Material response and reversible cracks in viscoelastic polymers

Abstract Deformation processes in viscoelastic polymers are examined in terms of an energy balance involving work, strain energy, viscous dissipation and damage. The concepts of time dependent damage and reversible cracks are presented. The latter, while giving rise to novel mechanical behavior in viscoelastic materials, are important considerations in temperature dependent recovery phenomena of deformed polymers. Constitutive equations are derived for systems with reversible cracks analogous to Maxwell and Kelvin viscoelasticity models. Retractive forces arising from crack closure occur by conversion of surface energies to strain energy and subsequently to mechanical work. This effect is investigated during contraction of hard‐elastic polypropylene fibers under constant load at different temperatures.