Material

Question 1

What is elastic deformation?

Answer 1

A temporary shape change that is reversible when the applied force is removed.

Question 2

What is plastic deformation?

Answer 2

A permanent shape change that remains even after the load is removed.

Question 3

Which material property describes a material’s stiffness?

Answer 3

Young’s modulus (Elastic modulus).

Question 4

What does ductility mean?

Answer 4

A material’s ability to deform plastically before fracturing.

Question 5

What is the yield strength?

Answer 5

The point at which a material begins to deform plastically.

Question 6

What happens on a microscopic level during elastic deformation?

Answer 6

Atomic bonds are stretched but not broken.

Question 7

What happens on a microscopic level during plastic deformation?

Answer 7

Dislocations move within the crystal structure, causing permanent rearrangements.

Question 8

What is diffusion?

Answer 8

The movement of atoms or molecules within a material, driven by concentration gradients.

Question 9

What is thermal expansion?

Answer 9

The change in a material’s size due to temperature changes.

Question 10

What is sintering?

Answer 10

A process of compacting powder materials using heat below their melting point to form a solid structure.

Question 11

What is a unit cell?

Answer 11

The smallest repeatable structure in a crystal lattice that defines the material’s properties.

Question 12

Name the three main types of polymers.

Answer 12

Thermoplastics, thermosets, and elastomers.

Question 13

What is a thermoplastic?

Answer 13

A type of polymer that softens when heated and can be reshaped.

Question 14

What is the material index?

Answer 14

A combination of material properties optimized for specific applications. Example: balancing strength, weight, and cost.

Question 15

Why is metal recycling important?

Answer 15

It reduces raw material usage, lowers energy consumption, and minimizes environmental impact.

Question 16

What are crystalline materials?

Answer 16

Materials with a regular, repeating atomic structure, such as metals and ceramics.

Question 17

What are amorphous materials?

Answer 17

Materials with randomly arranged atoms, such as glass and some polymers.

Question 18

What is a brittle fracture?

Answer 18

A sudden failure without significant deformation, often occurring in ceramics.

Question 19

What is fatigue in materials?

Answer 19

Progressive structural damage due to cyclic loading, leading to the forming and spreading of cracks in the material

Question 20

What are the benefits of using High Strength Low Alloy (HSLA) steel?

Answer 20

High strength-to-weight ratio and durability, making it ideal for load-bearing applications.

Question 21

How does atomic bonding affect the stiffness of a material? Compare how stiffness varies between metals, ceramics, and polymers.

Answer 21

A material’s stiffness is determined by its atomic bonding. Metals, with metallic bonds, have moderate stiffness. Ceramics, with strong covalent or ionic bonds, are very stiff but brittle. Polymers, with covalent bonds between atoms and weak van der Waals forces between chains, have much lower stiffness.

Question 22

Describe how composites can be designed to enhance the stiffness of a material. Provide an example where a composite material might be more suitable than a homogeneous material.

Answer 22

Composites enhance stiffness by embedding strong fibers (like carbon or glass) in a softer matrix (like a polymer). This structure lets fibers bear most of the load, increasing stiffness while keeping weight low. For instance, carbon fiber composites are used in aircraft for their high stiffness and low weight

Question 23

Explain the different hardening mechanisms that can strengthen a metal. Provide examples of how solution hardening and precipitation hardening work.

Answer 23

Hardening mechanisms increase a material’s strength by hindering dislocation movement:

Solution hardening: Alloying elements are added to a metal, creating local stress fields that impede dislocations (e.g., copper alloyed with zinc in brass).

Precipitation hardening: Small particles form in the material after heat treatment, obstructing dislocations (e.g., aluminum alloyed with copper in 2000-series alloys)

Question 24

Explain how materials behave differently at elevated temperatures. What is creep, and under what conditions does it occur?

Answer 24

At high temperatures, materials deform more easily as atomic bonds weaken. Creep, a slow, permanent deformation under constant stress, happens above 0.5 times a material’s melting point (in Kelvin), especially in metals and polymers.

Question 25

What are the primary characteristics of ceramics that differentiate them from metals and polymers? How do these characteristics affect their applications?

Answer 25

Ceramics have high melting points, stiffness, hardness, and brittleness. They don’t deform plastically and are poor conductors, making them ideal for high-temperature uses like cutting tools but unsuitable where toughness is needed.

Question 26

Ceramics cannot typically be cast like metals. Describe the process of sintering and why it is commonly used in the manufacturing of ceramic components.

Answer 26

Sintering compacts and heats ceramic powders to about two-thirds of their melting point, bonding particles through diffusion. It’s used because ceramics, with high melting points and brittleness, can’t be easily cast or shaped like metals or polymers.

Question 27

What are the differences between thermoplastics, thermosets, and elastomers? Give an example of where each type of polymer might be used.

Answer 27

Thermoplastics: Can be melted and reshaped multiple times (e.g., polyethylene used in packaging).

Thermosets: Form irreversible bonds and cannot be remelted (e.g., epoxy resins used in adhesives).

Elastomers: Exhibit elastic properties and can stretch significantly (e.g., rubber used in tires).

Question 28

Examine the challenges associated with metal recycling, including technical, economic, and material-specific issues

Answer 28

Metal recycling faces challenges such as technical difficulties in separating metals, economic factors like fluctuating market values, and material-specific issues such as contamination and alloy separation.