Thermal stress fracture of solar control window panes caused by shading of incident radiation

The phenomenon of thermal stress fracture in solar control window panes in high-rise buildings due to shading of incident radiation is investigated in this paper. An experimental method, in which a bank of infra-red lamps was used as the simulated solar source, was developed to measure thermal strains and hence thermal stresses built up at the cool edges of the glass pane which was glazed in a 480 mm square aluminium frame. Horizontal and diagonal shadows both increased the thermal stresses by approximately 10% when compared with the unshaded glass panes. It is shown that fracture mechanics can be used to analyse and predict fracture stresses once the mirror radius and the fracture toughness of the glass pane are known. These predictions agree very well with experimental measurements. Finally, a new glazing technique using a thermal conducting sealant in the rebate is suggested to minimise the incidence and risk of thermal stress fracture. This is achieved by raising the temperature of the cool edges and thus lowering the differential heating effect. Preliminary experiments show that the method is promising.