The strength of waterjet cut float glass

For well over a millennium glass has been “cut” by scoring it with a diamond or similar hard material and bending it putting the score into tension. The result is a “clean” break of the glass along the score. As this has sharp edges, nowadays the edges are usually post-processed using grinding and polishing techniques. Unfortunately cutting works best for orthogonal shapes, although skilled personnel can cut complex shapes. Modern techniques such as water jet cutting are very suited for complex shapes and can be adapted to CNC techniques. However there is very little information on the strength of waterjet cut glass. To investigate this a large series of specimens were prepared using waterjet cutting using the settings suggested by the manufacturer. Small rectangular specimens in thicknesses of 4 mm, 6 mm, 8 mm and 10 mm were made, the edges examined using a digital microscope, tested in four point bending and the fracture patterns were studied. It was found that the 4 mm thick specimens had a lower average strength and higher coefficient of correlation than the 6, 8 and 10 mm specimens. The average strength and coefficient of correlation were comparable for the 6, 8 and 10 mm specimens. The upper side, facing towards the water jet, is slightly less strong than the lower side. The strength of waterjet cut glass is comparable to some batches of conventionally cut glass with ground, arrised and polished edges while the coefficient of correlation is lower. It was found that for the waterjet cut glass virtually all failures originated at the edges, in many cases multiple failures were observed in a single specimen.