Mechanical Reliability of Glass : The Transparent Road Surface Layer

Transcription

1 Mechanical Reliability of Glass : The Transparent Road Surface Layer Carlo G Pantano Department of Materials Science and Engineering Materials Research Institute The Pennsylvania State University University Park, PA Materials Research Institute strengths in materials and nanotechnology

2 Apple Store, 5 th Ave., NYC Glasgow, Scotland

3 Train Station/Strasbourg, France

4 the former Sears Tower Chicago, IL

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6 New applications will benefit from stronger glass..

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8 Strength of Glass GLASS th E d o 2 MILLIONpsi! but typically, σ fracture = 5-20 ksi

9 What controls the strength? 1. Surface MICROcracks - intrinsic - extrinsic 2. Fatigue 3. Residual Stress + - controlled - thermal tempering - chemical tempering uncontrolled due to forming (anneal them out)

10 fundamental issues in glass strength mechanical damage/flaws at the glass surfaces fatigue (stress corrosion/slow crack growth) low fracture toughness of the glass Materials Research Institute strengths in materials and nanotechnology

11 THE practical issue in glass strength: minimizing surface flaws failure strength versus flaw size: f = [2 g f E /p c*] 1/2 Materials Research Institute strengths in materials and nanotechnology

12 Figure 6.7. (a) Surface damage produced by light abrasion of one glass rod on another

13 Figure Horse-shoe shaped cracks in the surface of glass produced by a small ball, sliding from left to right.

14 Failure strain measurements may provide information about less brittle glasses Setsuro Ito, 2002 IMI-14

15 Coatings for Strength H 2 0 GLASS intrinsic strength and damage tolerance of the glass (E, γ, K 1C, H) condition of the original surface (flaws, moisture, roughness) properties of the coating (E, H, friction, diffusion, residual stress) interfaces (weak vs strong) Materials Research Institute strengths in materials and nanotechnology

16 DiamondGuard Glass that s nearly diamond-like -- tough and beautiful. DiamondGuard is a family of permanent protective coatings that provides glass with exceptional scratch resistance. In fact, glass with one of our DiamondGuard coatings is proven to be over 10 times more scratch resistant than tempered and chemically strengthened glass. Developed by Guardian s Science and Technology Center using a patented process of diamond-like carbon deposition on glass, these coatings are not only renowned for their toughness, but their versatility and beauty as well. Scratch resistant Low maintenance Highly transparent Chemically inert DiamondGuard is available on clear glass and sold in thicknesses ranging from 1.7 mm to 12 mm.

17 Hertzian Indentation Concentric Ring Cracks First Ring Crack Radial Cracks Median Cracks Cone Crack Quasi-plastic Damage Zone Green and Pantano

18 Commercial DiamondGuard - diamond-like carbon on float Reduced modulus values from Hertzian contact Sample Reduced Modulus (GPa) DLC Coated Glass 78.0 ± 10. Uncoated Glass 70.6 ± 8.6 Sample Weibull Modulus (m) DLC Coated Glass 14.1 Uncoated Glass 15.4 Sample Characteristic Mean Failure Median Failure Median Failure Strength (GPa) Stress (GPa) Stress (GPa) Load (N) DLC Coated Glass Uncoated Glass Spalling of coating

19 Surface Treatments for Glass Strength compressive surface residual stress - Thermal(Physical) Tempering - Chemical Tempering >>>> perhaps best applied in combination with a coating.. Materials Research Institute strengths in materials and nanotechnology

20 Figure 72. Distribution of stresses in thermally toughened and chemically strengthened glass.

21 Figure 3. Processing and equipment used to temper glass. (a) Plot of surface and midplane glass temperatures versus time to show narrow tempering range. (b) Cross-section of heating portion of a tempering furnace. (c) Cross-section of quenching portion of a tempering furnace.

22 Annealed, Tempered, and Laminated Glass Fracture Patterns

23 CHEMICAL/ION EXCHANGE STRENGTHENING/TEMPERING Corning Gorilla Glass

24 Strength comparison for: annealed, heat strengthened, thermally tempered and chemically strengthened glasses.

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26 Laminated Safety Glass

27 Textured Glass

28 nano-structured thin films nano-composite coatings

29 PRINTING ON GLASS: LEDS, solar cells, sensors.

30 Summary Glasses are damage intolerant. Coated, tempered and laminated panels will be required. Surface textures need to be developed to optimize both friction and resistance to contact damage. Glass road surfaces are possible in selected areas, especially if developed in cooperation with future all-electric vehicles.