Mixed Deck — All ME Topics Flashcards

What is the primary objective of failure analysis in materials engineering?

Answer: To identify the cause of material failure and prevent future occurrences

Failure analysis in materials engineering is a systematic investigation to determine the root cause of a material or component failure. Its primary objective is not just to understand why something broke, but to use that knowledge to implement corrective actions, improve material selection, design, or manufacturing processes. This ultimately prevents similar failures from happening again, enhancing safety, reliability, and cost-effectiveness.

Investment casting (lost-wax casting) is preferred for complex shapes because:

Answer: It uses an expendable wax pattern to produce intricate, near-net-shape parts

In investment casting, a wax pattern is coated with ceramic slurry, the wax is melted out, and metal is poured into the cavity, allowing complex geometries with excellent surface finish.

Precipitation hardening (age hardening) of Al-Cu alloys achieves maximum strength at peak aging because:

Answer: Fine, coherent GP zones and θ'' precipitates create maximum lattice strain fields

Peak hardness corresponds to fine coherent or semi-coherent precipitates (GP zones and θ'') that maximally strain the surrounding lattice, impeding dislocation motion.

Silica glass (SiO2) has an amorphous structure because:

Answer: Rapid cooling from the melt prevents long-range atomic ordering

Silica glass is formed by cooling the melt rapidly enough that the SiO4 tetrahedra cannot arrange into a periodic crystalline lattice, resulting in a random network.

Which alloying element is added to steel primarily to improve hardenability?

Answer: Chromium

Chromium (and elements like molybdenum, nickel, and manganese) shift the TTT curve to the right, improving hardenability by allowing martensite formation at slower cooling rates.

Sandwich composite structures use a low-density core between face sheets to maximize:

Answer: Flexural stiffness-to-weight ratio

Sandwich structures place stiff, strong face sheets far from the neutral axis with a lightweight core, enormously increasing bending stiffness with minimal weight addition.

Optical fibers used in telecommunications are made from high-purity silica glass primarily because of its:

Answer: High refractive index enabling total internal reflection and low optical attenuation

High-purity silica has very low optical attenuation (low signal loss) and supports total internal reflection via refractive index profiling, making it ideal for long-distance optical communications.

Chemical vapor deposition (CVD) is commonly used to apply hard coatings (e.g., TiN, TiC) to cutting tools because:

Answer: It produces dense, adherent coatings with excellent uniformity even on complex geometries at elevated temperatures

CVD deposits hard, wear-resistant ceramic coatings by thermally decomposing gas-phase precursors on the heated tool substrate, producing dense, conformal coatings with strong adhesion.

Young's modulus (elastic modulus) is a measure of a material's:

Answer: Stiffness under elastic loading

Young's modulus represents the ratio of stress to strain in the elastic region, quantifying a material's stiffness or resistance to elastic deformation.

Work hardening (strain hardening) increases a metal's strength by:

Answer: Increasing dislocation density

Cold working increases dislocation density; as dislocations multiply and interact, they impede each other's motion, requiring higher stresses for further deformation.

Pearlite is a microstructure consisting of alternating lamellae of:

Answer: Ferrite and cementite

Pearlite forms by the eutectoid reaction and consists of alternating layers of alpha-ferrite and cementite (Fe3C).

Which copper alloy is known for its excellent spring-back properties and electrical conductivity?

Answer: Beryllium copper (Cu-Be)

Beryllium copper has the highest strength and hardness of any copper alloy, combined with excellent spring properties, making it ideal for electrical connectors and springs.

Which of the following is a key environmental concern in the use of composite materials?

Answer: Difficulty in recycling due to the combination of different materials

A key environmental concern with composite materials is the difficulty in recycling them due to their heterogeneous nature. Composites are made from a combination of different materials, such as fibers embedded in a polymer matrix, which are often difficult to separate and process individually. This complexity makes traditional recycling methods challenging and costly, often leading to composites being landfilled or incinerated.

Chemically strengthened glass (e.g., Gorilla Glass) achieves high strength by:

Answer: Ion exchange: replacing smaller Na+ ions with larger K+ ions in the surface layer to create compressive stress

Chemical strengthening uses an ion exchange bath to replace Na+ in the glass surface with larger K+ ions, which cannot fit into the original sites and create a compressive stress layer.

The glass transition temperature (Tg) of a polymer is the temperature at which:

Answer: Amorphous regions transition from glassy to rubbery behavior

Below Tg, amorphous polymer chains are frozen in a glassy state; above Tg, segments gain sufficient mobility to exhibit rubbery, viscoelastic behavior.

In polymer science, creep refers to:

Answer: Time-dependent deformation under sustained stress below the yield point

Creep in polymers is the slow, time-dependent increase in strain under a constant applied stress, driven by viscoelastic flow of polymer chains.

Which of the following materials is commonly researched for its potential to reduce environmental impact?

Answer: Biodegradable polymers

Biodegradable polymers are commonly researched for their potential to reduce environmental impact because they can naturally decompose into harmless substances after their useful life. Unlike conventional plastics that persist in the environment for hundreds of years, biodegradable polymers offer a solution to plastic pollution and waste accumulation. This makes them ideal for applications where end-of-life disposal is a concern, such as packaging and agricultural films.

Which of the following is a thermoplastic polymer commonly used in engineering applications for its high impact strength and transparency?

Answer: Polycarbonate (PC)

Polycarbonate is a thermoplastic known for high impact resistance, optical clarity, and good thermal stability, widely used in safety glazing and electronic housings.

Cemented carbide (WC-Co) cutting tools are an example of which composite type?

Answer: Cermet (ceramic-metal composite)

WC-Co is a cermet: tungsten carbide (ceramic) particles embedded in a cobalt (metal) binder, combining ceramic hardness with metallic toughness.

The 0.2% offset yield strength is used because many materials:

Answer: Have no clear yield point

Many materials, especially non-ferrous alloys, do not have a distinct yield point, so the 0.2% offset method provides a standardized yield strength value.