨ/L


    T – Torsional moment (T is in N-mm)
    J – Polar moment of inertia (J is in mm⁴)
    q – Shear stress in the element (q is in N/mm²)
    r – Distance of element from centre of shaft (r is in mm)
    G- Modulus of Rigidity (G is in N/mm²)
    Ө – Angle of twist (Ө is in radians)
    L – Length of the shaft (L is in mm)

  46. Question 31. What Are The Common Profiles Used For Splines In Machine Elements?

    Answer :

    The profiles used for splines in machine elements are straight sided splines, triangular splines and in volute splines.

  47. Question 32. What Type Of Threads Are Used For Pressure Tight Joints And For Power Transmission?

    Answer :

    Pipe threads are used for pressure tight joints and square threads for power transmission.

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  49. Question 33. How Computer Helps In Designing?

    Answer :

    Computer is able to store lot of information and same can be retrieved fast.

    It performs calculations very fast. The design can be visualized on screen and any alterations made and its effects clearly seen. Thus optimum designs can be achieved much faster and these are thoroughly tested from all angles.

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  51. Question 34. Can You Tell Something About Hazop Study?

    Answer :

    In Hazop (Hazards and operatibility) study each and every conceivable process deviation from normal operating condition of a system having identical design intention, is thoroughly analysed for causes and consequence and required action plan to mitigate hazard/operability problems are suggested on the basis of available protective system.

  52. Question 35. Why Slenderness Ratio Is Considered In Design Of Members?

    Answer :

    When length of the member is increased, the member may fail due to buckling even though the member is symmetrical in all respects and the load is concentric.

  53. Question 36. What Do You Mean By Allowance In Limits And Fits?

    Answer :

    Allowance in limits and fits refers to maximum clearance between shaft and hole.

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  55. Question 37. A Wire Rope Is Designated As 6 X 19 Standard Hoisting. What Do The Numbers 6 X 19 Represent?

    Answer :

     Number of strands x number of wires in each strand.

  56. Question 38. Why A Sleeve Is Fitted On A Ball Bearing?

    Answer :

    To prevent relative axial movement between the shaft and the bearing.

  57. Question 39. What Is The Constant Factor In Case Of R-10 Series Of Preferred Numbers?

    Answer :


  58. Question 40. On What Basis A Transmission Shaft Subjected To Bending Loads Must Be Designed?

    Answer :

    Maximum shear stress theory.

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  60. Question 41. In Designing A Clutch Plate, What Assumption Is Made?

    Answer :

    Uniform wear condition is assumed because it leads to safer design.

  61. Question 42. The Critical Speed Of Rotating Shaft Depends Upon What?

    Answer :

    Mass and stiffness.

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  63. Question 43. What Is The Empirical Formula Used To Give The Number Of Bolts In Flange Coupling?

    Answer :

    n = 0.2d + 3

  64. Question 44. How The Size Of The Gearis Usually Specified?

    Answer :

    By pitch circle diameter.

  65. Question 45. While Taking A Turn, What Action Differential Makes?

    Answer :

    An increase in the speed of the outer wheel.

  66. Question 46. Rankine’s And Guest’s Theory Of Failure Are Applicable For What Materials?

    Answer :

    Rankine’s theory of failure is applicable for brittle materials. Guest’s theory of failure is applicable for ductile materials.

  67. Question 47. What Is The Main Purpose Of A Gear Box In A Vehicle?

    Answer :

    To vary the torque at the road vehicles.

  68. Question 48. What Is Endurance Limit?

    Answer :

    Endurance limit or fatigue limit is the maximum stress that a member can with stand for an infinite number of load applications without failure when subjected to completely reversed loading.

  69. Question 49. For Tight Leakage Joints, Which Type Of Thread Is Best Suited?

    Answer :

    NPT( National Pipe Threads)

  70. Question 50. A Bench Vice Has Which Type Of Thread?

    Answer :