Inspired by the innate ability of natural organisms to repair themselves, the main challenge of this research was to design and fabricate a porous hollow thermoplastic vascular network (thermoplastic polyurethane), though additive manufacture/3D printing, with the long term potential for repeated self-healing of fibre reinforced polymer (FRP) composites
Grand challenges in the design and manufacture of vascular self-healing
Development of 3D printed vascular networks for repeated self-healing
The susceptibility of fibre-reinforced composites to brittle fracture has led to the emergence of self- healing materials. This functionality has been demonstrated in bulk polymers and fibre-reinforced composites, most recently through the addition of vascular networks into the host material. How- ever, fracture of the vascular network is required in order to allow the healing agents to enter the damage site, terminating its ability to transport fluid and thus limiting any further healing cycles.
The work presented in this thesis describes a new approach to vascularised self-healing through the development of a porous, thermoplastic vascular network fabricated via additive manufacture that is embedded in a thermoset matrix. This concept exploits the adhesive failure that occurs between the thermoplastic and thermoset materials on arrival of a propagating crack, exposing the pores and allowing the healing agents to flow into the damage site, without fracturing the network. By maintaining their structural integrity, the vascules are able to retain their function of transporting healing agents, enabling the possibility of multiple healing cycles.
A computational model for the flow of resin in self-healing composites
To explore the flow characteristics of healing agent leaving a vascular network and infusing a damage site within a fibre reinforced polymer composite, a numerical model of healing agentflow from an orifice has been developed using smoothed particle hydrodynamics. As an initial validation the discharge coefficient for low Reynolds number flow from a cylindrical tank is calculated numerically, using two different viscosity formulations, and compared to existing experimental data.
Results of this comparison are very favourable; the model is able to reproduce experimental results for the discharge coefficient in the high Reynolds number limit, together with the power-law behaviour for low Reynolds numbers. Results are also presented for a representative delamination geometry showing healing fluid behaviour and fraction filled inside the delamination for a variety of fluid viscosities.
This work provides the foundations for the vascular self-healing community in calculating not only the flow rate through the network, but also, by simulating a representative damage site, the final location of the healing fluid within the damage site in order to assess the improvement in local and global mechanical properties and thus healing efficiency.