Mechanical Properties and Tensile Testing
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Questions and Answers

Which phase is represented at the composition of 0.76% carbon in the Fe-C phase diagram?

  • Liquid steel
  • Cementite
  • Pearlite (correct)
  • Austenite

    • What is a characteristic of congelation in Cu-Ni alloys associated with micro-segregation?

  • Differences in the chemical composition within a grain (correct)
  • Solidification occurs only at a fixed temperature
  • Uniform distribution of elements within a grain
  • High nickel concentration at the grain boundaries

    • What happens to alloys during solidification compared to pure metals?

  • All materials solidify at the same temperature
  • Alloys solidify at a fixed temperature
  • Alloys have a variable solidification range (correct)
  • Alloys do not undergo phase changes during solidification

    • Which method is NOT effective in avoiding micro-segregation during solidification?

    <p>Rapid cooling of the molten alloy</p> Signup and view all the answers

    Which of the following is NOT considered a phase in the Fe-C phase diagram?

    <p>Martensite</p> Signup and view all the answers

    What is the primary purpose of a tensile test on materials?

    <p>To evaluate the force required to stretch a material before it fails</p> Signup and view all the answers

    Which quantity describes the ratio of elongation to the original length in a tensile test?

    <p>Engineering strain</p> Signup and view all the answers

    When performing a tensile test, what is the significance of necking in the specimen?

    <p>It is where the specimen begins to fail due to localized deformation</p> Signup and view all the answers

    What is the relationship between tensile stress and tensile strain characterized by?

    <p>An initial linear relationship that may vary depending on material properties</p> Signup and view all the answers

    In the context of stress analysis, what does 'engineering stress' (σ) represent?

    <p>The total load divided by the original cross-sectional area</p> Signup and view all the answers

    What best describes 'creep' in the context of material degradation?

    <p>Gradual deformation of a material over time under constant stress</p> Signup and view all the answers

    Which of the following statements is true regarding shear stress and shear strain?

    <p>Shear strain is defined by the angle of shear and the cube's edge length</p> Signup and view all the answers

    What type of stress is described as applying a pulling force at right angles to the sample face?

    <p>Tensile stress</p> Signup and view all the answers

    What is the main characteristic of steel that has undergone slow furnace cooling?

    <p>Thicker pearlite layers with large grains</p> Signup and view all the answers

    Which cooling method results in the formation of a martensitic microstructure in steel?

    <p>Quenching in water</p> Signup and view all the answers

    What happens to the atomic lattice structure of iron when steel is quenched in water?

    <p>It distorts from FCC to BCC</p> Signup and view all the answers

    What is the primary purpose of tempering martensite?

    <p>To enhance toughness and ductility at the expense of strength</p> Signup and view all the answers

    During which cooling process does steel exhibit a higher yield strength and hardness?

    <p>Water quenching</p> Signup and view all the answers

    Which of the following statements about martensitic steel is correct?

    <p>It consists of needle-shaped grains that are smaller than pearlite</p> Signup and view all the answers

    What effect does the chemical composition of steel have on its microstructure?

    <p>It influences the type of steel class and microstructure formed</p> Signup and view all the answers

    What occurs to microstructural features during the tempering of martensite?

    <p>They grow larger and rounder with time</p> Signup and view all the answers

    Which cooling method is also referred to as normalising?

    <p>Air cooling</p> Signup and view all the answers

    What is the correct equation for shear stress?

    <p>$\tau = F / A$</p> Signup and view all the answers

    Which condition describes the behavior of a material in the plastic region of a stress/strain graph?

    <p>The material undergoes permanent deformation.</p> Signup and view all the answers

    What happens to strain when the applied stress is removed, according to Hooke's Law?

    <p>Strain decreases to zero.</p> Signup and view all the answers

    At what point on the stress/strain graph does the elastic region end?

    <p>At the yield point.</p> Signup and view all the answers

    Young's Modulus is defined as which of the following?

    <p>The ratio of stress to strain.</p> Signup and view all the answers

    What does the term 'dilation' refer to in the context of pressure-induced strain?

    <p>Change in volume of a solid.</p> Signup and view all the answers

    When conducting tensile testing, what is measured against time to determine strain rate?

    <p>Displacement.</p> Signup and view all the answers

    What characterizes hydrostatic pressure?

    <p>Acts evenly in all directions on a submerged object.</p> Signup and view all the answers

    What is the correct unit of measurement for Young's Modulus?

    <p>Pascal (Pa)</p> Signup and view all the answers

    What does shear strain approximately equal when the strain is very small?

    <p>W/Lo</p> Signup and view all the answers

    What is the relationship between axial stiffness and elastic modulus?

    <p>Axial stiffness is directly proportional to elastic modulus.</p> Signup and view all the answers

    Under shear forces, the relationship between shear stress and shear strain is defined by which modulus?

    <p>Shear modulus</p> Signup and view all the answers

    What does the bulk modulus (K) indicate about a material under 3D pressure?

    <p>It represents the volume deformation in relation to pressure.</p> Signup and view all the answers

    What is Poisson's ratio (ν) defined as?

    <p>The ratio of lateral strain to axial strain.</p> Signup and view all the answers

    At what carbon content does steel exhibit a 100% pearlite microstructure?

    <p>0.76%</p> Signup and view all the answers

    What characterizes the microstructure of mild steel at room temperature?

    <p>100% ferrite</p> Signup and view all the answers

    What happens to the yield stress of steel when the layers of pearlite become thinner?

    <p>Yield stress increases.</p> Signup and view all the answers

    What is the primary phase present in mild steel with a carbon content around 0.0%?

    <p>Ferrite</p> Signup and view all the answers

    Which of the following is true regarding the yield stress of austenite compared to ferrite?

    <p>Ferrite has a higher yield stress than austenite.</p> Signup and view all the answers

    How does carbon solubility change within the phases of iron as the temperature decreases?

    <p>Carbon can dissolve only to 2.1% in ferrite.</p> Signup and view all the answers

    What is the yield strength of a material?

    <p>The stress at which a material begins to deform plastically.</p> Signup and view all the answers

    What happens when two like charges are brought close to each other?

    <p>They repel each other.</p> Signup and view all the answers

    The SI unit of charge is Tesla.

    <p>False</p> Signup and view all the answers

    What is the formula for current?

    <p>I = Q/t</p> Signup and view all the answers

    The charge of a single electron is ___ C.

    <p>1.6 x 10^-19</p> Signup and view all the answers

    Which materials retain a magnetization field after removal of an applied magnetic field?

    <p>Ferromagnetic materials</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Coulomb = SI unit of charge Ampere = SI unit of current Capacitor = Device for storing charge Magnetization = Response of a material to a magnetic field</p> Signup and view all the answers

    The force of attraction between opposite charges is ___ proportional to the distance between them.

    <p>inversely</p> Signup and view all the answers

    When two conductive plates in a capacitor are charged, what happens to the charges?

    <p>Charges flow from one plate to the other if connected.</p> Signup and view all the answers

    What does the electrical loss tangent (tan δe) represent in a dielectric material?

    <p>The ratio of the imaginary part to the real part of complex permittivity</p> Signup and view all the answers

    Permeability measures the ability of a material to store energy.

    <p>False</p> Signup and view all the answers

    What is characterized as paramagnetic if magnetic susceptibility (χ) is greater than 0?

    <p>Material</p> Signup and view all the answers

    The __________ motion of charge carriers is random and influenced by collisions within the material.

    <p>Brownian</p> Signup and view all the answers

    Match the following terms with their correct definitions:

    <p>Permittivity = Ability to store electrical energy Permeability = Ability to form a magnetic field Relative permittivity (εr) = Measure of permittivity relative to free space Magnetic susceptibility (χ) = Indicates whether a material is paramagnetic or diamagnetic</p> Signup and view all the answers

    What does the imaginary part (ε'') of complex permittivity represent?

    <p>Energy dispersion or loss</p> Signup and view all the answers

    In the absence of an electric field, electrons and holes move due to thermal energy being converted into potential energy.

    <p>False</p> Signup and view all the answers

    What is the symbol for magnetic susceptibility?

    <p>χ</p> Signup and view all the answers

    What is the approximate thermal velocity of electrons in pure silicon at 300K?

    <p>1 × 10^7 cm/sec</p> Signup and view all the answers

    Electrons lose velocity when they drift in the direction of the electric field.

    <p>True</p> Signup and view all the answers

    What does the term 'drift current' refer to?

    <p>The net movement of charge carriers (electrons and holes) under the influence of an electric field.</p> Signup and view all the answers

    The mean time between collisions in pure silicon at 300K is _____ ps.

    <p>0.1</p> Signup and view all the answers

    Which equation models the drift current of electrons?

    <p>Idrift = -An(-q)µnE</p> Signup and view all the answers

    Holes drift in the opposite direction to the electric field.

    <p>False</p> Signup and view all the answers

    In the context of quantifying currents, what does 'n' represent?

    <p>The concentration of charge carriers (electrons) in the material.</p> Signup and view all the answers

    What is the formula for the conductivity of a semiconductor?

    <p>σ = q(nµn + pµp)</p> Signup and view all the answers

    Thermistors have a constant resistance regardless of temperature changes.

    <p>False</p> Signup and view all the answers

    What is Boltzmann's constant (k) approximately equal to?

    <p>1.38 J K−1</p> Signup and view all the answers

    The resistance of thermistors decreases with temperature for ___ thermistors.

    <p>NTC</p> Signup and view all the answers

    Match the following terms related to semiconductor properties with their descriptions:

    <p>n = Electron concentration p = Hole concentration µn = Mobility of electrons µp = Mobility of holes</p> Signup and view all the answers

    Which of the following describes the total drift current in a semiconductor?

    <p>I = AEq(nµn + pµp)</p> Signup and view all the answers

    Recombination occurs between free electrons and holes in the barrier of a semiconductor.

    <p>True</p> Signup and view all the answers

    What does the symbol σ represent in the context of semiconductors?

    <p>Conductivity</p> Signup and view all the answers

    What is the primary characteristic of a p-type semiconductor?

    <p>More holes than free electrons</p> Signup and view all the answers

    The depletion region in a p-n junction consists of positive ions on the p-type side.

    <p>False</p> Signup and view all the answers

    What is the equation to calculate the change in resistance due to temperature?

    <p>R(T) = R(T0) x (1 + α∆T)</p> Signup and view all the answers

    The breakdown voltage for capacitors is given by the formula Vbd = Edsd, where E is the electric field strength at breakdown and D is the ______.

    <p>separation distance</p> Signup and view all the answers

    Match the following materials to their resistivity values:

    <p>Copper = 1.72 x 10-8 ohm-meter Gold = 2.44 x 10-8 ohm-meter</p> Signup and view all the answers

    Which of the following applications utilizes mutual capacitance?

    <p>Touch screens</p> Signup and view all the answers

    Most metals have a negative temperature coefficient.

    <p>False</p> Signup and view all the answers

    What is the primary property that defines dielectric strength?

    <p>The voltage at which an insulating material's insulating properties begin to break down.</p> Signup and view all the answers

    What does the Seebeck coefficient represent?

    <p>Measure of voltage per unit temperature difference</p> Signup and view all the answers

    The Peltier effect occurs when a temperature difference is created by applying a voltage across two dissimilar metals.

    <p>True</p> Signup and view all the answers

    What is the unit of measurement for the Seebeck coefficient?

    <p>µV K−1</p> Signup and view all the answers

    In the Thomson effect, heating travels from the ______ to the ______ side of a conductor.

    <p>cold, hot</p> Signup and view all the answers

    Match the following effects with their descriptions:

    <p>Seebeck Effect = Voltage generation by temperature difference Peltier Effect = Temperature difference created by current Thomson Effect = Heating or cooling in a temperature gradient Hall Effect = Voltage across material in magnetic field</p> Signup and view all the answers

    Which of the following equations relates the Seebeck, Peltier, and Thomson effects?

    <p>K = dΠ/dt - S</p> Signup and view all the answers

    A negative Thomson coefficient indicates that a conductor will heat up when current flows from the hot side to the cold side.

    <p>True</p> Signup and view all the answers

    What causes the Hall effect in a conductor?

    <p>A magnetic field applied perpendicular to the current</p> Signup and view all the answers

    Study Notes

    Mechanical Properties

    • Mechanical properties studied: stiffness, strength, toughness, hardness
    • Materials can degrade through wear, creep, fatigue, and corrosion
    • Mechanical forces can cause materials to deform and/or fail

    Tensile Forces

    • Tensile test involves applying tensile stress to a material sample
    • The sample is stretched, and force and elongation are measured
    • Tensile specimens have parallel sides and equal cross-sectional area throughout the sample
    • A tensile testing machine pulls the specimen ends at a constant rate
    • Necking occurs in the specimen, which gradually decreases in cross-sectional area, until fracture
    • Tensile force vs elongation data can be plotted

    Normalizing Quantities

    • Engineering stress (σ or S) = F/A₀ (N/m² = Pa)
    • Engineering strain (ε or e) = ΔL/L₀ (no units)

    Stress-Strain Curve

    • Different shapes on the curve represent different materials
    • Stress may increase or decrease as strain increases
    • The breaking point of a material sample is denoted by X
    • Tensile stress: pulling force at 90° to sample face
    • Shown by positive value
    • Compressive stress: pushing force at 90° to sample face
    • Shown by a negative value
    • If force acts at an angle to the face, resolve into normal and shear components.
    • Strain rate (é) = change in strain over time (de/dt) - important for tensile testing results as results vary with speed

    Shear Stress/Strain

    • Shear stress causes sliding (shear strain)
    • Shear stress = F/A
    • Shear strain = w/L₀ = tan θ (approximately θ if θ is small)

    Pressure

    • Pressure = F/A
    • Positive when compressive
    • Strain due to pressure is a change in volume (dilation)
    • D = ΔV/V₀

    Elastic Deformation in Tensile, Compressive, and Bending Tests

    • Tensile testing standardisation uses ASTM E8 guidelines for metals and alloys.
    • Strain rate is important as tensile testing results vary with speed.

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    Description

    This quiz explores key concepts in mechanical properties of materials, including stiffness, strength, and toughness. It also covers the process of tensile testing, explaining how material deformation is measured, along with stress-strain curves and normalizing quantities. Perfect for engineering students looking to deepen their understanding of material mechanics.

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