PSI - Issue 60

A.B. Penurkar et al. / Procedia Structural Integrity 60 (2024) 355–363 A. B. Penurkar/ StructuralIntegrity Procedia 00 (2023) 000 – 000

356

2

1. Introduction As a transparent material, glass is extensively used despite its inherent brittle nature. The role of glass in buildings is moving forward from non-structural elements, such as windows and facades, to load-bearing ones, e.g. beams, staircases and balconies. In an automobile application, the rear and front windows are an integral part responsible for the total stiffness and it also resists the considerable forces generated by the air pressure at high-speed driving. Further, glass has found extensive use in day-to-day life as screen of mobiles, computer screen and various other electronic gadgets. Glass being a brittle material behaves as an elastic solid in fracture. Fracture of glass initiates at the location of a crack that first opens due to the stresses acting on it. This is the critical crack. Due to the flaws distribution, the critical crack is not necessarily located at the point of maximum tensile stress. Determination of the reliable value of the glass strength is a challenge. The tensile strength cannot easily be determined, since glass in direct tensile test will break at the grip. In certain cases, bending test results provide scattered values of the bending strength with a spread of 30 to 50% of the mean strength. Their distribution can be adequately described using the Weibull statistic approach leading to a probabilistic strength for the glass used (Kingson et al. 2000 and Keshavan et al. 1980). Results of bending experiments by various authors suggest that the processing and specimen size influence the results and suggest systematic data deviation from the Weibull statistic distribution (Veer et al. 2006, 2007, 2008). A likely explanation for this is that the usual processing of float glass results in multiple types of defects which provides a multi-linear Weibull plot (Veer et al. 2009). In order to study the effect of glass specimen thickness on its fracture strength and its scatter, several three point bend tests (Fig. 1) have been conducted on different thickness (4 mm and 8 mm) of glass material. Probability of fracture of glass specimen was evaluated using two parameter Weibull model.

Fig. 1: Glass specimen subjected to 3 point bend test.

Nomenclature β

Weibull exponent or shape parameter

P

Maximum load required for the glass to fracture

θ

Weibull scale parameter Equivalent fracture stress Width of the specimen

s

Span of the attachment Thickness of the specimen length of the specimen

σ f

t l

b

2. Design, fabrication of the three point bend specimen and description of experimental procedure For the bend tests, three point bend (TPB) specimen has been obtained from 300x300 mm plate (Fig. 2(a)) of different thickness. Chemical composition of glass material is obtained through powdered glass using EDXRF and ICPOES techniques. Final composition used for fabrication of specimen is shown in Table 1. Three point bend (TPB) specimen have been designed for evaluating the fracture stress of glass material. This type of specimen was chosen as it is easy to perform bend test on glass material. Performing standard tensile test to obtain the scatter in glass properties is difficult to carry out. Thickness of the glass specimen is around 4 mm and 8 mm. Length of the specimen is 65 mm whereas width is taken as 20 mm as shown in Fig. 2(b).