Materials Lecture 8 - Glass

History of Glass

• ± 3000 BC: First man-made glass as glaze.

• ± 1500 BC: First all-glass vessels produced.

• ± 30 BC: Introduction of the first blow-pipe for glass blowing techniques.

• ± 50 AD: Development of the first window glass.

• ± 1300 AD: Venetians dominate the glass industry, marking a significant period in glass production.

• 1674: Lead or Flint glass is manufactured in England.

• 1688: Louis Lucas invents plate glass in France.

• 1902: Continuous sheets of glass are produced in Belgium.

• 1912-15: Development of "Pyrex" glass by Taylor in the USA.

• 1959: Pilkington (UK) invents the "float glass" process known as the “Pilkington Float Process.”

Properties of Glass

• Density: Approximately $2500 ext{ kg/m}^3$

• Modulus of Elasticity: Ranges from $70,000 ext{ MPa}$ to $74,000 ext{ MPa}$

• Compressive Strength: Up to $1000 ext{ MPa}$

• Noted for its brittleness and poor tensile strength.

Mechanical Behavior

• Glass is characterized as a brittle material that behaves purely elastically.

• A stress/strain curve comparison shows major distinctions between steel and annealed glass (reference: Chaunac and Serruys).

Chemical Makeup of Glass

• Soda-lime glass, which constitutes about 90% of manufactured glass, consists of:

  • Silica: 60-75%

  • Soda ash/Sodium Carbonate: 12-18%

  • Lime: 5-12%

  • Dolomite: included in certain compositions.

• Classified as an amorphous solid due to its non-crystalline molecular structure.

Molecular Structure of Glassy Solids

• Molecular Layout:

  • Crystalline solids exhibit organized lattice patterns.

  • Glassy solids feature disorganized molecular distribution.

Definition of Amorphous Solids

• An amorphous solid is defined as any non-crystalline solid in which atoms and molecules lack organization in a definite lattice pattern. Examples include glass, plastic, and gel.

Properties of Glass

• Glass has several properties:

  • Chemical Inertness: Fairly inert and resistant to most chemicals.

  • Chemical Susceptibility: Vulnerable to alkali attacks; caution needed when dealing with cleaning substances or runoff from concrete structures.

Manufacturing Glass

Pilkington Float Process (PFP)

• Glass flows from a furnace onto a bath of molten tin at approximately $1050^ ext{o}C$.

• The glass is gradually cooled to $600^ ext{o}C$ where it becomes viscous enough to be moved by rollers.

• The speed of rollers creates a variety of glass thicknesses.

• Glass surfaces are differentiated as a “tin side” and an “air side.”

Glass Manufacturing Steps

• Continuous ribbon of glass is produced.

• Cooling lehr and coating chamber are utilized.

• Key components include:

  • Cross cutters for sizing
    affects

  • Large plate lift-off devices and small plate lift-off devices.

Types of Glass

1. Ordinary Annealed Glass

   • Transitioned through rollers into an annealing bay and cooled gradually to avoid residual stresses.

   • Breaks into large, sharp shards upon breaking.

2. Fully Tempered/Toughened Glass

   • Conventional glass heated to $600-800^ ext{o}C$ and cooled rapidly.

   • Results in glass that develops compressive strength and breaks into small, rounded pieces.

3. Heat Strengthened/Partially Tempered Glass

   • Similar heating process, but cooled more slowly than fully tempered glass, leading to increased strength while still being vulnerable to sudden fracture. Breakage is similar to annealed glass.

   • Maximum thickness before becoming fully toughened is $12 ext{ mm}$.

4. Laminated Glass

   • Comprises two or more layers of glass bonded together with interlay materials such as:

     • Polyvinyl Butyral (PVB)

     • Sentryglas Plus (SGP)

     • Ethylene Vinyl Acetate (EVA)

5. Other Varieties

   • Heat-absorbing, tinted, patterned, wired, self-cleaning glass, chromatic glass, insulated glass, glass wool insulation, and glass used in fiber optic cables.

Glass Engineering and Design Considerations

Advantages

• High Compression Strength: A beneficial property for structural applications.

• Transparency: Provides aesthetic and functional advantages.

• Alterable Transparency: Options for modifying transparency in design.

Limitations

• Brittle Nature: Glass is inherently brittle, posing risks in structural applications.

• Stochastic Failure: Predictive modeling of failure relies on statistical methods, adding risk.

• Poor Tensile Strength: This necessitates careful engineering design.

• Importance of managing fit and stress concentrations in design.

Safety Considerations

• Emphasizes redundancy in design to ensure safety.

• Safety Factors: Recommended as $2$ for non-critical and $3$ for critical elements.

• Adherence to building codes like AS 1288: 2006 and AS HB 125: 2007 is crucial.

• Always adopt a fail-safe approach in structural design.

• Considerations regarding thermal efficiency, acoustic performance, and user pathways to avoid crossing glass.

Physical Considerations

• Be aware that cracks propagate faster with increasing temperature.

• Thermal gradients induce risk of cracking and delamination during high temperatures.

Types of Glazing Considerations

Single vs. Double Glazing

• 
  

• Comparison of glazing types includes performance factors such as insulation values expressed in U-Value (W/m²K):
  

  Type	Makeup	U-Value (W/m²K)
  Clear Float Glass	3mm	5.9
  Clear Float Glass	19mm	5.4
  Clear Float Glass	4 to 6mm	3.7
  Laminated Single Glazing	6.38mm	3.6
  Float Insulating Glazing Unit (Air)	6mm glass/12 air/6mm glass	2.7
  Float Insulating Glazing Unit (Argon)	6mm glass/12 Ar/6mm glass	2.5-2.6
  Float Insulating Glazing Unit (Standard)	6mm/12 air/6mm	1.9
  Float Insulating Glazing Unit (High Efficiency)	6mm/12 Ar/6mm	1.7
  Relevant Australian Standards for Glass

  • AS 1288-2006: Guidelines for glass in buildings.

  • Additional useful standards include:

    • AS 1530: Fire tests on building materials.

    • AS 1735.2: Regulations for lifts.

    • AS 1926.1, AS 1926.2: Safety fencing for swimming pools.

    • AS 2047: Windows in buildings.

    • AS 2208: Safety glazing materials.

    • AS 2820: Acoustics recommendations.

    • AS/NZS 1170 series: Structural design actions and load codes.

  Real-World Applications of Glass in Structures

  • Examples of structural glass applications, such as the Amazon Waterlily Pavilion, emphasize innovative uses of glass that highlight its aesthetic and structural capabilities.

  • Prominent use in the Crystal Palace (1851) showcases historical significance in engineering innovation using glass.

  Conclusion and Future Directions

  • Continued innovations in glass technology and recycling methods, particularly for laminated glass, are essential for sustainable practices in the industry.

  • Adopting Closed Loop Recycling techniques for glass, ensuring as much glass material is reused and minimized in landfills, is a major focus moving forward.

  Questions and Further Resources

  • Explore various video resources and academic journals to gain deeper insights into glass properties, production techniques, safety standards, and sustainability in glass usage.