Manufacturing Technology: Properties of Materials

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Questions and Answers

What is the primary property described by resilience in materials?

  • The ability to withstand shear stress
  • The ability to absorb energy during elastic deformation and recover it upon unloading (correct)
  • The ability to withstand permanent deformation
  • The ability to conduct electricity

What is the modulus of resilience associated with?

  • Elastic deformation (correct)
  • Mechanical fatigue
  • Thermal expansion
  • Plastic deformation

Using Hooke's law, if a piece of copper with an original length of 305 mm is subjected to a tensile stress of 276 MPa, what principle do we apply to determine its elongation?

  • Compressive modulus
  • Secant modulus
  • Modulus of toughness
  • Elastic modulus (correct)

Ductility can be quantified in which of the following ways?

<p>As percent elongation and percent reduction in area (A)</p> Signup and view all the answers

What does fracture toughness measure in a material?

<p>Resistance to fracture when a crack is present (D)</p> Signup and view all the answers

When considering nonlinear elastic behavior, which moduli are determined?

<p>Secant and tangent moduli (D)</p> Signup and view all the answers

Which shape is the indenter used in the Vickers hardness test?

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

What is the primary measurement taken in the Brinell hardness test?

<p>Diagonal length of the indented square (B)</p> Signup and view all the answers

Which materials are typically used for the ball in the Brinell hardness test?

<p>Hardened steel or tungsten carbide (A)</p> Signup and view all the answers

How is the Vickers hardness number determined after measuring the indentation?

<p>Through a conversion calculation from measurements (C)</p> Signup and view all the answers

Which property is measured by a tensile test?

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

What is the primary purpose of measuring hardness in materials?

<p>To measure resistance to deformation (D)</p> Signup and view all the answers

What is an indication of a material's resilience?

<p>The ability to return to its original shape after deformation (C)</p> Signup and view all the answers

Which property describes the maximum stress that a material can withstand while being stretched or pulled?

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

In a tensile test, what does the term 'stiffness' refer to?

<p>The resistance to elastic deformation (C)</p> Signup and view all the answers

What is the term for the ability of a material to absorb energy and plastically deform without fracturing?

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

What does the limit of elasticity signify in materials?

<p>The stress beyond which a material will deform permanently (A)</p> Signup and view all the answers

Which property is primarily assessed when evaluating a material's ability to conduct electricity?

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

What is the thermal protection system for the Space Shuttle Orbiter primarily made of?

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

Which polymer has the highest thermal resistance based on the given properties?

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

What is the approximate porosity of the silica tiles used in the Space Shuttle Orbiter?

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

At what temperature do the silica tiles operate effectively?

<p>400-1260ºC (B)</p> Signup and view all the answers

Which material is not mentioned as part of the thermal protection system for the Space Shuttle?

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

What process is used to bond the silica fibers in the thermal protection tiles?

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

What is the purpose of using high porosity materials like silica tiles in thermal protection?

<p>To reduce heat transfer (B)</p> Signup and view all the answers

Which thermal protection material can operate at the highest temperature?

<p>Reinforced carbon-carbon (C)</p> Signup and view all the answers

What is the primary use of measuring the diameter of an indentation in materials?

<p>To indicate the hardness of the material (A)</p> Signup and view all the answers

What does Ohm's Law express the relationship between?

<p>Voltage, current, and resistance (D)</p> Signup and view all the answers

What does resistivity ($ ho$) describe?

<p>A material property independent of sample size (A)</p> Signup and view all the answers

Which metal has the highest conductivity based on the provided information?

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

Which equation correctly relates linear thermal expansion?

<p>$l_{final} = l_{initial} + eta l_{initial} (T_{final} - T_{initial})$ (A)</p> Signup and view all the answers

What unit is used to express conductivity ($ au$)?

<p>Siemens per meter (S/m) (D)</p> Signup and view all the answers

Which material has the lowest conductivity according to the comparison provided?

<p>Soda-lime glass (B)</p> Signup and view all the answers

What does the notation $k$ refer to in thermal conductivity?

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

Flashcards

Tensile Strength

The ability of a material to resist deformation under tensile load. Measured by the stress at the elastic limit.

Stiffness (Modulus of Elasticity)

The ability of a material to deform elastically under applied stress. Measured by the slope of the stress-strain curve in the elastic region.

Elastic Limit

The maximum stress a material can withstand before permanent deformation occurs. Beyond this point, the material will not return to its original shape.

Ductility

The ability of a material to deform plastically under tensile load before fracturing. Measured by the strain at fracture.

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Hardness

The resistance of a material to indentation or scratching. Measured by the depth of penetration of an indenter.

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Toughness

The energy a material can absorb before fracturing. Measured by the area under the stress-strain curve.

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Resilience

The ability of a material to absorb energy when deformed elastically. Measured by the area under the stress-strain curve in the elastic region.

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Electrical Conductivity

The ability of a material to conduct electrical current. Measured by the electrical conductivity.

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Fracture Toughness

Fracture toughness is a material's ability to resist breaking when a crack is present.

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Vickers Hardness

Vickers hardness is measured using a square pyramid-shaped indenter. The diagonal length of the indentation is measured and used to calculate the hardness number.

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Brinell Hardness

Brinell hardness measures a material's resistance to indentation using a hard steel or tungsten carbide ball. The diameter of the indentation is measured to determine hardness.

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Hooke's Law

The relationship between stress (force per unit area) and strain (deformation) in a material that undergoes elastic deformation. It states that stress is directly proportional to strain within the elastic limit.

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Elongation

The amount of elongation a material experiences under tension, measured as the change in length divided by the original length.

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Modulus of Resilience

The modulus of resilience is the area under the stress-strain curve in the elastic region.

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Ohm's Law

A relationship between voltage, current, and resistance in an electrical circuit. It states that the voltage drop across a conductor is directly proportional to the current flowing through it and the resistance of the conductor. Formula: V = IR.

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Conductivity

A material property that describes how easily an electrical current can flow through a material. It is the reciprocal of resistivity.

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Resistivity

A material property that describes how strongly a material resists the flow of electrical current. It is the reciprocal of conductivity.

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Thermal Expansion Coefficient

A measure of how much a material changes in length when its temperature changes. Measured in units of 1/K or 1/ºC.

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Thermal Conductivity

The rate at which heat energy is transferred through a material by conduction. Measured in units of W/m-K.

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Electrical Conduction

The process by which electrical current flows through a material. It depends on the availability of free electrons and the ease with which they move through the material.

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Voltage

The difference in electrical potential between two points in a circuit. It causes the flow of current.

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Thermal Resistance

The ability of a material to withstand high temperatures before permanent deformation or failure. Measured by the temperature at which the material starts to soften or melt.

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Heat Treatment

The process of using heat to change the structure and properties of a material. This can involve melting, solidification, or other transformations.

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Melting Point

The temperature at which a material changes phase, usually from solid to liquid.

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Re-entry Temperature

The temperature at which a material starts to soften and deform under load. It's a key indicator of a material's ability to withstand high temperatures.

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Silica Tiles

A composite material that has a high thermal resistance and is used in space shuttles to protect them from extreme heat during re-entry.

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Porous Structure

A type of material with small interconnected pores or spaces. This structure can improve thermal insulation by trapping air, which is a poor conductor of heat.

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Bonding

The process of bonding together fibers or particles to create a stronger and more stable material. This is often done using heat treatment.

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Study Notes

Lecture 2: Physical and Mechanical Properties of Materials

  • Topic: Physical and mechanical properties of materials.
  • Course: Manufacturing Technology (EIM1101)
  • Instructor: Dr. Mohamed Taha Eldaly
  • Reference Book: Materials Science and Engineering, Nine Edition, by William D. Callister, Jr. and David G. Rethwisch.
  • Course Outline: Weeks 1-16 cover topics including: introduction to manufacturing, physical and mechanical properties of materials, classification of metals and alloys, polymers and composites, metal casting, metal forming (rolling, extrusion, drawing), machining operations; tool life and materials; joining operations; shaping of plastics; and exams.

Physical and Mechanical Properties of Materials

  • Tensile Test: A test to determine a material's response to stretching forces.
  • Stiffness: A material's resistance to deformation under stress.
  • Limit of Elasticity: The point on a stress-strain curve beyond which the material will deform permanently.
  • Ductility and Tensile Strength: Measures the material's ability to be stretched before fracturing and its ability to withstand a tensile load.
  • Hardness: A measure of a material's resistance to indentation or scratching.
  • Toughness: A measure of a material's ability to absorb energy before fracturing.
  • Resilience: A measure of a material's ability to absorb energy during elastic deformation and have it recovered upon unloading.
  • Electrical Conductivity: A measure of how easily a material allows electric current to flow through it.
  • Thermal Conductivity: A measure of how easily a material transmits heat.

Tensile Testing Apparatus

  • Load Cell: Measures the applied load.
  • Extensometer: Measures the elongation of the specimen.
  • Moving Crosshead: Elongates the specimen.

Hooke's Law and Stress-Strain Diagrams

  • Hooke's Law: Relates engineering stress and engineering strain for elastic deformation.
  • Stress-Strain Diagrams: Illustrate the relationship between stress and strain during loading and unloading cycles, showing both elastic and plastic behaviors, tangent and secant moduli.

Solved Example (Copper Elongation)

  • Original Length (l₀): 305 mm
  • Stress (σ): 276 MPa
  • Young's Modulus (E): 110 x 10³ MPa
  • Resultant Elongation (Δl): 0.77 mm

Mechanical Properties (further details)

  • Ductility (percent elongation): Measures the material's ability to deform plastically before fracture, calculated as (lf − li) / li * 100%.
  • Ductility (percent reduction in area): (Ai - Af) / Ai *100%, where Ai is initial area and Af is final area.
  • Brittle vs. Ductile: Classification of materials based on their behavior under stress.

Hardness Testing

  • Brinell Hardness Test: Uses a hardened steel or tungsten carbide ball to indent the material.
  • Vickers Hardness Test: Uses a square-based pyramid-shaped indenter.
  • Rockwell Hardness Test: Measures the depth of indentation using a diamond or steel cone indenter.

Electrical Properties

  • Ohm's Law: V = IR (Voltage = Current × Resistance).
  • Resistivity (ρ): A material's intrinsic resistance to current flow, independent of size or shape.
  • Conductivity (σ): Reciprocal of resistivity.

Thermal Properties

  • Heat Capacity (C): The amount of heat required to raise the temperature of one mole of a substance by one degree.
  • Specific Heat (cp): Heat capacity per unit mass.
  • Modulus of Resilience: Energy absorbed during elastic deformation.
  • Thermal Expansion: Materials change size with temperature changes.
  • Linear coefficient of thermal expansion: Measures the change in length per unit length per degree change in temperature.

Thermal Conductivity (k):

  • Thermal Conductivity(k): Measures the amount of heat transmitted through a material.

Material Applications (Space Shuttle Orbiter)

  • Silica Tiles: Large-scale application in the Space Shuttle Orbiter thermal protection system, due to their high temperature resistance.

Additional Information

  • Units: Ensure you understand the units used for each property (e.g., MPa for stress, J/mol-K for heat capacity).
  • Material Classifications: Metals, Polymers, Ceramics, Semiconductors.
  • The provided URLs are for checking for further study material on these properties.

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Lecture 2: Physical and Mechanical Properties of Materials (PDF)

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