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CE materials > CE materials exam > Flashcards

CE materials exam Flashcards

1
Q

Define lumber grading, species groups, stress
grades

A

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

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2
Q

 Describe the two types of machine grading

A

Visual and machine grading

  1. MSR - Machine stress rated modulus of elasticy is evaluated by bending the board
  2. MEL - Machanically evaluated lumber density is evaluated and is correlated to stress grade
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3
Q

 Explain why timber is dried

A

Air drying is used to evaporate water before kiln drying

Kiln drying uses higher temperatures and circulating air to dry to a low MC

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4
Q

Explain the problems with drying timber too fast
or too slow

A

Too slow -uneconomical

Too fast - results in wood splitting and checks

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5
Q

Define Target MC

A

Softwood for framing - 15 to 19%
Softwood for furniture 10 to 12%
hardwood furnature - 7 to 9%

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6
Q

Decay fungi

A

stain the wood

Control - drying to less than 20%
Soaking the wood (no air)

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7
Q

Bark beetles

A

remove bark immediatly

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8
Q

Termittes

A

Insecticide is surrounding soil (stop contact with colony)

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9
Q

Carpenter bees

A

Inject insecticide into tunnel,
Thick paint or pressure treated lumber

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10
Q

Marine borers

A

Coat wood in coal tar creosote

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11
Q

Types of fungi stain

A

Sap stain and blue stain

do not affect strength

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12
Q

Define alloy, malleable, ductile

A

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

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13
Q

What are the two types of steel mills?

A

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

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14
Q

Describe the continuous casting process

A

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

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15
Q

List and describe three semi-finished products

A

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

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16
Q

How are finished steel products produced?

A

Rolling mills -

Strucural mills produce structural shapes

Bar mills produce round, square and hexagonal bars

Other produce wire, tubes, and plates

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17
Q

Describe the effect of carbon on the strength and
ductility of steel.

A

More carbon gives high strength and low ductility
Less carbon gives lower strength and more ductility

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18
Q

What are eight advantages of using steel?

A
  1. high strength, stiffness, and ductility
  2. Uniform matieral properties
  3. Unaffected by freeze thaw cycle
  4. Produced in wide varitey of shapes and sizes
  5. high strength to weight ratio
  6. simple connection of bolts pins and welds
  7. properties dont chance with time
  8. easy to recycle
19
Q

What are six disadvantages of using steel?

A
  1. corrosion by water and other chemicals
  2. reduced stiffness and strength under high temperatures
  3. economic use is limited to standard shapes
  4. brittle fractures at low tempertures due to fatigue loading
  5. creating steel from ore is expensive and engery intensive
  6. Price is dependent on world demand
20
Q

Define allotropic

A

A substance that exists in more than one crystalline form

21
Q

Define Ferrite

A

a body centered cubic

carbon cannot dissolve in this structure

22
Q

Define cementite

A

a mixture of iron and 6.67% carbon

23
Q

Define Austenite

A

face centered cubic that carbon can dissolve into this structure

24
Q

Define Pearlite

A

a microstructure formed in steel with .76% carbon that is slowly cooled

25
Q

Define Martensite

A

is formed in steel if cooled fast enough and is hard and brittle

26
Q

Define Tempered Martensite

A

martensite reheated to 480 to 1200 and slowly cooled
Steel is less strong but is much more ductile

27
Q

Define Tempering

A

heating steel to below the transition temp and then slowly cooled

28
Q

Define Phase

A

2800 - ferrite
2540 - austenite
1675 - ferrtie
1420- magnetic
(each change is a transition temperature)

29
Q

Define Transition Temperature

A

The temperature of iron as it change phases from ferrite to austenite and reversed

30
Q

Which iron phase can carbon dissolve into?
Why is this important?

A

Austenite

it is the phase when carbon is added to the steel (at specified temperature)

31
Q

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

A

Strength Cementite hardest
1. Martensite
2. Tempered Martensite
3. Pearlite
4. Ferrite

Ductility
1. Ferrite
2.Pearlite
3. Tempered Martensite
4. Martensite
Cementite

32
Q

How is Martensite made and how does this affect
its properties?

A

By quenching - rapid cooling

33
Q

How does elevated temperature affect yielding,
ultimate strength, and elastic modulus of steel?

A

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

34
Q

How does a slight increase or decrease in
temperature affect yielding and ultimate strength
of steel?

A

Increase temperature decreases ultimate strength and tensile strength

Decrease temp increases yeilding and ultimate strength

35
Q

Define toughness, notch-toughness

A

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

36
Q

 Name and describe the test used to evaluate
notch toughness.

A

Charpy - V notch on a beam and hit with a swinging pendulm

37
Q

Describe steel yielding from a metallurgical
perspective.

A

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

38
Q

Describe the steel yield plateau from a
metallurgical perspective.

A

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

39
Q

What kind of steel shapes are produced using
A36 or A992 steel? What is the yield strength of
each material?

A

A36 - yield strength 36 ksi, S, HP, C, L

A992 - yield strength 50 ksi, W

40
Q

What is meant by weathering steel?

A

additional elements added to give resistance to corrosion

41
Q

What is mean by the term residual stress?
 Describe several methods to cause residual
stresses in steel

A

locked in stress that existed prior to any external load

  1. uneven cooling after rolling or welding
  2. cold bending
  3. flame cutting
42
Q

 Describe the process by which residual stresses
are developed in hot-rolled wide-flange shapes.

A

Outer edges cool faster -
compress

thicker inner areas cool last - tension

43
Q

What is meant by weathering steel?

A

Low carbon steel that have addition elements that give corrosion resistance

CE materials (6 decks)

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