METHOD FOR DETERMINING TIME-DELAYED CHANGES OF TEMPERATURE-DEPENDENT OR STRESS-DEPENDENT PHYSICAL QUANTITIES OF A GLASS OR A GLASS CERAMIC

The invention generally relates to manufacturing or providing of glass or glass ceramic products. The invention is based on the object to allow for providing glass or glass ceramic products having very accurately characterized thermo-mechanical properties. For this purpose, a deformation of the glass or glass ceramic material is measured at least twice as a function of time with different rates of change in temperature or a mechanical stress. Based on the measurements, relaxation times and weighting factors are determined by modelling. Then, based on the relaxation times and weighting factors related to the distribution of relaxation processes occurring in the product, a time-delayed change of a temperature-dependent or stress-dependent physical quantity, such as thermal expansion or refractive index, is calculated as a function of a predefined temperature change or stress change. The invention is used for selecting during manufacturing suitable glass products exhibiting selected time-delayed properties.