Stress relaxation behavior of polymer glasses in uniaxial extension

Ductile polymers can undergo large tensile extension upon mechanical precondition (i.e. milling and melt-stretching). In the post-yield regime the tensile stress can still grow with the extension partially because of the elastic energy buildup as the chain tension grows from the stretching of the chain network [1]. To learn more about the nature of the mechanical stress, we carried out a series of stress relaxation experiments of both milled and melt-stretched PC. We found rescaling behavior, i.e., the stress relaxation is faster from a faster tensile extension by exactly the same amount. In other words, for an extension made at a cross-head speed of V$_{1}$, the stress relaxation occurs on a time scale of t$_{1}$. Then the stress relaxation from an extension produced at V$_{2}$ \textgreater V$_{1}$ occurs on a time scale of t$_{1}$(V$_{1}$/V$_{2})$. This is true for a range of nearly five orders of magnitude in V. We have studied this surprising scaling law as a function of the precondition. \\[4pt] [1] ``Strain hardening in homogeneous deformation of polymer glasses,'' P. P. Lin \textit{ et al.}, Phys. Rev. Lett., under review.