Material Science Interview Questions & Answers

  1. Question 1. What Is The Difference Between The Isotropic And An Isotropic Materials?

    Answer :

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

  2. Question 2. What Are Orthotropic Materials?

    Answer :

    Orthotropic materials are a special class of isotropic materials which can be described by giving their properties in three perpendicular directions
    ex: wood; composites.

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  4. Question 3. A Plain Carbon Steel Has Brinell Hardness Number (bhn) Of 180. What Are The Values Of Rc, Vhn And Ultimate Strength?

    Answer :

    Rc = BHN/10 = 18, VHN = BHN = 180

    Ultimate strength = 3.48 × BHN MPa = 620 MPa.

  5. Question 4. What Properties Are Needed To Be Considered For Application Calling For Following Requirements?
    I) Rigidity.
    Ii) Strength Of No Plastic Deformation Under Static Load.
    Iii) Strength To Withstand Overload Without Fracture.

    Answer :

    i) Reliability – elastic modulus and yield strength.

    ii) Strength (for no plastic deformation under static loading) – yield point.

    iii) Strength (overload) – Toughness and impact resistance.

    iv) Wear resistance – Hardness.

    v) Reliability and safety – Endurance limit and yield.

  6. Question 5. Explain The Effects Of Alloying Chromium And Nickel In Stainless Steel.?

    Answer :

    The addition of nickel and chromium increases the tensile strength and increase in resistance to corrosion takes place.

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  8. Question 6. Mention Two Types Of Dislocations?

    Answer :

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

  9. Question 7. What Are The Principal Constituents Of Brass?

    Answer :

    Principal constituents of brass are copper and zinc.

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  11. Question 8. What Is Curie Point?

    Answer :

    Curie point is the temperature at which ferromagnetic materials can no longer be magnetized by outside forces.

  12. Question 9. Specific Strength Of Materials Is Very High When They Are In Fibre Size But Lower When They Are In Bar Form – Why?

    Answer :

    The crystal structure has ordered, repeating arrangement of atoms. Fibers are liable to maintain this and thus have high specific strength. As for size increases, the condition of ordered and repeating arrangements can’t be guaranteed because of several types of defects and dislocations, and thus the specific strength gets lower.

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  14. Question 10. What Is The Percentage Of Carbon In Cast Iron?

    Answer :

    2.5%.

  15. Question 11. Which Element Is Added In Steel To Increase Resistance To Corrosion?

    Answer :

    Chromium.

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  17. Question 12. Whether Individual Components In Composite Materials Retain Their Characteristics Or Not?

    Answer :

    Yes.

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  19. Question 13. Why Is It That The Maximum Value Which The Residual Stress Can Reach Is The Elastic Limit Of The Material?

    Answer :

    A stress more than the elastic limit, with no external force to oppose it, we relieve itself by plastic deformation until it reaches the value of the yield stress.

  20. Question 14. Why Fatigue Strength Decreases As Size Of A Part Increases Beyond Around 10mm?

    Answer :

    The perfection of material conditions is possible at lower sizes, and as size increases, it is not possible to attain a uniform structure of the material.

  21. Question 15. Distinguish Between Creep And Fatigue?

    Answer :

    Creep is low and progressive deformation of a material with time under a constant stress at high-temperature applications. Fatigue is the reduced tendency of material to offer resistance to applied stress under repeated or fluctuating loading condition.

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  23. Question 16. While Normal Carburizing And Nit Riding Surface Treatments Increase Fatigue Strength, Excessive Treatment May Decrease The Fatigue Strength. Why?

    Answer :

    Normal carburizes/nits riding treatments increases volume due to phase transformation at the surface and introduce residual compressive surface stress and thus increases fatigue strength. By excessive treatment, the high compressive stresses ae introduced but these are balanced by high internal elastic stresses of equal value, and the surface fatigue cracks may develop in the regions of the high tensile stress and lead o early fatigue failure.

  24. Question 17. List At Least Two Factors That Promote The Transition From Ductile To Brittle Fracture?

    Answer :

    The manner of loading and the rate of loading promote the 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 the load is applied at a high velocity then failure may be brittle.

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  26. Question 18. Which Theories Of Failure Are Used For?
    (a) Ductile Materials
    (b) Brittle Materials?

    Answer :

    For ductile materials, theories of failure used are maximum shear stress theory and maximum energy of distortion theory;

    For brittle materials, the theory of maximum principal stress and maximum strain are used.

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  28. Question 19. What Is The Common Element Between The Brass And Bronze Metal Alloys?

    Answer :

    Copper.

  29. Question 20. What Does The Alloy Designation Fg 250 Indicate?

    Answer :

    FG 250 alloy designation indicates Grey cast iron with a tensile strength of 250 MPa.

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  31. Question 21. Define Ceramic?

    Answer :

    Ceramic is a solid formed by the combination of metallic and non-metallic elements.

  32. Question 22. Give One Example Of Metal Classified As Per Structure As Bcc, Fcc, Hcp And Ccp?

    Answer :

    Examples of BCC, FCC, HCP and CCP structures:

    BCC (Body Centred Cubic) structure – molybdenum;

    FCC (Face Centred Cubic) structure – Aluminum;

    HCP (Hexagonal Close Packed) structure – Zinc;

    CCP (Cubic Close Packing) structure – Copper.

  33. Question 23. What Is The Name Of Solid Solution Of Carbon In Alpha-iron And Delta Iron?

    Answer :

    Ferrite and Austenite respectively.

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  35. Question 24. Explain The Difference Between Pear Lite And Cementite?

    Answer :

    Pearlite is a eutectoid mixture of ferrite and cementite. Cementide is a chemical compound of iron and carbon.

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  37. Question 25. Give One Example Each Of The Following Proportion Of Materials – Dimensional, Physical, Technological And Mechanical?

    Answer :

    Roughness, enthalpy, toughness and hardness respectively.

  38. Question 26. For Which Parts The Wahl Factor And Lewis Factor Is Used?

    Answer :

    Wahl factor and Lewis factor is used for springs and gears respectively.

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  40. Question 27. How Oxygen Gas Can Be Removed From Steel During Melting? What Are Fully Killed Steel?

    Answer :

    Oxygen gas can be removed from steel during melting by adding elements such as manganese, silicon or aluminium which, because of their high affinity for oxygen, react with it to form non-metallic oxides such as manganese oxide, silicon oxide and aluminium oxide. Which rise into the slag. Steels in which have has most of their dissolved oxygen removed are called ‘fully killed steels’.

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  42. Question 28. Hydrogen Cannot Be Removed Easily From Molten Steel. What Harm Hydrogen Has On Property Of Steel?

    Answer :

    Excessive hydrogen in molten steel results in the formation of small fissures often described as hairline cracks or flakes in the steel. Large forgings an alloy steel are particularly sensitive to this phenomenon.

  43. Question 29. What Is Allot Rope? In What Forms Of Cubic Pattern, Iron Exists?

    Answer :

    Some elements exist in more than one crystalline form. Each crystalline form is known as ‘allotrope’ of the element. Iron exists in two crystalline forms of cubic pattern, namely, body-centered cubic (BCC) and face-centered cubic (FCC).

  44. Question 30. When A Material Is Known As Allotropy Or Polytropic?

    Answer :

    A material is known as allotropic aur polytropic if it exists in several forms at a different temperature.