This paper analyzes the viscoelastic phase of the forming process of glass fibers when the viscous and elastic material constants are variable with a coordinate normal to the fiber axis. This condition may be due to either a temperature gradient or a material inhomogeniety as in clad fibers. One employs the equations of classical viscoelasticity and obtains an approximate solution for the fiber stress. The analysis bears out the findings of previous investigators that the force used to draw such fibers from hot preforms or melts produces a viscoelastic stress that has large gradients directed transverse to the fiber axis. As the fiber cools, a strain proportional to the draw force is frozen into the fiber which contributes to the residual fiber stress. The merits of a solution for the frozen stress used by previous investigators is discussed. It is shown that an increase in the draw force can either weaken or strengthen a fiber depending on the attendant physical conditions, and one discusses how this factor may be exploited. The force induced stress is determined theoretically for two specific fibers. An experimental determination of the force-induced stress is given which is in substantial agreement with the theory.

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