Assessing damage and repair of healable polymer-matrix composites by acoustic emission testing and THz time-domain spectroscopy

The service life of a composite material can be improved by proper maintenance and repairing. However, repairing and maintenance incur a considerable amount of downtime. Self-Healing (SH) composites have the capability to autonomously regain their structural integrity and improve their service life. SH composites use healing agents, which are encapsulated in thin-walled capsules or vascular networks and are strategically dispersed in the structurally weak matrices or at the interfaces between the matrix and load carrying fibres. The propagating damage bursts the capsules or the vascular networks and releases the healing agent. This will arrest the propagating damage and retain the structural integrity of the composites. The development of new healing agents, designing new healing systems, or the improvement of number of healing cycles achieved by the SH composites are the areas targeted by researchers over the years. The retention of mechanical properties and other structural properties by the SH composites post healing in real structural applications is seldom addressed widely. Developing in-situ monitoring of the damage progression in these materials and the subsequent healing processes is thus essential. The use of advanced Non-Destructive Evaluation (NDE) techniques can identify and localize the damage and healing occurrences. Non-invasive techniques such as Acoustic Emission (AE) technique, optical techniques such as Digital Image Correlation (DIC) or spectroscopic techniques such as therahertz time-domain spectroscopy (THz-TDS) are quite powerful and promising for monitoring of structures and components. Here, we present some results obtained in the early stage of the PRIN research project entitled “IN MOOSHEAC - INnovative damage MOnitoring Of Self-HEAling Composites by acoustic emissions in civil and aerospace applications” [1]. The research program aims at utilizing NDE techniques for monitoring the healing process of SH composites and to investigate their structural properties post healing. Some composite samples were designed and manufactured on purpose, and then tested in the lab under tension or compression. The samples were supplied by a company that has developed a new type of resin - HealTech™ - giving composite materials the ability to heal cracks and delamination in a few minutes after a localized heat supply. AE technique was used to detect damage, while THz-TDS was employed to analyze the intact, damaged, and healed situations. References [1] https://www.polito.it/en/research/scenario/research-database?progetto=878/2023