The integrity of delaminated composite structures can be restored by introducing a thermally-based healing effect on continuous fiber-reinforced thermoplastic composites (CFRTPC). The phenomenon of thermoplastics retaining their properties after melting and consolidation has been applied by heating the delaminated composite plates above their glass transition temperature under pressure. In the current investigation, the composite is comprised of Methyl methacrylate (MMA)-based infusible lamination resin combined with benzoyl peroxide initiator, which polymerizes into a Polymethyl methacrylate (PMMA) matrix. For the reinforcement, unidirectional 220 gr/m² glass filament fabric was used. Delamination damage is artificially induced during the fabrication of laminate plates. The distributed delamination region before and after thermally activated healing was determined by using non-destructive testing with active thermography. An experimental approach is employed to characterize the thermal healing effect on mechanical properties. Experimentally determined technological parameters for thermal healing have been successfully applied to repair delamination defects on composite plates. Based on the compression-after-impact (CAI) test methodology, the intact, damaged, and healed composite laminates were loaded cyclically to evaluate the healing effect on stiffness and strength. During the CAI test, the 3D digital image correlation (DIC) technique was used to measure the displacement and deformation fields. Experimental results reveal the difference between the behavior of healed and damaged specimens. Additionally, the numerical models of intact, damaged, and healed composite laminates were developed using the finite element code LS-Dyna. Numerical models with calibrated material properties and tie-break contact constants provide good correlation with experimental results and allow for the prediction of the mechanical behavior of intact, damaged, and healed laminated plates. The comparison analysis based on CAI test results and modal characteristics obtained by the 3D Laser Doppler Vibrometer (Polytec GmbH, Karlsbad, Germany) proved that thermal healing partially restores the mechanical properties of damaged laminate plates. In contrast, active thermography does not necessarily indicate a healing effect.

Interlaminar failure of bonded composite structures is quite often. Nowadays there is a lot of lightweight high reliability carbon or glass fiber (CFRP or GFRP) reinforced polymer composite constructions with bonded carbon or glass fiber rods. In order to better understand the delamination processes of the rods, analytical equations were analyzed. Later, mode I interlaminar failure experiments with CFRP rods 3x3 mm were performed and fracture toughness G_IC = 135 J/m² was found. According to the analytic equations, experiment and values, given literature, finite element model (FEM) of the bonded carbon fiber rods was created in software LS-Dyna. Most of the differences between experimental and simulated force-displacement curves are not higher than 6 % what validates the FEM of the bonded CFRP rods. Also, additional methods, such as peridynamics of the bond area of the rods were analyzed. Offered finite element approach of the bonded CFRP rods is very useful for FEM creation to design and evaluate high reliability CFRP or GFRP constructions.

The aim of the present work is to compare the interlaminar shear strength and fracture toughness of glued carbon fiber rods obtained using different experimental approaches and provide the effective way to characterise the interlaminar properties for reliable simulation of the delamination. Five different test methods (tension, single shear test, and double shear test, mode I and mode II delamination tests) were performed. Using the explicit LS-DYNA code the finite element model capable of simulating the damage process of bonded connection was developed. The interlaminar connection and delamination criteria were calibrated using the parameter identification methodology implemented in LS-OPT optimization tool.