Morphology of Cleaved Surface and Observation of In Situ Crack Propagation During Cleaving

In laser cleaving, the thermal stress caused by laser heating and water-jet cooling propagates previously induced cracks in the workpiece material. The laser-cleaving conditions affect the quality of the fracture surface, and therefore, elucidating the relationship between the cleaved surface, cleaving conditions, and crack propagation is essential. Against this backdrop, in this study, we investigated the morphology of the cleaved surface and visualized the crack propagation and stress in situ using a high-speed polarization camera. The distance between the glass edge and cleaved surface was varied. When the laser-cleavage line was close to the glass edge, twist hackles were formed on the cleaved surface. The area in which the twist hackles formed on the cleaved surface coincided with the lagging section of the crack front. Furthermore, the twist hackle reached the specimen surface, and the edge of the surface exhibited a sawtooth shape. Observations with the high-speed polarization camera revealed that the internal stress was asymmetric with respect to the crack when the twist hackles were formed.

Post-tensioning of glass beams: Analytical determination of the allowable pre-load

The effectiveness of post-tensioning in enhancing the fracture resistance of glass beams depends on the level of compressive pre-stress introduced at the glass edge surface that will in service be exposed to tensile stresses induced by bending. Maximum pre-load that can be applied in a post-tensioned glass beam system, yielding maximum compressive pre-stress, is limited by various failure mechanisms which might occur during post-tensioning. In this paper, failure mechanisms are identified for a post-tensioned glass beam system with a flat stainless steel tendon adhesively bonded at the bottom glass edge, including the rupture of the tendon, glass failure in tension and adhesive/glass failure in the load introduction zone. Special attention is given to the load introduction failure given that the transparent nature of glass limits the use of vertical confinement usually applied in concrete. An analytical model for determination of the allowable pre-load in post-tensioned glass beams is proposed, based on the model applied for externally post-tensioned concrete beams. The model is verified with the results of a numerical model, showing good correlation, and applied in a parametric study to determine the influence of various beam parameters on the effectiveness of post-tensioning glass beams.

Edge Grinding Characteristics of Display Glass Substrate

Display glass substrate as a brittle material is very challenging to machine due to its excellent physical, mechanical, electrical, and optical properties such as high hardness, high strength, high wear resistance, good fracture toughness, good chemical stability, and good thermal stability. On the basis of Griffith fracture mechanics, our theoretical analysis indicated that edge grinding of the display glass substrate is under brittle mode when grinding with the given conditions, which was verified by the experimental studies of ground glass edge surface topography and fractured surface obtained. Grinding force (Fy) in the vertical direction was much larger than grinding force (Fx) in the horizontal direction, causing a large compressive stress acting on the grinding glass edge. Grinding torque was slightly increased with the increase of grinding speed. Grinding temperature was very high when measured under dry grinding compared with measurement under high-pressure coolant. Grinding of glass substrate edge was performed partially under ductile mode machining in the experimental conditions, which can be attributed to and contributed by those micro cutting edges generated by the fractured diamond grit on the grinding wheel surface.

Semantic segmentation with deep learning: detection of cracks at the cut edge of glass

In this paper, artificial intelligence (AI) will be applied for the first time in the context of glass processing. The goal is to use an algorithm based on artificial intelligence to detect the fractured edge of a cut glass in order to generate a so-called mask image by AI. In the context of AI, this is a classical problem of semantic segmentation, in which objects (here the cut-edge of the cut glass) are automatically surrounded by the power of AI or detected and drawn. An original image of a cut glass edge is implemented into a deep neural net and processed in such a way that a mask image, i.e. an image of the cut edge, is automatically generated. Currently, this is only possible by manual tracing the cut-edge due to the fact that the crack contour of glass can sometimes only be recognized roughly. After manually marking the crack using an image processing program, the contour is then automatically evaluated further. AI and deep learning may provide the potential to automate the step of manual detection of the cut-edge of cut glass to great extent. In addition to the enormous time savings, the objectivity and reproducibility of detection is an important aspect, which will be addressed in this paper.

The influence of different cutting parameters on the glass edge quality

The influence of different cutting parameters on the glass edge quality was investigated, including the cutter material, the sharpening angle of the cutting roll, the cutting speed and the load applied to the roll. The results show that there are less defects on the edge of the glass cut by diamond cutter. There is no obvious influence of cutting speed on the glass edge quality. The cutter with a smaller sharpening angle is more applicable for the cutting of thin glass, and the thick glass is more suitable to use a bigger sharpening angle cutter. Higher cutting load is helpful for the breaking of the glass along the cutting line. However, it may cause more defects on the edge and the surface of the glass.

Corner Transition Toolpath Generation Based on Velocity-Blending Algorithm for Glass Edge Grinding

Sharp corners usually are used on glass contours to meet the highly increasing demand for personalized products, but they result in a broken wheel center toolpath in edge grinding. To ensure that the whole wheel center toolpath is of G1 continuity and that the grinding depth is controllable at the corners, a transition toolpath generation method based on a velocity-blending algorithm is proposed. Taking the grinding depth into consideration, the sharp-corner grinding process is planned, and a velocity-blending algorithm is introduced. With the constraints, such as traverse displacement and grinding depth, the sharp-corner transition toolpath is generated with a three-phase motion arrangement and with confirmations of the acceleration/deceleration positions. A piece of glass with three sharp corners is ground on a three-axis numerical-control glass grinding equipment. The experimental results demonstrate that the proposed algorithm can protect the sharp corners from breakage efficiently and achieve satisfactory shape accuracy. This research proposed a toolpath generation method based on a velocity-blending algorithm for the manufacturing of personalized glass products, which generates the transition toolpath as needed around a sharp corner in real time.