CAMT Material Properties & Characterization 1 — Questions and Answers
Question 1: Which material property describes the ratio of stress to strain in the elastic region of a stress-strain curve?
- Yield strength
- Modulus of elasticity (Young's modulus) (Correct answer)
- Ultimate tensile strength
- Fracture toughness
Correct answer: Modulus of elasticity (Young's modulus)
Young's modulus defines the stiffness of a material as the slope of the linear elastic portion of the stress-strain curve.
Question 2: In additive manufacturing, anisotropy of mechanical properties is most commonly caused by:
- Incorrect bed temperature
- Layered build direction creating directional microstructure (Correct answer)
- Excessive infill density
- High ambient humidity during printing
Correct answer: Layered build direction creating directional microstructure
The layer-by-layer deposition creates a directional microstructure, making properties stronger along certain axes than others.
Question 3: Which test is used to measure the resistance of a material's surface to permanent indentation?
- Charpy impact test
- Tensile test
- Hardness test (Correct answer)
- Fatigue test
Correct answer: Hardness test
Hardness tests (Rockwell, Brinell, Vickers) measure resistance to surface indentation by a standardized indenter.
Question 4: Porosity in metal AM parts is most problematic because it:
- Increases the part weight
- Acts as a stress concentrator that reduces fatigue life (Correct answer)
- Improves surface finish
- Increases thermal conductivity
Correct answer: Acts as a stress concentrator that reduces fatigue life
Pores act as stress concentration points that initiate cracks under cyclic loading, significantly reducing fatigue life.
Question 5: Which phenomenon occurs when a polymer AM material absorbs moisture from the environment, affecting print quality?
- Oxidation
- Hygroscopy (Correct answer)
- Crystallization
- Delamination
Correct answer: Hygroscopy
Hygroscopy is the tendency of certain materials to absorb moisture, which can cause bubbling and inconsistent extrusion in FDM printing.
Question 6: The glass transition temperature (Tg) of a polymer is important in AM because it defines:
- The melting point where the material becomes fully liquid
- The temperature above which the material becomes rubbery and loses rigidity (Correct answer)
- The optimal bed temperature for all polymers
- The temperature at which crystallization begins
Correct answer: The temperature above which the material becomes rubbery and loses rigidity
Above Tg, amorphous polymers transition from a glassy rigid state to a rubbery state, which determines heat resistance of the finished part.
Question 7: In powder bed fusion (PBF) of metals, the powder particle size distribution affects:
- Only the color of the final part
- Powder flowability, packing density, and surface finish of the part (Correct answer)
- The speed of the laser only
- The electrical conductivity of the machine
Correct answer: Powder flowability, packing density, and surface finish of the part
Particle size distribution controls how well powder flows and packs, directly influencing melt pool behavior and surface finish.
CAMT Material Properties & Characterization 1
Which material property describes the ratio of stress to strain in the elastic region of a stress-strain curve?