PSI - Issue 42

5

Erik Calvo-García et al. / Procedia Structural Integrity 42 (2022) 251–258 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The heat strengthened glass fracture toughness sensitivity to laser blasting is lower than that of the annealed glass, as can be observed from the plot of Fig. 4.a, where higher and more stable values of the fracture surface energy are shown for the thermally enhanced structural glass. The strain-stress relationship measurement during four-point bending tests at different speeds of the loading actuator are depicted in the Fig. 4.b . No statistical differences on the averaged Young’s modulus were observed in the range 0.2 to 1.0 mm/s of testing speed, with a value of 72 GPa. The bending strength of annealed and heat strengthened glasses before and after laser blasting were obtained. Special attention was paid to the determination of the influence of the specimen edge conditions on the failure mechanism, as it is well known that sharp edges can lead to early failure. Weibull and cumulative probability plots of the tested sharp edge specimens are depicted in Fig. 5. It can be observed that the presence of sharp edges in the flexural specimens conducts to early failure, with characteristic bending strength and 5% failure strengths of 46 MPa and 37 MPa, respectively, for both reference and laser treated glasses. Therefore, it can be concluded that the microcracks generated at the edges during glass conventional cutting is the driving failure mechanism when non-beveled edge elements are loaded. This effect is to be specially considered when testing the flexural strength by four-point bending test and can be avoided by using a coaxial double ring experimental configuration, as shown by Pisano et al. (2022) and Olmos-Navarrete et al. (2017).

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c)

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Figure 5 – Weibull plot and cumulative failure probability plot for plates with unbeveled edges showing an edge driven early failure independent on the laser treatment: a) and c) unmodified glass plates; b) and d) laser blasted glass plates.