INSTUDERINGSFRÅGOR MED SVAR DUGGA 2 PDF

Structure of Metals What is the difference between a unit cell and a grain? A unit cell is the smallest repeating structure in a crystal, while a grain is a collection of unit cells with the same orientation List the three basic atomic arrangements in metals and provide two examples for each c...

Structure of Metals What is the difference between a unit cell and a grain? A unit cell is the smallest repeating structure in a crystal, while a grain is a collection of unit cells with the same orientation List the three basic atomic arrangements in metals and provide two examples for each crystal structure. BCC (Body-Centered Cubic): Each unit cell has one atom at the center and eight atoms at the corners. Examples: Iron (at room temperature), Tungsten. FCC (Face-Centered Cubic): Atoms are arranged at the corners and the centers of all cube faces. Examples: Aluminum, Copper. HCP (Hexagonal Close-Packed): Atoms are arranged in a hexagonal structure, maximizing packing efficiency. Examples: Magnesium, Titanium. Expand the abbreviations bcc, fcc, and hcp crystal structures to their full names. BCC: Body-Centered Cubic. FCC: Face-Centered Cubic. HCP: Hexagonal Close-Packed. What are the two general mechanisms of plastic deformation in metals? Slip: Dislocation motion occurs along specific crystallographic planes, leading to permanent shape change. Twinning: A part of the crystal lattice mirrors across a plane, commonly occurring in materials with limited slip systems, like HCP metals What is the main difference between elastic and plastic deformation? Elastic deformation is temporary and reversible; the material returns to its original shape once the stress is removed. Plastic deformation is permanent, where the material does not recover its original shape after the stress is released. Define anisotropy. Anisotropy refers to the directional dependence of a material's properties. For example, a material may exhibit different mechanical or thermal properties when measured along different axes. What is the Hall-Petch equation? Identify and name all the terms in the equation. The Hall-Petch equation relates the yield strength of a material to its grain size: σy=σ0+kdd−1/2 σy: Yield strength (MPa). σ0: Material's intrinsic strength (MPa). kd: Hall-Petch constant, dependent on the material (MPa·mm 1/2). dd: Average grain diameter (mm). How is grain size related to yield strength? Smaller grains increase yield strength due to more grain boundaries, which act as barriers to dislocation motion. This phenomenon is explained by the Hall-Petch relationship. Recovery, recrystallization, and grain growth occur when a cold-worked metallic sample is heated. What happens during recovery, recrystallization, and grain growth? Recovery: Dislocations rearrange or are annihilated, reducing residual stresses and restoring electrical and thermal properties without forming new grains. Recrystallization: New, stress-free grains nucleate and grow, replacing deformed grains, restoring ductility while lowering strength. Grain growth: Existing grains grow larger at the expense of smaller grains, reducing grain boundary area and further decreasing strength. Which property among the following increases during the recrystallization process? Strength, ductility, hardness, or residual stresses Ductility increases, as new grains form without the residual stresses and strain hardening from cold working. What is the difference between hot working and cold working? Hot working: Performed above the material’s recrystallization temperature; allows significant deformation without strain hardening, improving ductility. Cold working: Below recrystallization temperature; increases strength through strain hardening but reduces ductility and introduces residual stresses. What are the homologous temperature ranges for cold working, hot working, and warm working? Cold working: 0.5Tm Tm = melting point Two parts have been made from the same SS1672 material: one formed by cold working and the other by hot working. Explain the differences you might observe between the two. Cold-worked part: Higher strength and hardness due to strain hardening. Lower ductility and more residual stresses. Smoother surface finish. Hot-worked part: Lower strength and hardness. Higher ductility and reduced residual stresses. Rougher surface with potential scaling from high temperatures Mechanical Behavior Describe the events that occur during a tensile test on a specimen. Sketch a typical stress-strain curve for a low-carbon steel sample and label all significant regions and points on the curve. Assume the loading continues up to fracture.  Elastic deformation: The material stretches reversibly according to Hooke’s law. Yielding: The transition from elastic to plastic deformation occurs, and the material deforms permanently. Plastic deformation: The material elongates significantly under load. Necking: A localized reduction in cross-section occurs before fracture. Fracture: The material breaks into two parts. What is the transition point between elastic and plastic deformation called? Yield point: The stress level where the material transitions from elastic deformation to plastic deformation. What is meant by yield stress? Yield stress: The minimum stress required to initiate plastic deformation in a material. State Hooke’s law. Hooke’s law: Stress is directly proportional to strain within the elastic limit. σ=E⋅ϵ, where σ is stress, EE is Young’s modulus, and ϵϵ is strain. What is the formula for Young’s modulus in terms of stress and strain? E=ϵ/σ, where: E: Young’s modulus (Pa). σ: Stress (Pa). ϵ: Strain (dimensionless) Define Poisson’s ratio. Poisson’s ratio: The ratio of lateral strain to axial strain in a material subjected to uniaxial stress. What is the typical range of Poisson’s ratio for metals? Typical range: 0.25–0.35. What is ductility, and how is it measured? Ductility = plasticitet: The ability of a material to deform plastically without fracture. Measured by: Percent elongation or percent reduction in area after fracture. Explain the effect of temperature on the mechanical properties of carbon steel, particularly elongation, yield strength, tensile strength, and elastic modulus. Elongation: Increases with temperature, enhancing ductility. Yield strength: Decreases with higher temperature. Tensile strength: Decreases with temperature. Elastic modulus: Reduces slightly at elevated temperatures. Define the modulus of rigidity. Modulus of rigidity (Shear modulus): The ratio of shear stress to shear strain in a material, denoted as GG. What is hardness? List four different hardness testing methods. Hardness: The resistance of a material to deformation, indentation, or scratching.  Methods: Brinell, Rockwell, Vickers, and Mohs hardness tests. Describe the indenter used in the Vickers hardness test and provide the formula for the hardness number. Name all terms in the formula with their respective units. Indenter: A diamond-shaped pyramid with a square base and an apex angle of 136°. Formula: HV=(1.8544⋅F)/d2, where: HV: Vickers hardness number (kgf/mm²). F: Applied load (kgf). d: Diagonal length of the indentation (mm) What is meant by the endurance limit? Endurance limit: The maximum stress amplitude a material can withstand for an infinite number of cycles without failure Sketch a typical S-N curve for 1045 steel and the 2014-T6 aluminum alloy. Draw a schematic of a typical creep curve and label all the different stages of creep. What is the Charpy test, and why is it useful? Charpy test: A test that measures the energy absorbed during fracture of a notched specimen under impact. Usefulness: Helps evaluate toughness and the material's ductile-to-brittle transition. Describe the differences between brittle and ductile fractures. Brittle fracture: Sudden failure with little or no plastic deformation; the fracture surface is often flat and shiny. Ductile fracture: Failure with significant plastic deformation; fracture surface shows dimples and necking. What is meant by the ductile-to-brittle transition temperature? Ductile-to-brittle transition temperature: The temperature below which a material transitions from ductile to brittle behavior under impact loading Name two typical fracture modes in the brittle failure of metallic samples. Modes: Cleavage and intergranular fracture. What do beach marks on a fracture surface indicate? Beach marks: Indicate fatigue failure caused by cyclic loading. They represent incremental crack growth How does surface finish affect the fatigue strength of a steel shaft? Effect: A rough surface decreases fatigue strength by introducing stress concentrators, while a smooth surface improves fatigue resistance. Why are tensile residual stresses considered undesirable, and how can compressive residual stresses improve component performance? Tensile stresses: Promote crack initiation and growth, reducing fatigue life. Compressive stresses: Suppress crack formation, improving fatigue and wear resistance. Physical Properties of Materials Arrange the following materials in descending order of density: Aluminum, Gold, Steel, and Plastics. Gold > Steel > Aluminum > Plastics Order the materials Tungsten, Copper, Lead, and Aluminum by their melting points from highest to lowest. ungsten > Copper > Aluminum > Lead Name two low thermal expansion alloys. Alloys: Invar and Kovar. Which property is utilized in shrink fits? Property: Thermal expansion, as heating or cooling creates an interference fit by adjusting dimensions. Under which property classification does "breakdown potential" fall? Classification: Electrical properties. Name two applications of superconductors in modern technology. Applications: Magnetic resonance imaging (MRI) and particle accelerators. List three thermal properties. Thermal conductivity, thermal expansion, specific heat capacity List three electrical properties. Electrical conductivity, resistivity, dielectric strength. List three magnetic properties. Permeability, coercivity, magnetic susceptibility. List three optical properties. Refractive index, absorption, reflectivity Metallic Materials What is the carbon content in steel and cast iron? Steel: 0.02–2.1%. Cast iron: 2.1–4.0%. Name four types of cast irons. Types: Gray iron, white iron, ductile iron, malleable iron What type of crystal structure does α-iron has? Crystal structure: Body-centered cubic (BCC)  What type of crystal structure does γ-iron has? Crystal structure: Face-centered cubic (FCC) List one application each for low-carbon steel, medium-carbon steel, and high-carbon steel. Low-carbon steel: Structural beams. Medium-carbon steel: Automotive components. High-carbon steel: Cutting tools. How does the carbon content in steel affect its tensile strength and ductility? Higher carbon: Increases tensile strength but reduces ductility. Lower carbon: Enhances ductility but decreases tensile strength. Name two benefits of heat treatment. Benefits: Improves hardness and enhances toughness. Name four heat treatment processes primarily used for plain carbon steels. Processes: Annealing, quenching, tempering, normalizing. List any four processes used in case hardening. Processes: Carburizing, nitriding, carbonitriding, flame hardening. Name three common applications of case-hardened components. Applications: Gears, camshafts, bearings. Which element is primarily responsible for the corrosion resistance in stainless steel? Element: Chromium. What is the typical chromium content range in stainless steel? Range: 10.5–30%. What happens to steel with less than 10.5% chromium when exposed to oxygen? Effect: Forms rust due to insufficient chromium to create a protective oxide layer Name three precious metals. Metals: Gold, platinum, silver. Name three refractory metals. Metals: Tungsten, molybdenum, tantalum Why are aluminum and magnesium classified as light metals? Reason: Low density compared to most metals. What property of aluminum contributes to its excellent corrosion resistance? Formation of a protective oxide layer. What precautions are necessary when machining magnesium and why? Precautions: Avoid high heat to prevent ignition, as magnesium is highly flammable.  Name two common copper alloys and their primary alloying elements. Alloys: Brass (copper + zinc). Bronze (copper + tin). List four common trade names for nickel-based alloys. Trade names: Inconel, Monel, Hastelloy, Nimonic Name the three primary types of superalloys and their base elements. Types: Nickel-based (nickel). Cobalt-based (cobalt). Iron-based (iron) Name two common nickel-based superalloys. Superalloys: Inconel, Hastelloy What is the most widely used titanium alloy, and what phases does it contain? Alloy: Ti-6Al-4V. Phases: Alpha and beta phases What are the key properties of refractory metals that make them suitable for high- temperature applications? Properties: High melting points, excellent strength at elevated temperatures, and good thermal conductivity. Polymers, Ceramics, and Composite Materials What are the two main types of polymerization processes? Types: Addition polymerization, condensation polymerization. What type of bond links monomers together to form polymer chains? Bond type: Covalent bonds Name three types of secondary bonds that hold polymer chains together. Secondary bonds: Hydrogen bonds, van der Waals forces, dipole-dipole interactions. How does the molecular weight of a polymer affect its strength and viscosity? Effect: Higher molecular weight increases strength and viscosity by improving chain entanglement and interaction. What is the difference between an amorphous polymer and a semicrystalline polymer? Amorphous polymer: Lacks a defined structure, with molecules arranged randomly. Semicrystalline polymer: Has ordered crystalline regions interspersed with amorphous areas  What properties of a polymer are influenced by the degree of crystallinity? Properties: Strength, rigidity, density, thermal resistance, and chemical resistance. What is crystallization shrinkage, and why does it occur in polymers? Crystallization shrinkage: Reduction in volume as a polymer crystallizes, occurring because ordered crystalline structures occupy less space than disordered regions. What happens to thermoplastics when repeatedly heated and cooled? Effect: Thermoplastics soften upon heating and harden when cooled, allowing them to be reshaped repeatedly without chemical degradation. What are thermosetting plastics, and how are they structurally different from thermoplastics? Thermosetting plastics: Plastics that harden permanently after being heated and shaped, forming cross-linked polymer networks. Difference: Thermosetting plastics cannot be remelted, unlike thermoplastics. What is the main difference between thermoplastics and thermosetting plastics? Difference: Thermoplastics can be remelted and reshaped, whereas thermosetting plastics undergo irreversible chemical changes during curing. How are the strength and hardness of thermosetting plastics affected by temperature? Effect: Thermosetting plastics become more brittle at higher temperatures and may degrade if exposed to excessive heat. Name two thermoplastics and thermosetting plastics. Thermoplastics: Polyethylene, polystyrene. Thermosetting plastics: Epoxy, phenolic. Name the three different systems for producing biodegradable plastics. Systems: Bio-based plastics, compostable plastics, and biodegradable synthetic plastics. Describe the structure of elastomer molecules and their behavior under stress. Structure: Elastomer molecules consist of long, flexible polymer chains with cross-links that allow stretching. Behavior: They return to their original shape after stress is removed, exhibiting high elasticity. Name two advantages of synthetic rubbers over natural rubber. Advantages: Improved resistance to heat and ozone, and better mechanical properties. List three examples of elastomers. Examples: Natural rubber, styrene-butadiene rubber (SBR), neoprene. Name two general categories of ceramics and provide an example of each. Categories: Traditional ceramics: Porcelain. Advanced ceramics: Silicon carbide.  Why are ceramics considered much stronger than metallic materials? Reason: Ceramics have strong ionic or covalent bonds, giving them high strength and resistance to wear and deformation. What types of bonds are typically found in ceramic crystals, and how do they affect their strength? Bond types: Ionic and covalent bonds. Effect: These strong bonds contribute to the high strength and brittleness of ceramics. List three key characteristics of ceramics compared to metal. Characteristics: High hardness, high melting points, low ductility. How does the strength of ceramics in tension compare to their compressive strength? Comparison: Ceramics are much weaker in tension than in compression due to their brittle nature. What is static fatigue in ceramics, and under what conditions does it occur? Static fatigue: Gradual failure of ceramics under constant stress over time. It occurs due to the propagation of microscopic cracks What is the structure of glass? Structure: Glass is an amorphous solid with a disordered atomic arrangement, unlike crystalline solids. What is the main chemical component in all types of glasses? Component: Silica (SiO₂) How does the coefficient of thermal expansion of glass compare to metals and plastics? Comparison: Glass generally has a lower coefficient of thermal expansion than metals and plastics. Why is glass resistant to chemical attack? Reason: Glass is chemically inert due to its stable silica network structure. What is the structure of graphite? Structure: Graphite consists of layered planes of carbon atoms bonded covalently within each plane but held together by weak van der Waals forces between planes. Why does graphite act as a solid lubricant? Reason: The weak interlayer bonding in graphite allows layers to slide past each other easily, reducing friction. What are the thermal properties of graphite that make it suitable for high-temperature applications? Properties: High thermal conductivity and resistance to thermal expansion make it ideal for high-temperature applications. List three applications of graphite in high-temperature environments.  Applications: Furnace linings, thermal insulation, and brake linings. What are carbon nanotubes, and how are they produced? Carbon nanotubes: Cylindrical structures made of rolled graphene sheets. They are produced through chemical vapor deposition or arc discharge methods. What are the two main types of carbon nanotubes? Types: Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). What are the distinct electronic properties of armchair, zigzag, and chiral nanotubes? Armchair nanotubes: Metallic conductivity. Zigzag nanotubes: Can be either metallic or semiconducting, depending on the diameter. Chiral nanotubes: Semiconducting properties, depending on the chirality angle. What are fullerenes, and what is their typical molecular structure? Fullerenes: Molecules composed entirely of carbon, arranged in a hollow structure. The most famous fullerene is C60, resembling a soccer ball shape. What is graphene, and how is it structurally related to graphite? Graphene: A single layer of carbon atoms arranged in a hexagonal lattice. It is a fundamental building block of graphite, where multiple layers of graphene are stacked. What is diamond, and what is its primary structural characteristic? Diamond: A crystalline form of carbon with a tetrahedral lattice structure, where each carbon atom is covalently bonded to four other carbon atoms. What is diamond-like carbon, and where is it used? Diamond-like carbon (DLC): A form of carbon that exhibits some of the properties of diamond, such as hardness and low friction, but with a more flexible structure. It is used in coatings for tools and medical devices. List four industrial applications of diamond. Applications: Cutting tools, abrasives, heat sinks, and semiconductors. What is a composite material? Composite material: A material made from two or more different substances that, when combined, have superior properties compared to the individual components.  What are the three main types of composites? Types: Fiber-reinforced composites, particle-reinforced composites, and laminate composites. What are the four types of reinforcements commonly used in composites? Reinforcements: Fibers (glass, carbon, aramid), particles (ceramic, metal), woven fabrics, and nanomaterials. What is the role of the matrix in a composite material? Role: The matrix binds the reinforcement materials together, providing structural integrity and transferring stress. What is the purpose of reinforcement in a composite material? Purpose: Reinforcement provides strength, stiffness, and other desired properties to the composite material. What are the common types of glass fibers used in reinforced plastics? Types: E-glass, S-glass, and AR-glass. What is the typical percentage range of fiber content by volume in reinforced plastics? Range: 30–70% by volume. How is the bonding between the fiber and matrix in reinforced plastics enhanced? Enhancement: Through surface treatment of fibers (e.g., sizing) and chemical bonding agents (e.g., coupling agents). What are some common fiber materials used in metal-matrix composites? Fiber materials: Carbon, silicon carbide, boron. What type of composites retain strength up to 2500°C but lack oxidation resistance?