Podcast
Questions and Answers
Which of the following adjustments would most likely result in decreased density when striving to create a foam?
Which of the following adjustments would most likely result in decreased density when striving to create a foam?
- Compressing the material to reduce its volume.
- Increasing the atomic weight of the constituent elements.
- Decreasing the mass of the material while maintaining a constant volume. (correct)
- Increasing mass while maintaining constant volume.
A material is subjected to a bending moment. What type of stress is experienced on the top and bottom surfaces, respectively?
A material is subjected to a bending moment. What type of stress is experienced on the top and bottom surfaces, respectively?
- Shear and Compression
- Tension and Compression (correct)
- Tension and Shear
- Compression and Tension
Which of the following best describes the relationship between Young's modulus (E), stress ($\sigma$), and strain ($\epsilon$) in the elastic region of a material?
Which of the following best describes the relationship between Young's modulus (E), stress ($\sigma$), and strain ($\epsilon$) in the elastic region of a material?
- $E = \sigma / \epsilon$ (correct)
- $E = \sigma \times \epsilon$
- $E = \sigma + \epsilon$
- $E = \epsilon / \sigma$
A material returns to its original shape after the removal of an applied stress. Which term most accurately describes this behavior?
A material returns to its original shape after the removal of an applied stress. Which term most accurately describes this behavior?
What microstructural feature is LEAST sensitive to the Elastic Modulus (Young's Modulus)?
What microstructural feature is LEAST sensitive to the Elastic Modulus (Young's Modulus)?
Consider a scenario where a material is constrained from changing shape in the transverse direction. How will this constraint affect the material's Young's modulus when subjected to tension?
Consider a scenario where a material is constrained from changing shape in the transverse direction. How will this constraint affect the material's Young's modulus when subjected to tension?
In the context of material science, what does a higher cohesive energy between atoms in a solid typically indicate?
In the context of material science, what does a higher cohesive energy between atoms in a solid typically indicate?
Which type of atomic bonding is characterized by electrons detaching from parent atoms to form a negatively charged swarm, leaving behind positively charged ions?
Which type of atomic bonding is characterized by electrons detaching from parent atoms to form a negatively charged swarm, leaving behind positively charged ions?
A material exhibits different properties when measured in different directions. What term best describes this behavior?
A material exhibits different properties when measured in different directions. What term best describes this behavior?
Increasing modulus and density in a material can be achieved by what general class of materials modification?
Increasing modulus and density in a material can be achieved by what general class of materials modification?
What is the most accurate definition of 'true stress'?
What is the most accurate definition of 'true stress'?
What characterises an elastomeric material?
What characterises an elastomeric material?
What is the typical application of the process of Solution Hardening?
What is the typical application of the process of Solution Hardening?
For a given material, which represents the idealized force necessary to break interatomic bonds?
For a given material, which represents the idealized force necessary to break interatomic bonds?
What is the effect of crystalline imperfections on the ideal strength of materials?
What is the effect of crystalline imperfections on the ideal strength of materials?
What role do dislocations have with material properties?
What role do dislocations have with material properties?
Which of the following statements most accurately describes the effect of increasing the yield strength of a metal on its fracture toughness?
Which of the following statements most accurately describes the effect of increasing the yield strength of a metal on its fracture toughness?
What is the primary purpose of using fibers in a composite material to improve toughness?
What is the primary purpose of using fibers in a composite material to improve toughness?
In the context of fatigue failure, what is the significance of the endurance limit?
In the context of fatigue failure, what is the significance of the endurance limit?
How does shot peening mitigate fatigue cracking? Choose the most accurate statement.
How does shot peening mitigate fatigue cracking? Choose the most accurate statement.
Flashcards
Stiffness
Stiffness
Resistance to elastic shape change. Material returns to its original shape after stress.
Strength
Strength
Resistance to permanent distortion or total failure. Measured by yield strength, tensile strength, or fracture strength.
Density (ρ)
Density (ρ)
Mass per unit volume. Influences material weight and applications.
Young's Modulus (E)
Young's Modulus (E)
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Strain (ε)
Strain (ε)
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Stress (σ)
Stress (σ)
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Yield Strength (σy)
Yield Strength (σy)
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Surface Treatment
Surface Treatment
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Ductility
Ductility
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Composite material
Composite material
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Soldering
Soldering
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Melting Point
Melting Point
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Thermal expansion
Thermal expansion
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Grain
Grain
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Quenching
Quenching
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Amorphous
Amorphous
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Tempering
Tempering
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Hardness
Hardness
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Atomic Packing
Atomic Packing
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Vacancy
Vacancy
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Study Notes
- Modifying polymer with fillers, impact modifiers, and reinforcement can significantly alter fracture toughness
Predicting Fatigue Life
- Fatigue failure follows a predictable pattern
- Fatigue life is estimated according to Coffin's Law for low-cycle fatigue
- Basquin's Law is used for high-cycle fatigue
Example of Basquin's Law
- Using Basquin's Law, a component with specified fatigue life and material properties fails
- Fatigue life if stress amplitude increases from 60 MPa to 120 MPa is 200,000 cycles
Stress Amplitude
- Stress amplitude is generally not constant
Mean Stress and Variable Amplitude
- Fatigue is affected by mean stress and variable amplitudes under cyclic loading
Goodman's Rule
- The amplitude of the alternating stress component decreases linearly as the mean stress increases
Miner's Rule
- Damage analysis accounts for fatigue failure when stress amplitude changes
- Failure occurs when "Ni" exceeds 1
Fatigue Damage and Cracking
- High-cycle fatigue yields a tiny plastic zone, folding forward during compression
- Low-cycle fatigue makes the plastic zone large enough for voids to nucleate and coalesce, advancing crack
- Crack propagates during tensile part of stress cycle; compressive stress presses crack faces together
- Material acts to resist crack growth with shot peening
Cyclic Stress Intensity Range
- Crack grows during the crack growth phase
Safe Design
- Designs need to calculate the number of loading cycles
- Possible before cracks grow to dangerous lengths
- The Paris Law accounts for crack analysis due to fatigue
Endurance Limit
- The endurance limit is the most important property indicating fatigue strength
- Steels and polymers have an endurance limit 0.33 to 0.6 of tensile strength
- Glass and ceramics have an endurance limit of 0.9 of tensile strength
Remedies for Fatigue and Cracks:
- Use surface treatments and polish
- Avoid sharp corners
- Do not use any irregularities and notches
- Apply compressive stress at the surface
Phase Diagrams and Phase Transformation
- Indicates the chemical status of an alloy at a certain temperature
- Chemical status is the equilibrium state of lowest energy material
Phases
- Phase is a homogeneous portion of a system with uniform physical and chemical characteristics
- Same composition, varying cell structures, a, B, and L (Alpha, Beta, and Liquid)
Alloys
- Alloy examples are brass (Cu + Zn), Monel (Cu + Ni), bronze (Cu + Sn), and solder (Pb + Sn)
Binary Eutectic Phase Diagram
- Liquid solidifies into two unique solids, α and β, at non-solubility
- The liquidus line indicates the temperature above which the substance is liquid
- The solidus line indicates the temperature below which the substance is solid
- The solvus line indicates the solubility limit that crosses the line upon cooling
- α and β contain material A and B; dissolved in different conditions
- Solvus line solubility is α or β, crossed during cooling
- Precipitates of a second phase form can be dissolved in alpha or beta
Isomorphous Diagrams
- Shows high or low solubility levels in primary phase
- Eutectic undergoes liquid transformation into two intermixed solid phases
Phase Transformation: Eutectic
- Indicates starting with one phase and ending with two
Eutectoid Phase Transformation
- The solid transformation into two intermixed solid phases undergoes a transformation
- Composition, process, and the microstructure of alloy elements is characteristic and affect their properties
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