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Questions and Answers
Which of the following properties measures the energy required to crack a material without causing fracture?
Which of the following properties measures the energy required to crack a material without causing fracture?
- Castability
- Weldability
- Resilience
- Toughness (correct)
What does the linear thermal expansion coefficient, $\alpha$, indicate?
What does the linear thermal expansion coefficient, $\alpha$, indicate?
- The original length of a specimen at high temperature
- The temperature change during the cooling phase
- The change in length due to cooling only
- The thermal strain per degree of temperature change (correct)
What characterizes the glass temperature ($T_g$) in polymers?
What characterizes the glass temperature ($T_g$) in polymers?
- It reflects the color change of polymers.
- It indicates the density of the polymer.
- It shows a transition from hard and brittle to soft and flexible. (correct)
- It marks the melting point of polymers.
Which of the following conductors has an electrical resistivity of more than $10^{-8} \Omega - m$?
Which of the following conductors has an electrical resistivity of more than $10^{-8} \Omega - m$?
What is the significance of the melting temperature ($T_m$)?
What is the significance of the melting temperature ($T_m$)?
What does the electrical conductivity, $\sigma_e$, measure?
What does the electrical conductivity, $\sigma_e$, measure?
Which property describes the ability of a material to be deformed plastically into a specified shape without defects?
Which property describes the ability of a material to be deformed plastically into a specified shape without defects?
What is the range for the dielectric constant, $\epsilon_r$, for insulators?
What is the range for the dielectric constant, $\epsilon_r$, for insulators?
Which of the following statements about resilience is incorrect?
Which of the following statements about resilience is incorrect?
What is the significance of a material having high ductility?
What is the significance of a material having high ductility?
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Study Notes
Thermal Properties
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Linear Thermal Expansion Coefficient (α): Measures thermal strain per degree Celsius.
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Change in Length (∆L): Length change due to temperature variation, with original length (Lo) at room temperature and temperature change (∆T) in °C.
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Glass Temperature (Tg): Crucial for polymer behavior.
- Below Tg: Polymers are hard and brittle.
- Above Tg: Polymers become soft and flexible.
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Melting Temperature (Tm): The point at which solid and liquid states of a substance coexist in equilibrium. Heating a solid increases temperature until melting occurs.
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Maximum Service Temperature (Tmax): The highest temperature for material use without risk of oxidation, chemical changes, or creep.
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Minimum Service Temperature (Tmin): The lowest temperature at which a material remains safe and does not become brittle.
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Specific Heat (cp): The amount of heat needed to raise the temperature of one gram of a substance by 1°C, typically measured at constant atmospheric pressure.
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Thermal Shock Resistance (∆Ts): Indicates the maximum temperature difference a material can endure during sudden quenching without damage. Significant fluctuations cause thermal stresses and potential micro-cracks.
Electrical Properties
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Electrical Resistivity (ρe): Indicates how strongly a material opposes electric current.
- Good conductors have resistivity greater than 10⁻⁸ Ω·m.
- Best insulators show resistivity over 10¹⁶ Ω·m.
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Electrical Conductivity (σe): Measures a material's ability to allow electric current to flow, varying across different materials.
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Dielectric Constant (εr): Expresses an insulator's tendency to polarize in an electric field.
- For gases: εr = 1.
- For insulators: 2 < εr < 30.
Mechanical Properties
- Resilience: Ability to absorb and release maximum energy upon elastic deformation.
- Toughness: Capacity to withstand shock loading without fracturing, quantified by the energy necessary to crack the material.
- Weldability: Indicates how well a material can be welded while retaining its properties post-welding.
- Formability: Refers to the ability to undergo plastic deformation into a specific shape without defects.
- Castability: Describes the ease of pouring molten material into a mold to create a defect-free casting.
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