core 4 - p2 Flashcards
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Toughness is a material’s ability to absorb energy (impact) without fracturing. Measured via the Charpy impact test using a notched specimen struck by a pendulum.
What is the difference between elasticity and plasticity?
Elasticity: Material returns to original shape after force is removed (reversible).
Plasticity: Material retains permanent deformation after force is removed (irreversible).
What does Young’s modulus measure? Provide its formula.
What does Young’s modulus measure? Provide its formula.
E= Stress / Strain = (F / A) / ( ( Ln - Lo) / Lo ) )
State Hooke’s Law and its equation.
Hooke’s Law states that deformation is proportional to applied force within the elastic limit. Equation:
F = −kX
(k: spring constant; X: displacement).
Compare thermoplastics and thermosets in structure and properties.
Thermoplastics: Linear chains, soften when heated (recyclable, e.g., PVC).
Thermosets: Cross-linked chains, harden permanently (non-recyclable, e.g., epoxy).
Name three types of polymer structures based on molecular arrangement.
Linear, branched, network (cross-linked).
What is the glass transition temperature (Tg)?
The temperature at which a polymer transitions from rigid to flexible (amorphous regions soften).
Compare hot rolling and cold rolling in metal processing.
Hot rolling: Done above recrystallization temp; improves ductility, less precise.
Cold rolling: Done below recrystallization temp; increases strength, better surface finish.
What is sintering? What properties does it enhance?
Sintering fuses powdered materials using heat/pressure without melting. Enhances:
-Strength
-Electrical/thermal conductivity
-Density
List three types of casting processes.
Sand casting, die casting, investment casting.
How does the Brinell hardness test differ from the Vickers test?
Brinell: Uses a steel ball indenter; measures impression diameter.
Vickers: Uses a pyramidal diamond indenter; measures diagonal length of impression.
What is the purpose of a salt spray test?
Evaluates corrosion resistance of coatings by exposing specimens to a saline mist.
Define electrical conductivity and its formula.
Conductivity (σ) measures how well a material conducts electricity. Formula:
σ = 1 / ρ = l / AR
(ρ: resistivity; l: length; A: area; R: resistance).
What are FRPs? Give two examples.
Fiber-Reinforced Polymers (composites with fiber + resin matrix). Examples:
Carbon Fiber Reinforced Polymer (CFRP)
Glass Fiber Reinforced Polymer (GFRP)
What is the Taber abrasion test used for?
Measures wear resistance of materials (e.g., coatings) by rotating abrasive wheels against the surface.
Explain the Wohler test (fatigue testing).
Applies repeated tensile/compressive stresses to determine a material’s fatigue life (resistance to cyclic loading).
What are van der Waals forces? Where are they significant?
Weak intermolecular forces between molecules. Critical in polymers (e.g., holding chains together in plastics).
What is the difference between crystalline and amorphous structures?
-Crystalline: Ordered, repeating atomic lattice (e.g., metals).
-Amorphous: Random, disordered structure (e.g., glass).
How does cold working affect metal properties?
Increases strength/hardness via dislocation movement but reduces ductility. Causes residual stresses.
What is hardenability? How is it different from hardness?
Hardenability is a material’s ability to be hardened by heat treatment (quenching). Hardness measures resistance to surface indentation.
Name two injection moulding materials and their applications.
-ABS: Durable, used in automotive parts.
-Polycarbonate (PC): Transparent, used in eyewear lenses.
What is a composite laminate?
Layers of fibrous composite materials (e.g., CFRP) bonded to achieve desired engineering properties.
Define permeability in materials.
Ability to allow magnetic flux to pass through (e.g., iron has high permeability).
What is the stress-strain curve’s necking region?
The point where a material’s cross-section locally reduces before fracture, indicating plastic instability.
