A Study on the Aging Resistance of Injection-molded Glass Fiber Thermoplastic Composites

J of Applied Polymer Sci

Elmas

Seyyednourani

et al. 2022

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.

Section: Resultsmentioning

confidence: 95%

“…19 As stated in some other studies, these plasticization/anti-plasticization/ swelling phenomena lower the T g of thermoplastic polymers and deteriorate the mechanical properties such as strength, modulus, and stiffness. 20…”

Section: Accelerated Hydrothermal Agingmentioning

confidence: 99%

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

J of Applied Polymer Sci

Elmas

Seyyednourani

et al. 2022

“…The literature states that, for semicrystalline polymers, water can penetrate the amorphous region more quickly than the crystalline region and acts as a plasticizer rather than a solvent 39 . As stated in various studies, the plasticization/antiplasticization/swelling phenomenon reduces the T g of thermoplastic polymers and causes impairment in mechanical properties such as strength, modulus, and stiffness 40 . The mass gain of composite laminates manufactured with Set 1 parameters is given in Figure 7.…”

Section: Resultsmentioning

confidence: 99%

An experimental implication of long‐term hot‐wet‐aged carbon fiber/polyether ketone ketone composites: The impact of automated fiber placement process parameters and process‐induced defects

J of Applied Polymer Sci

Elmas

Eskizeybek

et al. 2023

During the service life of aerospace‐grade composites, process parameters and process‐induced defects may become crucial. Most studies in this field have mainly focused on the relationship between process‐induced defects and mechanical performance. However, the potential impact of process parameters and process‐induced defects on the service life of composites serving under severe service conditions has received little attention. In this work, the effects of hydrothermal conditioning on the mechanical performance of carbon fiber/polyether ketone ketone (CF/PEKK) composites are examined, along with the correlation between automated fiber placement (AFP) process parameters and process‐induced defects. For this, gap and overlap defects integrated CF/PEKK laminates were exposed to a long‐term (90 days) hot‐wet aging environment to simulate the actual service conditions. Defect‐induced composite samples reached saturation point at the end of 30 days with a mass gain of 0.2 wt%. The aging process resulted in an increase in the degree of crystallization by almost 14% without a change in the chemical structure, indicating the postcrystallization of the PEKK matrix. Even though the thermo‐mechanical performance diminished (~25%) with the aging process, storage modulus was slightly affected by process parameters and process‐induced defects. Considering the flexural and shear test results after the aging process, the impact of gap and overlap defects on the service life of AFP composites can be minimized with higher compaction forces (600 N) and lower lay‐up speeds (0.1 m/s).

“…[8] In industrial applications, the composite structural parts are exposed to various compelling chemical and physical service environments, mainly high or low temperatures, ultraviolet exposure, extreme pH, and high humidity. [14][15][16][17] Among them, temperature and humidity are the most common and critical environments in aerospace applications leading to the decreased mechanical performance of fiber-reinforced composite parts. [16,18] The moisture mainly causes matrix plasticization and swelling, weakens the adhesion at the fiber-matrix interface, and triggers fiber-matrix interface failure mechanisms such as fiber-matrix debonding.…”

Section: Introductionmentioning

confidence: 99%

“…[14][15][16][17] Among them, temperature and humidity are the most common and critical environments in aerospace applications leading to the decreased mechanical performance of fiber-reinforced composite parts. [16,18] The moisture mainly causes matrix plasticization and swelling, weakens the adhesion at the fiber-matrix interface, and triggers fiber-matrix interface failure mechanisms such as fiber-matrix debonding. [12,19] Thermal effects on aerospacegrade thermoplastic composites can be divided into two classes, low and high temperatures.…”

Section: Introductionmentioning

confidence: 99%

Thermally conditioned aerospace‐grade carbon fiber reinforced polyether ketone ketone composites: Structure, impact response, and thermomechanical performance

2023

Polymer Composites

Carbon fiber‐reinforced high‐performance thermoplastic composites have recently become an efficient alternative for aerospace engineering applications. However, the temperature sensitivity of semi‐crystalline carbon fiber/polyether‐ketone‐ketone (CF/PEKK) polymers revealed the necessity of investigating their performance in service conditions. This study aims to evaluate the effect of extreme service conditions on thermomechanical performance and fracture characteristics of CF/PEKK composite laminates. For this, aerospace‐grade composite laminates were manufactured with the automated fiber placement process and were exposed to extreme service temperatures of −50°C (Conditioned I), 180°C (Conditioned II), and initially 180°C following −50°C (Conditioned III), simulating critical service temperature ranges in aerospace applications. According to impact tests, the energy absorbance of CF/PEKK composites decreased in all thermal conditioning scenarios by up to 25%. Additionally, Conditioned I samples represented relatively low glass transition temperature and degree of crystallinity compared to the control samples; however, Conditioned II and Conditioned III samples exhibited an opposite behavior. Dynamic mechanical analysis (DMA) investigations revealed a 13% reduction in the storage modulus for all thermal conditionings. While CF/PEKK composites represented ductile/brittle behavior at room temperature and high/low conditioning temperatures, their brittleness increased at −50°C, and the structure became ductile at 180°C. This study confirms that DMA is a powerful tool for determining the glass transition temperature for fiber‐reinforced composites with higher sensitivity and accuracy than DSC.