Modelling and Simulation of Self-healing Thermosetting Polymers

Julia Mergheim

Chair of Applied Mechanics, FAU Erlangen-Nürnberg

Tuesday, 19. January 2016, 17:15
WW8, Room 2.018-2, Dr.-Mack-Str. 77, Fürth

The present contribution introduces a phenomenological model for self-healing polymers. Self-healing polymers are a promising class of materials which mimic nature by its capability to autonomously heal micro-cracks. The self-healing process in thermosetting polymers is accomplished by integrating microcapsules filled with a healing agent and a dispersed catalyst into the material. Propagating microcracks break the capsules which release the healing agent into the microcracks where it polymerizes with the catalyst, closes the cracks and ‘heals’ the material.
The present modelling approach is attached to the macroscopic scale and the microscopic effects of crack propagation and healing are described by means of continuous damage and healing variables. The basic concept of continuum damage mechanics is that microstructural defects are represented by means of a continuous damage variable. The damage variable evolves when a certain failure limit is exceeded and describes the degradation of the material. In isotropic-elastic damage models a scalar damage variable is defined, that reduces the elastic properties, ranging from 0 (undamaged state) to 1 (fully damaged state). Since healing of the material, i.e. the recovery of material stiffness or integrity at a material point, is directly related to the curing process of the healing agent in microcracks, the evolution of the healing variable is based the evolution of the mechanical properties during the process of cure. In contrast to existing damage-healing models, the healing variable is not merely introduced as an ‘opposite variable’ to the damage variable, but it defines the amount of newly emerging material (due to polymerization), equipped with its own strain energy density. This strain energy density takes into account that the curing process of the healing material only increases the stiffness, but not its stress or strain energy unless the strain state is changed.
The model is implemented into a finite element code and its capabilities are studied by means of numerical experiments.