AIT Material Science 5 — Questions and Answers
Question 1: Which material property is described by the area under a stress-strain curve up to the fracture point?
- Hardness
- Toughness (Correct answer)
- Stiffness
- Strength
Correct answer: Toughness
Toughness is the energy per unit volume a material can absorb before fracturing, represented by the total area under the stress-strain curve.
Question 2: What is the main difference between low-carbon steel and high-carbon steel in a trade setting?
- Low-carbon steel is harder and more brittle
- High-carbon steel is more weldable and ductile
- Low-carbon steel is more weldable but less hard than high-carbon steel (Correct answer)
- High-carbon steel has better corrosion resistance
Correct answer: Low-carbon steel is more weldable but less hard than high-carbon steel
Low-carbon steel (mild steel) is easier to weld and more ductile, while high-carbon steel is harder and stronger but less weldable.
Question 3: What is galvanic corrosion and how is it prevented?
- Corrosion from high temperature exposure; prevented by painting
- Corrosion from dissimilar metals in electrical contact in the presence of an electrolyte; prevented by isolation or matching metals (Correct answer)
- Corrosion from UV radiation; prevented by coating
- Corrosion from acid rain; prevented by alkaline treatment
Correct answer: Corrosion from dissimilar metals in electrical contact in the presence of an electrolyte; prevented by isolation or matching metals
Galvanic corrosion occurs when two dissimilar metals are in electrical contact in an electrolyte, with the less noble metal corroding faster; using insulating gaskets or compatible metals prevents it.
Question 4: In an apprenticeship context, why is it important to verify material certifications (Mill Test Reports) before use?
- To confirm the material's color matches specifications
- To ensure the material meets required chemical and mechanical property standards for the application (Correct answer)
- To verify the shipping date of the material
- To check the manufacturer's profit margin
Correct answer: To ensure the material meets required chemical and mechanical property standards for the application
Mill Test Reports (MTRs) confirm that the material's chemical composition and mechanical properties meet the specified standards, ensuring safety and code compliance.
Question 5: Which heat treatment is applied to relieve residual stresses in welded structures without significantly changing hardness?
- Quench hardening
- Carburizing
- Post-weld heat treatment (stress relieving) (Correct answer)
- Martempering
Correct answer: Post-weld heat treatment (stress relieving)
Post-weld heat treatment (PWHT) or stress relieving heats the weldment to a temperature below the critical point and holds it there to reduce residual stresses without major hardness changes.
Question 6: What is the purpose of a 'grain structure' analysis in metals?
- To determine the color and aesthetics of the metal surface
- To assess mechanical properties, processing history, and predict performance (Correct answer)
- To measure the electrical resistance of the metal
- To identify the brand of the steel manufacturer
Correct answer: To assess mechanical properties, processing history, and predict performance
Grain structure analysis reveals information about the metal's processing history, mechanical properties, and can predict behavior under service conditions.
Question 7: When a blueprint calls for '304 SS' pipe, what material is specified?
- Carbon steel, Schedule 40
- Type 304 stainless steel (Correct answer)
- 304-grade structural aluminum
- Schedule 304 black iron pipe
Correct answer: Type 304 stainless steel
304 SS refers to Type 304 austenitic stainless steel, a common corrosion-resistant alloy containing approximately 18% chromium and 8% nickel.
AIT Material Science 5
Which material property is described by the area under a stress-strain curve up to the fracture point?