Continuum mechanical description of an extrinsic and autonomous self-healing material based on the theory of porous media

Abstract

Polymers and polymeric composites are used in many engineering applications, but these materials can spontaneously lose structural integrity as a result of microdamage caused by stress peaks during service. This internal microdamage is hard to detect and nearly impossible to repair. To extend the lifetime of such materials and save maintenance costs, self-healing mechanisms can be applied that are able to repair internal microdamage during the usual service load. This can be realized, for example, by incorporating microcapsules filled with monomer and dispersed catalysts into the polymeric matrix material. If a crack occurs, the monomer flows into the crack, reacts with the catalysts, and closes the crack. This contribution focuses on the development of a thermodynamically consistent constitutive model that is able to describe the damage and healing behavior of a microcapsule-based self-healing material. The material under investigation is an epoxy matrix with microencapsulated dicyclopentadiene healing agents and dispersed Grubbs’ catalysts. The simulation of such a multiphase material is numerically very expensive if the microstructure is to be completely resolved. To overcome this, a homogenization technique can be applied to decrease the computational costs of the simulation. Here, the theoretical framework is based on the theory of porous media, which is a macroscopic continuum mechanical homogenization approach. The developed five-phase model consists of solid matrix material with dispersed catalysts, liquid healing agents, solidified healed material, and gas phase. A discontinuous damage model is used for the description of the damage behavior, and healing is simulated by a phase transition between the liquid-like healing agents and the solidified healed material. Applicability of the developed model is shown by means of numerical simulations of the global damage and healing behavior of a tapered double cantilever beam, as well as simulations of the flow behavior of the healing agents at the microscale.