Final Exam Review - ENGR 54

Periodic Trends

Ionic Character

What is the relationship between elastic modulus (E) and thermal expansion coefficient (a)?

Materials that are easier to stretch (small E) generally shower bigger thermal expansion (a). The elastic modulus is directly related to the stiffness of the material so you could also say the more stiff a material is, the smaller thermal expansion it will have

What ionic character suggests a covalent bonded material and which suggests an ionic bonded material?

- 25% > I.C. suggest a covalent bond

- 25% < I.C. suggest an ionic bond

What is the side length (a) and APF for a simple cubic?

a = 2R

APF = 52%

What is the side length (a) and APF for body centered cubic?

a = 4R/sqrt3

APF = 68%

What is the side length (a) and APF for face centered cubic?

a = 2Rsqrt2

What is the crystallographic notation for direction?

[1 1 1]

What is the crystallographic notation for a plane?

(1 1 1)

XRD selection rules

BCC: (h+k+l) even

FCC: h, k ,l either all even or all odd

SC: All

What are point defects?

- vacancies

- interstitial atoms

- substitutional atoms

What are line defects?

- dislocations

What are area defects?

- free surfaces

- grain boundaries

What are the conditions for substitutional solid solutions (Hume-Rothery Rules)?

- change in atomic radius < 15%

- similar electronegativities (proximity in periodic table)

- same crystal structure

- valency

What is needed for diffusion to occur?

activation energy which is the energy required to overcome the energy maximum in order for the jump to occur

What is the difference between tensile and ultimate strength?

Tensile stress refers to any stress under a tensile load and ultimate stress refers to the highest tensile strength the material can take before failure mechanisms like necking or fracture occur

Given a strain-stress curve, how is young modulus (E) calculated?

- the slope during the linear portion of the graph

Given a stress-strain curve, how is resilience calculated?

- area under the elastic part, or linear portion, of the graph right before it begins to curve

Given a stress-strain curve, how is toughness calculated?

- entire area under the stress-strain curve from 0 to fracture

What is yield strength?

stress at which plastic deformation begins

What is the difference between engineering and true stress-strain?

Engineering uses a constant area causing the curve to drop after ultimate tensile stress and length AND true uses instantaneous area and length causing the curve to continue rising after necking

What does poisson's ratio tell us about a material?

A material with a high poisson's ratio is easier to pull and a material with a low poisson's ratio is easier to compress

When does slip occur?

when the shear stress exceeds the critically resolved shear stress

How can we prevent deformation?

alloying

grain size reduction

coldworking

For alloying, what is the difference between solid solution strengthening and precipitate strengthening?

solid solution strengthening: substituting one material for another with small or large impurities

precipitate strengthening: introducing new particles

What are the three stages of annealing?

recovery

recrystallization

grain growth

What is fatigue life?

the number of cycles until failure

What are the three stages of creep

primary creep: dislocation motion

secondary creep: steady-state (most important)

tertiary creep: rupture

What is the relationship between coordination number and cation/anion ratio?

Coordination number increases with increasing cation to anion ratio

What defines a frenkel defect?

a cation vacancy-cation interstitial pair

What defines a schottky defect?

a paired set of cation and anion vacancies

Is elastic deformation permanent? Is it recoverable?

No, it is not permanent

Yes, it is recoverable

Is non-elastic deformation permanent? Is it recoverable?

Yes, it is permanent

No, it is not recoverable

What is fatigue limit?

the point at which there is no change in S (stress amplitude) over a certain number of cycles

What is fatigue strength?

the stress level at which failure will occur for some specified

Annealing

What is the number of atoms per unit cell for SC, BCC, and FCC?

SC: 1

BCC: 2

FCC: 4