Optics, Vol. 6, Pages 31: Nondestructive Hardness Assessment of Chemically Strengthened Glass

Optics doi: 10.3390/opt6030031

Authors:
Geovana Lira Santana
Raphael Barbosa
Vinicius Tribuzi
Filippo Ghiglieno
Edgar Dutra Zanotto
Lino Misoguti
Paulo Henrique Dias Ferreira

Chemically strengthened glass is widely used for its remarkable fracture strength, mechanical performance, and scratch resistance. Assessing its hardness is crucial to evaluating improvements from chemical tempering. However, conventional methods like Vickers hardness tests are destructive, altering the sample surface. This study presents a novel, rapid, and nondestructive testing (NDT) approach by correlating the nonlinear refractive index (n2) with surface hardness. Using ultrafast laser pulses, we measured the n2 cross-section via the nonlinear ellipse rotation (NER) signal in Gorilla®-type glass subjected to ion exchange (Na+ by K+). A microscope objective lens provided a penetration resolution of ≈5.5 μm, enabling a localized NER signal analysis. We demonstrate a correlation between the NER signal and hardness, offering a promising pathway for advanced, noninvasive characterization. This approach provides a reliable alternative to traditional destructive techniques, with potential applications in industrial quality control and material science research.

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