The strength of aged glass

Glass is known for its excellent durability, but the strength of glass is very sensitive to the characteristics of its surface, which is known to accumulate damage during its service life. There is however, a lack of strength data on weathered or aged glass, particularly on thermally or chemically treated glass. In this study a carefully calibrated sand trickling test is used to produce surface damage equivalent to erosive action of 20 years of natural weathering on different types of glass: soda-lime-silica annealed, soda-lime-silica fully toughened and aluminosilicate chemically toughened. The soda-lime-silica glass specimens are tested destructively in their as-received and artificially aged form in a conventional coaxial double ring set-up, while the alumino-silicate chemically toughened specimens are tested in an improved coaxial double ring set-up. Fractography is subsequently used to identify and measure the critical flaw size on each specimen. The strength data are analysed statistically and the design strengths for each glass type are obtained. It is found that all glasses suffer a loss in strength after artificial ageing, with fully toughened glass providing the best post-aged performance. It was also found that the degree of toughening in the glass affects the erosion resistance, with chemically toughened glass outperforming the other glasses in this respect.EPSRC, Eckersley o' Callaghan, Onassis Foundatio

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

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)

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

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

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

Artificial ageing of glass with sand abrasion

The strength of glass is governed by the condition of its surface which deteriorates progressively as surface flaws accumulate on exposure to weathering action during its service life. Therefore, knowledge of the strength of naturally aged glass is crucial in order to ensure its safe use in load-bearing applications. Artificial ageing tests can be very useful in this regard, but they have traditionally focused on degradation in light transmittance properties rather than the strength of glass. Experimental testing has been undertaken in this study to investigate the effectiveness of a falling abrasive method for the artificial ageing of glass. Abrasive medium is allowed to fall freely on monolithic glass and induce a random surface flaw population. 390 annealed glass specimens grouped in 26 series were artificially aged using different combinations of ageing parameters. The specimens were subsequently subjected to destructive and non-destructive testing to determine the influence of each ageing parameter and to establish a combination that produces strength characteristics similar to those of naturally aged glass. Existing artificial ageing recommendations were found to significantly overestimate design strengths by up to 253% at low probabilities of failure, Pf = 0.008 and are therefore, deemed unsafe. However, it was found that the falling abrasive method using a different combination of ageing parameters provides good correlation to the strength of naturally aged glass.The authors gratefully acknowledge financial and technical support from Eckersley O’Callaghan, and financial support from the Engineering and Physical Sciences Research CouncilUK (EPSRC) and Onassis Foundation

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

Additive manufacturing of glass with laser powder bed fusion

Its transparency, esthetic appeal, chemical inertness, and electrical resistivity make glass an excellent candidate for small‐ and large‐scale applications in the chemical, electronics, automotive, aerospace, and architectural industries. Additive manufacturing of glass has the potential to open new possibilities in design and reduce costs associated with manufacturing complex customized glass structures that are difficult to shape with traditional casting or subtractive methods. However, despite the significant progress in the additive manufacturing of metals, polymers, and ceramics, limited research has been undertaken on additive manufacturing of glass. In this study, a laser powder bed fusion method was developed for soda lime silica glass powder feedstock. Optimization of laser processing parameters was undertaken to define the processing window for creating three‐dimensional multilayer structures. These findings enable the formation of complex glass structures with micro‐ or macroscale resolution. Our study supports laser powder bed fusion as a promising method for the additive manufacturing of glass and may guide the formation of a new generation of glass structures for a wide range of applications

Artificial ageing of glass with sand abrasion

The strength of glass is governed by the condition of its surface which deteriorates progressively as surface flaws accumulate on exposure to weathering action during its service life. Therefore, knowledge of the strength of naturally aged glass is crucial in order to ensure its safe use in load-bearing applications. Artificial ageing tests can be very useful in this regard, but they have traditionally focused on degradation in light transmittance properties rather than the strength of glass. Experimental testing has been undertaken in this study to investigate the effectiveness of a falling abrasive method for the artificial ageing of glass. Abrasive medium is allowed to fall freely on monolithic glass and induce a random surface flaw population. 390 annealed glass specimens grouped in 26 series were artificially aged using different combinations of ageing parameters. The specimens were subsequently subjected to destructive and non-destructive testing to determine the influence of each ageing parameter and to establish a combination that produces strength characteristics similar to those of naturally aged glass. Existing artificial ageing recommendations were found to significantly overestimate design strengths by up to 253% at low probabilities of failure, Pf = 0.008 and are therefore, deemed unsafe. However, it was found that the falling abrasive method using a different combination of ageing parameters provides good correlation to the strength of naturally aged glass