Simulation Study On Self-healing Mechanism Of CFRPs Aerospace Composites

Compared with traditional metallic materials,carbon-fiber reinforced polymer(CFRP)composites own high specific strength and high stiffness,and are widely used in aeronautic manufacturing fields.Due to their own layered structural characteristics,the composite laminates will inevitably encounter damage when impacted by external loading,with the microcracks as the main damage form.By introducing microcapsules containing urea-formaldehyde(UF)resin into the resin matrix of CFRP composites,the microcapsules can spontaneously respond to the extended microcracks and initiate a biological self-healing process by releasing the repair agent dicyclopentadiene(DCPD)encapsulated in the microcapsules into the microcracks,thus providing an effective self-healing mechanism for CFRP composites on active service.The purpose of this paper is to explore the behavior of microcrack expansion in microcapsule self-repairing composites and the filling mechanism of repairing agent within crack surfaces.The numerical simulation results are compared with experimental data of existing tapered double cantilever beams specimens.The rupture of pre-embedded microcapsules in the resin matrix,the outflow of repairing agents after microcapsule rupture and the influence of the diameter and volume fraction of different microcapsules on the repaired fracture toughness are respectively studied.All these research work will provide indispensible instructions for self-healing composite design,having important engineering application value and innovation academic research significance.The main contents include the following aspects:Firstly,by establishing a mesoscale finite element(FE)model of microcapsule self-repairing resin matrix of CFRP composites,the extended finite element method(XFEM)was used to simulate the crack propagation process,so as to study the fracture behavior of UF microcapsules.The effect of the diameter and volume fraction of microcapsules on the inherent fracture toughness of the epoxy resin matrix was also investigated.Based on the single-cell FE model,the multi-cell FE models were established to reflect the actual stochastic distribution of microcapsules.Secondly,the fluid-solid coupling FE model was used to simulate the repairing process after rupture of microcapsules.The surface tension and wall adhesion of repair agents were adopted to characterize the outflow behavior of repair agents.The effects of different microcapsule diameters and microcrack width on the inflow of the repair agent into the crack surface were investigated in detail.Diameter of the microcapsule is proportional to the dosage of the repair agent.Times needed for the repair agent to flow into the crack and reach a stable state is much shorter than its curing time.The mechanism of key factors affecting whether the repair agent in the microcapsule can successfully fill cracks was revealed too.Finally,the mesoscale FE model of the repaired microcrack region was established,to further carry out the quantitative evaluation of the self-healing efficiency and effect for the resin matrix of CFRPs.By analyzing the second-rupture mechanism of the repaired microcrack region under different diameters of microcapsules,the important influence of microcapsule diameter on self-healing effect was revealed.In addition,the close relationship between the elastic modulus ratio of the resin matrix to microcapsules and the total amount of repair agent per unit area of microcracks was determined,too.