Module 1

Stiffness

How much force (stress) does it take to flex the material (not permanently deformed)

Strength

How much force (stress) does it take to permanently deform the material (deformed, but not broken)

Toughness

How much energy it requires to break the material

Stress

Load/Area

Strain

(Change in Length)/(Initial Length)

Elastic Deformation

A deformation that is reversible (material will go back to original shape after load is released)

Elastic Modulus

Stiffness

Poisson’s Ratio

The negative of the ratio of the transverse (lateral) strain to the axial (longitudinal) strain in the axial tensile loading

Plastic Deformation

Deformation is permanent; Stress is not proportional to strain

Yield Stress

The stress required to permanently deform the material

Ultimate Tensile Strength

The stress beyond which the material fails/fractures

Ductility

The maximum amount of strain (% elongation) at failure

Resilience

A materials property that describes the amount of energy per volume restored to the material after the load is gone

Coefficient of restitution

The corresponding performance parameter

Toughness

Measures the energy per volume required to break a material (integral of a stress-strain curve)

Hardness

A surface property of a material that describes how difficult it is to scratch a material and can be semi-quantitatively assessed using the Moh’s hardness scale

Acoustic Impedance (Z)

When sound travels from one material to another, the difference in the acoustic impedance determines how much of the sound is transmitted or reflect (large Z mismatch means that the sound is mostly reflected and a small Z mismatch means that the sound is most transmitted)

Heat Capacity

A materials constant; the heat energy required to raise the temperature of a material by 1 degree C

Thermal Conductivity

The rate at which heat flows through a material at steady state

Thermal Diffusivity

A material property used to describe a transient heat flow

Thermal Expansion Coefficient

Change in volume of a material with change in temperature; Cross property: Thermal and Mechanical

Electrical Conductivity

How “quickly” electrons travel through the material

Electrical Resistivity

The opposite of conductivity, it is the impediment to electron flow

Piezoelectricity

A cross-property combining both the electrical and mechanical response of a material; electrical insulators because they must support an internal applied voltage to function

Piezoelectric Coefficient

Large d indicates larger effect; Direct effect: Q = d*F; Reverse effect: S = d*E

Semiconducting Materials

Can behave either as insulators or as conductors; At an unbiased state, they will behave as insulators; They can become conductive when you apply energy; They are very useful in switching applications

Transistors

Use semiconducting materials to act as switches; In an enhancement-mode MOSFET, when a voltage above the threshold is applied to the gate, the semiconductor is conducting and the switch is on; When there is no signal, or the signal is not sufficient, the switch is off

Magnetization

Material’s response to an applied magnetic field (H)

Magnetic Susceptibility

Materials property, but is complex because it is mathematical function of magnetic field

Saturation Magnetization

Maximum magnetization response of to an applied field

Remanent Magnetization

Magnetization remaining when applied field is zero

Coercive Field

How easily the magnetization will switch directions

Curie Temperature

Permanent magnets lose their magnetization when heated above this point; This loss of magnetization is permanent

UV/Vis Spectroscopy

Technique to measure wavelength dependence of RAT; High R/Low A are the colors we see and High A/Low R are the colors we do not see

Refractive Index

The ratio of the velocity of light in vacuum to the velocity of light traveling in material (light actually slows down in material)

Diffusion

The random motion of atoms/molecules in a system. While local motion is random, more global motion typically occurs from areas of high concentration to areas of low concentration in order to homogenize system’s composition

Diffusivity

Material property that determines how fast atoms diffuse through a material

Durability

The material and the environment determine dominant degradation mechanism

Solubility

Material is dissolving in a liquid; this is a physical change not a chemical change

Oxidation

material chemically react with oxygen

Corrosion

“Bad” oxidation, often in aqueous environment

Photodegradation

Light (UV) breaking bonds in a material (typically with polymers)

Oxidation

A chemical reaction between a metal and oxygen gas

Anodization

The surfaces of some materials can be purposely oxidized using electrochemical methods to form thicker, more protective oxide coatings

Galvanic Corrosion

A corrosion process that occurs when two different metals are in electrical contact with one another in the presence of a liquid water environment

Polymers Mechnical Properties

Low elastic modulus (low stiffness easily flexed)

When in ductile mode, reasonably high toughness

May be brittle or ductile

Polymers Electrical Properties

Usually electrically insulating

Polymers Thermal Properties

Low thermal conductivity

Low service temperature

Polymer Optical Properties

Often transparent or translucent

Can be dyed to create different colors of plastic

Polymers Chemical Properties

Corrosion resistance: can be used as a corrosion barrier

Often dissolve or swell in organic solvents

Also reacts with strong oxidizers and UV light

Polymers Properties (other notes)

Very low density

This low density makes their strength per weight ratio similar to that of metals

Easily processes into various shapes (low service temperature and highly flexible)

Ceramics

Often composed of Oxides (metal + oxygen)

Gem stones and other “rocks” are mostly ceramics

The term ceramic is often used to refer to the crystalline form of these inorganic solids

Crystalline materials have an ordered atomic structure

Glass

Sub-class of ceramics with an amorphous structure

Brittle and resistant to corrosion

Ceramics Mechanical Properties

Stiff but brittle

Brittle = low strain at failure, essentially no plastic deformation, fractures at/near the yield point

Ceramics Electrical Properties

Most ceramics are good electrical insulators

Ceramics Thermal Properties

Thermal conductivity between polymers and metals

Excellent temperature stability, stable above 1000C or 2000C

(glasses have lower service temperatures and lower thermal conductivity)

Ceramics Optical Properties

Ceramics: Opaque or Translucent

Glasses: Transparent

Ceramics Chemical Properties

Corrosion resistant

Durable against acids and organic solvents

Ceramics Properties (other notes)

High hardness

Can withstand mechanical loading in compression but not in tension

Often difficult to machine or shape (due to their high service temperature)

Semiconductors

Sub-class of ceramics (most are not oxides they are semimetals)

Have similar properties to ceramics except they can be electrical conductors

Electrical conductivity can be adjusted by composition or applying a voltage

Group IV Elements: Si, Ge

III-V Semiconductors: GaAs, GaP, InAs, GaN

II-VI Semiconductors: CdTe, CdSe, ZnTe, ZnSe

Metals and Metal Alloys

Inorganic solids made of only metallic elements

Nearly all metals are crystalline solids

A solid metal may be composed of a single element or a mixture of multiple elements (alloys)

Metal Alloys

An atomic-scale mixture of two or more elemental metals

Still crystalline, but elements are randomly arranged on the repeating atomic sites

Metals Mechanical Properties

High elastic modulus

Pure elemental metals have a lower yield strength (easier to deform)

Alloying or adding defects improves yield strength

Good toughness (expect plastic deformation)

Metals Electrical Properties

Good electrical conductors

Metals Thermal Properties

Good thermal conductors

Most have intermediate service temperatures

Metals Optical Properties

Generally opaque but in different ways

Reflective in the visible and UV

Absorptive in the IR and longer wavelengths

Metals Chemical Properties

Susceptible to corrosion and chemical attack by acids

Metals Properties (other notes)

Easier to machine and deform into various shapes, compared to ceramics: lower service temperature, more ductile (ability to plastically deform)

Composites

Combine two or more materials classes in an attempt to get “merged” properties

Often more expensive than each individual component because of additional manufacturing/processing steps required to combine the materials