Question

How do you understand time dependent properties of polymers. Show a graph stress vs strain behavior of typical polymers and typical steel.

Answer 1

All materials are time-dependent, i.e., they vary with time in response to an applied load or deformation. This phenomenon is simply a consequence of the Second Law of Thermodynamics according to which a portion of the imparted energy of deformation is always dissipated as heat by viscous forces even while the rest may be stored elastically.he dissipation is neither instantaneous nor infinitely slow and is therefore a rate process. It is this that renders the physical properties time-dependent

Time-dependent behavior may be virtually purely elastic to virtually purely viscous or it may be anything in-between. The behavior may be expressed suitably by the Deborah number 'De' the ratio of the material time scale '?_mat' on which molecular rearrangements take place, to the experimental time scale 't_exp'.

purely elastic material, De=? ;   purely viscous one De=0 and for viscoelastic material De=1