THERMAL SHOCK RESISTANCE OF A SODA LIME GLASS

We studied the thermal shock of a three millimeters thickness soda lime glass using the hot-cold thermal shock technique. The cooling was made by ambient air jet on previously warmed samples. The heat transfer coefficient was about 600 W/degrees C.m(2) (Biot number beta = 0.3). The thermal shock duration was fixed at 6 seconds. The hot temperature was taken between 100 degrees C and 550 degrees C while the cold temperature of the air flux was kept constant at 20 degrees C. The acoustic emission technique was used for determining the failure time and the critical temperature difference (Delta TC). By referring to experimental results, thermal shock modelling computations are conducted. Our aim is especially focused on the fracture initiation moments during the cooling process and on the crack initiation sites. The used modeling is based on the local approach of the thermal shock during the experimental data treatment. For each test, the temperature profile and the transient stress state through the samples thickness are determined. By applying the linear superposition property of the stress intensity factors, evolution of the stress intensity factor KI in function of the pre-existing natural flaws in the glass surface is established. The size of the critical flaw is determined by the linear fracture mechanics laws. Computation results confirm the experimental values of the critical difference temperature obtained that is the source of the glass degradation.