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. (c) 2012 Elsevier Ltd. All rights reserved.