Strength of annealed soda-lime float glass at elevated temperatures up to the glass transition range
Final Report Abstract
Within the framework of the research project " Strength of annealed soda-lime float glass at elevated temperatures up to the glass transition range", the strength of soda-lime silicate glass and borosilicate glass at temperatures up to 550 °C was determined experimentally via double ring bending test. The strength of glass depends, due to its brittle material behaviour, especially on the degree of pre-damage. Therefore, the glass was pre-damaged in a reproducible manner with a scratch, which was applied to the glass surface with a diamond, and treated with heat at 200 °C for 4 hours. Subsequently, these specimens were subjected to the double ring bending test at temperatures up to 550 °C until they broke. Based on the measured force and the geometry, the strength of the glass was calculated using a closed-analytical model of the test set-up. During the test, the deformation in the middle of the circular glass was also recorded. The measured force and deformation were used to determine the stiffness of the material for the different test temperatures. The method of local deformation measurement on glass specimens is a unique test setup which does not require any consideration of the flexibility of the testing machine. The strength test of the pre-damaged glasses shows that the fracture strength increases only slightly with increasing test temperature at first and then increases strongly in the high temperature range (550 °C). It is assumed that the increase in strength of the glasses in the transformation range (550 °C) results from effects of crack healing and crack tip blunting. However, further research activities are necessary in order to be able to make statistically sound statements regarding the fracture strength of the glasses. The observations regarding the Young’s modulus show a steady slight decrease in the stiffness of soda-lime silicate glass with increasing temperature, until finally at 500 °C a strong decrease in stiffness can be seen. In the case of borosilicate glass, a stiffening of the material up to 450 °C can initially be seen, whereas at 500 °C almost the same stiffness results as at 20 °C. At the moment, however, there is still a lack of knowledge as to why borosilicate glass behaves in this way in these temperature ranges. For the research activities concerning the additive production of glass (glass 3D printing) and the thermal toughening process of glass used in industry, further and above all current research results concerning strength, rigidity and fracture behaviour of soda-lime silicate glass and borosilicate glass are now available. In the field of structural analysis of structural glazing, which will be increasingly used in the building industry in the future in line with current trends in architecture and civil engineering, the data obtained provide relevant results. In particular, impulses can be given with regard to the temperature dependence of the glass strength in the current glass construction standardisation.
Publications
- Double ring bending tests on heat pretreated soda–lime silicate glass. Glass Struct Eng (2020)
Schwind, G., von Blücher, F., Drass, M. et al.
(See online at https://doi.org/10.1007/s40940-020-00129-3) - Experimental investigations on the fracture strength of sodalime silica glass at elevated temperatures. Postponed Engineered Transparency Conference 2020. Conference Book
Schwind, G., von Blücher, F., Drass, M., Schneider, J.
(See online at https://doi.org/10.1002/cepa.1631)
