3rd Quiz - Materials Science Quiz PDF

Dislocations and Strengthening Mechanisms Multiple Choices Questionnaire (2pts each) 1. What is a dislocation in the context of materials science? A. A type of atom that causes material strength B. A linear crystalline defect in the atomic structure C. A defect caused by heat t...

Dislocations and Strengthening Mechanisms Multiple Choices Questionnaire (2pts each) 1. What is a dislocation in the context of materials science? A. A type of atom that causes material strength B. A linear crystalline defect in the atomic structure C. A defect caused by heat treatment D. A type of grain boundary ANSWER: B 2. When was the existence of dislocations directly observed? A. 1920s B. 1940s C. 1950s D. 1970s ANSWER: C 3. What are the two primary types of dislocations? A. Point and line dislocations B. Edge and screw dislocations C. Edge and surface dislocations D. Twinning and screw dislocation ANSWER: B 4. Which of the following best describes an edge dislocation? A. A dislocation where atoms move in parallel to the stress direction B. A dislocation where an extra half-plane of atoms is inserted C. A dislocation with no atomic bond distortions D. A dislocation with no associated stress fields ANSWER: B 5. What is the motion of a screw dislocation? A. The dislocation moves in the direction of the applied stress B. The dislocation moves perpendicular to the applied stress C. The dislocation does not move under stress D. The dislocation causes atom displacement in only one plane ANSWER: B 6. What is the term used to describe permanent deformation of materials by dislocation motion? A. Creep B. Elastic deformation C. Slip D. Strain hardening ANSWER: C 7. Which of the following is true about a slip system? A. The slip system consists of only one dislocation direction B. The slip system involves the movement of dislocations along a slip plane and direction C. The slip system only occurs in materials with cubic crystal structures D. The slip system involves only edge dislocations ANSWER: B 8. What is a slip plane? A. A plane where slip occurs least easily B. The plane with the lowest density of atoms C. The plane with the highest density of atoms D. The plane where atoms are compressed together ANSWER: C 9. What is slip direction? A. The direction in which atoms are displaced B. The plane where the dislocation line is located C. The direction in which dislocations move within the slip plane D. The direction of applied stress ANSWER: C 10. What does grain size reduction do to a material's strength? A. Decreases strength by reducing dislocation movement B. Increases strength by increasing grain boundaries C. Has no effect on strength D. Decreases ductility without changing strength ANSWER: B 11. According to the Hall-Petch Equation, what happens as grain size decreases? A. Yield strength increases B. Yield strength decreases C. Ductility increases D. Ductility decreases ANSWER: A 12. Which of the following strengthening mechanisms involves adding alloying elements to a metal? A. Grain size reduction B. Solid solution strengthening C. Strain hardening D. Recovery ANSWER: B 13. What type of impurity atom replaces a host atom in solid solution strengthening? A. Interstitial impurity B. Substitutional impurity C. Both interstitial and substitutional impurities D. None of the above ANSWER: B 14. What type of impurity atoms fill the gaps between atoms in solid solution strengthening? A. Substitutional impurities B. Interstitial impurities C. Both substitutional and interstitial impurities D. Alloying impurities ANSWER: B 15. Which strengthening mechanism involves the metal becoming stronger after plastic deformation? A. Strain hardening B. Grain size reduction C. Recovery D. Solid solution strengthening ANSWER: A 16. What is the effect of strain hardening on a metal? A. It makes the metal more ductile B. It makes the metal more brittle C. It decreases the yield strength D. It decreases the hardness of the material ANSWER: B 17. What is percent cold work (PCW) a measure of? A. The amount of strain applied during heat treatment B. The amount of deformation in a material expressed as a percentage C. The number of dislocations in a material D. The yield strength of a material ANSWER: B 18. Which of the following is the formula for percent cold work? A0− Ad A. %CW = ( ) x 100 Ad− Ao B. %CW = ( ) x 100 A0 A0 C. %CW = ( ) x 100 A d A D. %CW = ( d) x 100 A0 ANSWER: A 19. What is recovery in the context of metal deformation? A. The process of restoring strength through cold work B. Mild heating to allow dislocations to rearrange without affecting hardness C. High-temperature heating to create new grain structures D. The process of adding impurity atoms to increase strength ANSWER: B 20. What occurs during recrystallization? A. Dislocation density increases B. New, strain-free grains form, reducing dislocation density C. The material becomes more brittle D. The material retains its original grain structure ANSWER: B 21. What happens during grain growth? A. Grain boundaries increase, which increases strength B. The grains shrink, making the material more ductile C. The new grains grow larger, reducing the number of grain boundaries and strength D. The material becomes harder and more brittle ANSWER: C 22. What is the primary role of grain boundaries in strengthening metals? A. They act as obstacles to dislocation motion B. They increase the ductility of the material C. They promote the movement of dislocations D. They reduce the yield strength of the material ANSWER: A 23. Which technique is most effective for strengthening polycrystalline materials? A. Solid solution strengthening B. Grain size reduction C. Strain hardening D. Recovery ANSWER: B 24. What happens when metals undergo extensive plastic deformation at low temperatures? A. They recover their ductility B. They become softer C. They experience strain hardening D. Their crystal structure becomes more ordered ANSWER: C 25. Which of the following is NOT a stage in the recovery, recrystallization, and grain growth process? A. Recovery B. Recrystallization C. Precipitation hardening D. Grain growth ANSWER: C Multiple Choice (1 point each) 1. What are polymers? a) Small molecules b) Large molecules made up of repeating units c) Mixtures of different substances d) Single atoms Answer: b 2. What are the repeating units in polymers called? a) Monomers b) Isomers c) Dimers d) Atoms Answer: a 3. Which of the following is a natural polymer? a) Nylon b) Teflon c) Rubber d) Polystyrene Answer: c 4. Which polymer is used to make plastic bags? a) Polyethylene b) Polystyrene c) Polypropylene d) Polyvinyl chloride Answer: a 5. Which polymer is known for its elasticity? a) Nylon b) Rubber c) Polyethylene d) PVC Answer: b 6. Which polymer is commonly used to make pipes? a) PVC b) Nylon c) Polystyrene d) Bakelite Answer: a 7. Which polymer is lightweight, strong, and used in packaging? a) Polyethylene b) Nylon  c) Bakelite d) Teflon Answer: a 8. Which of the following is a synthetic polymer? a) Silk b) Wool c) Teflon d) Starch Answer: c 9. What is the main monomer used to make polystyrene? a) Ethylene b) Styrene c) Propylene d) Vinyl chloride Answer: b 10. What is cross-linking in polymers? a) Joining of monomers b) Formation of covalent bonds between polymer chains c) Breaking of polymer chains d) Mixing two polymers Answer: b 11. What is the main feature of biodegradable polymers? a) High durability b) Break down into harmless substances in the environment c) Resistance to chemicals d) High melting point Answer: b 12. Which polymer is used for making bottles? a) PVC b) PET c) Bakelite d) Nylon Answer: b 13. What is Bakelite used for? a) Packaging b) Electrical insulators c) Clothing d) Food containers Answer: b 14. What is the process called when monomers join without producing any byproduct?  a) Addition polymerization b) Condensation polymerization c) Crystallization d) Vulcanization Answer: a 15. What property allows polymers to stretch and return to their original shape? a) Rigidity b) Elasticity c) Plasticity d) Compressibility Answer: b 16. Which polymer is used for making bulletproof vests? a) Polypropylene b) Kevlar c) Nylon-6 d) Polystyrene Answer: b 17. What property of polymers makes them suitable for use as insulators in electrical applications? a) High conductivity b) Low density c) Poor thermal and electrical conductivity d) High flexibility Answer: c 18. What is a key factor affecting the strength of a polymer? a) The size of the polymer b) The number of impurities in the polymer c) The arrangement of molecular chains (degree of crystallinity) d) The color of the polymer Answer: c 19. Which property of polymers is enhanced by cross-linking? a) Solubility in water b) Flexibility c) Thermal and chemical resistance d) Transparency Answer: c 20. Why are polymers like polystyrene used for insulation? a) High toughness b) Low thermal conductivity c) High biodegradability  d) High electrical conductivity Answer: b 21. What does the molecular mass of a polymer represent? a) The mass of a single polymer chain b) The total mass of monomers used c) The average mass of polymer molecules in a sample d) The mass of a single repeating unit Answer: c 22. Which term is used to describe the average molecular mass of polymers weighted by the number of molecules? a) Weight-average molecular mass b) Number-average molecular mass c) Polydispersity index d) Relative molecular mass Answer: b 23. The Polydispersity index (PDI) is calculated using which formula? a) PDI=Mn + Mw b) PDI=Mw - Mn c) PDI=Mw / Mn d) PDI=Mn / Mw Answer: c 24. What is the value of the Polydispersity index (PDI) of natural polymers? a) 0 b) ½ c) 1 d) 2 Answer: c 25. Which of the following accurately describes weight-average molecular mass (Mw)? a) The molecular mass averaged by the number of molecules b) The molecular mass averaged by the weight of molecules c) The molecular mass of the longest chain in the polymer sample d) The molecular mass of the lightest chain in the polymer sample Answer: b 1. Why is it important to study failure? a) To increase production speed b) To understand the mechanics of various failure modes – fracture, fatigue, and creep. c) To decrease material costs d) To improve aesthetic design of components ANSWER: b 2. What is one of the three usual causes of failure? a) Excessive use of lubricants b) Improper material selection and processing c) Frequent maintenance d) Excessive safety margins ANSWER: b 3. Which type of fracture is usually preferred? a) Brittle fracture b) Ductile fracture c) Complex fracture d) Instantaneous fracture ANSWER: b 4. Why is ductile fracture preferred over brittle fracture? a) It occurs with no prior deformation b) It provides a warning before failure due to plastic deformation c) It is less energy-intensive to induce d) It has a smoother fracture surface ANSWER: b 5. Which type of environment-assisted fatigue failure involves fluctuating thermal stresses? a) Chemical fatigue b) Thermal fatigue c) Mechanical fatigue d) Electrical fatigue ANSWER: b 6. What are the three usual causes of failure? a) Improper material selection and processing, inadequate component design, component misuse b) Excessive use, environmental factors, poor design c) High temperatures, high pressures, corrosive environments d) Mechanical overload, thermal expansion, vibration ANSWER: a 7. Which type of fracture occurs with very little accompanying plastic deformation? a) Ductile fracture b) Brittle fracture c) Fatigue fracture d) Creep fracture ANSWER: b 8. What is the main characteristic of brittle fracture? a) It occurs with extensive plastic deformation b) It spreads rapidly and is perpendicular to the tensile load c) It requires high energy to propagate d) It forms a cup-and-cone profile ANSWER: b 9. What type of failure is the single largest cause of failure in metals? a) Creep b) Fatigue c) Fracture d) Corrosion ANSWER: b 10. Which testing techniques are used to measure impact energy? a) Tensile and compression tests b) Charpy and Izod tests c) Hardness and toughness tests d) Bending and shear tests ANSWER: b 11. What is fatigue? a) Failure due to static stress b) Failure that occurs after repeated stress or strain cycling c) Failure caused by thermal expansion d) Failure due to corrosion ANSWER: b 12. What is the definition of creep? a) Time dependent and permanent deformation of materials when subjected to a constant load or stress b) Sudden failure under static load c) Temporary deformation under cyclic load d) Instantaneous failure due to thermal stress ANSWER: a 13. Which phase of creep involves a constant creep rate? a) Primary creep b) Secondary creep c) Tertiary creep d) Initial creep ANSWER: b 14. What type of creep occurs at elevated temperatures due to fluctuating stresses? a) Thermal creep b) Chemical creep c) Static creep d) Dynamic creep ANSWER: a 15. Which type of crack is more stable, requiring an increase in applied stress to propagate? a) Brittle crack b) Ductile crack c) Micro crack d) Macro crack ANSWER: b 16. What does the stress concentration factor depend on? a) Material hardness b) Temperature c) Crack tip radius and crack length d) Load frequency ANSWER: c 17. In which type of fracture do cracks spread extremely rapidly? a) Ductile fracture b) Brittle fracture c) Fatigue fracture d) Creep fracture ANSWER: b 18. What is the primary cause of thermal fatigue? a) Chemical attack b) High mechanical loads c) Fluctuating thermal stresses d) Constant static load ANSWER: c 19. What is the main focus of fracture mechanics? a) Designing components for aesthetic purposes b) Understanding the formation and propagation of cracks c) Increasing the speed of production processes d) Reducing the cost of materials ANSWER: b 20. Which phase of creep occurs first and involves a continuously decreasing creep rate? a) Primary creep b) Secondary creep c) Tertiary creep d) Final creep ANSWER: a 21. What does the Charpy test measure? a) Material hardness b) Impact energy c) Tensile strength d) Creep resistance ANSWER: b 22. Which factor can significantly increase the maximum stress at the crack tip? a) Temperature increase b) Small tip radius of curvature c) Large component size d) Reduced load frequency ANSWER: b 23. What type of fracture is characterized by a cup-and-cone profile? a) Brittle fracture b) Ductile fracture c) Fatigue fracture d) Creep fracture ANSWER: b 24. Which environment-assisted fatigue failure involves chemical attack during cyclic stress? a) Thermal fatigue b) Corrosion fatigue c) Mechanical fatigue d) Electrical fatigue ANSWER: b 25. In the context of creep, what does tertiary creep signify? a) Decrease in creep rate b) Constant creep rate c) Acceleration of the creep rate leading to failure d) Initial stage of creep ANSWER: c