Characterisation of the scratch resistance of annealed and tempered architectural glass

The brittle nature of glass prevented real structural applications of glass in architecture up to the 1990s. As a result of intense research, nowadays tempered architectural soda-lime-silica (SLS) glasses are particular capable for modern architectural, structural and solar applications due to their superior mechanical strength and resistance to thermal break. The problem for the application of tempered glass in civil engineering is the sensitivity to scratching and the visibility of the scratches on the surface. To analyse the sensitivity to scratching for commercial annealed and thermally tempered glass scratch tests were performed with the Universal Surface Tester. The tests have shown that the crack width strongly depends on the indenter geometry, the used normal load and the type of glass (annealed or tempered glass). Macroscopically visible chipping of glass fragments at the scratch faces widens scratch tracks from typically 20–30 μm to 200–300 μm. Blunt indenters were identified to cause chipping at lower normal forces than sharp indenters and tempered glass was found to be more sensible for chipping. Contrary, the indentation depth and permanent deformation did not significantly change between annealed and tempered glass.