MATSCI Exam 2 Questions and Answers: A Complete Solution for 2024/2025, Exams of Nursing

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For impurities diffusing in solid materials, the diffusion rate will be [A] at higher temperature, and will be [B] when the required activation energy is greater. - CORRECT ANSWERS Higher, Lower Interstitial diffusion - CORRECT ANSWERS Motion of atoms from an interstitial position to a neighboring one Vacancy diffusion - CORRECT ANSWERS Motion of atoms from a normal lattice position to an adjacent empty position Steady-state diffusion - CORRECT ANSWERS The diffusion in which the diffusion flux is constant Nonsteady-state diffusion - CORRECT ANSWERS Diffusion in which the concentration of species is changing with time T or F: The diffusion in solid material is similar to that in liquids. It happens because all atoms are in random motion. - CORRECT ANSWERS False T or F: For atoms diffusing in solid materials, they have to overcome energy barriers to move one step at a time - CORRECT ANSWERS True T or F: The diffusion flux in a material will be zero if the concentrations of all atoms are uniform throughout the material - CORRECT ANSWERS True

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T or F: The diffusion flux in a material will be zero if the temperature is uniform throughout the material. - CORRECT ANSWERS False What is the difference between diffusion in solid materials and that in liquids? - CORRECT ANSWERS In liquids, diffusion is caused by random motion of all atoms. In solids, diffusion depends on atoms moving along vacancy or interstitial sites, they have to overcome energy barriers and move one step at a time. Ductility - CORRECT ANSWERS Degree of plastic deformation at fracture Hardness - CORRECT ANSWERS Resistance to localized plastic deformation Resilience - CORRECT ANSWERS The maximum energy that can be absorbed by the material through elastic deformation Toughness - CORRECT ANSWERS The maximum energy that can be absorbed by the material before fracture Stiffness - CORRECT ANSWERS The ratio between stress and strain in elastic deformation Yield Strength - CORRECT ANSWERS Stress at which plastic deformation begins

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Fatigue - CORRECT ANSWERS Failure of a material due to dynamic stresses Creep - CORRECT ANSWERS Slow and permanent deformation of materials under constant stresses Steel composed of iron and a small amount of carbon is a lot stronger than pure iron. - CORRECT ANSWERS Interstitial impurities dissolved in the host material can anchor dislocations and restrict their motion. When you cut a piece of metal, the edge of the piece is usually harder than the other regions. - CORRECT ANSWERS A plastically deformed region will have more dislocations that hinder the motion of nearby dislocations. If you measure the hardness of metal at the same location twice using a hardness tester, the second reading is larger than the first one. - CORRECT ANSWERS A plastically deformed region will have more dislocations that hinder the motion of nearby dislocations. Metals fracture easily after repeated bending. - CORRECT ANSWERS Micro cracks can gradually form, grow, and propagate through the material. The slip plane of a crystalline material usually refers to - CORRECT ANSWERS The crystal plane with the highest planar density in this crystal structure T or F: It is always true that the less defects, the stronger the material. - CORRECT ANSWERS False

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T or F: If we can make a metal to be single crystalline, it must be stronger than its polycrystalline form - CORRECT ANSWERS False T or F: When we heat a piece of metal and then cool it down, we are very likely to have reduced the amount of defects in it, but we may also have made it weaker. - CORRECT ANSWERS True T or F: A new piece of metal will probably become weaker if we strike it with a hammer. - CORRECT ANSWERS False The most common reason that leads to the failure of metallic materials in engineering applications is: - CORRECT ANSWERS The use of metals under changing stresses Treatments to make a metal last longer: - CORRECT ANSWERS - Diffuse some carbon into the metal

• Polish the surface of the material
• Compress the metal until it is plastically deformed under room temperature, then cut it into the desired shape Strengthening Mechanisms that hinder dislocation motion: - CORRECT ANSWERS Grain Size Reduction, Solid Solution Strengthening, Work hardening

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Which material below is under the highest stress? A. A ceramic tile with a 200-lb man standing on it, the contact area is 5" by 5" B. A toy car roof with a 30-lb child standing on it, the contact area is 1.5" by 2" C. A rope with a 10-lb rock hanging on it, the diameter of the rope is 1" - CORRECT ANSWERS C Which material below is under the highest strain (comparing the absolute value)? A.A 1m long post shortened by 1cm under compression B.A 20m wire elongated by 5cm under tension C.A 2cm long rubber band elongated by 2mm under tension - CORRECT ANSWERS C Young's modulus is a measure of a material's _______. - CORRECT ANSWERS Stiffness Poisson's ratio is a measure of a material's... - CORRECT ANSWERS Ratio of the lateral and axial strains, when the force is in axial direction

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Which of the following is NOT related to the strength of a material: A.Young's modulus B.Yield strength C.Tensile strength D.Hardness - CORRECT ANSWERS A Which of the following defects is responsible for the plastic deformation of materials: A.Point defects B.Linear defects C.Interfacial defects D.Volume defects E.All of the above - CORRECT ANSWERS B What is the fundamental mechanism behind common strategies to strengthen ductile metals? A.The increase of linear defects B.The decrease of linear defects C.The decrease of total defects