Properties of Float Glass at High Strain Rates

This study has evaluated the stress rate dependency of the flexural strength and stiffness of soda lime silica glass (float glass) at stress rates from 2 MPa/s to 5.8x10^6 MPa/s. An experimental setup was developed, supported by FEM models and considerations regarding the brittle nature of glass. The setup consisted of a high-speed hydraulic test machine in combination with a small double-ring test, where circular glass specimens were tested. In addition, high-speed recordings and fractography were utilised to validate that the test specimens failed due to biaxial bending.

Results showed a clear stress rate dependency of the flexural strength, where an increase of 87% was observed at the highest tested rate, compared to the static strength. The maximum failure stress was found to 510MPa. However, very large scattering was obtained since the tensile strength of glass is highly dependent on mechanical surface defects. To circumvent the large scattering, a series of intentionally scratched glass specimens were tested. These tests showed remarkable lower scattering compared to test specimens without any surface treatment. It was found that the flexural strength increased up to 60% at one of the highest tested rates. In general, the behaviour of the flexural strength increased as function of stress rate, but some inconsistencies were observed. A stiffness investigation at varying stress rates indicated an increase of the E-modulus. However, tolerances were present during the tests. This have led to a description of how the tests could have been conducted in a more accurate manner.