DESTRUCTIVE TESTS

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• Q1: What is a Hardness Test?
  Ans: A hardness test is a method used to determine a material's resistance to indentation, scratching, or wear.
• Q2: State the classification of Hardness Test.
  Ans: Hardness tests are classified as:

  • ➔ Brinell Hardness Test
  • ➔ Rockwell Hardness Test
  • ➔ Vickers Hardness Test
  • ➔ Shore Hardness Test
  • ➔ Rebound Hardness Test
• Q3: What is the Brinell Hardness Test?
  Ans: The Brinell hardness test measures hardness by pressing a hard steel or tungsten carbide ball into the material and measuring the diameter of the indentation.
• Q4: Name the parts of Brinell Hardness Testing Machine.
  Ans: The main parts are:

  • ➔ Load application system (weights or hydraulic)
  • ➔ Indenter (steel or tungsten carbide ball)
  • ➔ Specimen table
  • ➔ Measuring microscope or optical system
• Q5: State some limitations of Brinell Hardness Test.
  Ans: Limitations include:

  • ➔ Not suitable for very hard or thin materials
  • ➔ Surface must be smooth and clean
  • ➔ Indentation may be too large for small specimens
  • ➔ Slower and requires optical measurement
• Q6: Briefly discuss the working of Brinell Hardness Testing Machine.
  Ans: A load is applied to a ball indenter which presses into the material.
  After removing the load, the diameter of the indentation is measured using a microscope.
  Formula:
  
  HB = 2P / (π D (D - √(D² - d²)))
  
  Where
  P = load
  D = ball diameter
  d = indentation diameter
• Q7: What is the Rockwell Hardness Test?
  Ans: The Rockwell hardness test measures hardness by applying a minor and major load through a conical or ball indenter and reading the depth of penetration directly on a dial.
• Q8: Briefly discuss the working of Rockwell Hardness Testing Machine.
  Ans: First, a minor load is applied to seat the indenter.
  Then a major load is applied and removed.
  The depth of indentation is measured automatically and converted to a Rockwell hardness number (HR) on the dial.
• Q9: State some limitations of Rockwell Hardness Test.
  Ans: Limitations include:

  • ➔ Not suitable for very thin specimens
  • ➔ Surface must be smooth
  • ➔ Minor errors if indenter is worn
• Q10: Compare Rockwell Hardness Test and Brinell Hardness Test
  Ans: Comparison:

  • ➔ Rockwell is faster; Brinell requires optical measurement
  • ➔ Rockwell gives direct reading; Brinell needs calculation
  • ➔ Rockwell uses depth; Brinell uses indentation diameter
  • ➔ Brinell is better for rough surfaces; Rockwell for precise, thin specimens
• Q11: What is the Vicker’s Hardness Test?
  Ans: Vickers hardness test measures hardness using a diamond pyramid indenter and calculates hardness from the diagonal length of the indentation under a known load.
• Q12: Briefly discuss the working of Vicker’s Hardness Testing Machine.
  Ans: A diamond indenter is pressed onto the surface under a specific load.
  After removing the load, the two diagonals of the indentation are measured under a microscope.
  Hardness is calculated using:
  
  HV = 1.854 P / d²
  
  Where
  P = applied load
  d = average diagonal of indentation
• Q13: State some limitations of Vicker’s Hardness Test.
  Ans: Limitations include:

  • ➔ Requires optical measurement
  • ➔ Slow for mass testing
  • ➔ Surface must be polished
• Q14: What is the Shore Hardness Test?
  Ans: Shore hardness test measures the hardness of rubber or plastics by the depth of penetration of a spring-loaded indenter.
• Q15: Briefly discuss the working of Shore Hardness Testing Machine.
  Ans: A spring-loaded indenter is pressed onto the specimen.
  The depth of penetration is measured on a dial and converted to Shore hardness value.
• Q16: State some limitations of the Shore Hardness Test.
  Ans: Limitations include:

  • ➔ Only for soft materials like rubber and plastics
  • ➔ Sensitive to surface conditions
  • ➔ Cannot be used for metals
• Q17: What is the IZOD Impact Test?
  Ans: IZOD impact test measures the energy absorbed by a material during fracture from a sudden blow using a pendulum hammer.
• Q18: Briefly discuss the working of IZOD Hardness Testing Machine.
  Ans: A notched specimen is clamped vertically.
  A pendulum strikes the specimen and breaks it.
  The energy absorbed to fracture the specimen is measured from the pendulum swing.
• Q19: State some limitations of the IZOD Hardness Test.
  Ans: Limitations include:

  • ➔ Only measures impact toughness
  • ➔ Specimen preparation critical
  • ➔ Not suitable for large specimens
• Q20: What is a U.T.M?
  Ans: A U.T.M (Universal Testing Machine) is a machine used to test the mechanical properties of materials under tension, compression, bending, or shear.
• Q21: What is a U.T.M used for?
  Ans: A U.T.M is used to determine:

  • ➔ Tensile strength
  • ➔ Compressive strength
  • ➔ Flexural strength
  • ➔ Elongation and deformation properties
  • ➔ Modulus of elasticity
• Q22: State different parts of the Universal Testing machine.
  Ans: The main parts of a U.T.M are:

  • ➔ Load frame or main structure
  • ➔ Crosshead (movable part applying load)
  • ➔ Grips or fixtures to hold specimen
  • ➔ Load measuring unit (load cell or proving ring)
  • ➔ Extensometer for measuring elongation
  • ➔ Control and display system (manual or digital)
• Q23: Define Young’s Modulus.
  Ans: Young’s Modulus, or Modulus of Elasticity, is the ratio of tensile stress to tensile strain in the elastic range of a material.
  
  E = σ / ε
  
  Where σ = stress, ε = strain.
• Q24: What is a Shear Test?
  Ans: A shear test measures the ability of a material to resist forces that cause one layer to slide over an adjacent layer.
• Q25: State the scope of Shear Test.
  Ans: The shear test is used to:

  • ➔ Determine shear strength of materials
  • ➔ Study failure under torsional and cutting forces
  • ➔ Design machine elements like keys, bolts, and shafts
• Q26: What is a Point Bend Test?
  Ans: Point bend test is a type of bending test where a concentrated load is applied at the center of a supported specimen to determine flexural strength.
• Q27: Briefly explain the procedure of tensile test of mild steel.
  Ans: Steps of tensile test:

  • ➔ Prepare a mild steel specimen with standard dimensions.
  • ➔ Place the specimen in the grips of a U.T.M.
  • ➔ Apply tensile load gradually until the specimen fractures.
  • ➔ Record load and elongation data to calculate stress-strain characteristics.
  • ➔ Plot stress-strain curve and determine yield strength, ultimate tensile strength, and elongation.
• Q28: What is Proof Stress?
  Ans: Proof stress is the stress required to produce a specified permanent deformation, usually 0.2% strain, in a material.
• Q29: What is a Flexure Test?
  Ans: A flexure test measures the material’s ability to resist bending by applying a load at one or more points on a supported specimen.
• Q30: Which apparatus is used for the Flexure Test?
  Ans: A Universal Testing Machine (U.T.M) or a dedicated bending test apparatus is used for the flexure test.
• Q31: State the behaviour of material under Shearing Test.
  Ans: Under shearing test, the material resists sliding or cutting forces.
  It may fail by shearing along the plane of maximum shear stress.
• Q32: What is a Troptometer?
  Ans: A troptometer is an instrument used to measure torsional properties of shafts and materials under twisting loads.
• Q33: What is a Fatigue Test?
  Ans: Fatigue test evaluates how a material behaves under repeated cyclic loading and determines its fatigue life before failure.
• Q34: Briefly explain the procedure of Fatigue Test.
  Ans: Procedure of fatigue test:

  • ➔ Prepare a standard specimen.
  • ➔ Apply cyclic or repeated load using a fatigue testing machine.
  • ➔ Record the number of cycles until failure occurs.
  • ➔ Plot S-N curve (stress vs. number of cycles) to determine fatigue strength.
• Q35: What is Fatigue Failure?
  Ans: Fatigue failure is the progressive and localized structural damage that occurs when a material is subjected to repeated loading, leading to fracture at stress levels below the ultimate tensile stress.
• Q36: What is the effect of fatigue on metals?
  Ans: Effects of fatigue on metals include:

  • ➔ Cracks initiate at stress concentration points
  • ➔ Gradual reduction in strength
  • ➔ Premature failure even under low stress
  • ➔ Surface defects and roughness may accelerate failure
• Q37: Name the types of Fatigue Testing Machine.
  Ans: Types of fatigue testing machines:

  • ➔ Rotating Beam Fatigue Testing Machine
  • ➔ Axial Fatigue Testing Machine
  • ➔ Bending Fatigue Testing Machine
  • ➔ Torsional Fatigue Testing Machine
• Q38: What is a Loading Cycle?
  Ans: A loading cycle is one complete sequence of applied stress from zero to maximum and back to zero in a fatigue test.
• Q39: What is 82HRB?
  Ans: 82HRB indicates a Rockwell Hardness value measured on the B-scale with a hardness number of 82.
• Q40: What is Torsion?
  Ans: Torsion is the twisting of a material or shaft due to applied torque, producing shear stress in the cross-section.
• Q41: Name the parts of Torsion Testing Machine.
  Ans: Parts of a torsion testing machine include:

  • ➔ Torque applying system
  • ➔ Specimen grips or clamps
  • ➔ Angular displacement measuring device
  • ➔ Base frame and support structure
• Q42: What is the Endurance Limit?
  Ans: Endurance limit is the maximum stress a material can withstand indefinitely without failure under repeated or cyclic loading.