Q.3 The following expression states the definition of viscosity n for a large range of viscous materials \eta=\frac{\sigma}{d \varepsilon / d t} where o is the tensile stress and dɛ/dt

the strain rate. Assume a 4 mm diameter rod of soda-lime glass (90 mm long) which is loaded with a tensile force of 1 N along its axis. If its deformation is to be less than 1 mm over a week's time, using the Figure below, determine the maximum temperature to which the specimen may be heated. (4 marks)