Strength of annealed soda-lime float glass at elevated temperatures up to the glass transition range

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The objective of this research project is the experimental investigation of the temperature dependency of the flexural strength of annealed soda-lime-silica float glass in a temperature range from the ambient temperature up to the glass transition range.In order to make predictions on the glass failure during the thermal tempering process of glass and during the additive manufacturing with glass, the flexural strength of glass in the relevant temperature range, the related stress rate from the cooling process as well as typical surface damages resulting from the prior production processes have to be known.Regarding the temperature dependency of the flexural strength up to the glass transition range there are only a few experimental results available for soda-lime glass and borosilicate glass. The previous works focus on the temperature dependency of the fracture toughness (soda-lime glass) and the temperature dependency of the flexural strength (borosilicate glass). In addition, the tests mostly were carried out at very high stress rates with up to 320 MPa/s. According to the duration of the cooling process of the thermal tempering process and the cooling rate during additive manufacturing of glass, the stress rate should be lower for the applicability of the results in civil engineering. Accordingly, in this research project particularly the flexural strength at elevated temperatures up to the glass transition range and with two stress rates (2 MPa/s, 20 MPa/s) shall be investigated. The influence of the temperature and the stress rate shall be investigated on specimens with a typical surface damaging resulting from the glass processing (defined scratches, cylindrical drill holes from a diamond driller).Since in civil engineering primarily soda-lime glass is used, the investigations shall mainly be carried out with soda-lime-silica float glass, one test series with borosilicate glass for a comparison.