Plastic deformation MCQs With Answer

Introduction: Plastic deformation MCQs With Answer are essential for B. Pharm students studying mechanical behavior of pharmaceutical solids. Understanding plastic deformation helps explain tablet compaction, powder consolidation, and material failure during processing. This concise guide emphasizes key concepts—yield strength, ductility, work hardening, dislocation motion, slip systems, and the role of temperature and strain rate—in a pharmaceutical context. Familiarity with deformation mechanisms informs formulation choices, lubrication, and compression parameters to optimize tablet strength and reduce defects. Clear, exam-focused MCQs with answers reinforce theory and practical relevance for production and quality control. ‘Now let’s test your knowledge with 50 MCQs on this topic.’

Q1. What is plastic deformation?

• The reversible elastic stretching of a material
• The permanent change in shape after the yield point is exceeded
• The increase in temperature during compression
• The creation of voids in a material

Correct Answer: The permanent change in shape after the yield point is exceeded

Q2. Which defect primarily enables plastic deformation in crystalline solids?

• Vacancies
• Grain boundaries
• Dislocations
• Precipitates

Correct Answer: Dislocations

Q3. In powder compaction for tablets, which mechanism most directly contributes to particle bonding by permanent shape change?

• Elastic recovery
• Plastic deformation
• Surface tension
• Thermal expansion

Correct Answer: Plastic deformation

Q4. What term describes a material that exhibits large plastic deformation before fracture?

• Brittle
• Malleable or ductile
• Elastic
• Viscous

Correct Answer: Malleable or ductile

Q5. Which region of a stress–strain curve represents plastic deformation?

• Initial linear portion
• Beyond the yield point
• At zero stress
• Hooke’s law region

Correct Answer: Beyond the yield point

Q6. Work hardening (strain hardening) leads to which effect on the material?

• Decrease in yield strength
• Increase in ductility
• Increase in strength and hardness
• No change in mechanical properties

Correct Answer: Increase in strength and hardness

Q7. Which process can reverse work hardening in a metal or crystalline pharmaceutical excipient?

• Cold working
• Anodizing
• Annealing (recrystallization)
• Quenching

Correct Answer: Annealing (recrystallization)

Q8. Which test measures compressive strength relevant to tablets?

• Tensile test
• Hardness (crushing strength) test
• Impact test
• Bend test

Correct Answer: Hardness (crushing strength) test

Q9. Which factor increases the tendency for plastic deformation during tablet compression?

• Low compression force
• High brittleness of particles
• High temperature and ductile material
• Extremely high porosity without contact

Correct Answer: High temperature and ductile material

Q10. What is elastic recovery (springback) in tablets?

• Permanent deformation during compaction
• Recovery of some deformation after decompression
• Formation of cracks during compression
• Chemical degradation due to pressure

Correct Answer: Recovery of some deformation after decompression

Q11. Which equation is commonly used to analyze powder densification during compaction?

• Heckel equation
• Arrhenius equation
• Henderson equation
• Van ’t Hoff equation

Correct Answer: Heckel equation

Q12. In compaction, particle rearrangement occurs predominantly at which stage?

• At very high pressure after bonding
• Initial low-pressure stage
• During elastic recovery
• Only during storage

Correct Answer: Initial low-pressure stage

Q13. Which mechanism is NOT a major mode of particle deformation during compaction?

• Fragmentation
• Plastic deformation
• Elastic deformation
• Thermal melting

Correct Answer: Thermal melting

Q14. What is the role of lubricants (e.g., magnesium stearate) in tablet compaction regarding deformation?

• Increase interparticle bonding by welding
• Reduce die wall friction and change deformation behavior
• Cause fragmentation of particles
• Eliminate all elastic recovery

Correct Answer: Reduce die wall friction and change deformation behavior

Q15. Which property is most directly measured by a hardness tester for tablets?

• Viscosity
• Tensile/fracture strength under compression
• Thermal conductivity
• Electrical resistance

Correct Answer: Tensile/fracture strength under compression

Q16. Dislocation glide requires which of the following?

• Diffusion of atoms over long distances
• Movement of dislocation along slip planes under shear stress
• Complete fracture along grain boundaries
• Phase transformation

Correct Answer: Movement of dislocation along slip planes under shear stress

Q17. Which crystal characteristic affects ease of plastic deformation?

• Number of available slip systems
• Color of the crystal
• Magnetic properties
• Optical transparency

Correct Answer: Number of available slip systems

Q18. Twin formation in crystals is which type of deformation?

• Diffusive creep
• Reversible elastic deformation
• Crystal lattice reorientation (a plastic mechanism)
• Surface erosion

Correct Answer: Crystal lattice reorientation (a plastic mechanism)

Q19. High strain rate during deformation typically results in what effect?

• More time for dislocation recovery and softer material
• No change compared to low strain rate
• Increased apparent strength and less ductility
• Immediate annealing

Correct Answer: Increased apparent strength and less ductility

Q20. Creep refers to:

• Immediate elastic deformation under load
• Time-dependent plastic deformation under constant stress
• Thermal expansion only
• Fracture without plasticity

Correct Answer: Time-dependent plastic deformation under constant stress

Q21. Which pharmaceutical excipient is known for plastic deformation behavior under compression?

• Lactose monohydrate (brittle)
• Microcrystalline cellulose (MCC)
• Calcium phosphate (very brittle)
• Silicon dioxide (inert)

Correct Answer: Microcrystalline cellulose (MCC)

Q22. Which of the following indicates brittle fracture rather than plastic deformation?

• Large necking before failure
• Sudden crack and little prior deformation
• Significant elongation
• High work hardening

Correct Answer: Sudden crack and little prior deformation

Q23. What is the significance of porosity in compaction and plastic deformation?

• Porosity is irrelevant to compaction
• Higher porosity always increases tablet strength
• Porosity affects contact points, densification and final mechanical strength
• Porosity only affects color

Correct Answer: Porosity affects contact points, densification and final mechanical strength

Q24. Which measurement evaluates powder compressibility including plastic deformation?

• Friability test
• Tapped density and compressibility index
• pH measurement
• Moisture vapor transmission rate

Correct Answer: Tapped density and compressibility index

Q25. Which phenomenon reduces tablet strength if excessive during mixing with lubricant?

• Enhanced plasticity
• Over-lubrication causing coating of particle surfaces and reduced bonding
• Increased porosity leading to stronger bonds
• Improved dislocation motion

Correct Answer: Over-lubrication causing coating of particle surfaces and reduced bonding

Q26. Which parameter from stress–strain testing is a direct indicator of yield strength?

• Maximum strain at failure
• Stress at which permanent deformation begins
• Initial slope (elastic modulus)
• Area under curve

Correct Answer: Stress at which permanent deformation begins

Q27. Which atomic-scale barrier must dislocations overcome to move, influencing plasticity?

• Peierls–Nabarro stress
• Boiling point
• Melting enthalpy
• Van der Waals force

Correct Answer: Peierls–Nabarro stress

Q28. Which of the following increases ductility in crystalline materials?

• Fine grain size (extremely small)
• Increased temperature promoting dislocation mobility
• High concentration of brittle second phases
• Strong grain boundary embrittlement

Correct Answer: Increased temperature promoting dislocation mobility

Q29. Which process is dominant for plastic flow in amorphous pharmaceutical polymers?

• Dislocation glide
• Viscous flow and molecular chain mobility
• Slip on crystallographic planes
• Twinning

Correct Answer: Viscous flow and molecular chain mobility

Q30. During tablet compression, fragmentation of brittle particles contributes to:

• Decreased surface area for bonding
• Increased contact area and potential bonding
• Complete prevention of plastic deformation
• Reduction in density only

Correct Answer: Increased contact area and potential bonding

Q31. Which parameter describes the elastic stiffness of a material?

• Yield strength
• Young’s modulus (elastic modulus)
• Fracture toughness
• Poisson’s ratio only

Correct Answer: Young’s modulus (elastic modulus)

Q32. Which behavior is characteristic of viscoelastic materials under stress?

• Purely reversible elastic deformation only
• Time-dependent combination of viscous and elastic deformation
• Instant fracture without deformation
• Permanent deformation irrespective of time

Correct Answer: Time-dependent combination of viscous and elastic deformation

Q33. Grain boundaries often act as:

• Barriers to dislocation motion and sites for fracture
• Perfect slip planes aiding plastic deformation
• Sources of light emission
• Only thermal insulators

Correct Answer: Barriers to dislocation motion and sites for fracture

Q34. Which test is commonly used to assess tablet friability related to deformation and surface damage?

• Friabilator test
• pH meter test
• Disintegration only
• Viscometer test

Correct Answer: Friabilator test

Q35. What effect does increasing lubricant concentration generally have on tablet mechanical strength?

• Always increases strength
• Can decrease strength if excessive due to reduced bonding
• Has no effect on strength
• Makes tablets explode on ejection

Correct Answer: Can decrease strength if excessive due to reduced bonding

Q36. Which is a common sign of elastic-dominated deformation in a compressed tablet?

• Permanent flattening of particles
• Significant springback and capping
• Enhanced interparticle bonding
• Improved hardness

Correct Answer: Significant springback and capping

Q37. Which phenomenon is important when considering high-temperature plastic deformation?

• Increased Peierls stress
• Reduced dislocation mobility
• Enhanced diffusion and dislocation climb
• Magnetostriction

Correct Answer: Enhanced diffusion and dislocation climb

Q38. The Kawakita equation is used to describe:

• Chemical degradation kinetics
• Volume reduction and compressibility of powders under pressure
• Surface tension changes
• Moisture sorption isotherms

Correct Answer: Volume reduction and compressibility of powders under pressure

Q39. Which factor reduces die wall friction during compaction and affects plastic flow?

• Absence of lubrication
• Use of appropriate lubricants and smooth tooling surfaces
• Increased particle size only
• High humidity alone

Correct Answer: Use of appropriate lubricants and smooth tooling surfaces

Q40. Which microstructural change strengthens a material by impeding dislocation movement?

• Grain growth
• Precipitation hardening and particle dispersion
• Complete recrystallization
• Homogenization of phases

Correct Answer: Precipitation hardening and particle dispersion

Q41. Which of the following best describes slip systems?

• Paths for thermal conduction
• Specific crystallographic planes and directions along which dislocations move
• Only grain boundary locations
• Regions of chemical impurities

Correct Answer: Specific crystallographic planes and directions along which dislocations move

Q42. What is the primary result of cold working on metals or crystalline excipients?

• Decrease in dislocation density
• Increase in dislocation density and strength
• Instant melting
• Transition to amorphous state

Correct Answer: Increase in dislocation density and strength

Q43. Which property is directly relevant to preventing tablet capping and lamination?

• Tablet color
• Uniform plastic deformation and sufficient interparticle adhesion
• Tablet odor
• Electrical conductivity

Correct Answer: Uniform plastic deformation and sufficient interparticle adhesion

Q44. Recrystallization temperature after cold work is typically:

• Lower for heavily deformed materials and depends on purity
• Independent of prior deformation
• Always at room temperature
• Only relevant to polymers

Correct Answer: Lower for heavily deformed materials and depends on purity

Q45. Which phenomenon explains permanent set in amorphous polymer compacts under load?

• Dislocation glide
• Chain segment rearrangement and plastic flow
• Crystal slip systems activation
• Ion exchange

Correct Answer: Chain segment rearrangement and plastic flow

Q46. What is the effect of moisture on plastic deformation of hygroscopic powders?

• Moisture generally reduces plasticity in all cases
• Moisture can act as a plasticizer increasing ductility and promoting plastic deformation
• Moisture converts particles to gas
• Moisture has no mechanical effect

Correct Answer: Moisture can act as a plasticizer increasing ductility and promoting plastic deformation

Q47. Which parameter from Heckel analysis indicates yield under pressure (plasticity)?

• Intercept only (A)
• Slope (k), related to yield and compressibility
• Surface area alone
• Molecular weight of drug

Correct Answer: Slope (k), related to yield and compressibility

Q48. Fracture toughness is most closely related to which material behavior?

• Resistance to crack propagation
• Elastic modulus only
• Color change under stress
• Electrical conductivity

Correct Answer: Resistance to crack propagation

Q49. Which is a desirable property of excipients to promote plastic deformation during tablet formation?

• High brittleness and no ductility
• Good plasticity, compressibility and bonding ability
• Complete insolubility in all solvents
• Strong magnetism

Correct Answer: Good plasticity, compressibility and bonding ability

Q50. Why is understanding plastic deformation important for B. Pharm students?

• It only matters to metallurgists, not pharmacists
• It helps in designing formulations, optimizing compaction and ensuring tablet quality and mechanical integrity
• It replaces knowledge of chemical compatibility
• It is only relevant for color matching

Correct Answer: It helps in designing formulations, optimizing compaction and ensuring tablet quality and mechanical integrity

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