Industrial Materials & Metallurgy Flashcards
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Read the first 7 Industrial Materials & Metallurgy flashcards as text
What distinguishes a thermoplastic from a thermoset polymer in manufacturing applications?
Answer: Thermoplastics soften when reheated; thermosets permanently cure and cannot be remelted
Thermoplastics have linear or branched polymer chains that soften upon reheating, while thermosets form permanent cross-linked networks during curing and cannot be remelted.
What is the primary advantage of powder metallurgy (PM) manufacturing over conventional casting for producing small, precise parts?
Answer: Near-net-shape production with controlled porosity and tight dimensional tolerances
Powder metallurgy produces near-net-shape parts with tight tolerances, controlled porosity (useful for self-lubricating bearings), and minimal material waste compared to casting.
In metal fatigue, what is the endurance limit?
Answer: The maximum stress below which a metal can theoretically withstand infinite load cycles without fatigue failure
The endurance limit (fatigue limit) is the maximum cyclic stress below which a material can endure an infinite number of cycles without fatigue failure, notably observed in ferrous metals.
Which grain structure characteristic generally improves the mechanical properties of metals, especially toughness and tensile strength at room temperature?
Answer: Fine grain size
Fine grain size improves strength and toughness by increasing the total grain boundary area, which obstructs dislocation movement per the Hall-Petch relationship.
What is the function of a flux in welding and brazing operations?
Answer: To prevent oxidation and remove oxides from the metal surfaces being joined
Flux chemically reacts with and dissolves metal oxides, preventing oxidation during heating and allowing the molten filler metal to wet and bond properly with the base material.
Which non-destructive testing (NDT) method is best suited for detecting subsurface cracks in ferromagnetic materials?
Answer: Ultrasonic testing
Ultrasonic testing uses high-frequency sound waves to detect subsurface discontinuities in materials, while magnetic particle testing is limited to surface and near-surface defects.
What is the significance of the glass transition temperature (Tg) in polymer materials?
Answer: The temperature below which an amorphous polymer transitions from rubbery to glassy (brittle) behavior
Below the glass transition temperature, polymer chain segments lose mobility and the material becomes rigid and brittle; above Tg, the material is rubbery and flexible.