PSI - Issue 71

A.B. Penurkar et al. / Procedia Structural Integrity 71 (2025) 150–157

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components. Float glass is generally brittle, which can be strengthened by treatments like tempering, making it useful in a variety of applications. The determination of strength of float glass is necessary to accurately design any components under different loading conditions. However, determining the float glass strength necessitates a mix of rigorous testing procedures and a thorough understanding of the variables that impact its performance. Surface defects, treatment procedures, and lamination all have a substantial impact on the strength of the material (Wiederhorn et al. (2015)). While glass is highly resistant to compressive stress, it is substantially less resistant to tensile stress due to prevalent surface flaws. These flaws also account for the significant distribution in experimental tensile strength measurements. The distribution in strength of float glass generally follows a Weibull distribution (Weibull (1939)) that is based on the weakest link principle. The tensile strength is a critical parameter determining the bearing capacity of most glass structures. However, determination of the tensile properties using standard specimen is very difficult. For evaluation of strength of glass, three-point bend tests, four-point bend tests or Coaxial double ring test (EN 1288-2:2001), indentation tests using different indenters may be used as shown in Fig. 1.

Cylindrical indenter Float glass

Compression plates

Float glass

Float glass

Compression plates

TPB attachment (c)

(b)

(a)

Fig. 1: Schematic of test setup for determination of strength of float glass (a) cylindrical indentation (b) Compression (c) three-point bend test. Veer et al. (2005, 2007, 2009) utilized a four-point bend test setup to assess the strength of annealed float glass and compare it with heat-strengthened and tempered glass. Their findings indicated that strength is influenced by edge quality, the orientation of the glass in relation to the load, aspect ratio, and pre-stress levels. Similarly, Bouska et al. (2014) performed four-point bend tests on float glass of varying thicknesses to establish characteristic flexural strength values. Penurkar et al. (2023) conducted three-point bend tests on different thicknesses of annealed float glass, observing that the Weibull model most accurately represented the experimental variability in bending strength, with a noted strength reduction as thickness increased. Various indentation tests were performed on float glass to evaluate its load-carrying capacity. Hertz (1896) noted that pressing a hard spherical indenter into a brittle material creates a cone-shaped crack. Johnson et al. (1973) pointed out that Hertz's theory applies only to elastically similar materials; in dissimilar materials, friction causes relative sliding, shifting the maximum tensile stress away from the contact area. Spence (1975) developed solutions for dissimilar elastic contact under finite friction, showing that a stick-slip contour forms independently of loading and contact profile. This was later expanded by Storakers and Elaguine (2005). Marimuthu et al. (2017) used spherical indenters to assess brittle fracture toughness with the X-FEM technique, enhancing Roesler’s method while considering the friction, Poisson’s ratio and cone -crack kinking effects. Geandier et al. (2003) performed a Hertzian indentation test to evaluate the fracture toughness of float glass by analyzing the crack that forms on the surface and the cone crack that develops beneath it. Antoniou et al. (2006) used a cylindrical indenter to study the in-situ deformation behavior of metallic glass, finding that the development of shear bands beneath the indenter closely aligns with the solutions derived from slip line analysis. Nomenclature β Shape parameter S x Tensile stresses during indentation θ Weibull scale parameter TPB Three point bend b Width of the specimen PDF Probability density function P Maximum load required for the glass to fracture CDF Cumulative density function t Specimen thickness l length of the specimen The strength of glass is also affected by surface defects (such as cracks), edge defects, the uniformity of chemical composition, loading duration, manufacturing techniques including annealing, environmental conditions, and sample geometry (Min'ko et al., 2013). It is evident that discrepancies in edge finish among specimens complicate the comparison of results from different test series (Bukieda et al., 2020). Additionally, failures can originate from processed edges, air or Sn-side surfaces, or from internal defects, which are confirmed to exist by Molnár and Bojtár