PSI - Issue 77

Claudia Barile et al. / Procedia Structural Integrity 77 (2026) 3–10 Barile and Kannan/ Structural Integrity Procedia 00 (2026) 000 – 000

4

2

1. Introduction Fibre-Reinforced Polymer composites (FRPs) are widely used in several industrial and commercial sectors, replacing the conventional engineering materials. The tremendous increase in the FRP use in the last few decades is attributed to their exceptional qualities including high strength-to-weight ratio, high specific strength, and low coefficient of thermal expansion. However, their poor reusability and resistance to out-of-plane damage are seldom discussed. Several practices such as repairing, recovery of high-strength fibres by incineration or chemical etching are explored to extend their service life and carbon footprint, most of these approaches are unsustainable. One of the recent sustainable solutions is to incorporate healing capability into the polymer systems. This is achieved by modifying the architecture of the polymer matrix by incorporating reversible covalent bonds. These reversible bonds are activated by external stimuli, which helps the resin to flow and arrest the progressing damage. While this approach has proven to recover bulk properties of polymers, their applicability in fibre-dense composites remains to be explored (Cohades et al., 2018; Scazzoli et al., 2022). In this study, the mechanical performance of fibre-dense self-healing CFRP composites is investigated. The mechanical tests are complemented by AE tests to investigate the real-time failure progression and damage states of the composites. To process the AE data, the ML-based data clustering algorithm, k-means++ unsupervised clustering, is used. This method is used for the unsupervised classification of AE signals generated from different sources. CWT, the time-frequency analysis, is used to verify this association of AE signals with the damage sources. The main aim of this research is to identify the failure progression in the fibre-dense self-healing CFRPs using AE testing and to estimate their ability to recover the mechanical properties. 2. Experimental 2.1. Materials The intrinsically healable resin used in this study is a commercially available thermoset resin HealTech TM (CompPair Ltd., Renes – Switzerland). Healing is activated in the resin at a moderate temperature range 100 ℃ and 150 ℃ , while the glass transition state starts approximately around 170 ℃ . To prepare the self-healing CFRPs, high strength Toray T700 carbon fibres are pre-impregnated with the thermoset resin. The fibres in the prepregs are arranged in twill-weave configuration with a high fibre-percentage of 62%. The prepregs are stacked in [( ± 45)/(0/90)]3s laminate configuration. The laminates are cured in an oven for 3 hours at 140 °C followed by 2 hours at 180 °C. Fifteen test specimens, following the ASTM D790 standard, with nominal dimensions of 200 mm × 10 mm × 4.5 mm are taken from the composite slab. Three specimens are tested in virgin conditions following ASTM D790 standard (explained in detail in Section 2.2) and the flexural strength σ f is calculated. Two levels of internal damage states are created by loading the specimens up to 10% and 30% of σ f . The specimens are healed by placing them in a preheated oven at 150 ℃ . The specimens are removed from the oven 15 minutes after their surface reaches 100 ℃ . Then they are cooled at room temperature. A total of fifteen specimens is tested as a part of this study. Three specimens per each group: virgin (V), damaged at 10% σ f (DS-1), healed after DS-1 (DS-1-Healed), damaged at 30% σ f (DS-2), and healed after DS-2 (DS-2-Healed). 2.2. Methods The flexural tests are carried out following the ASTM D790 test standard. The specimens are placed in a three point bending test setup, in which the distance between the supporting edges is 160 mm. The specimen is loaded with a ⌀ 9 mm cylindrical loading nose. Fig 1. shows the flexural test setup. The tests are carried out at a crosshead displacement rate of 8 mm/min until failure. The applied load and deflections are recorded during the test. The flexural properties such as flexural stress, flexural strain, tangent and chord moduli are calculated following the ASTM D790 standard.