Experimental evaluation of scatter in fracture stress of silicate glass and its thickness dependence

Abstract

Glass is widely used in various structural application, where a transparent, durable, and stiff material is needed. Although glass is primarily not a load-bearing member in applications, however, even in common usage of glass as windows panes it is exposed to loads, such as wind loads, thermal and other mechanical loads, and may also be exposed to vibratory, impact and blast loading. However, these materials are brittle in nature and cannot withstand thermal loads beyond a certain limit. Moreover, there is a substantial scatter in their fracture stress and the median values of fracture stress is dependent upon the thickness of the specimen used in the tests. In order to study the effect of specimen thickness on fracture stress and its scatter, several experiments have been conducted on different thickness of glass material. Three point bend test was conducted on various glass specimens of 4 mm and 8 mm thickness to ascertain the scatter in the fracture strength of the glass specimen. A lot of scatter in the fracture strength of the glass specimen was observed which is attributed to the presence of micro crack on the surface of the glass specimen. Scatter in fracture stress is higher for 8 mm thickness of glass as compared to 4 mm glass specimen. It was seen that the cumulative experiment probability of fracture strength of glass follows a Weibull model. It was seen that the fracture strength of the glass reduces from 46 MPa to 40 MPa with the increase in thickness from 4 mm to 8 mm respectively indicating the decrease in fracture toughness with increasing thickness.