PSI - Issue 42

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

252

2

(2017), Wang et al. (2019), Cho et al. (2021), and Amiri et al. (2022). Among the available surface treatments, the laser surface blasting is a high productivity version of laser surface texturing, very attractive due to capabilities in terms of production rates, cleanliness, and spatial selectivity as highlighted by Penide et al. (2019), Allen and Raeymaekers (2021) and Costa et al. (2022). Nevertheless, the generalized use of surface-modified bearing glass is precluded by the lack of knowledge about their mechanical performance. The modification of the surface of these load bearing glass elements generally lead to mechanical strength and toughness reduction by mechanisms related to stress concentration and crack nucleation. As a result, the implementation of structural calculations required by the European countries national standards, such as prEN 16612, Önorm B 3716, or prNBN S23-002, require a deep knowledge about the effect of texturing treatments. Ballarini et al. (2016) and Pisano et al. (2022) conducted the calibration study of partial factors that relies on improved statistical distributions of glass strength, while Pisano et al. (2021) studied the size and stress state effect on glass strength. The impact on the engineering design with bulk and glass laminate must be precisely determined to fulfill safety requirements and avoid overweight at the same time. This experimental investigation carries out the assessment of the fracture toughness and strength of glass subjected to laser blasting. Annealed glass and heat strengthened glass plates were subjected to mid-infrared laser surface treatment to increase the surface roughness and improve the slip resistance in wet and dry conditions. The fracture toughness and fracture surface energy were experimentally determined from the observed radial cracks after micro-indentation with a pyramidal diamond indenter, and the results were analyzed in correlation to the laser processing conditions and the obtained surface roughness. The Weibull graph and the cumulative failure probability of the as-received and laser modified glass were obtained by the four-point bending tests. 2. Experimental 2.1. Laser blasting of structural glass The Fig. 1.a shows the operation principle of laser blasting. A medium to high power laser source provides a beam of optical radiation. The guiding and conditioning optics guide and modify both the size and focusing condition of the laser beam to be adapted to the scanning system and surface to be treated. The scanning system allows to produce a two dimensional swept of the surfaces, as unique element or in combination to a translation stage. This scanning system can include fixed focusing optics, or adaptative focusing optics if three-dimensional surfaces are to be treated. In addition, the process can be performed within a controlled atmosphere/vacuum depending on the surface reactivity. In relation to the required characteristics of the employed radiation, to different approaches can be followed. One option is the short pulse duration approach, using femtosecond laser sources 14,15 . Another option is the wavelength approach, using laser sources with a wavelength that ensures a high energy absorbance at the surface 16,17 . The experimental system employed in this work implements a wavelength-based approach. Particularly for “eye transparent” surfaces such as those of structural elements of soda -lime silicate glasses, the laser wavelength must be outside of a high transmissivity window. Thus, the use of lasers in the visible or near-infrared spectrum is ruled out. The experimental system used in this work include a CO 2 laser source with a mid-infrared with a 10.6 micrometer wavelength. The laser beam accounted for a 300W of optical power and was focused by a high focal length ZnSe lens to treat extensive areas within the same conditions. The bi-dimensional surface treatment was produced by combination of a fixed axis polygonal scanner with a single direction translation stage. Different translation stage speeds were tested to produce a range of optical energy density at the glass element surface. The glass treated elements presented a common soda-lime silicate composition, typical of flat elements in structural applications. The slip resistance of the processed surfaces was tested following the DIN 51130 ramp test specifications in different surface conditions. 2.2. Specimen mechanical tests For mechanical testing and characterization, 60 mm wide annealed glass plates and heat strengthened glass plates were tested. Fracture toughness K Ic and fracture surface energy were measured from the radial cracks immediately after Vickers micro-indentation with a 2.942 N force (HV0.3) over 15 seconds following the procedure stablished by Miyoshi (1985). To et al. The value of the Young`s modulus for the toughness and surface energy computation was