part 2 maybe Flashcards
Q1: What is Yield Strength (σy)?
A: The stress at which noticeable plastic deformation has occurred.
Q2: What is Tensile Strength (TS)?
A: The maximum stress on the engineering stress-strain curve.
For metals: Occurs when noticeable necking starts.
For polymers: Occurs when polymer backbone chains are aligned and about to break.
Q3: What is a “neck” in materials under tension?
A: A localized reduction in cross-section that acts as a stress concentrator during tensile loading.
Q4: What is ductility?
A: The plastic tensile strain at failure, indicating how much a material can stretch before breaking.
Q5: What is resilience?
A: The ability of a material to absorb energy during elastic deformation and recover the energy when the load is released. It is quantified by the modulus of resilience (Ur).
Q6: How is the modulus of resilience (Ur) calculated?
A: By finding the area under the stress-strain curve up to the yield point.
Q7: What is toughness?
A: The energy required to break a unit volume of material, approximated by the area under the entire stress-strain curve.
Q8: Compare toughness between materials.
A:
Metals: Large toughness
Ceramics: Small toughness
Unreinforced polymers: Very small toughness
Q9: What is true stress and true strain?
A: True stress is the applied load divided by the instantaneous cross-sectional area, while true strain is the natural log of the ratio of instantaneous length to original length.
Q10: What is hardness?
A: Hardness measures a material’s resistance to surface plastic deformation, such as denting or scratching.
Q11: What does a high hardness value indicate?
A: High resistance to deformation from compressive loads and better wear properties.
Q12: What are common methods for measuring hardness?
A:
Rockwell Hardness: Uses various loads and indenters (e.g., diamond, ball).
Brinell Hardness (HB): Uses a spherical indenter to measure resistance.
Q13: What are the Rockwell hardness testing scales?
A:
A scale: 60 kg load with a diamond indenter.
B scale: 100 kg load with a 1/16 in. ball.
C scale: 150 kg load with a diamond indenter.
Q14: What is Brinell Hardness (HB)?
A: A hardness test using a spherical indenter where the result is proportional to tensile strength:
TS (psia) = 500 × HB
TS (MPa) = 3.45 × HB
Q15: What is a design/safety factor (N)?
A: A factor used to account for uncertainties in material properties or loading, ensuring that structures operate safely below their failure limits.
Q16: What is stiffness?
A: A material’s resistance to elastic deformation, quantified by Young’s modulus or elastic modulus.
Q17: What is the difference between elastic and plastic deformation?
A:
Elastic deformation: Non-permanent, linear stress-strain behavior, occurs at low stress levels.
Plastic deformation: Permanent, nonlinear stress-strain behavior, occurs at higher stress levels.
Q18: How is hardness typically denoted in the Rockwell hardness test?
A: As a combination of hardness value and scale (e.g., 57 HRA or 63 HR15T).
Q19: What are the characteristics of a material with high hardness?
A: Smaller indentations from a hardness test indicate higher resistance to surface deformation and better wear resistance.
Q20: What is the relationship between hardness and tensile strength?
A: For Brinell hardness, tensile strength is proportional to hardness:
TS (psia) = 500 × HB
TS (MPa) = 3.45 × HB
Q21: What is the difference between elastic and plastic strain recovery?
A:
Elastic strain recovery: The material returns to its original shape when the load is removed.
Plastic strain: Permanent deformation remains even after the load is removed.
Q22: What is the significance of Rockwell hardness scales?
A: They allow hardness to be measured with minimal damage to the sample using different load levels and indenters.
