Method for determining time-delayed changes of temperature-dependent or stress-dependent physical quantities of a glass or a glass ceramic

Patent metadata

Field	Value
Publication number	US-10012562-B2
Application number	US-201314437229-A
Country	US
Kind code	B2
Filing date	Oct 24, 2013
Priority date	Oct 24, 2012
Publication date	Jul 3, 2018
Grant date	Jul 3, 2018

Abstract

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.

First claim

The invention claimed is:

1. A method for determining time-delayed changes of temperature-dependent or stress-dependent physical quantities of a glass or a glass ceramic material, which depend on the relaxation state of the glass or glass ceramic, the method comprising:
measuring a deformation of the glass or glass ceramic material at least twice with different rates of change in temperature and/or with a mechanical stress as a function of time, wherein the measurements are carried out at temperatures of not higher than 100 K below a glass transition temperature of the glass or glass ceramic material; and
determining a plurality of relaxation times of the glass or glass ceramic material for a reference temperature;
determining weighting factors, which represent a weight of the relaxation times in the relaxation of the glass or the glass ceramic material; and
calculating a time-delayed change of a temperature-dependent or stress-dependent physical quantity as a function of a predefined temperature change or stress change based on the relaxation times and weighting factors.

2. The method as claimed in claim 1 , further comprising:
determining a fictive temperature of the glass or the glass ceramic material; and
determining a time dependence of the fictive temperature.

3. The method as claimed in claim 1 , wherein the measuring of deformation of the glass or glass ceramic material at least twice with different rates of change in temperature or mechanical stress as a function of time in a temperature range is performed within a temperature interval from −70° C. to +100° C.

4. The method as claimed in claim 1 , further comprising:
determining model parameters based on a measurement of time-dependent deformation; and
verifying the model parameters by a cyclic measurement of deformation during which temperature or mechanical stress is cyclically changed repeatedly.

5. The method as claimed in claim 1 , further comprising calculating, based on the relaxation times determined and assuming a predefined temperature-time profile, a temporal development of thermal expansion and/or a thermal expansion at a certain time.

6. The method as claimed in claim 1 , further comprising determining a coefficient of thermal expansion (CTE) of the glass or glass ceramic material as a function of a rate of change in temperature.

7. The method as claimed in claim 1 , further comprising:
predefining a temperature profile or profile of mechanical stress;
calculating a deformation under the effect of the predefined profile as a function of time for a plurality of glasses or glass ceramics; and
choosing, based on the calculation, a glass or glass ceramic material among the plurality of the glass or glass ceramic materials that exhibits a smallest deformation.

8. The method as claimed in claim 1 , further comprising determining a future deformation of the component for a time between 1 year and about 40 years in the future.

9. The method as claimed in claim 1 , further comprising:
measuring at least twice a deformation of a glass or glass ceramic material as a function of time under a mechanical stress varying over time;
determining relaxation times based on these measurements; and
calculating a deformation of a component as a function of a mechanical stress varying over time.

10. The method as claimed in claim 9 , further comprising calculating a deflection of an optical component following a material removal under mechanical stress.

11. The method as claimed in claim 10 , wherein the deflection previously calculated is accounted and compensated for during the material removal under mechanical stress.

12. The method as claimed in claim 1 , wherein the step of calculating the time-delayed change comprises performing a calculation selected from the group consisting of calculating a change in length, calculating a change in volume, calculating a change in refractive index, calculating a change in heat capacity, calculating a change in shear modulus, calculating a change in bulk modulus, calculating a change in torsion modulus, and calculating a change in Young's modulus.

13. The method as claimed in claim 12 , wherein a thermal displacement function is expressed as a ratio of viscosity η to a reference viscosity, wherein the viscosity is determined by measuring permittivity and internal mechanical friction of the glass or glass ceramic article, and by deflection tests on the glass or glass ceramic article.

14. The method as claimed in claim 12 , further comprising:
determining relaxation times (τ k ) at a reference temperature (T ref ), weighting factors (w k ), and parameters of a displacement function (a T ), a displacement function specifying how the relaxation of the glass or glass ceramic material changes as a function of temperature;
determining therefrom state variables T fA , T fAi , where T fA is represented as a spectrum of the differently relaxing state variables T fAi , by fitting the parameters of the following equations to the measured values:

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Assignees

• Schott Ag

Inventors

• Jedamzik Ralf
• Kunisch Clemens
• Johansson Thoralf

Classifications

• G02B1/00

  Optical elements characterised by the material of which they are made; Optical coatings for optical elements · CPC title

• G01N19/00

  Investigating materials by mechanical methods (G01N3/00 - G01N17/00 take precedence) · CPC title

• G01M11/005 Primary

  Testing of reflective surfaces, e.g. mirrors · CPC title

• G01N25/02 Primary

  by investigating changes of state or changes of phase; by investigating sintering {(investigating or analysing oils or hydrocarbon fluids by measuring cloud point or pour point G01N33/2811)} · CPC title

• G01N33/386

  Glass · CPC title