The Mullins Effect:  Constitutive Modeling and Experiments

Professor Millard F. Beatty
Department of Engineering Mechanics
University of Nebraska - Lincoln
Lincoln, Nebraska   68588-0526

Date: Tuesday, February 27, 2001
Time: 3:30 p.m.
Place: W128 Nebraska Hall


Common experience teaches that prestretching a balloon several times prior to its primary inflation noticeably reduces the pressure required to inflate it. This preconditioning, or stress-softening, phenomenon of rubberlike materials is commonly known as the Mullins effect. A phenomenological theory that characterizes stress-softening in isotropic, incompressible elastomers is presented. Some general results, including the predicted effect in balloon inflation, are described analytically. A new phenomenological stress-softening (or damage) function is introduced. It is shown how the stress-softening parameter may be found from experiment. The parameter is determined for some data due to Johnson. Based on this experimental value, theoretical results are then compared with the response of a simple neo-Hookean virgin material model in uniaxial tension. Results for stress-softening of two non-Gaussian molecular network models in uniaxial extension are compared with the experimental data provided by Johnson and Beatty and by Mullins and Tobin for the stress-softened material response of certain elastomers.