Structural glass Flashcards
How is glass usually made?
By supercooling a liquid
Compare the theoretical and actual structural properties of glass.
Theoretical flaws could be very strong.
-Theoretical bending strength ~14 000 MPa
-Actual bending strength 20-200 MPa
How is the strength of glass determined?
By the size of the largest flaw
What is the process of tempering glass?
Heating a sheet of glass, then quenching surfaces rapidly
Describe how tempering glass works.
-Quenching puts the surface into compression and the centre in tension, strengthening the surface
-To break tempered glass, a crack must form between the surface region into the core region
-Fracture leaves cubic fragments due to stored strain energy
How is laminated glass made?
A polymer film is sandwiched between two glass sheets
Describe how laminated glass works.
-Polyvinyl-butyral is the most common film used which is rolled out and heated to exclude air and bond polymer to glass
-Protects surfaces and holds in the broken glass fragments is fracture occurs, cracks in a spider web pattern
-Used a lot in car windscreens and other places that are likely to break
How is bullet proof glass made?
Multi-layered tempered glass/polycarbonate laminate, or multiple layers of laminated glass ~20-75 mm thick
Describe how bullet proof glass works.
-Optical properties of materials must be matched
-Polymer layers are much more elastic than glass
How is multiple glazed glass made?
2 or 3 sheets of glass are sealed into a unit, with a gas layer in between
Describe how multiple glazing glass works?
-Sometimes a vacuum can be used if the temperature differential is not going to be too high
-Desiccants are sometimes used in the gas space
-Each interface gives resistance to heat transfer
-Need similar thickness of glass inside and outside to prevent shearing
-Temperature mismatch between inside and outside can cause cracking
-Dimensional changes in units can break seals around unit edges and let moisture in
