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

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

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

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 snap-through 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

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)

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

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