Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair

The first author would like to acknowledge the financial support from the European Union under the FP7 COFUND Marie Curie Action. N.M.P. is supported by the European Research Council (ERC StG Ideas 2011 n. 279985 BIHSNAM, ERC PoC 2015 n. 693670 SILKENE), and by the EU under the FET Graphene Flagship (WP 14 “Polymer nano-composites” n. 696656)

Ultrasonic activation of mendable polymer for self-healing carbon-epoxy laminates

Healing of matrix cracks or delamination in fibre-reinforced composites containing mendable polymers requires heating to melt the thermoplastic agents. This paper presents the first investigation into the use of ultrasonic welding to activate a mendable polymer, poly[ethylene-co-(methacrylic acid)] (EMAA), for healing a carbon-epoxy laminate. Mode I interlaminar fracture toughness tests were carried out on specimens containing two different concentration levels of interlaced EMAA fibres to quantify the healing efficiency of ultrasonic vibration. Experimental results reveal that bursts of short-duration, high frequency ultrasonic pulses are able to thermally activate the mendable polymer to repair delamination cracks. Examinations of the fracture surface indicate partial healing of delamination cracks, which were sufficient to completely recover delamination toughness (repair efficiency up to 130%). Furthermore, multiple repairs and recoveries of interlaminar fracture toughness of the composite were achieved with ultrasonic welding. The repair efficiency using ultrasonic welding, however, was found to be less than conventional heating by thermal oven. Nevertheless, the ultrasonic welding technique is portable and can be used for rapid in-field repair of composite structures containing mendable polymers

Healing of mendable polymer composite by ultrasonic vibration

Ultrasonic vibration, which has been employed to weld thermoplastics, is investigated as an efficient in-situ activation technique for self-healing composites. Carbon-fibre composite laminates containing two different concentration levels of interlaced EMAA fibres are first tested using mode I interlaminar fracture method. The fractured coupons are then subjected to ultrasonic vibration using an ultrasonic welder; the resulting heat melts and thus re-bond the delamination. Experimental results show that bursts of short-duration, high frequency ultrasonic pulses are able to thermally activate the mendable polymer to repair delamination cracks. Furthermore, multiple repairs and recoveries of interlaminar fracture toughness of the composite can also be achieved with ultrasonic welding

Effects of processing conditions of poly(methylmethacrylate) encapsulated liquid curing agent on the properties of self-healing composites

A series of microcapsules were prepared by solvent evaporation technique using liquid curing agent, polyetheramine as the core material and poly(methylmethacrylate) as the shell material. The desired morphology, shell wall thickness, curing agent content, and size distribution of microcapsules have been obtained by fine tuning the processing conditions such as reaction temperature, core-shell weight ratio, agitation speed, and emulsifier concentration in the medium. The resulting microcapsules exhibit excellent thermal and curing agent storage stability. Maximum healing efficiency of 93.50% has been obtained with 15 wt.% epoxy containing microcapsules. The microcapsules containing liquid curing agent can efficiently be utilized for the fabrication of epoxy-based self-healing composites

Solvent effects on structural changes in self-healing epoxy composites

Nowadays, there is a very high importance of composite research and variety of their applications in the modern world. In that sense, we researched hollow glass capillaries filled with dissolved Grubbs catalyst (GC) and dicyclopentadiene (DCPD) were incorporated into a fiber-reinforced epoxy with the aim of improving the flow of healing agents to the crack site. The morphological investigation of the crack site was performed using field emission scanning electron microscopy (FESEM), showing the difference between the samples depending on the used solvent. The software analysis of sample photographs has been performed by calculating the fractured/healed surface area of the samples, revealing that approximately 20% of the volume was affected by the impact. Fourier transform infrared spectroscopy (FTIR) revealed that poly (dicyclopentadiene) (PDCPD) formed at the healed interface. However, the FTIR investigation of catalyst stability in different solvents showed structural changes in GC and partial deactivation. The mechanical tests of the samples showed that a recovery of 60% after 24 h at room temperature could be achieved through the use of a solvent and very low concentration of GC. The performed research results are a good base to develop the model for predicting the processes and morphology, with the goal to design the final mechanical and in the future, thermal, properties in advance. This opens a new direction for future research in the field of composite healing