Steel Flashcards
What is the other component in steel other than iron? Where does it come from?
Carbon
It comes from coal
What is the name given to the material when there is excessive Carbon (greater than 1.7%)?
Cast iron
Why would you not want to use cast iron in construction?
It is very brittle and weak in tension
What are the 3 ways of strengthening steel?
- Alloying
- Strain hardening
- Heat treatment (quenching/annealing)
What is the main downside of strengthening steel in connections besides reduced ductility?
Reduced weldability
What is the alternative connection besides welding? What is the problem with using it?
Bolting
It consumed more resources (expensive and time consuming) - more work and labor intensive; overall, increased project costs
What is toughness?
The ability of a material to absorb energy before failure
Name the most practical method of measuring toughness in structural steels.
Taking the area under the stress-strain curve
Why is taking the area under the stress-strain curve to calculate toughness not good for non-structural steels?
The area method only works for ductile materials
While structural steels are ductile, non-structural ones are more brittle
How does strain hardening affect toughness?
Decreased toughness
Decreased area under the stress-strain curve since you no longer count all of the area to the left of the unloading curve
Order the following materials from most to least variable: concrete, timber, steel. For each, explain the reasons for their variability or lack thereof.
Most variable: timber - random macroscopic defects since it is not manufactured but rather naturally grown
Medium variability: concrete - made in the field with usually unskilled labor BUT specific set of ingredients
Least variable: steel - made in factory with consistent controlled conditions
How do you account for the variability of materials in design?
Concrete and steel: phi factor
Concrete - 0.6 or 0.65
Steel - 0.85 or 0.9
Timber: other design adjustment factors
5% exclusion limit
Other adjustments (you can reference the slides but “probably not important”)
Comment on the difference in the phi factor between steel and concrete.
Steel is less variable so you can assume that you can use more of its strength, giving you a greater phi factor
If you are loading steel in tension, what is the permanent strain in the linear elastic region?
0
How do you find the Elastic modulus from a stress-strain graph?
It is the slope of stress over strain
What is a unique characteristic of steel in the linear elastic region compared to other materials?
For steel, the proportional limit is the same as the yielding point
Why is ductility preferred in construction materials like steel?
You can get a warning before failure
What is the mechanical property that is used to indicate failure of steel in a structure?
Yielding
Why do we take yielding as failure?
Once a member reaches yielding, it begins to deform and collapse
These deformations are unideal for the structure but they also give a warning before ultimate collapse
What is the physical difference between the uniform and localized plastic deformation regions of the stress-strain curve?
Uniform: same reduction of cross sectional area throughout the specimen (ie. the whole thing gets stretched out)
Localized: necking occurs (in one specific place along the specimen)
What is the difference in failure planes between a ductile steel coupon and a brittle cast iron coupon?
Brittle: perpendicular failure plane
Ductile: 45 degrees and sloping (cup and cone)
What is the difference in the corrosion reaction in submerged vs exposed steel?
Submerged: you don’t have much oxygen so you will stop at the first stage of rust
Exposed will progress beyond just the first stage
What reactant is limited in the submerged condition of corrosion?
Oxygen
Which condition of corrosion (submerged vs exposed) will have greater expansion?
Exposed since the reaction progresses further
