CE materials exam Flashcards
Define lumber grading, species groups, stress
grades
Lumber grading - Sorting lumber into species groups by their assumed mechanical properties
Species group - grouped by similar mechanical properties
Stress grades - Groups of lumber with similar mechanical properties that 95% have better properties
Describe the two types of machine grading
Visual and machine grading
- MSR - Machine stress rated modulus of elasticy is evaluated by bending the board
- MEL - Machanically evaluated lumber density is evaluated and is correlated to stress grade
Explain why timber is dried
Air drying is used to evaporate water before kiln drying
Kiln drying uses higher temperatures and circulating air to dry to a low MC
Explain the problems with drying timber too fast
or too slow
Too slow -uneconomical
Too fast - results in wood splitting and checks
Define Target MC
Softwood for framing - 15 to 19%
Softwood for furniture 10 to 12%
hardwood furnature - 7 to 9%
Decay fungi
stain the wood
Control - drying to less than 20%
Soaking the wood (no air)
Bark beetles
remove bark immediatly
Termittes
Insecticide is surrounding soil (stop contact with colony)
Carpenter bees
Inject insecticide into tunnel,
Thick paint or pressure treated lumber
Marine borers
Coat wood in coal tar creosote
Types of fungi stain
Sap stain and blue stain
do not affect strength
Define alloy, malleable, ductile
alloy - a metal made of two or more elements (Iron and carbon)
Malleable - the ability to be hammered or pressed permanently out of shape without breaking
Ductility - the ability to be plastically deformed under tensile stress without breaking
What are the two types of steel mills?
Integrated mill -
1. Blast furnace- Iron ore > pig iron
2. BOF (basic oxygen furnace)- Pig iron > molten stell
3. Ladle- Molten steel > steel with specified chemsity
4. Continuous casting- gives Bloom, Billet, slab, beam blank
5. Rolling mills- Finish structural steel, rails, bars, plate, rod
Mini Mill-
1. Electric arc furnace- Steel scrap > molten steel
2-4 the same as integrated
Describe the continuous casting process
Molten steel is poured into a trough called a tundish,
The steel falls through a hole into a short water cooled mold and then rollers
A saw cuts the steel
List and describe three semi-finished products
Bloom - square 6x 6 to 12 x 12 cross section
Billet - square 1.5x1.5 to 6x6 cross sectopm
Slab- a rectangular cross section and a rea greater than 16 in^2
How are finished steel products produced?
Rolling mills -
Strucural mills produce structural shapes
Bar mills produce round, square and hexagonal bars
Other produce wire, tubes, and plates
Describe the effect of carbon on the strength and
ductility of steel.
More carbon gives high strength and low ductility
Less carbon gives lower strength and more ductility
What are eight advantages of using steel?
- high strength, stiffness, and ductility
- Uniform matieral properties
- Unaffected by freeze thaw cycle
- Produced in wide varitey of shapes and sizes
- high strength to weight ratio
- simple connection of bolts pins and welds
- properties dont chance with time
- easy to recycle
What are six disadvantages of using steel?
- corrosion by water and other chemicals
- reduced stiffness and strength under high temperatures
- economic use is limited to standard shapes
- brittle fractures at low tempertures due to fatigue loading
- creating steel from ore is expensive and engery intensive
- Price is dependent on world demand
Define allotropic
A substance that exists in more than one crystalline form
Define Ferrite
a body centered cubic
carbon cannot dissolve in this structure
Define cementite
a mixture of iron and 6.67% carbon
Define Austenite
face centered cubic that carbon can dissolve into this structure
Define Pearlite
a microstructure formed in steel with .76% carbon that is slowly cooled
Define Martensite
is formed in steel if cooled fast enough and is hard and brittle
Define Tempered Martensite
martensite reheated to 480 to 1200 and slowly cooled
Steel is less strong but is much more ductile
Define Tempering
heating steel to below the transition temp and then slowly cooled
Define Phase
2800 - ferrite
2540 - austenite
1675 - ferrtie
1420- magnetic
(each change is a transition temperature)
Define Transition Temperature
The temperature of iron as it change phases from ferrite to austenite and reversed
Which iron phase can carbon dissolve into?
Why is this important?
Austenite
it is the phase when carbon is added to the steel (at specified temperature)
What are the properties of each of the following?
Rank them in order of increasing strength, then in
order of ductility: ferrite, cementite, pearlite,
Martensite, tempered Martensite
Strength Cementite hardest
1. Martensite
2. Tempered Martensite
3. Pearlite
4. Ferrite
Ductility
1. Ferrite
2.Pearlite
3. Tempered Martensite
4. Martensite
Cementite
How is Martensite made and how does this affect
its properties?
By quenching - rapid cooling
How does elevated temperature affect yielding,
ultimate strength, and elastic modulus of steel?
yielding - less than 500 minimal decrease
500-800 linear decrease
800 - rapid decrease
ultimate strength - same as yeilding
Elastic modulus -
0 - 800 linear decrease
800 - rapid decrease
How does a slight increase or decrease in
temperature affect yielding and ultimate strength
of steel?
Increase temperature decreases ultimate strength and tensile strength
Decrease temp increases yeilding and ultimate strength
Define toughness, notch-toughness
Toughness - Ability of a material to absorb energy and deform without fracture
Notch Toughness - Ability of a material to absorb energy in the presnece of a flaw
Name and describe the test used to evaluate
notch toughness.
Charpy - V notch on a beam and hit with a swinging pendulm
Describe steel yielding from a metallurgical
perspective.
steel is randomly oriented crystals
when loaded beyond elastic stress slip planes occur 45 degrees from tensile direction
The bonds break and rearrange and lock in their new positions
Describe the steel yield plateau from a
metallurgical perspective.
Strains are measure on a gage length
when a plane slides it takes additional stress to slide again
it slips than loaded more than slips again etc.
each gage length will be a high load than the last
the yield plateau is a product of this method
What kind of steel shapes are produced using
A36 or A992 steel? What is the yield strength of
each material?
A36 - yield strength 36 ksi, S, HP, C, L
A992 - yield strength 50 ksi, W
What is meant by weathering steel?
additional elements added to give resistance to corrosion
What is mean by the term residual stress?
Describe several methods to cause residual
stresses in steel
locked in stress that existed prior to any external load
- uneven cooling after rolling or welding
- cold bending
- flame cutting
Describe the process by which residual stresses
are developed in hot-rolled wide-flange shapes.
Outer edges cool faster -
compress
thicker inner areas cool last - tension
What is meant by weathering steel?
Low carbon steel that have addition elements that give corrosion resistance
