Non-destructive testing of the strength of glass by a non-linear ultrasonic method
The paper presents basis and experimental results of a non-destructive method aimed at determination of the presence of large surface cracks in glass samples by measurements with NAW® technology (Nonlinear Acoustic Wave). The method is based on a transmitted ultrasonic wave in the material from which the non-linear content of the signal can be analysed. A sample containing defects presents nonlinearities in the form of distortions, such as, higher order harmonics that are detected. Nonlinearities in the signal are primarily formed at crack-tips and the number of nonlinearities is proportional to the amount of damage, or defects, in the sample that is investigated. The result of the measurement and evaluation, that only takes a few seconds, is a damage value that is easy to understand and to use for immediate application. A number of preliminary test results and comparisons with destructive testing for various test setups, as well as a recent test strategy including fabricated defects with a nanoindenter will be discussed.