Lecture Notes Review - Metals, Plastics, Composites, Smart Materials, Glass, Timber, Properties

Flashcards covering key concepts from lecture notes on metals, plastics, composites, smart materials, glass, timber, and material properties.

What are the three main metal strengthening processes?

Work hardening (plastic deformation), controlling grain size, and alloying.

What happens internally to the microstructure of a metal when it is plastically deformed?

Dislocation density is increased (more dislocations are created).

What do all three metal strengthening processes do to the internal structure to make it stronger?

They inhibit (hinder/stop) atom movement.

How does controlling grain size strengthen a metal?

By increasing grain boundary area through fast cooling (smaller grains), which inhibits atom/dislocation movement.

How does work hardening (plastic deformation) strengthen a metal?

It creates dislocations, increasing dislocation density, which inhibits atom/dislocation movement.

How does alloying increase the strength of a metal?

Adding foreign atoms inhibits atom/dislocation movement.

What are Brinell and Rockwell tests used for?

Hardness testing for metals.

What are Vickers and Knoop tests used for?

Hardness testing for harder and brittle materials like glass.

Which metal is produced from the extraction of iron from the ore?

Pig iron.

What are the two main constituents in plain steel (not stainless)?

Iron and carbon.

What are the two types of plastics we are studying?

Thermoplastics and thermosets.

Describe the internal structure of thermoplastics.

Linear (hydrocarbon) chain molecules with no (or very few) crosslinks.

Describe the internal structure of thermosets.

Lots of crosslinks, forming a ladder-like structure.

Which type of plastic is recyclable and why?

Thermoplastics, because increased temperature diminishes secondary bond strength, allowing hydrocarbon chains to move and melt the plastic.

What happens if you heat a thermoset plastic?

Thermosets get harder with more heat applied (the number of crosslinks increases).

Describe what happens to the internal structure of plastic when a load is applied until it is plastically deformed.

Initially coiled linear chains uncoil and straighten. Secondary bonds break, and the chains slide over one another.

Name four thermoset plastics.

Polyurethane (PU), Urea-formaldehyde (U-F or UFFI), Melamine Resin/formaldehyde, Epoxy Resin.

Where do plastics generally come from?

Petrochemicals.

What are the properties of Urea-formaldehyde?

Stiff and brittle, hard, strong, and a good electric insulator.

What are the applications of Urea-formaldehyde?

Glue, fire retardant, water repellant, and insulation.

What is the definition of a composite material?

A mixture composed of two or more materials that are bonded together to improve their properties (mechanical, physical, chemical, or electrical).

In composites, what is the role of fibers?

They are filaments with a length to thickness ratio of at least 80, providing strength.

In composites, what is the role of the matrix?

It is the 'glue' (resin) holding the fibers together.

What are smart materials?

Materials whose properties can be drastically altered (e.g., viscosity, volume, conductivity) by external stimuli.

How are Magneto-rheostatic materials considered 'smart'?

They can rapidly change their viscosity and flow properties when encountering a magnetic field.

How are Electro-rheostatic materials considered 'smart'?

They can rapidly change their viscosity and flow properties when encountering an electrical field, allowing precise control of mechanical systems.

How do Piezoelectric materials respond to their external environment?

They convert mechanical energy to electrical energy (and vice versa); they give off an electrical discharge when deformed and increase in size when electricity goes through them.

How do Photochromic materials demonstrate 'smart' behavior?

They change their color with light intensity, usually colorless in the dark and exhibiting color when UV radiation is applied, with the color disappearing when the light source is removed.

How are Thermoelectric materials considered 'smart'?

They have the ability to directly convert waste heat into electricity (the Seebeck effect).

What is Kevlar?

An aramid (aromatic polyamide) fiber.

What are the key strengths of Kevlar?

It has very high tensile strength, being 5 times stronger than the same weight of steel, and is non-stretch and non-absorbent.

What is the main ingredient of standard glass?

Silicon dioxide (sand, silica).

Why is boron oxide added to standard glass?

To give it good thermal shock characteristics.

What property describes how much a material expands when heated?

Thermal expansion coefficient.

What is thermal shock in the context of glass?

When a heated piece of glass is exposed to a cold liquid, or vice versa, causing stress.

How does toughened glass break when fractured?

It breaks into thousands of small pieces, reducing injuries.

How is toughened glass manufactured and what does it achieve?

By heating glass almost to melting point and then rapidly cooling its surfaces, creating internal stresses that make it up to 5x stronger than regular glass.

What is laminated glass and how is it manufactured?

It is made by sandwiching a thin layer of material (usually plastic PVB) between layers of glass.

Why does laminated glass stay together after impact?

Because of the internal layer of plastic, which also provides better UV protection and can be made bulletproof.

What are natural timbers comprised of?

Cellulose fibers and a lignin matrix (glue).

In general, how do softwood trees differ from hardwood trees in terms of maturity and cost?

Softwoods mature in about 30 years and are less expensive, while hardwoods take around 100 years to mature and are more expensive.

What is particle board made from and what are its common applications?

It is made from wood particles glued together under pressure, often used for cabinets and desks with veneer plastic sheets.

Describe plywood's composition and a key feature of its layers.

Multi-layers of veneer glued together under heat/pressure into the desired shape, always having an odd number of layers for balance.

What is OSB (oriented strand board) and how does it compare to plywood?

It is made from big wood chips glued together under pressure, has a rough surface, and is cheaper than plywood, often used for roofing.

What is MDF and how does it compare to particle board?

Medium Density Fiberboard is similar to particle board but is stronger, denser, and has a smoother surface, making it more appealing when painted for furniture and shelving.

What are physical properties?

Measurable properties that describe a physical system's state, such as density, electrical resistivity, and hardness.

What are mechanical properties?

The behavior of a material when it's linked to the application of force, such as tensile strength, stiffness, and ductility.

What is hardness?

The resistance of a material to penetration or scratching.

What is tensile strength?

The resistance of a material to pulling forces.

What is compression strength?

The resistance of a material to pushing forces.

What is stiffness?

The resistance of an elastic body to an applied force, important for maintaining shape, defined by k = P/S (stiffness = force/deflection).

What is toughness?

A combination of strength and ductility; the ability to withstand sudden shocks or blows without fracturing and to resist the propagation of cracks.

What is ductility?

The ability of a material to stretch, twist, or bend without breaking (bendability or crushability).

What is malleability?

The ability of a material to deform in all directions by hammering and pressing without cracking or splitting.

What is the relationship between ductile and malleable materials?

All ductile materials are malleable, but not all malleable materials are necessarily ductile.

What is elasticity?

The ability of an object or material to resume its normal shape after being stretched or compressed; stretchiness.

What is plasticity?

The quality of being easily shaped or molded; when the material deforms, it does not return to its original form.