A rational study on the hydrothermal aging of AFP manufactured CF/polyetherketoneketone composites with in situ consolidation supported by acoustic emission inspection

Abstract

In this study, carbon fiber (CF)/polyetherketoneketone (PEKK) composites with 5% void content, manufactured via an in situ consolidated automated fiber placement (AFP) lay‐up process, are aged in hot water at 70°C for 30 days. Firstly, a deep understanding of the deterioration in the mechanical performance is developed with a comprehensive and complementary set of material characterization strategies, including (i) microstructural characterization with Fourier‐transform infrared spectroscopy (FTIR), (ii) thermal characterization with differential scanning calorimetry (DSC), and (iii) dynamic mechanical analysis (DMA). The material characterization concurrently highlights the plasticization and post‐crystallization phenomena after aging with changes in the peak densities with FTIR, formation of second glass transition temperature (Tg) in DSC and DMA, and drop in storage modulus, loss modulus, and tan delta (δ) amplitudes. Then, acoustic emission (AE) is utilized as an inspection tool to identify the damage mechanisms regarding the 6.5%, 5.2%, and 4% decrease in tensile strength, strain at failure and modulus, respectively, in a comparative manner. The AE findings, remarking the weakening of the fiber–matrix interface after aging, are validated with scanning electron microscopy analysis. This study introduces an aging process‐induced damage mechanism triggered with inhomogeneous water absorption for AFP manufactured CF/PEKK composites with in situ consolidation.

Online characterization of moisture transport in a high-performance carbon fiber-reinforced thermoplastic composite at high temperatures: Identification of diffusion kinetics

“…As for the desorption curves, the first stage is relatively fast (couple of hours) and is represented by the initial slope. Similar behavior has also been observed, in the literature, on CF/PEEK composite [20,18] and on CF/PEKK composite, placed under more severe conditions (80 • C at 90 %RH [26], and water immersion at 70 • C [25]).…”

“…As shown in Figure 8, a good correlation can be observed between the diffusion coefficients obtained by other authors on CF/PEKK [25] and CF/PEEK [18] and the estimated value with the Arrhenius law (Figure 8). Moreover, there is a small difference between the diffusion coefficient predicted by the Arrhenius trend and the experimental value we determined during the sorption test at 40 • C. Such a symmetry sorptiondesorption during transient regime is in-line with results already reported in the literature for cured fiberreinforced epoxy matrix composites [55,45] and neat PEEK polymer [56,57].…”

“…Most of them focused on CF/PEEK. Only five recent articles have been found on CF/PEKK [24,25,26,27,28].…”

Effects of meso‐ and micro‐scale defects on hygrothermal aging behavior of glass fiber reinforced composites

“…The micro‐crack generation step was evaluated using the acoustic emission (AE) method 39 . AE data was analyzed to determine the maximum tensile load at which load/unload tests induce micro‐cracks in the samples.…”

“…The micro-crack generation step was evaluated using the acoustic emission (AE) method. 39 AE data was analyzed to determine the maximum tensile load at which load/unload tests induce micro-cracks in the samples. Mistras PCI 2 acoustic emission apparatus with AEwin PCI2 software was utilized to obtain and record the AE data (Figure 2C).…”