PSI - Issue 81

Valeriy Lazaryuk et al. / Procedia Structural Integrity 81 (2026) 529–535

530

facilitating directed crack growth (Singh et al., 2013; Livingstone et al., 1997; Tsai and Liou, 2003). However, these approaches are not suitable for dimensional, layer-by-layer surface micromachining. Silicate glass exhibits low thermal shock resistance, a narrow plasticity range, and a strong tendency to develop residual tensile stresses; this leads to significant cracking of the molten groove surface and its heat-affected zone (HAZ) (Tsai and Liou, 2003; Alayed et al., 2025). CO 2 laser irradiation induces steep transient temperature gradients that generate tensile stress fields exceeding the local strength of the glass, resulting in subsurface crack initiation (Allcock et al., 1995; Kang and Shin, 2020). Laser scribing, as one of the methods of laser micromachining, uses the ability of the material to absorb laser-radiation energy within a thin surface layer whose thickness is comparable to the radiation wavelength. The use of pulsed laser radiation reduces inter-pulse heating of the glass, lowers thermal stresses and thermally induced cracking, and results in a more uniform scribed groove. Laser scribing enables operations such as laser engraving, shallow microstructuring, and guiding-groove formation in glass, and these operations are widely used in microelectronics, optoelectronics, sensor fabrication, microsystem technologies, and glass ceramic processing (Singh et al., 2013; Kang and Shin, 2020). For example, CO 2 laser scribing can be used for fast prototyping of the shape and topology of microfluidic channels. This approach is suitable for glass-based microfluidic devices used in sensing applications where the wall quality of the channels is not critical (Perrone et al., 2021; Wang et al., 2012). Early studies on soda lime glass and borosilicate glass showed that under high scanning speeds and moderate power levels, narrow grooves are formed, and the glass can be removed not only as short flakes but also as long chip-like fragments (Allcock et al., 1995). Further studies on CO 2 - laser “layer peeling,” th ermal ablation, and microchannel formation (Zettl et al., 2021; Alayed et al., 2025) confirmed that stable microrelief formation occurs only when the local thermal load remains within a narrow parametric range. Material removal in glass under CO 2 laser irradiation occurs because the glass surface absorbs the laser photon energy. Two factors are crucial: how much energy is absorbed and how fast this energy is delivered. These parameters determine the thermal gradient and the resulting surface effects — melting, ablation, thermal stress, and crack formation. It is therefore important to examine how the laser’s energy conditions affect these surface phenomena, especially in relation to pulse energy and scanning speed, which together define the actual energy delivered into the glass. At the same time, the morphology of laser-induced damage is much more complex, with many types of defects that have their own mechanisms of energy absorption, stress localisation, and fracture development. Transitions between these regimes are determined by the interaction of thermal conductivity, local evaporation, and the evolving stress – strain state (Livingstone et al., 1997; Wang et al., 2012; Kang and Shin, 2020). Analysis of damage morphology allows assessment of the dominant material removal mechanism and the stability of the scribing process. A key parameter that describes this transition is the specific linear energy input, which combines laser power and scanning speed into an integral measure of thermal loading per unit length (Livingstone et al., 1997). Despite considerable progress in ultrafast laser micromachining (Wang et al., 2018; Zettl et al., 2021; Yasman et al., 2024). CO 2 -laser scribing remains technologically important due to the accessibility of the equipment, high material-removal rates, and the ability to operate with large beam diameters (Shanaida and Lazaryuk, 2021). However, a complete mechanistic model is still lacking. Existing studies rarely integrate fracture mechanics concepts — such as fracture energy, the volume of material involved, or the evolution of crack density — into the parametric analysis of the process. This study combines thermal, morphological, and fracture-mechanics approaches to analyse CO 2 -laser scribing of silicate glass. By correlating different types of defects with specific linear energy input, we establish a rational methodology for selecting processing regimes. This methodology allows for controlled micrometre-scale removal of the surface layer while minimizing localized damage, which is crucial for precision laser micromachining of brittle silicate and ceramic materials. 2. Material and test procedure Laser scribing experiments were performed using an MTech L640 Optima laser processing system equipped with a sealed-tube RECI W2 CO 2 laser source (100 W) (Fig. 1). The laser beam was focused onto the glass surface at constant output power, while the scanning speed was adjusted across a range of values to see how it affected groove formation, thermal changes, and crack development. The morphology of surface damage was examined by optical microscopy in reflected and transmitted light using objectives of different magnifications on metallographic and biological microscopes. Surface morphology and near-surface defects were examined using a MIM-10 metallographic microscope (Fig. 2). Examination using biological microscopes made it possible to vary the illumination of defects and reveal their spatial nature. Dimensional parameters, including groove width, melt zones, defect areas, defect morphology, and crack length, were measured using a calibrated eyepiece micrometer. All micrographs in the paper share the same calibrated field of view of 1.10 х 0.82 mm; therefore, scale bars are not shown individually. The substrate material was commercial soda – lime silicate glass with a typical composition of 70 – 72 wt.% SiO 2 , 12 – 14 wt.% Na 2 O, 10 – 12 wt.% CaO, and minor additives. Its density was 2.5 – 2.55 g/cm 3 , the softening point approximately 530 – 540 0 C, the thermal expansion coefficient 8.5- 9.0 х 10 -6 0 C -1 , and the thermal conductivity 0.8 – 1.0 W/(m · K). The elastic modulus was close to 70 GPa, while the flexural strength reached 45 – 60 MPa. Due to its brittle nature and low thermal-shock resistance, this type of glass is suitable for examining laser-induced damage mechanisms.