CHEMMAT 121-Engineering Part 1 UOA

Strength

The amount of force a material can resist before failure

Stress

Caused when a material has a force loaded onto it

Strength

The amount of force a material can resist before failure

Stress

Caused when a material has a force loaded onto it

Elastic Strain

Recoverable deformation. Object will revert back to it's original form when stress is removed

Plastic Strain

Permanent deformation. Object will not revert back to it's original form when stress is removed.

Young Modulus

Indicates the stiffness of a material. High Young's Modulus indicates high stress and low strain

Ductility

A material with the ability to undergo permanent/plastic deformation

Brittle

Unable to undergo plastic deformation. May deform elastically before breaking but will return to its original dimensions when force is removed

Ultimate Tensile Stress

Max point on a Engineering stress-strain curve, where necking commences

Failure

Fracture or permanent deformation

Elastic proportional limit

Point at which material begins to plastically deform if anymore force is applied

Yield Stress

The stress at which permanent deformation will start

Poisson's Ratio

Ratio between how thin a material gets as it gets longer during elastic deformation

Necking

A localised reduction in area that occurs during tensile testing

Work Hardening

Occurs after passing through a yield point-material gets stronger from plastic strain until point of fracture

Long Range Order

Tidy, neat and geometric

Elongation

Change in length

Isotropic Material

A material with the same properties in every direction

Anisotropic Material

A material which has different properties in different directions

True Stress

Stress that takes the instantaneous area into account

Toughness

Energy required to break or fracture the material

0.2% proof Stress

Method used to repeatedly determine yield stress

Crystalline

When the atoms of a material have Long Range Order(neat, tidy and geometric)

BCC

Body centered cubic-Crystalline structure where unit cell has an atom on each corner of the cube and one in the middle

FCC

Face centered cubic-Crystalline structure where unit cell has an atom on each corner of the cube and one in the middle of each face

Atomic packing factor

Shows how closely packed the atoms are

Coordination Number

Number of neighbouring atoms for each atoms

Safety Factor

The multiple of an expected load that an object is theoretically able to withstand without failure

Polymorphism

Materials that exist in more than one form or crystal structure

Crystallographically Equivalent

When the atomic spacing along each direction is the same, or the atomic packing on each plane is the same.

Close-packed direction

A direction in which atoms are touching

Close-packed plane

A plane where atoms are as closely packed as possible

Miller Indices

Planes in crystal lattice defined by the (h,k,j) system

Point defect

A point in a crystal lattice that is different from the overall lattice
E.g. Vacancy (missing atom)
Interstitial (small atom in a gap
in the lattice)
Substitution (Different atom
occupying space)

Dislocation

Planer defects, including edge dislocation and screw dislocation

Slip

Atoms effectively "sliding past" one another, breaking and forming new bonds with neighbours. Occurs by the movement of dislocations

Equiaxed grain structure

A structure where all the grains are equal in axis

Grain

Another word to say crystal in the metal structure

Polycrystalline

Made of many crystals or grains. Are typically metals

Single Crystal / Monocrystalline

Comprising of only one crystal

Hardness

Resistance to localised deformation. Can be defined as Rockwell hardness

Cold Work

The amount of plastic deformation done

Annealing

Applying heat treatment to a work hardened material to bring it back to the properties and grain structure that existed prior to work hardening

Recovery

First stage of Annealing. Dislocations rearrange themselves to a lower energy arrangement but number is not reduced

Recrystallisation

Second stage of annealing, new strain-free grains form, dislocation number reduced, until equaixed

Grain Growth

Third stage of annealing, grains grow, minimising grain boundary area

Recrystallisation Temperature

The temperature at which a 50% cold worked metal will just fully recrystallise in one hour

Hot Work

Deforming a metal when it's hot enough for recrystallisation to occur at the same time. There is no work hardening

Diffusivity

A measure of how easily an atom can diffuse

Phase

A component within a system that has uniform physical characteristics

Solid Solution

A crystalline solid compromising more than one metal type where the atoms of one metal occupy either:
* Lattice sites in another metal's lattice
* Interstitial sites in another metal's lattice

Complete Solid Solution

A situation where every atom in a metal's crystal lattice can be replaced with an atom of another metal

Tie Line

A horizontal line drawn through a two-phase region that hits each phase boundary. When it hits the phase boundary, it tells the composition of the phase at that temperature

Eutectic

The eutectic alloy in a binary alloy system is the alloy with the lowest melting point and melts at a single, well-defined temperature

Eutectic Point

The eutectic point is where this is shown on a phase diagram. When a eutectic alloy solidifies, it goes from liquid to two solid phases

Eutectoid SOlid

A combination of two phases in a layered structure

Pearlite

The eutectoid solid of steel, which is composed of two solid phases-Fe3C and a

Proeutectic Solid

Solid that forms before the eutectic solid forms

Proeutetoid soild

Solid that forms from the first transformation of an existing solid phase as it cools through a two phase region

Solid solution strengthening

Distortion of the crystal lattice in a metal by the presence of solute atoms, making it harder for dislocations to move