For many viscous materials, the viscosity $\eta$ may be defined in terms of the expression
$$
\eta=\frac{\sigma}{d \epsilon / d t}
$$
where $\sigma$ and $d \epsilon / d t$ are, respectively, the tensile stress and the strain rate. A cylindrical specimen of a borosilicate glass of diameter 4 mm ( 0.16 in.$)$ and length 125 mm ( 4.9 in .) is subjected to a tensile force of $2 \mathrm{~N}\left(0.45 \mathrm{lb}_f\right)$ along its axis. If its deformation is to be less than $2.5 \mathrm{~mm}(0.10 \mathrm{in}$.$) over a week's time,$ using Figure 13.7, determine the maximum temperature to which the specimen may be heated.
activation energy between temperatures of 900 and $1600^{\circ} \mathrm{C}$.
14 For many viscous materials, the viscosity $\eta$ may be defined in terms of the expression
$$
\eta=\frac{\sigma}{d \epsilon / d t}
$$
where $\sigma$ and $d \epsilon / d t$ are, respectively, the tensile stress and the strain rate. A cylindrical specimen of a borosilicate glass of diameter 4 mm ( 0.16 in.$)$ and length 125 mm ( 4.9 in .) is subjected to a tensile force of $2 \mathrm{~N}\left(0.45 \mathrm{lb}_f\right)$ along its axis. If its deformation is to be less than $2.5 \mathrm{~mm}(0.10 \mathrm{in}$.$) over a week's time,$ using Figure 13.7, determine the maximum temperature to which the specimen may be heated.