The mechanical response of cold bent monolithic glass plates during the bending process

Cold bending of glass involves the straining of relatively thin glass components, (typically plates), at ambient temperatures, and is a low energy and cost effective manner of creating curvilinear forms required in modern glass applications. Cold bending is also popular because it is thought to eliminate the optical imperfections in curved glass plates that arise during alternative and more conventional thermal bending techniques. Experimental and numerical investigations on the cold bending of monolithic glass plates into anticlastic shapes are undertaken and described in this paper. The aim is to characterise the cold bending behaviour during the bending process and to evaluate the surface/optical quality of the curved plates. Two distinct phenomena of interest are observed: (i) a change in the deformation mode that under particular boundary and loading conditions lead to snapthrough buckling and; (ii) a local instability termed “cold bending distortion” that appears on curved plates when certain applied displacement limits are exceeded. This cold bending distortion is found to occur at stresses significantly below the fracture strength of the glass plate, but the distortions can be sufficiently large to breach optical serviceability requirements. An optical quality evaluation procedure for predicting the cold bending response and the resulting optical quality of monolithic glass plates are provided at the end of this paper.The authors gratefully acknowledge financial and technical support from Eckersley O'Callaghan, and financial support from the Research Fund for Coal and Steel of the European Community and the Engineering and Physical Sciences Research Council UK (EPSRC).This is the final version of the article. It first appeared from Elsevier via https://doi.org/ 10.1016/j.engstruct.2016.03.01

Design and Performance of Cold Bent Glass

The demand for flat glass is high and increasing significantly in the building industry as a direct result of architectural requirements for lightness, transparency and natural light. Current architectural trends require glass in curvilinear forms for smooth free-form façades. Two principal challenges arise from this: to cost-effectively produce the desired curvature and; to ensure its safe performance after exposure to ageing. The recent availability of high strength glass provides an opportunity to address the first challenge by developing cold bent glass. Cold bending involves the straining of relatively thin glass components, at ambient temperatures, and is a low energy and cost effective manner of creating curvilinear forms. However, cold bending is not yet widely established as a reliable method. The aim of this thesis is to develop the understanding of cold bent glass during the bending process and to evaluate its post-ageing performance. This thesis, firstly, investigates the mechanical response of monolithic glass plates during the cold bending process. The stability of cold bent glass is investigated experimentally by bending it in double curved anticlastic shapes. A parametric numerical analysis involves different boundary conditions, geometrical plate characteristics and bending parameters. The principal outcome is that a local instability, now termed cold bending distortion, occurs when certain displacement limits are exceeded and could degrade the optical quality of the glass. An evaluation procedure is also formulated to set limits and aid designers/manufacturers to predict the mechanical response and the optical quality of the glass. Cold bent glass is subjected to permanent bending stresses throughout its service life and therefore, its strength degradation after ageing needs to be quantified. Analytical, experimental and numerical investigations are undertaken in this thesis to identify the most effective method for estimating glass strength (evaluation of destructive tests, required number of specimens, statistical analysis methods and sub-critical crack growth). The limited availability of naturally aged toughened glass and the absence of a reliable ageing standard impede the evaluation of its aged performance. Therefore, a parametric experimental investigation of artificial ageing methods on glass is undertaken in this thesis. A procedure for the evaluation of the strength of aged glass is finally, formulated to allow the selection of artificial ageing parameters that correspond to a target level of erosion. The knowledge on artificial ageing and strength prediction acquired above is finally implemented on different types of glass to determine their strength after ageing and assess their safe use in cold bending / load bearing applications. The investigation showed that fully toughened glass has a superior performance to chemically toughened or annealed glass. Overall, the research presented in this thesis demonstrates that high quality cold bent toughened glass can be created when certain applied displacement limits are respected. These can be used as a safe, cost-effective and energy efficient replacement to the more conventional hot bent glass. However, cold bending / load bearing applications in which the stressed glass surface is exposed to ageing, require glass with a relatively high case depth such as fully toughened or bi-tempered glass.Engineering and Physical Sciences Research Council UK (EPSRC), Eckersley o’Callaghan, Onassis Foundatio

Weibull parameter estimation and goodness-of-fit for glass strength data

Strength data from macroscopically identical glass specimens is commonly described by a two-parameter Weibull distribution, but there is lack of research on the methods used for fitting strength data to the Weibull distribution. This study investigates 4 different methods for fitting data and estimating the parameters of the Weibull distribution namely, good linear unbiased estimators, least squares regression, weighted least squares regression and maximum likelihood estimation. These methods are implemented on fracture surface strength data from 418 annealed soda-lime-silica glass specimens, grouped in 30 nominally identical series, including as-received, naturally aged and artificially aged specimens. The strength data are evaluated based on their goodness of fit. Comparison of conservativeness of strength estimates is also provided. It is found that a weighted least squares regression is the most effective fitting method for the analysis of small samples of glass strength data

Repair of Soda-Lime-Silica Glass

Glass strength is very sensitive to damage accumulation during its service life. Repair methods for glass have been proposed over the last decades to volumetrically fill or remove existing flaws from the surface of glass. However, the lack of information on the strength recovery attributable to glass repair methods restrict their use to low consequence class applications in buildings thereby making replacement of damaged installed glass the only safe and practical solution when dealing with damaged glass. Repair methods involving volumetric filling of visible flaws with resins, removal of visible flaws with polishing and chemical repair with acid treatment of visible flaws are undertaken in this study to investigate the strength recovery in 60 artificially aged annealed glass specimens. It is found that the polishing provides the most promising strength recovery results showing a 132% and a 40% increase in design and mean strength whilst the acid treatment provides the worst performance. Polishing repairs are further investigated in this study to determine their efficacy in strength recovery after environmental ageing (exposure to UV, humidity and freeze-thaw cycles)

Powder‐fed directed energy deposition of soda lime silica glass on glass substrates

© 2022 The Authors. Journal of the American Ceramic Society published by Wiley Periodicals LLC on behalf of American Ceramic Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Novel glass processing by powder-fed directed energy deposition was explored as a method of adding glass décor to glass surfaces and bottles. Consistent, semitransparent, single-line tracks of soda lime silica glass could be processed onto glass substrates of the same composition, without significant cracks forming in the substrate. A suitable processing window was found with laser power and scan speed showing independent effects on processing. Consideration of processing surface conditions and reduction of laser transmission through transparent substrates was necessary, and the use of an adhesive tape layer aided adhesion of glass feedstock to substrate surfaces. The work demonstrates the potential for a one-step method of glass bottle decoration for the packaging industry, with scope to create 3D designs of high geometric complexity and customizability on glass substrates, thereby adding value to glass packaging by brand differentiation without the high costs associated with molds and tooling.Peer reviewe

Laser powder bed fusion of soda lime silica glass: Optimisation of processing parameters and evaluation of part properties

© 2021 The Authors. Published by Elsevier B.V. his is an open access article under the CC BY license. https://creativecommons.org/licenses/by/4.0/Glass has a number of attractive properties, such as transparency, chemical resistance, good thermal stability and high electrical resistivity, that make it a favourable material for a range of applications, including medical technology, electronics, chemical and pharmaceutical industries. However, compared to metals and polymers, the additive manufacturing of glass is still at a primitive stage. The inherent material properties of glass, i.e. its amorphous structure, lack of ductility and high processing temperatures, make processing of glass by additive manufacturing challenging. This paper describes the laser powder bed fusion of a soda lime silica glass. Optimisation of the laser powder bed fusion process was undertaken and the physical and mechanical properties of the manufactured parts were characterised revealing an average porosity of 12%, a mean flexural strength of 6.5 MPa and a fully amorphous structure. Feasibility examples were successfully demonstrated, indicating that geometrically complex shapes are possible. Even though the manufactured parts are opaque, they could potentially find use in applications where the need for chemical inertness and geometrical complexity surpass the need for transparency as in the chemical and pharmaceutical industries e.g. in the form of continuous flow reactors or structured catalysts.Peer reviewedFinal Published versio

Evaluation of Artificial Ageing Methods for Glass

Surface damage that accumulates on the surface of glass is known to govern the strength of this material. It would therefore be very useful to use artificial ageing techniques to replicate this level of damage; this would allow a rapid and cost effective assessment of the expected glass strength and the long term performance of novel glass products and treatments. Some artificial ageing methods exist but it is unclear whether the surface damage induced is correlated with the physical damage found in naturally aged glass. The aim of this paper is therefore, to evaluate available artificial ageing methods of glass using as a reference naturally aged annealed glass. The artificial ageing methods of the as-received specimens involved the induction of: (a) a single flaw on the as-received specimens with a custom-made scratching device (SC series); and (b) uniform damage to the specimens with the use of dropped grit (SA series). Each ageing method was then evaluated with destructive and non-destructive testing. These results were then compared to those obtained from the naturally aged glass (NA series). A 65% reduction in mean strength with the respect to the as-received annealed glass was noted for the naturally aged series. This reduction was approximated (62-79%) by the artificial aged series. However, a perfect match has yet to be found especially when other fractile values of strength as well as surface roughness data are also taken into account. Nevertheless, in general the SA series were found to perform better than the SC series

Surface Tensile Strength and Hertzian Fracture Resistance of Patterned Acid-Etched Glass

Patterned acid-etched glasses are frequently used in horizontal glass surfaces that may be walked on, such as floors and staircase treads. These glasses provide useful antislip properties, but the foot traffic cause contact stresses and ageing mechanisms that are poorly understood and can affect the strength of the acid-etched glass. This study explores these strength-reducing effects by undertaking nondestructive and destructive evaluations of two acid-etched glasses with geometrically different surface patterns and comparing their mechanical performance to unetched float glass. In particular, residual surface stress, Hertzian fracture resistance, and fractographic characteristics are determined for each glass type. The surface tensile strength of the glasses is also evaluated by means of destructive flexural tests before and after artificial ageing. The flexural tests reveal that the ridge areas of the acid-etched surface patterns are more susceptible to the formation of digs and deeper surface flaws and are therefore weaker than both the valley areas of the acid-etched pattern and the surface of the unetched float glass. Correspondingly, the acid-etched glass with the highest proportion of ridges was more susceptible to ageing-induced flaws and had the lowest surface tensile strength. The contact (Hertzian) fracture resistance was also significantly affected by the presence of a surface pattern in the acid-etched glass; specifically, the lowest contact strengths were recorded for hard body contact on the ridges of the pattern. The fracture phenomena and new data presented in this paper provide useful insights on the long-term performance of etched patterned glass. The findings can provide the bases for real-world design decisions and for glass forensics.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care. Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Architectural Technolog

Abstract of: Repair of soda–lime–silica glass

Glass strength is very sensitive to damage accumulation during its service life. Repair methods for glass have been proposed over the last decades to volumetrically fill or remove existing flaws from the surface of glass. However, the lack of information on the strength recovery attributable to glass repair methods restrict their use to low consequence class applications in buildings thereby making replacement of damaged installed glass the only safe and practical solution when dealing with damaged glass. Repair methods involving volumetric filling of visible flaws with resins, removal of visible flaws with polishing and chemical repair with acid treatment of visible flaws are undertaken in this study to investigate the strength recovery in 60 artificially aged annealed glass specimens. It is found that the polishing provides the most promising strength recovery results showing a 132 and a 40% increase in design and mean strength whilst the acid treatment provides the worst performance. Polishing repairs are further investigated in this study to determine their efficacy in strength recovery after environmental ageing (exposure to UV, humidity and freeze-thaw cycles)