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![Figure 2-Glass Strength VS Flaw depth (From T.Rouxel, S.Yoshida [91])](profile/Guglielmo-Macrelli/publication/319471996/figure/fig12/AS:668887892897806@1536486709722/Glass-Strength-VS-Flaw-depth-From-TRouxel-SYoshida-91_Q320.jpg)
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... With thin and high strength specimens (for example 3 mm fully tempered glass), there is a risk of slipping out of the supporting rollers before the maximum breaking stress is reached. Considering even thinner glass and the expected higher strength of chemically toughened glass [5] with a laser-cut edge, this conventional test set-up can no longer be used to determine the bending tensile strength. To overcome this technical limitation, alternative methods and test equipment are being developed to determine the bending tensile strength for thin glass with a thickness of 0,5 to 3 mm and high expected breaking stresses of up to 400 N/mm 2 . ...
The use of thin glass in construction promises a variety of potentials for a more sustainable use of resources. Innovative constructions can enable thin glass to become an important component of structural glass engineering. However, there is still a lack of in-depth knowledge and corresponding standards for a reliable and standardized use of thin glass. One particular challenge is the determination of the bending tensile stresses for building product standardization. Due to the low geometric stiffness, conventional test methods such as the four-point bending test can no longer be applied. Alternative test methods have already been developed and investigated. Thereby, an increased influence of Poisson´s Effect with decreasing thickness of the glass has been suspected. The test specimens deform far beyond the small deformation field and activating non-linear behavior which leads to a significant shift from unidirectional to a multidimensional stress situation. Rather, it leads to a considerable bending along the width of the specimen, depending on the aspect ratio, thickness and the extent of the curvature. This research investigates the influence of the geometric dimensions of a test specimen as well es the load magnitude on the stresses calculated by the linear elastic Euler-Bernoulli beam theory. For this purpose, an extensive parameter study is carried out by means of the finite element method. With more than 200 variants, the maximum stresses as well as their distribution over the width is compared. This leads to a more accurate understanding of the effect of lateral strain at large deformations and helps in the selection of geometry and a more realistic evaluation of ultimate stresses in thin glass. Influence of Poisson's Effect on the determination of the bending tensile stress of thin glass
This work introduces a novel, fractographic method to extend the current, state-of-the-art, fractographic techniques to chemically strengthened (CS) glasses with large, surface flaws. The proposed method uses proven relationships based on dimensional analysis to correlate the flexural fracture strength to newly-introduced, fractographic length-scales. The technique requires knowledge of the residual stress profile and access to standard visualization tools such as optical microscopes. The proposed methodology was validated on three sets of aluminosilicate CS glass plates with depth of the compressive layer (DOL)ranging between 28~54μm and surface stress 980~1140 MPa, and one set of untreated plates. For the CS and untreated glass plates considered, the proposed fractographic technique estimated the fracture strength within (2 ± 11)% of experimental values, which is comparable to the accuracy of fractographic techniques currently used for annealed, brittle specimens.
The relationship between diffusion kinetics (interdiffusion coefficients, effective diffusion coefficients and activation energy) of the ion-exchanged float soda lime silicate (SLS) glass in the air and tin surfaces were determined by the Boltzmann-Matano and Green’s function. The compressive stresses generated by ion exchange were discussed from a different viewpoint that compressive stress depth profile gradient (CSG) measurements were performed on both surfaces and analysed in symmetrical depths using FSM 6000LE surface stress metre. This method is easy, practical and non-destructive compared to other methods. Thus, this technical method will importantly result in distinguishing the compressive stress difference of symmetrical depths between air and tin surfaces. The interrelationship among the concentration profiles, CSG and diffusion kinetics of ion-exchanged glasses were evaluated. The results showed that the K+ ion concentration was increased with temperature and time and was always higher on the air surface. Results found will provide a simple guideline for both the process control and the flatness of large-area glasses in strengthening of ion-exchanged SLS float glasses.
Glass that used for architectural and structural purpose will undergo long term exposure to the natural outdoor environment. Exposure to outdoor weather such as temperature, humidity, UV-radiation, pH, etc. may cause deterioration of glass strength. This paper aims to study the effect of short-term exposures to natural outdoor environment on the strength of glass panel. Four sets of tempered glass samples were prepared for direct exposure to the outdoor environment. The samples were exposed to the outdoor environment for 40-, 80- and 120-days. A total of two tests namely microscopic observation on glass surface and four-point bending test on glass panel were conducted. Based on microscopic observation, the intensity of surface defects such as surface scratches, bubbles, and dust were increased for longer period of outdoor exposure. The bending and residual strengths of the glass panel reduced as the duration of the outdoor exposure was increased. The tempered glass material tends to undergo deterioration in strength by weathering process.
