labs

lab 2: hardness (strength) testing

brinell test
- to get approximate strength of material
- load
  - 3000kg steel
  - 1500kg brass
  - 500kg aluminum
- 1ksi = 1000psi
- hardness correlation (steel only)
rockwell test
- lighter 15-150kg
- 14 different scale (B max 100,C max 150 are common) (quiz)
- distance of indentation bw minor and major yield result
- start with c scale first if we don’t know the material
the stronger the material, the less ductile
next week quiz
- brinell
  - adv
    - surface finish not as critical
    - better repeatability
    - wider range of hardness
  - disadv
    - measure dia (possible human error)
    - a little slower
    - not good for thin or narrow section
- rockwell
  - adv:
    - automatic readout
    - a little quicker
    - good for thinner or narrower sections
  - disadv
    - surface finish needs to be more smoother
    - more variation between results
    - multiple scale, but smaller range

lab 3: tensile testing

determine how strong and ductile is
majority of metal does not have yield point
quiz 2 - strain is measure using a strain extenemeter

lab 4: toughness testing

toughness is the ability of metal to absorb energy before fracturing
2 measure of toughness: FATT, ECTT (more common, most important)
the test specimens is a 10mm bar, 55mm long or 10x10x50mm
the Charpy Impact Test equipment use a 300ft.lbs or 407J pendulum
v-notch is the most common used
- 45 degree v-notch
- 2mm deep
- 0.25mm root radius

lab 5: heat treatment of steel

harden heat treatment (quenching)
- the cooling rate to create martensite is called “the critical cooling rate”
- the critical cooling rate mainly depends on chemical composition
  - carbon, chromium, molybdenum can determine how quickly a metal has to cool to form martensite
- anything faster than critial cooling rate is not based on phase diagram
- quenchants (order from fastest to slowest)
  - brine (soap add to water)
  - water
  - oil
  - air
- “never cool a metal faster than required (it can crack)”
- quenching is rarely the final heat treatment done on a metal like steel; further heat treating is required to restore ductility and toughness
cenmentaite: (carbon carbide) right side
ferrite: left side of dia
austenite : FCC
bainite stronger than pearlite

lab 6: strain hardening

lab 8: Magnetic Particle Inspection & Liquid penetrant

MPI

testing mediums (sorted best to lowest sensitivity)
- wet florescent
- contrast (black on white)
- dry powder
magnetic 2 directions (x and y) to catch all cracks

Advantage	Disadvantage
- portable (yoke)	- if the part is not ferromagnetic, MPI does not work
- relatively cheap	- parts has to be cleaned, free of oil, grease, etc.
- quick result	- parts need to be demagnetized
- safer	- best suited for surface flaw detection
- easy

Liquid penetrant inspection

steps
- clean parts
- apply penetrant
- remove excess penetrant
- apply developer
- inspect parts
- clean parts

Advantages	Disadvantages
- portable	- cracks have to be opened to surface
- relatively cheap	- slow (dwell time, cleaning)
- easy	- messy
- good sensitivity

lab 10: ultrasonic testing

can detect size and location of defects.
velocity of sound waves is dependent on
- type of material
  - bronze: 4700m/s
  - steel: 5960m/s
  - aluminum: 6400m/s
- temperature
  - speed of sound @ 15C at sea level 1225 kph or 340m/s
  - speed of sound @ -25C at sea level 1140 kph or 315m/s
- density
- pressure
sound is the mechanical vibration of particles in a material
advantage:
- superior penetrating (up to 20ft)
- high sensitivity
- greater accuracy (size, shape, orientation, shap_
- safe
- portable
disadvantage
- part geometry (difficult to inspect rough, irregular parts)
- need couplants to provide an effectivee transfer of energy
application: weldments, corrosion surveys
methods:
- straight beam: wall thickness, bar
- angle beam: weld inspection

lab 11: casting and forging

corrosion

factors that affect corrosion
- v
- environment (corrosiveness)
- operating conditions
  - temp
  - fluid velocity
  - pressures
  - loading conditions
measuring corrosion, 2 ways to measure
- thickness change
  - metric mmpa (mm per annum)
  - imperial mpy (mil per year) 1mil = 0.001”
- weight change
group 1, general corrosion type 1
- sometime called uniform
- most common type
- easiest to detect and control
- accounts for the highest amount of metal lose on an annual basis.
6 methods to control or work with general corrosion
1. add a corrosion allowance
  - increase the wall thickness
2. add galvanic protection
  - sacrificial anode (give the electrons for cathode)
  - impressed current: apply a current to the metal to be protected by forcing it to become cathodic
3. material selection
  - some materials have better corrosion resistance than others; considerations:
    - cost
    - welding
4. change the environment if possible
5. add inhibitors
  - are chemicals that slow or stop the corrosion reaction.
6. coatings
  - provide a barrier between the metals and its environment; 2 types
    - inert.
      - e.g. paint
    - active. (reaction)
      - e.g. galvanic steel (Zn coating)
  - considerations for selecting a coating
    - corrosion resistance
    - cost
    - ease of application
    - adherance
    - abrasion resistance
    - expand and contract with base metal
    - apprearance

lecture

what is an engineering material ?
- anything used to build something
metals
- metallic lustre
- conduct thermally
- conduct electricity
- ductile (stretch it, gold has very good ductivity)
- crystallized pattern of the atoms in the solid state
- malleable (ability withstand beaten up)
- metallic bonding
- classification
  - ferrous (iron based)
  - non-ferrous (non-iron based)
non-metals
- ceramic
  - inorgnaic
  - very hard/brittle
- polymers
  - organic (pvc)
- composites (carbon fiber)
when designing equipment what needs to be considered?
- operating conditions
  - stresses
  - loading conditions
    - torsion
    - shear stress
  - temperatures
  - corrosive environment
  - easy fabrication
    - welding
    - machining
  - cost
  - availability of material
  - thermal expansion, weight
solidification
1. nucleation (initial solidification)
2. grain or crystal growth
in the solid form, metals have a crystalline structure on the atomic level
these geometric patterns are called space lattices
95% of all metals will be one of 3 lattices (handout)
- BCC: body center cubic
  - chromium
  - sodium
  - vanadium
  - tungstien
  - iron
- FCC: face center cubic (more ductile, don’t change with heat)
  - gold
  - silver
  - nickle
  - aluminum
  - iron
- HCP: hexigonal close packed
  - zinc
  - titanium
  - cobalt
some metals can change their lattices shape from one to another based on temperature
- iron: BCC (low temp) -> FCC (high temp) -> BCC (low temp)
- this ability is called allotropy
  - iron is allotropic
what is steel?
- an alloy of iron and carbon
- an alloy is a material with metallic properties containing 2 or more elements. At least one element has to be a metal.

steel making

most common orce is Taconite

pig iron is brittle due to high carbon content

typical   Chemistry
  %C      3.5 - 4.5%
  %Mn     0.5 - 2.0%
  %Si     0.3 - 2.0%
  %S*     0.01 - 0.1%
  %P*     0.05 - 2.0%   - (*) bad

steel making steel
- basic oxygen furnace is the most commonly used 60% world ouput

phase diagrams

phase
- uniform chemical composition (usually)
- surround by boundaries and can be identified under a microscope
- used to show the different phases that can occur with alloys systems
- based on chemical composition and temperature
AISI : American Iron and Steel Institute
- C1010
  - first 2 digits alloy family; 10 : plain carbon steel
  - last 2 digits is the percent of carbon
ferrite : BCC, UTS ~ 30ksi or under 250mpa
pearlite : contains 2 phases (exact 0.8 % of C) much stronger than ferrite (UTS~100ksi)
- white ferrite
- cementile
%c go up, strength go up
%c go up, ductivity go down
the iron/carbon phase diagram is based on slow equilibrium cooling
if the cooling rate becomes too quick, then carbon doesn’t have a chance to diffuse. The lattice gets distorted into a body centered terragonal shape called Martensite (BCT)
Martensite is a hard (HRC 55 and up) and very brittle structure.
further heat treating is usually required

the role of carbon and alloy content of steels

when alloying elements are added to a base metal, one of three things can happen (or combination of the three)

solid solution

SSS: gold alloy with silver
ISS: carbon added to iron is interstitial
interstice is a “open space” in lattice

elements can seperate into their own phases

intermetallic compounds can form

hard brittle
e.g. Fe_3C - iron cardide (cementite)
tungsten carbide

organizations and societies

steel designations

there are many different designations and technical societies
e.g. ASTM
- A: ferrous metals
- B: non ferrous
- C: calibration and testing
AISI: American Iron and Steel Institute
- 4-5 digits
- first 2 alloy group
- last 2/3 %C/100
- 10xx plain carbon steel
- 41xx chromium/molybdenum
- 86xx low chrome/nickel/moly
API: American Petroleum Institute
- API uses ASTM/AISI grades and they use their own designations
  - e.g. API 5CT (casing/tubing) grade J-55 min 0.2%ys max 0.2ys min uts 55ksi 80 ksi 75ksi (380mpa) (550mpa) (520mpa) grade N-80 80ksi 110ksi 100ksi (550mpa) (760mpa) (690mpa)

cast iron

on the iron carbon phase dia CI’s have bw 2-6.5% carbon
most commercial CI’s have between 2-4% carbon and 1-3% silicon
ci’s cannot be formed by forging or rolling; they have to be shaped by molding
weldability tends to be poor
4 types (groups): white, malleable, gray, nodular (ductile ci)

stainless steel

developed for their corrosion resistance
in order for a steel to become stainless chromium is required
a minimum of 11% Cr is needed to form a protective chromium oxide layer (\(Cr_2O_3\)) 11-30%
this layer self heals. If the oxide layer is damaged or removed it will reform as long as oxygen is present
5 main groups of stainless steels (based on the metallurgy and heat treatment)

ferritic (AISI 400 series)

12-27% Cr
low carbon (usually 0.12% max)
can not strengthen by heat treating
magnetic
poor weldability
corrosion resistance bw martensitic and austenitic
applications:
- cook ware
- exhaust systems
- high temp application

martensitic (AISI 400 series)

12-17% Cr
% carbon up to 1.2%
- there are low carbon types as well.
design for higher strength and hardness
strengthened by heat treating
magnetic
some grades are weldable
applications:
- high quality blade steel e.g. 440C
- low carbon grades are used for values, chokes, flange (e.g 410)
- high strength fasteners

austenitic (AISI 200 and 300 series)

most widely used type of stainless* (about 50%)
16-25% Cr and 7-20%Ni (FCC) (300 series), ‘rarely use marganesee (200 series)’
Ni is an austenite stabilizer, so these types are FCC (very good toughness)
non-magnetic
cannot strengthened by heat treating
easiest type of stainless to weld (account for about 90% of all stainless welding)
very good low temperature toughness (due to nickel content)
good or high temp application
applications:
- chemical and food processing
- fuel lines
- valves, chokes, piping
- refrigerator cars

duplex (trade name e.g. ferralium 255))

two phased microstructure (ferrite and austenite)
20-25% Cr
4-7% Ni
2-4 Mo
better strength and corrosion resistance to chlorides than austenitic stainless.
good toughness and weldability
applications:
- heat exchanger tubing
- offshore drilling equipment
- desalination plants

precipitation hardened (sometimes named after %Cr/%Ni content) (ASTM 600 series)

are hardened and strengthened to the highest levels of all stainless steels
usually named after the Cr/Ni content e.g. 17-4 (17%Ni, 4%Cr) (martensitic microstructure)
magnetic / weldable
good toughness
applications:
- aerospace components
- petroleum equipment e.g. valve stems
- high strength fasteners

review midterm

List the three components of a charge loaded into a blast furnace to make pig iron and briefly explain what each component is for?
- iron ore: the source of element iron after chemical reduction in the blast furnace.
- lime stone: an fluxing agent that remove impurities and forms a slag over the molten metallic iron. Slag not only contains most of the impurities but also acts as an oxidation shield.
- coke (solid product of destructive distillation of coal.) Reducing agent (carbon monoxide) to remove oxygen from the ore. \(\\ O_2 + 2C (coke) -> 2CO\\ Fe_2O_3 +3CO -> 2Fe + 3 CO_2\)
What are the 2 stages in the transition of a liquid to a solid state?
- nucleation
- gain or crystal growth
What is the most common type of furnace used in steel making?
- basic oxygen furnace
What is the name of the device that measures strain on the UTM?
- strain extensometer
What does the term fully killed steel mean?
- completely remove oxygen
Name the two phases in Pearlite. What is the carbon content of Pearlite?
- white ferrite & cementile
What is the crystalline structure of Martensite?
- body center tetragonal (BCT)
What 2 elements are known for deoxidizing the melt during steel making?
- manganese, silicon, or aluminum
Describe a Substitution Solid Solution.
- formed when atoms of a solute metal substitute for atoms of a solvent metal
Carbon in steel is substitutional? True or False
- carbon in steel is substitutional
What is the crystalline form for austenite and what is the maximum solubility of Carbon?
- FCC; max 2% C
What marks are common with fatigue failures?
- beach marks are centered around a common point, fatigue crack origin
What is Allotropy?
- metal’s ability to change lattices shape from one to another based temperature
What are the A3 and A1 lines called on the iron carbon phase diagram?
- A1: lower critical temperature (LCT)
- A3: upper critical temperature (UCT)
What is the difference between Yield Point and 0.2% offset Yield Strength.
- yield point is the stress at witch the material exhibits an increase in strain without a corresponding increase in stress.
- 0.2% offset yield strength is the stress at which the material exhibits 0.002mm/mm of permanent (plastic) deformation.
A material shows with a diameter of 15.9 mm shows a strain of 0.0004 mm/mm at 105 Kilo-newton’s. What is the modulus of elasticity? \(\\ Area = 15.9 * 15.9 * 0.7954 = 198.56mm^2\\ Stress = Load / Area = 105000N / 198.56mm^2 = 528.81Mpa\\ MoE = Stress / Strain = 528.81Mpa / 0.0004 mm/mm = 1322Gpa\)
Modulus of Elasticity is a measure of what property?
- measures the stiffness and the ability to bend of material
The charpy impact machine generates how much foot-lbs of energy?
- 300 ft.lbs or 407J
What are the dimensions of a standard chary impact test sample?
- 10mm x 10mm x 55mm
- 45 V-notch, 2mm deep, 0.25mm root radius
What types of indenters are used for Brinell, Rockwell B and C scales? What are the loads?
- Brinell’s indenter: 10mm diameter tungsten carbide ball
  - loads: 500kg, 1500kg, 3000kg
- Rockwell’s B scale indenter: 1/16” diameter tungsten carbide ball
  - loads: 10kg/100kg
- Rockwell’s C scale indenter: 120 cone-shaped diamond (Brale diamond)
  - loads: 10kg/150kg
Describe fatigue. What is the endurance limit and fatigue strength?
- fatigue are failures associated with fluctuating or cyclic stress
- fatigue strength is the cyclic stress level that a material fails at; the higher stress level, the fewer number of cycles that will be required to cause the material to fail.
- endurance limit is a limiting stress below which a load may be applied an infinite number of times without causing failure
What are the 3 stages of creep?
- Primary: creep occurring at a decreasing rate (cold working)
- Secondary: exhibit minimum creep rate, constant rate
- Tertiary: exhibit creep at an accelerating rate, followed by fracture.
What is ECTT and FATT?
- Fracture Appearance Transition Temperature (FATT) is the temperature when the fracture surface is 50% ductile and 50% brittle
- Energy Criteria Transition Temperature (ECTT) is the temperature where the fracture requires some specific amount energy (20 joules or 15 ft-lbs)
What is the microstructure of hypoeutectic steels?
- 0.008 to 0.8% C
- contain pearlite and ferrite
A bar 10mm X 8mm is subjected to a force of 15,000 Newton’s. What is the stress on the bar? \(stress = load /area = 15000N / (10*8) = 187.5Mpa\)
What is the approximate carbon content of an AISI 1010 steel?
- 0.10% (last 2 digit)
What are the four groups of cast irons? Which type has flaked shape graphite? Which type has no freed-up graphite?
- white cast iron (carbides)
- malleable cast iron (freed up graphite)
- gray cast iron (flaked shape graphite) (most common)
- nodular cast iron (rounded graphite)
Which type of cast iron is used for pump housings or sewer covers?
- gray cast iron
What is the minimum carbon content of cast irons on the iron carbon phase diagram?
- minimum 2%
Which association is responsible for the prevention of corrosion?
- NACE (National Organization of Corrosion Engineers
Which association is responsible for the design of pressure vessels?
- ASME (American Society of Mechanical Engineers)
What is a common type of steel used for pressure vessels?
- fully killed astm A516 Cr70
Which group of stainless steel is used for high quality blade steels?
- martensitic AISI 400 series e.g 440C
Which group of stainless steels are non-magnetic
- austenitic
Which group of stainless steels are considered the easiest to weld?
- austenitic
How does chromium make stainless steel stainless?
- a minimum of 11% Cr is needed to form a protective chromium oxide layer (\(Cr_2O_3\)) 11-30%
- this layer self heals. If the oxide layer \(Cr_2O_3\) is self heals or removed it will reform as long as oxygen is present
What is the minimum amount of chromium needed to make stainless steel stainless?
- minimum 11% Cr
What were the 3 stages of heat treatment for the cold working lab?
- recovery, recrystalization, grain growth
Does the hardness continue to go up from cold working?
- No, there is a limit
Directional properties resulting from cold working is called?
- anisotropy
What happens to the ductility of a cold worked metal?
- ductivity decreases when the material is cold worked
What is sensitization?

Flanar flaws - disavantage of radiaction

it would pickup thin crack that is horizontal with the source

non-ferrous metals

non-iron based
there are non-ferrous alloys that do contain small amounts of iron.
the metal covered
- aluminum
- copper
- tin/lead alloys
- nickel
- cobalt
- zinc
- cemented carbides

aluminum

next to iron based alloys, Al is the second most widely used metal on the planet
comes from the ore bauxite \(Al(OH))_3\)
like iron it is very easily alloyed
very versitile/economical
density 2.7 g/cm3 (1/3 the density of iron)
FCC lattice
non-magnetic
corrosion resistance come from a \(Al_2O_3\) oxide layer
some grades can be strengthened by heat treating, others have to be cold worked
some grades are weldable
Al has about 60% the electrical conductivity of copper
high thermal conductivity
some grades have a high weight to strength ratio e.g 7075 - uts 80ksi or 540mpa
- designation AA/ANSI, 4 digit system
  - .xxxx wrought (forging)
  - .xxx.x casting

copper and copper alloys

ranks 3rd behind steel and al production
most Cu is found in sulphides but small amounts can be found in its native state
known for excellent thermal and electrical conductivity (second behind silver)
denser than iron (8.9g/cm3)
FCC structure
very good ductility; cold work easily
due to high thermal conductivity it can be difficult to weld; high preheats required
soldering (<450C) and brazing (>450C - used bronze) is used to join copper (don’t melt the material, not strong as welding)
above 80% is used in its commercially pure form, the remainder is used for alloying
the two common alloys brass (yellow) and bronze (reddish, for long time found 5000years ago)

brass

alloy of copper and zinc (Zn)
depend on alloy content there can be a wide range of properties
- easy to work
- easy to machine
- good corrosion resistance
cold work brass + ammonia = bad (season cracking can occur)

bronze

traditionally an alloy of Cu and Sn (Tin)
other metals / elements will also make bronze
- nickel
- chromium
- silicon
- phosphorus
- aluminum
tin bronze has good strength and good fatigue strength
low coefficient of friction (good for bearing surfaces)

tinc and lead

tin + lead = babbitt
babbitt is a bearing material

nickle

Ni is a very important engineering material for modern industry.
Ni uses (2011)
- stainless steel 65%
- other alloys (superalloys) - 22%
- electroplating - 8%
- other - 5%
pure Ni = uts 65 ksi or 450mpa
density 8.9g/cm3 iron 7.8g/cm3
fcc
magnetic up to 360C
can dramatically improve toughness for low temp applications

cobalt

is between Fe and Ni on the periodic table
8.8g/cm3
allotropic: HCP-FCC-HCP
magnetic
largest use is for superalloys

super alloys

developed for high temperatures up to 1100C or 2000F
many uses
- aerospace
- petrochemical
- offshore marine apps
3 groups of superalloys

nickel based

most common of the 3 groups
known for good corrosion resistance
some have excellent low temp impact strength e.g. 718 inconel

cobalt based

have the best creep resistance
some have excellent wear resistance e.g. stellite #6

iron based

high end austenitic stainless steel with better strength and corrosion resistance.

zinc

soft material with a low melting temp (420C)
HCP
good atmospheric corrosion resistance
most common use:
- sacrificial anode (galvanized steel)

cemented carbides

considered a ceramic
part of a group of materials that are hard with good wear resistance
e.g. tungsten carbide
- parts are made in molds at high temperatures and pressures
- the tc particles are held together by a metal binded (cobalt or nickel)

thermal expansion

material subjected to changing temperatures can undergo changes in dimensions.
the amount of dimensional change is dependent on
- type of material
- changing temperatures.
formula: \(\Delta L=\alpha L \Delta T\)
- \(\alpha\) = coefficient of thermal expansion
- \(\Delta L\) = change in length
- L = original length
- \(\Delta T\) = temp change
\(\alpha\) unit: (mm/mm C) or (in/in F)
steel: \(11.7*10^{-6}\)
aluminum: \(23 * 10^{-6}\)
Cu: \(17.2*10^{-6}\)
if expansion is restricted or not permitted then stresses will build up.
- formula: \(\sigma = \alpha E \Delta T\)
  - \(\sigma\) : stress in mpa or psi
  - \(\alpha\): coefficient of T.E.
  - E: modulus of elasticity
  - \(\Delta T\): change in temp
sample question
1. what is the change in length in a steel bridge 300m long temp change -30 to 30 C
  - \[\Delta L = \alpha L \Delta T = 11.7*10^{-6} (mm/mm) * 300 m * 60 = 0.211m\]
2. if the bridge is not allowed to expand what stress will be build up
  - \[\sigma = \alpha E \Delta T = 11.7*10^{-6} * 207Gpa * 60C = 0.145GPa (21000psi)\]
3. imperial units
  - \[E_{steel} = 30,000,000psi\]
  - \[\alpha = 6.6*10^{-6}\]
  - A bar 1/2”x1/2”x24” long changes in temp from 60F to 120F
    - what is the \(\Delta L\)
      - \[\Delta L = \alpha L \Delta T = 6.6*10^{-6}*24"*60F = 0.01"\]
    - not allowed to expand
      - \[\sigma = \alpha E \Delta T = 6.6*10^{-6} * 30,000,000psi * 60 = 11.9ksi\]
    - we can calculate the force acting on the bar
      - \[\sigma = F/ A => F = \sigma * A = 11.9ksi * 1/2"*1/2" = 2970lb\]
4. what change of length does a 30 foot boom on a crane go through from 0F to 80F? \(\alpha_{steel}=6.6*10^{-6} in/in\), \(E_{steel}=30,000,000psi\)
  - \[\Delta L = \alpha L \Delta T = 6.6*10^{-6} in/in * 30 * 12" * (80F) = 0.19"\]
5. a 1.5m magnesium rod is snuggly placed between 2 fixtures at 20C. what stress will be created if the rod is not allowed to expand and the temperature goes up to 45C? \(\alpha = 25.9 * 10^{-6} mm/mm\), \(E_{Mg} = 45,000MPa\)
  - \[\sigma = \alpha E \Delta T = 25.9*10^{-6} mm/mm * 45,000MPa* (45C - 20C) = 29.1MPa\]

shear stress

shear stresses act parallel to the stress surface
\(\sigma_s\): occurs in bolts, shear pins, lap welds
simplest type of \(\sigma_s\) happens in bolts
- \(\sigma_s\) = force causing shear / area resisting shear = F/A
- single shear: 2-lap welds
- double shear: 3-lap welds
sample questions
- find maximum stress for 1/2” thick plate with two semicircular notches, F=25000lbf, b= 0.5”, h=6”, r=1”
  - \[b/r = 0.5 / 1 = 0.5\]
  - \[r/h = 1 / 6 = 0.17\]
  - \[k=1.85\]
  - \[\sigma_{max} = {k * F \over A} = {1.85 * 25000lbf \over {6*1/2}} = 15416.7 psi\]
- calculate the following for 10mm thick plate, hole dia d=17mm, width of the plate w=130mm, F=20kN
  - max stress @ the hole
    - \[d/w = 17/130 = 0.13\]
    - \[k = 2.45\]
    - \[\sigma_{max} = {k * F \over A} = {2.45 * 20000N \over {(130mm-17mm)*10mm}} = 43.4MPa\]
  - max stress on the full width of the plate
    - \[\sigma = {F \over A} = {20000N \over {130mm * 10mm}} = 15.3MPa\]
- 10mm dia bolt fastens 2 plates together. if the allowable shear stress \(\sigma = 150mpa\) what load can be applied
  - \[F = \sigma_s*A = 150mpa * \pi * 10^2 / 4 = 11.8kN = 2650lbf\]
- a clevis pin is subjected to 50,000lbf the dia of the pin is 2”. what is the \sigma_s
  - \[\sigma_s = F / A = 50,000lbf / (2 * (\pi*2^2)/4) = 7.96ksi\]
- two aluminum sheets are joined by 6 spot welds. Each spot weld is 6.5mm in diameter. Determine the shear stress
  - \[\sigma_s = F / {i*A} = {4500N*4} / {6*\pi*6.5^2} = 22.6Mpa\]
- calculate the shear stress on the 7/8 diameter bolt, F = 10,500lbf
  - \[\sigma_s = {F \over A} = {10,500lbf \over {\pi*{(0.5 * 0.875)}^2}} = 17.5ksi\]
- a \(1.25"\) diameter bolt can take a maximum shear stress of 50,000psi. what is the maximum load that the bolt can take?
  - \[F = \sigma_s * A = 50,000psi * \pi * (0.5 * 1.25)^2 = 61,328psi = 61.4 kips (kilo pound)\]

torsion

caused by twisting or rotating
imperial
- \[HP = {TN \over 63,000}\]
  - T: torque in lb
  - N: RPM
  - HP: horse power
metric
- \[KW = {TN \over 9540}\]
  - T: N.m
  - 1 HP = 746 watts
\[\sigma_s = Tr/J\]
- \[J = {\pi * {(D_o^4 - D_i^4)}\over 32 }\]
  - \(D_o\) outside diameter
  - \(D_i\) inside diameter
  - r: distance to center of shaft
angle of twist \(\theta\) of shaft
- \[\theta = TL/GJ\]
  - \(\theta\) radians
  - \[1 radian = 180/\pi = 57.3\]
  - \[1 degree = 0.0175\]
  - L = length
  - G = modulus of shear
  - G_steel = 83 Gpa (imperial)
ex: sample torque questions
- determine the max \(\sigma_s\) in a shaft transmitting 300kw @ 300 rpm
  - solid 100mm dia (don’t use inside dia in solving)
    - KW = TN/9540 => T = 300kw*9540/300rpm = 9540N.m
    - \[\sigma_s = Tr / J = (9540N.m * 0.05m) / \pi * 0.1m^4 / 32 = 48.6mpa\]
  - hollow shaft \(D_o=100mm\), \(D_i = 50mm\)
    - \[\sigma_s = Tr / J = (9540N.m * 0.05m) / \pi * (0.1m^4 - 0.05m^4) / 32 = 51.8mpa\]
- design a solid shaft to transmit 50kw @ 1130rpm; the allowable shear stress = 70mPa
  - find T
    - \[T = KW * 9540 / N = 50 * 9540 / 1130rpm = 422.12 N.m\]
  - find diameter
    - \[\sigma_s = Tr / J\]
    - \[\sigma_s = {Tr * 32 \over {\pi * D^4} } = {T * 0.5 * D * 32 \over {\pi*D^4}} = {T * 16 \over {\pi*D^3}}\]
    - \[D^3 = T*16/\pi*\sigma_s = 422N.m * 16 / \pi * 70000000N/m^2 = 0.0000307\]
    - \[D = 31mm\]
- determine the maximum torsional stress on a shaft that is transmitting 750KW at 250 RPM if
  - Find T
    - \[T = {KW*9540 \over N} = {750KW * 9540 \over 250RPM} = 28620N.m\]
  - the shaft is solid and 125mm in dia
    - \[\sigma_s = {Tr \over J} = {Tr*32 \over {\pi * D^4}} = {T*0.5*32 \over {\pi * D^3}} = {28,620N.m * 16 \over {\pi * 0.125^3}} = 74.5MPa\]
  - the shaft is hollow. \(D_o=125mm\), \(D_i=75mm\)
    - \[\sigma_s = {Tr \over J} = {Tr*32 \over {\pi * (D_o^4 - D_i^4)}} = {28,620N.m * 0.5 * 0.125 * 32\over {\pi * (0.125^4 - 0.075^4)}} = 85.9MPa\]

corrosion

generic electrochemical cell

anode - only one reaction can occur at the anode; anode loses electrons (oxidation)
cathode - 4 possible reactions; accepts electrons (reduction)
electrolyte
pathway for electron travel

Zinc/Platinum cell in non-aerated hydrochloric acid

anodic reaction: (Zinc)
- losing electron
- \[Zn \to Zn^{2^+} + 2e^-\]
cathodic reaction:
- picking up electron
- \[2H^{+} + 2e \to H_2 (gas)\]
other possible cathodic reaction
- aerated acidic environment
  - \[O_2 + 4H^+ + 4e^- \to 2H_2O\]
- basic (caustic) or neutral environment
  - \[O_2 + 2H_2O + 4e^- \to 4OH^-\]
- metal plating
  - \(me\)(metal)
  - \(Xe^-\)(number of electrons)
  - \(me^{+x} + xe^- \to me\) (plated on cathode)
corrosion definition: deterioation of a material due to a reaction with its environment; non metals can corrode as well
corrosion accounts for billions of dollars in lost material
cost of corrosion can fall into 2 categories
1. direct
  - replacement costs (value, labor, paint, etc.)
2. indirect
  - down time
  - loss of production
  - loss of a customer
2 main types of corrosion
1. dry
  - elevated temps
2. wet
  - a liquid phase has to be present
8 types of wet corrosion
- group 1: general (uniform) form 1
- group 2: localized:
  - galvanic corrosion - 2
    - sometimes called 2-metal corrosion
    - 3 requirements
      - electrochemically different metals
      - electrically connect
      - must be exposed to an electrolyte
    - area effect of galvanic corrosion
      - large anode + small cathode = low corrosion rate @ anode
      - small anode + large cathode = high corrosion rate @ anode
    - prevention
      - avoid dissimilar metals if possible
      - if dissimilar metals are used, insulate them from each other
      - use a 3rd metal to act as a sacrificial anode
      - inhibitors
  - crevice - 3
    - sometimes called gasket corrosion
    - occurs in gaps or cracks where an electrolyte can get into
    - prevention
      - eliminate any crevices or cracks (welding or coating)
      - non-absorbant gasket or insulating material
  - pitting - 4
    - very similar to crevice corrosion but can occur on open surfaces -2 steps
      - initiation
      - propogation
    - occurs on metals like stainless steel where the oxide layer gets damaged
    - once initiation begins a crevice is tarted and corrosion takes off
    - prevention
      - smooth surfaces have better have better pitting resistance than rough surfaces
      - inhibitors
      - coating
  - intergranular - 5
    - this form of corrosion occurs at the grain boundaries.
    - gain boundaries become anodic due to a different chemical composition.
    - when this occurs the metal will fall apart
    - cold worked Al + chlorides will undergo this type of corrosion and its called exfoliation
  - dealloying (selective leaching) - 6
    - occurs in alloys where one element becomes anodic and is leached out.
    - eg. Brass => cooper (cathode) & Zn (anode) (reddish - copper, yellowish - brass)
- group 3: cracking
  - stress corrosion cracking (SCC) - 7
    - 3 requirements
      - Susceptible material
      - Corrosive environment
      - Tensile stress (can be applied or residual)
    - Many materials are prone to SCC - Al, Ti, Cu, Austenitic Stainless
      - E.g
      - Brass + ammonia = not good
      - Austenitic stainless steel + chlorides = not good
    - One prevention is to minimize the tensile stress
  - hydrogen induced cracking - 8
    - Caused by the interaction of atomic hydrogen and a metal
    - Atomic is small enough migrate through steel if it get strapped in a void in the steel H_2 gas forms damaged the steel as the pressure builds.
    - With pressure vessel plate or any metals used for valves (petroleum) fully killed steel is required.
- erosion is inluded
  - cavitation
  - flashing
note: corrosion is a chemical reaction
factors that affect corrosion
- material properties
  - chemical composition
  - metallurgical factors
    - cold working increases, corrosion increases
    - residual stress (welding)
    - inclusions
    - multiple phases

final review questions

What are methods commonly used to heat treat steel and what result do they produce?
- full anneal (above UCT)
  - slow-furnace cooled, max time for carbon diffusion
  - produce the softest, most ductile steel
- normalizing (above UCT)
  - still air cooled, minimum time for carbon diffusion
  - produce a smaller ferrite and fine pearlite structure
- hardening (quenching) (above UCT)
  - water/brine quenched, no time for carbon diffusion
  - produce max hard steel by forming martensite (BCT)
- tempering (below UCT)
  - no crystal structure change takes place
  - restore some ductility and toughness to the steel
- stress-relief anneal
  - heat, hold and cool slow
  - remove locked-in localized stresses
What metal can exfoliate?
- Aluminum
What are the 2 most common radiographic sources used in industrial radiography?
- Cobalt 60, Iridium 192
In radiography the denser the material being examined the lighter the image will be.
What is the function of a penetrameter in radiography?
- it uses to measure the radiographic quality based on definition (shapeness of the image) and contrast
What are the advantages and limitations the different methods NDE we looked at?

	advantage	disadvantage
RT	- can be portable (isotope camera)	- can be extremely dangerous
	- permanent record (film)	- expensive startup cost
	- good visual detail from radiographs	- can’t tell how deep a defect is
UT	- superior penetrating (up to 20ft)	- part geometry (difficult to inspect rough, irregular parts)
	- high sensitivity	- need couplants to provide an effectivee transfer of energy
	- greater accuracy (size, shape, orientation)
	- safe
	- portable
MPI	- portable (yoke)	- if the part is not ferromagnetic, MPI does not work
	- relatively cheap	- parts has to be cleaned, free of oil, grease, etc.
	- quick result	- parts need to be demagnetized
	- safer	- best suited for surface flaw detection
	- easy
LPI	- portable	- cracks have to be opened to surface
	- relatively cheap	- slow (dwell time, cleaning)
	- easy	- messy
	- good sensitivity

What is UT used for?
- used for detect size and location of defects (cracks, etc.)
What does the x and y axis on a typical UT machine represent?
- x: time/distance, y: amplitude
In UT what is a couplent used for?
- couplants used to provide an effective transfer of energy bw the transducers and test pieces
What is copper alloyed with to make brass?
- zinc + cooper = brass
What is the crystalline structure of aluminum? What series is used for pop cans?
- FCC lattice
- Al series 3004 for pop can
Why were superalloys developed?
- for the need of good materials can retain strength under long exposure to high heat environment, and good low temp ductivity
- for creep resistance
Duplex stainless steels are a combination of what types of stainless steels?
- autenistic and ferritic stainless steels
Which stainless steel is used for high grade blades steel?
- martensitic AISI 400 series e.g 440C
What is the crystal structure of nickel?
- FCC
What is the main use of nickel?
- used for create stainless steels
What are the components of a corrosion cell?
1. anode - only one reaction can occur at the anode; anode loses electrons (oxidation)
2. cathode - 4 possible reactions; accepts electrons (reduction)
3. electrolyte
4. pathway for electron travel
What is the anodic reaction when steel is exposed to aerated dilute H2SO4? What are the cathodic reactions?
- anodic reaction: \(Fe \to Fe^{2^+} + 2e^-\)
- cathodic reaction: \(2H^{+} + 2e \to H_2 (gas)\) H2 goes off
What is meant by corrosion allowance?
- an added additional thickness compensate for general corrosion
What is galvanic corrosion? What conditions are required for galvanic corrosion to occur?
- corrosion damage induced when two dissimilar metals are coupled in a corrosive electrolyte
- 3 requirements
  - electrochemically different metals
  - electrically connect
  - must be exposed to an electrolyte
What happens when a zinc block is fastened to a steel structure that is exposed to aerated fresh water?
- galvanic corrosion happen
What is meant by the term crevice corrosion? What conditions must be present for this type of attack to occur?
- sarifical anode
What is de-alloying?
- occurs in alloys where one element becomes anodic and is leached out.
- brass: zinc out, cooper left over
What is erosion corrosion?
- induced by the velocity of a fluid and metal surface
What is cavitation?
- caused by fluid bubble collapsing and pitting on metal surface
What is intergranular corrosion?
- occur at grain boundaries which become anodic, and then removed
What is stress corrosion cracking?
- metal failure due to combined effects of corrosion (metal + corrosive env) and tensile stress (external or residual)
What is used in domestic water heaters to cathodically protect them?
- magniseum strip