EIT Materials Science 2 — Questions and Answers
Question 1: Young's modulus (modulus of elasticity) is defined as:
- Stress divided by strain in the plastic region
- Stress divided by strain in the elastic region (Correct answer)
- Ultimate tensile strength divided by yield strength
- The slope of the stress-strain curve at fracture
Correct answer: Stress divided by strain in the elastic region
Young's modulus E = σ/ε applies only in the linear elastic region where Hooke's Law holds.
Question 2: What is the approximate Young's modulus for structural steel?
- 10 GPa
- 70 GPa
- 200 GPa (Correct answer)
- 400 GPa
Correct answer: 200 GPa
Steel has a Young's modulus of approximately 200 GPa (207 GPa), a standard value used in structural engineering calculations.
Question 3: In a Brinell hardness test, hardness is determined by:
- Measuring the depth of a diamond cone indentation
- Measuring the rebound height of a dropped ball
- Measuring the diameter of a spherical indentation from a hardened ball (Correct answer)
- Measuring the width of a surface scratch
Correct answer: Measuring the diameter of a spherical indentation from a hardened ball
Brinell hardness (BHN) is calculated from the applied load and the area of the indentation left by a hardened steel or tungsten carbide ball.
Question 4: What does a standard Charpy impact test measure?
- Hardness at low temperature
- Energy absorbed during fracture of a notched specimen (Correct answer)
- Tensile strength at high strain rates
- Fatigue life under cyclic loading
Correct answer: Energy absorbed during fracture of a notched specimen
The Charpy test measures the energy absorbed when a notched bar is struck by a swinging pendulum, assessing toughness and ductile-to-brittle transition.
Question 5: The endurance limit in fatigue testing is best described as:
- The maximum stress a material can withstand before fracture
- The stress amplitude below which a material can theoretically endure infinite cycles (Correct answer)
- The number of cycles to failure at a given stress
- The minimum stress that causes plastic deformation
Correct answer: The stress amplitude below which a material can theoretically endure infinite cycles
For ferrous alloys, the endurance limit is the stress amplitude below which fatigue failure will not occur regardless of the number of cycles, seen as the horizontal asymptote on an S-N curve.
Question 6: A material that undergoes significant plastic deformation before fracture is classified as:
- Brittle
- Ductile (Correct answer)
- Elastic
- Resilient
Correct answer: Ductile
Ductile materials exhibit large plastic deformation (necking, high percent elongation) prior to fracture, absorbing significant energy.
Question 7: Percent elongation in a tensile test is used to quantify:
- Elastic stiffness of the material
- Fracture toughness
- Ductility of the material (Correct answer)
- Ultimate tensile strength
Correct answer: Ductility of the material
Percent elongation = [(Lf - L0)/L0] × 100% measures how much a specimen permanently stretches before fracture, quantifying ductility.
EIT Materials Science 2
Young's modulus (modulus of elasticity) is defined as: