Composite Materials and Stress Analysis
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Questions and Answers

What is the unit of strain?

  • Joule
  • It has no units (correct)
  • Megapascal (MPa)
  • Newton
  • What is the strain offset when a straight line is constructed parallel to the elastic portion of the stress-strain curve?

  • 0.005
  • 0.002 (correct)
  • 0.01
  • 0.001
  • Resultant stress is a combination of which types of stress?

  • Tensile stress and compressive stress
  • Shear stress and normal stress (correct)
  • Yield stress and tensile stress
  • Elastic stress and plastic stress
  • Modulus of elasticity is defined as which of the following?

    <p>E = stress / strain (B)</p> Signup and view all the answers

    What kind of stress acts along the length of a fuselage?

    <p>Longitudinal (Axial) stress (D)</p> Signup and view all the answers

    A metal that experiences very little or no plastic deformation upon fracture is termed as what?

    <p>Brittle (C)</p> Signup and view all the answers

    What is the purpose of adding a catalyst or hardener to the composite?

    <p>Starts the cross-linking process and sets the composite (D)</p> Signup and view all the answers

    For brittle materials, which stress is most effective in predicting failure?

    <p>Ultimate stress (D)</p> Signup and view all the answers

    The properties of a composite are highly characterized as what?

    <p>Anisotropic (A)</p> Signup and view all the answers

    In plane stress problems, how is the thickness of the material treated?

    <p>Zero (B)</p> Signup and view all the answers

    If the number of unknowns is less than the number of equations in a structural problem, what type of problem is it?

    <p>Statically determinate (B)</p> Signup and view all the answers

    Which of the following matrices has better bonding characteristics with fiber?

    <p>Epoxy (D)</p> Signup and view all the answers

    In a cross-ply composite laminate, the directions of the fiber are arranged in which way?

    <p>0 degrees and 90 degrees (C)</p> Signup and view all the answers

    In plane strain problems, how is the strain characterized?

    <p>The strain is in one plane (B)</p> Signup and view all the answers

    The Von Mises stress criterion is primarily applicable to which type of materials?

    <p>Ductile materials (B)</p> Signup and view all the answers

    In the context of principal stresses, how is the shear stress assumed?

    <p>Zero (C)</p> Signup and view all the answers

    Which one of the following is NOT a defined material main property?

    <p>Conductive (C)</p> Signup and view all the answers

    What term describes the ability of a metal to be deformed significantly without breaking?

    <p>Ductility (A)</p> Signup and view all the answers

    Which material is known to have less resistance to fracture?

    <p>Concrete (D)</p> Signup and view all the answers

    Which of the following is not categorized under advanced materials?

    <p>Micromaterials (B)</p> Signup and view all the answers

    Which type of crystal structure has a lower packing factor?

    <p>Body-Centered Cubic (D)</p> Signup and view all the answers

    Which material group is typically less stiff compared to others?

    <p>Polymers (B)</p> Signup and view all the answers

    What term describes a portion of a system with uniform characteristics?

    <p>Phase (B)</p> Signup and view all the answers

    Which type of composite material exhibits greater stiffness and strength?

    <p>Carbon fiber reinforced (B)</p> Signup and view all the answers

    What is the maximum stress that can be experienced by a given structure?

    <p>Tensile strength (C)</p> Signup and view all the answers

    What effect does the rate of cooling have on material strength?

    <p>Makes the material stronger (D)</p> Signup and view all the answers

    Which category do piezoelectric ceramics belong to?

    <p>Smart materials (A)</p> Signup and view all the answers

    Before reaching the yield point, how is the material deformation characterized?

    <p>Elastic (A)</p> Signup and view all the answers

    What happens to strain if the load is removed before the yield strength is reached?

    <p>Strain becomes zero (A)</p> Signup and view all the answers

    What type of structure is directly observable under a microscope?

    <p>Microstructure (D)</p> Signup and view all the answers

    What is the state called when the approach to equilibrium is extremely slow?

    <p>Metastable state (B)</p> Signup and view all the answers

    Which formula correctly represents stress?

    <p>Stress = Force / Area (A)</p> Signup and view all the answers

    What is the carbon content typically found in low-carbon steel?

    <p>Less than 0.3% (B)</p> Signup and view all the answers

    What does free energy depend on?

    <p>Internal energy (C)</p> Signup and view all the answers

    In iso-strain conditions, how do the strains of the matrix and fiber compare?

    <p>Strains of both matrix and fiber are equal (D)</p> Signup and view all the answers

    Which type of composite is concrete classified as?

    <p>Particle-reinforced composite (A)</p> Signup and view all the answers

    In composite materials, what term is used to describe fibers and particles?

    <p>Dispersed phase (B)</p> Signup and view all the answers

    Which type of composite exhibits the best impact resistance characteristics?

    <p>Aramid fiber reinforced composites (D)</p> Signup and view all the answers

    What is the typical diameter range for particles in dispersion-strengthened composites?

    <p>0.01 μm -- 0.1 μm (D)</p> Signup and view all the answers

    The critical length of the fiber in a composite is primarily dependent on which factor?

    <p>Diameter of the fiber (C)</p> Signup and view all the answers

    In a uni-directional laminate, how are the fibers arranged?

    <p>Only at 0 degrees or 90 degrees (A)</p> Signup and view all the answers

    What is the internal shear force's orientation relative to the plane in composite materials?

    <p>It is parallel to the plane (D)</p> Signup and view all the answers

    Edge dislocation falls under which category of defects?

    <p>Linear defect (A)</p> Signup and view all the answers

    What term describes the relationship between deformation and applied force?

    <p>Mechanical properties (C)</p> Signup and view all the answers

    Which type of properties relates to temperature changes in materials?

    <p>Thermal properties (D)</p> Signup and view all the answers

    Which element is predominant in the composition of stainless steel?

    <p>Iron (C)</p> Signup and view all the answers

    What term is used when a solution cannot dissolve more solute?

    <p>Solubility limit (D)</p> Signup and view all the answers

    Which material typically shows less resistance to fracture?

    <p>Concrete (D)</p> Signup and view all the answers

    In thermodynamics, a system is at equilibrium when its free energy is at which level?

    <p>Minimum (C)</p> Signup and view all the answers

    What property describes materials that have the same physical properties in all directions?

    <p>Isotropy (A)</p> Signup and view all the answers

    Flashcards

    Ductility

    A material's ability to deform without breaking, measured by the amount of plastic deformation before fracture.

    Concrete

    This material has a lower resistance to breaking when compared to others.

    Micromaterials

    Materials like nanomaterials, biomaterials, and smart materials are all considered advanced.

    Polymers

    This group of materials is known for being flexible and less rigid.

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    Metals

    This group of materials is very good at conducting electricity and heat.

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    Carbon fiber reinforced

    This type of composite is known for its strength and stiffness.

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    Prevent crack propagation

    Rounding the hatch corners is not effective in preventing cracks from spreading.

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    Ductile metal alloys

    This material is less resistant to fracture at very low temperatures.

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    Design factor

    This is the ratio of yield strength to applied strength, indicating how much stronger the material is than the applied load.

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    Tensile strength

    This is the maximum stress a material can handle before permanent deformation.

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    Iso-strain condition

    A composite material where the strain (deformation) in both the matrix and the reinforcing fibers is the same.

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    Particle-reinforced composite

    A type of composite material where the strengthening element is dispersed as small particles within a continuous matrix.

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    Dispersed phase

    The strengthening component in a composite material, like fibers or particles.

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    Impact resistance

    The ability of a composite material to withstand sudden impacts without fracture.

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    Particle size in dispersion-strengthened composites

    The size range of particles used in dispersion-strengthened composites.

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    Critical length of a fiber

    The length of a fiber required to achieve full load transfer from the matrix to the fiber.

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    Uni-directional laminate

    A type of laminate where all fibers are aligned either parallel or perpendicular to the load.

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    Internal shear forces

    The internal forces that act parallel to the plane of a structure, particularly in thin-walled structures like aircraft fuselages.

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    What is strain?

    Strain is a measure of the deformation of a material caused by stress. It is expressed as the change in length divided by the original length and has no units.

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    Strain offset

    The strain offset is a small value that defines the elastic limit on a stress-strain curve. It helps determine the yield strength and is typically set to 0.002.

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    Modulus of elasticity (E)

    Modulus of elasticity (E) is a material property that indicates its stiffness. It is calculated by dividing the stress by the strain in the elastic region of its stress-strain curve.

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    Brittle material

    A brittle material exhibits little or no plastic deformation before breaking. It fractures suddenly when subjected to stresses beyond its elastic limit.

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    Purpose of catalyst or hardener in composites

    A catalyst or hardener is added to a composite to initiate the cross-linking process, which sets the composite and gives it its final strength and properties.

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    Anisotropic properties of composites

    The properties of a composite are highly anisotropic, meaning they vary with direction. This is due to the different properties of its constituent materials (fiber and matrix).

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    Best matrix for bonding with fibers

    Epoxy resins are known for their superior adhesion to fibers compared to other matrices like polyester or vinyl ester. This leads to stronger and more durable composites.

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    Carbon fiber identification

    Carbon fibers are identified by their characteristic black color. This is due to their unique structure and composition.

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    What is a phase?

    A homogeneous portion of a system with uniform physical and chemical characteristics.

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    What is a phase transformation?

    The process of a material changing its state over time, usually due to a change in temperature or pressure.

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    What is yield strength?

    A material's resistance to permanent deformation, measured by the stress at which it starts to deform plastically.

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    What is tensile strength?

    The maximum stress a material can withstand before breaking, measured by the stress at which it fractures.

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    What are smart materials?

    An advanced material category that responds to external stimuli, like temperature or pressure changes, with a change in properties.

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    What is toughness?

    A material's ability to absorb energy before fracturing, measured by the area under its stress-strain curve.

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    What are isotropic materials?

    Materials that exhibit characteristics that are independent of the direction of applied stress.

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    What is a microstructure?

    The structural elements within a material that can be visualized using a microscope.

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    Resultant stress

    A combination of forces acting perpendicular and parallel to a surface.

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    Longitudinal (Axial) stress

    The force experienced by a material along its length, often found in structures like airplane fuselages.

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    Ultimate stress

    The maximum stress a brittle material can withstand before breaking.

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    Plane stress problem

    A simplified analysis where the material's thickness is considered negligible, making it easier to calculate stress and strain.

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    Statically determinate problem

    A scenario where the number of unknown forces is fewer than the number of equations needed to solve them.

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    Plane strain problem

    A situation where the strain (deformation) occurs mainly within a single plane.

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    Von Mises stress criterion

    A criterion used to predict the yielding (permanent deformation) of ductile materials.

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    Internal normal forces

    The internal forces within a beam that counteract the applied load and create a bending moment.

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    What is a point defect?

    A point defect is a localized imperfection in the crystal lattice of a material, affecting a single atom or a small group of atoms.

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    Define planar defects.

    A planar defect involves a discontinuity in the crystal lattice that extends across a two-dimensional plane. These defects can significantly affect the material's mechanical properties.

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    What is a linear defect?

    A linear defect, or dislocation, is a one-dimensional defect in the crystal structure that arises from the misalignment of atoms along a line within the crystal.

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    Explain volume defects.

    A volume defect describes a three-dimensional imperfection within a crystal structure, such as voids, inclusions, or cracks.

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    What are mechanical properties?

    Mechanical properties describe a material's response to applied forces or loads, including its strength, stiffness, ductility, toughness, and resistance to deformation.

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    Define thermal properties.

    Thermal properties describe a material's response to changes in temperature, including its heat capacity, thermal conductivity, and thermal expansion.

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    What is the solubility limit?

    The solubility limit refers to the maximum amount of solute (e.g., sugar) that can be dissolved in a solvent (e.g., water) at a specific temperature and pressure. Beyond this limit, no more solute can be dissolved, and it will start to precipitate out.

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    Define isotropy.

    A material is considered isotropic if it exhibits the same physical properties in all directions. This means the material's response to an applied force remains constant regardless of the direction from which it's applied.

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    Study Notes

    Material Properties and Definitions

    • Material main property that is not defined: Conductive
    • Ability of metal to extend without breaking: Ductility
    • Material with low fracture resistance: Concrete
    • Material not part of advanced materials: Micromaterials
    • Material group with less stiffness: Polymers
    • Best material conductor group: Metals

    Composite Materials

    • Stiffer and stronger composite material: Carbon fiber reinforced
    • Method to prevent crack propagation: Heat treatment, stress relieving, material substitution (rounding hatch corners is not a solution)
    • Cause of brittle metal alloys: Cooled to very low temperatures
    • Design factor calculation: Yield strength (200 MPa) / Applied strength (100 MPa) = 2
    • Material with better bonding with fiber: Epoxy

    Material Properties (Cont.)

    • Measure of plastic deformation at fracture: Ductility
    • Average tensile strength (200, 210, 220 MPa): 210 MPa
    • Deformation before yield point: Elastic
    • Effect of removing load before yield strength on strain: Strain becomes zero
    • Maximum stress a structure/material can experience: Tensile strength
    • Hooke's law implementation: Before the yield point
    • Stress formula: Stress = Force / Area
    • Unit of stress: Megapascal (MPa)
    • Units of yield strength: MPa or psi
    • Material energy absorption capacity: Resilience
    • Strains unit: No units
    • Strain offset for stress-strain curve: 0.002
    • Modulus of elasticity formula: E = stress / strain
    • Material with little plastic deformation: Brittle
    • Purpose of adding catalyst/hardener to composite: Strengthens the composite

    Composite Properties and Classification

    • Composite material property: Anisotropic
    • Matrix bonding characteristic: Epoxy
    • Carbon fiber identification: Black color
    • Composite continuous phase: Matrix
    • Fiber directions in cross-ply laminate: 0 degrees and 90 degrees
    • Strain condition: Matrix and fiber strain are the same

    Stress and Deformation

    • Concrete composite type: Particle-reinforced composite
    • Fibers and particles in composites: Dispersed phase
    • Best impact resistance composite: Aramid fiber reinforced composites
    • Particle size in dispersion-strengthened composites: 0.01 µm – 0.1 µm
    • Fiber arrangement in uni-directional laminate: Either 0 degrees or 90 degrees
    • Load causing iso-strain: Longitudinal (axial) stress
    • Fuselage structure assumption: Thin-walled structure
    • Internal shear forces direction: Parallel to the plane
    • Resultant stress combination: Shear stress and normal stress
    • Stress acting along fuselage length: Longitudinal (axial) stress
    • Stress used to predict brittle material failure: Ultimate stress
    • Thickness assumption in plane stress problems: Negligible
    • System type when unknowns < equations: Statically determinate
    • Strain in plane strain problems: In one plane
    • Stress criteria for ductile materials: Von Mises

    Additional Material Properties and Definitions

    • Solubility limit definition: When a solution cannot dissolve any more solute
    • Material resistance to localized plastic deformation: Hardness
    • Effect of rolling on material: Reduces ductility
    • Relation between grain size and material strength: Smaller grain size, stronger material
    • Solidus line separation: Liquid region from the liquid-solid region
    • Strain after yield strength removal: Stops with some recovery

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    Material Science Quiz PDF

    Description

    Test your knowledge on the fundamental concepts of composite materials and stress analysis. This quiz covers subjects such as strain, modulus of elasticity, and composite laminate properties. Ideal for students studying materials science and engineering principles.

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