The present paper describes a method for non-destructive testing of the glass strength. Square 10 × 10 cm2 samples of annealed float glass was inflicted with a controlled defect in the centre of the atmospheric side using Vickers microindentation-induced cracking with a force of 2 N, 5 N and 10 N and compared to an un-indented reference. The samples were non-destructively tested using a nonlinear acoustic wave method resulting in defect values. The average of the defect values was found to linearly correlate to the indentation force in a log–log relationship. The samples were subsequently tested in a ring-on-ring setup that allows for an equibiaxial stress state. The indentation-induced cracking gave practically realistic strength values in the range of 45 to 110 MPa. The individual sample values for failure stress as a function of normalized defect value show linear trends with approximately half of the data within 95% confidence limit. In summary, this study provides an initial proof-of-concept for a non-destructive testing of the strength of glass.

Glass is a unique but unfortunately brittle material whose strength is primarily limited by the presenceof cracks on the surface [1]. The strength of glass is limited by the fact that very high stresses arise atthe crack tips when subjected to tensile load. In principle, without the presence of surface cracks, glasswould have a strength far exceeding many other structural materials, e.g., steel. The size and thedistribution of surface cracks vary greatly, which results in the strength of glass exhibit a great variationand thus requires that large safety margins must be applied for glass in practical applications, e.g., whenused as a load bearing building material.Today, there are no methods to determine the strength of flat glass non-destructively. Instead, thestrength is determined by different experimental methods requiring >10 samples for sufficient statistics.This procedure requires both lots of glassy materials and time. The future aim is to investigate if the useof nonlinear acoustic waves (NAW) could be an alternative for developing a standardized designstrength value. Developing a non-destructive inspection method for determining the glass strength is ascientific breakthrough that will have a great industrial impact for the sustainable development of glassmanufacturing.With the use of NAW it is possible to detect and quantify the defects in materials [2,3]. The nonlinearwaves are transmitted through the object and the nonlinear effects, caused by the defects in thematerial, corresponds to the level of damage in the material. This work present result from samplescontaining relatively precise defects. The defects were created using a microindenter with a sufficientload to cause indentation induced cracking in the glass. The indentations were created using a Vickersdiamond tip in the middle of commercial 4 mm float glass samples of the dimensions 10x10 cm2. Theapplied loads were 0.5N, 1N, 2N, 5N and 10N. The “damage value” of the sample series was thenquantified using the NAW technique. The fracture strength of the samples was correlated destructivelyusing a conventional ring-on-ring setup.The results show that there is a clear correlation between the indenter load, the damage value from theNAW inspection and the fracture strength. We noted that the standard deviation for the ring-on-ringtests for the 1N, 2N, 5N and 10N was low while the 0.5N and the reference samples presented a highstandard deviation. A possible explanation for this observation is that for 0.5N not all indents give radialcracks but in some cases the indentation produces only plastic deformation. The main conclusion fromthe research is that is possible to detect realistically large defects in glass using the non-destructive NAWmethod and these defects cannot be seen with the naked eye. Moreover, the results can be directlycorrelated with the strength of glass [4].

References[1] Veer, F.A. and Y.M. Rodichev, The structural strength of glass: hidden damage. Strength of Materials, 2011.43(3): p. 302-315. DOI: 10.1007/s11223-011-9298-5.[2] Persson, K., K. Haller, S. Karlsson, and M. Kozłowski, Non-destructive testing of the strength of glass by a nonlinearultrasonic method. Challenging Glass Conference Proceedings, 2020. 7. DOI: 10.7480/cgc.7.4498.[3] Haller, K., Doctoral Thesis: Acoustical measurements of material nonlinearity and nonequilibrium recovery.2008: Department of Mechanical Engineering, Blekinge Institute of Technology.[4] Karlsson, S., L. Grund Bäck, S. Andersson, K. Haller, M. Kozłowski, and K. Persson, Strength classification of flatglass for better quality – validation of method by well-defined surface defects and strength testing, in ÅForskReport,19-479. 2021: http://dx.doi.org/10.13140/RG.2.2.32992.40962.

The stone wool manufacturer Paroc (a part of Owens Corning) considers blending in additional waste materials into the production to obtain a more sustainable product. By using waste material that otherwise would go to the landfill also less virgin raw material (volcanic rock) would be used. The waste material contains manganese (Mn) which may potentially affect the iron (Fe) redox equilibria that greatly affects the melt and product properties. Paroc therefor wish to understand and simulate the effect of blending in additional waste material in their product.

The current project was a collaborative project between the involved partners: RISE Glass, Lund University and Acoustic Agree. It is funded by ÅForsk (Grant No. 19-479). The project is a follow-up project from a Smart Housing Småland (Grant No. 2016-04218) pre-study where we used a nonlinear acoustic wave (NAW) to determine the damage value in float glass simultaneously with four-point bending tests. Glass is a brittle material whose strength is primarily determined by its surface characteristics i.e., the presence of flaws, defects or cracks on the surface. The strength of glass is greatly limited by stress-concentrations at the crack tips generating very high stresses when the glass is under load. The size and distribution of surface defects vary greatly, this gives a great variation of strength of glasses so that conventionally very large safety measures must be employed for glass products. If these defects and/or cracks could be detected in a non-destructive way, it would be beneficial for glass manufacturers as well as final building users. Nonlinear acoustic wave (NAW) techniques can be used to detect defects in materials. In these methods, acoustic waves are transmitted through an object and nonlinear effects, caused by the defects in the material, is analysed from the signal obtained at the receiver. The aim of the current project was to establish a calibration and a clear correlation between nonlinear acoustic wave measurements and the ultimate strength of annealed glass samples with controlled defects. Controlled defects were made as indentation imprints with a microindenter, equipped with a Vickers diamond head, in the middle of float glass samples with the dimensions 4×100×100 mm3. The applied loads were 0.5N, 1N, 2N, 5N and 10N. The indents were inspected with a microscope in order to see the cracks and the depth of the indents were also determined. The formed defects (cracks) were detected with NAW technique. Analysing the waves after propagating in the glass the nonlinear content in the wave was analysed. Due to the objects damage, the propagated wave distorts proportionally to the damage. After the NAW-inspection the strength of the glass samples were tested with ring-on-ring tests. Using the results from NAW-inspection, a clear correlation between the nonlinear response and the indenter load was found. There was also an obvious correlation between the failure load on the ring-on-ring-tests and the indenter load. The standard deviation for the ring-on-ring-tests for the 1N, 2N, 5N and 10 N was low but for the 0.5 N load was very high. A possible explanation is that the indenter imprint in most of the cases only gave rise to plastic deformation and in some samples, cracks were formed too. There were visible cracks for all the higher indenter loads and thus a lower scatter of the results. The main conclusion of the project is that it is possible to detect small cracks, which cannot be seen with the naked eye, with NAW technique and it can be directly correlated to the strength of the glass.

For the solar energy industry to increase its competitiveness, there is a global drive to lower the cost of solar-generated electricity. Photovoltaic (PV) module assembly is material-demanding, and the cover glass constitutes a significant proportion of the cost. Currently, 3-mm-thick glass is the predominant cover material for PV modules, accounting for 10%–25% of the total cost. Here, we review the state-of-the-art of cover glasses for PV modules and present our recent results for improvement of the glass. These improvements were demonstrated in terms of mechanical, chemical and optical properties by optimizing the glass composition, including addition of novel dopants, to produce cover glasses that can provide (i) enhanced UV protection of polymeric PV module components, potentially increasing module service lifetimes; (ii) re-emission of a proportion of the absorbed UV photon energy as visible photons capable of being absorbed by the solar cells, thereby increasing PV module efficiencies and (iii) successful laboratory-scale demonstration of proof of concept, with increases of 1%–6% in Isc and 1%–8% in Ipm. Improvements in both chemical and crack resistance of the cover glass were also achieved through modest chemical reformulation, highlighting what may be achievable within existing manufacturing technology constraints. © 2020 The Authors.

In this article, we investigate the correlation of selected physical properties with structural changes in quaternary mixed modifier alkali/alkaline earth oxide silicate glass  systems,  focusing  either  on  the  mixed  alkali  effect  [(20−x)Na2O–xK2O– 10CaO–70SiO2 (x = 0, 5, 10, 15, 20)] or on the mixed alkaline earth effect [20Na2O– (10−y)CaO–yBaO–70SiO2 (y = 0, 5, 10)]. A maximum microhardness and packing density, as well as a minimum glass transition temperature were observed for mixed alkali glasses. The mixed alkaline earth glasses do not exhibit any clear extrema in any  of  the  properties  studied.  The  hardness  and  glass  transition  temperature  de-creases, while the density and molar volume increases with increasing BaO content. Raman spectroscopy showed an increase in the Q3 group compared to the Q2 and Q4 groups as the high field strength ions Na+ or Ca2+ are substituted by their low field strength analogs K+  or Ba2+. In the mixed alkali series, the high field strength ion Na+, seems to push the low field strength ion K+ into lower energy sites when present simultaneously, while such an effect is not apparent for the mixed alkaline earth glasses, where the far IR spectra of mixed glasses are equivalent to the weighted averages of the pure glasses.

In the current paper we present a concept combining metal organic chemical vapor deposition with thermal strengthening process of flat glass. As the flat glass is heated to be thermally strengthened, which takes up to 20 minutes, there is an opportunity for performing a surface modification. We describe the application of transparent and amorphous Al₂O₃ thin films during the thermal strengthening process. Al₂O₃ was chosen due to the following desirable properties: increased surface mechanical properties and increased chemical durability, the latter has not been investigated in the current paper. The residual surface compressive stresses after performed strengthening of the coated glasses were quantified to be in the range of 80–110 MPa. The Al₂O₃ content in the surface was measured using the Surface Ablation Cell employed with Inductively Coupled Plasma Atomic Emission Spectroscopy and found to be at least doubled at the surface and having an increased Al₂O₃ content at least 0.5 μm underneath the glass surface. During the surface reaction, sodium is migrating to the surface giving a hazy salt layer on the glass which can easily be washed off with water. The applied coatings are transparent and provide increased surface hardness and crack resistance at low indentation loads. At higher indentation loads the interaction volume is larger and displays the same effect on the surface mechanical properties as for thermally strengthened glass. The contact angle with water compared to annealed float glass is significantly increased from 5° to 45° due to the different surface chemistry and surface topography.

The local structures of Cu(I) and Cu(II) in (20-x)Na₂O-xK₂O-10CaO-70SiO₂ glasses with a copper content of 0.4 mol% have been investigated by Cu K-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES). Complementary data for Cu(II) was derived using UV–Vis-NIR spectroscopy. Indication for mainly linear two-fold coordination of the Cu⁺ ion was found by both EXAFS and XANES, but other coordination between Cu⁺ and O^2– cannot be excluded. The Cu(I)-O bond lengths were found to be 1.79–1.83 ± 0.02 Å. EXAFS results showed that Cu(II) was mostly present in a Jahn-Teller distorted environment with oxygen, an octahedron with four shorter Cu(II)-O bonds and two longer in axial position. The equatorial bond lengths were found to be 1.89–1.91 ± 0.02 Å and the axial 2.20–2.24 ± 0.02 Å with no effect of the Jahn-Teller distortion of the octahedron when the glass composition was altered.

I vilken omfattning kan ökad återvinning av glas leda till minskad energianvändningoch minskade koldioxidutsläpp vid glasproduktion, minskad miljöpåverkan genomdeponi samt på lång sikt möjligen minskad brytning av icke-förnyelsebar naturråvara?