Recent advancements in thermoplastic composite materials in aerospace industry

Studies on weight reduction in aviation and space vehicles have gained momentum recently. Thermoplastic matrix composite materials are important alternative materials, especially due to their high specific strength, formability and recyclability. In this study, it is aimed to investigate the mechanical behavior of fiber reinforced thermoplastic composites for different fiber and layer configurations. Thermoplastic composite materials used in the study were produced by lamination technique. In composite production; Glass fiber and carbon-aramid hybrid fabrics were used as fiber, and polyethylene granules were used as matrix. Thermoplastic sheets were obtained by keeping polyethylene granules and woven fibers in the hot press for a certain period of time. The damage behavior of the composite test specimens under tensile load was tested for the number of layers and fiber type. As the number of layers increased, stiffness, damage load and deformations increased in thermoplastic composites. Using hybrid fabric instead of glass as fiber material increased the maximum damage load by 100%.

<abstract> <p>In this work, a novel method for a more sustainable recycling and cost-efficient manufacturing technique of polyether ketone ketone (PEKK) based thermoplastic composite materials is proposed to recover and reprocess waste and end-of-life materials in the aerospace industry. For the recycling of carbon fiber reinforced thermoplastics (CFrTP), an innovative scrapping process based on mechanical cutting was developed and the properties of the obtained scrap and the recycled panel were analyzed. Thus, a cutting tool was developed for the delamination of the input material so that long fibers can be retained in the resulting scrap. Different processing approaches of material scrapping were evaluated, aiming to obtain manageable scrap that can be subsequently used for a compression molding process. Additionally, an automatic process was evaluated to manage the scrap and perform the corresponding lay-up to manufacture high-quality thermoplastic composite products with recycled materials.</p> </abstract>

Recently, as the development of thermoplastic resin with excellent property and forming process of thermoplastic resin composite material, research of thermoplastic resin becomes a hot issue in related areas. Comparing with common composite material, thermoplastic resin composite material has many advantages, such as, excellent impacting resistance and many processes. So, more and more researchers focus in thermoplastic resin composite material. In this article, applications of carbon fiber strengthen thermoplastic resin composite materials are comprehensive.

Automated fibre placement (AFP) machines are able to place simultaneously several bundles of fibres, called tows, on a surface. Using AFP machines, it is also possible to manufacture composite laminates with fibres placed in curvilinear paths. The fibre orientations and stiffness properties of these laminates are spatially varied and hence they are called variable stiffness (VS) laminates in contrast to the traditional laminates with straight fibres which are called constant stiffness (CS) laminates. Past research has shown that the structural performance of laminated composite structures can be improved by spatial tailoring of laminate stiffness. One of the widely used structural components in aerospace industry are cylindrical shells. In this thesis, a computationally efficient framework was developed for circumferential laminate stiffness tailoring of unstiffened and longitudinally stiffened cylindrical shells with arbitrary cross sections to maximise the buckling capacity with consideration of strength constraints. In addition, the AFP manufacturing constraint on the maximum curvature of curvilinear fibre paths was considered. This constraint was applied to avoid wrinkling of the fibres placed inside the turn of a curved tow. The aforementioned framework utilised computationally efficient analysis and optimisation tools.

Many industries, notably the automotive and aerospace industries, are now utilizing thermoplastic matrix composites (TPMCs) for their improved strength and stiffness properties compared to pure thermoplastic polymers, as well as their manufacturability compared to traditional thermoset matrix composites. The increase in the utilization of TPMCs ushers in the need for the development and characterization of joining methods for these materials. A widely used technique for joining thermoplastics is ultrasonic spot welding (USSW). During USSW, high frequency, low amplitude vibrations are applied through an ultrasonic horn resting on the polymer surface. The vibrations induce frictional heat, producing a solid state joint between polymer sheets. Advantages such as short weld cycle time, fewer moving components and reproducibility make this technique attractive for automation and industrial use. Prior work showed USSW as a feasible, repeatable joining method for a polycarbonate matrix filled with chopped glass fibers. The mechanical properties required for full characterization of the TPMC used in this work were not provided by the manufacturer. As such, the constitutive behavior of both as-received and USSW thermoplastic composite material (polypropylene matrix filled with 30 wt% chopped glass fibers) was characterized. The fiber orientation and distribution in TPMCs has a direct impact on constitutive behavior. To characterize these qualities, optical techniques such as scanning electron microscopy (SEM) and micro computed tomography (micro-CT) were employed. Digital image correlation (DIC) was used to acquire full field strain measurements from the composite material under different loading scenarios. Because the constitutive behavior of polymers is greatly dependent on temperature, temperature measurements during the USSW process and measurement of mechanical properties as a function of temperature will be conducted through infrared (IR) imaging and dynamic mechanical analysis (DMA), respectively. Following the calibration of the constitutive model for the polypropylene matrix TPMC, the mechanical and thermal properties will be used to develop a computational framework for the purpose of predicting the structural response of a composite joint under various loadings.

This paper reviews the effects of various reinforcements with the various thermoplastic polymer matrices. The articles contain the various thermoplastic polymers such as ABS, HDPE, LDPE, PP, PEEK, PC, PA, PI, UHMWPE and PMMA etc. The review contains the evaluation of tribological properties such as sliding wear and coefficient of friction (COF) of polymer matrix composites (PMCs). This review also evaluation of mechanical properties such as tensile strength, compressive strength, young modulus and hardness of polymer matrix composites (PMCs). The thermoplastic polymer composite used in various applications such as automotive industry, food processing machine industry, household appliance, military, structural and aerospace industry etc. The properties of thermoplastic polymer composite are varying with the fabrication techniques of composite.

Thermoplastic composite (TPC) tapes can be consolidated in situ via automated fiber placement (AFP) at relatively high temperatures (>250°C) and local pressures (up to a few MPa). In situ consolidation of TPC parts requires special tooling and heated molds to prevent warping. Creating complex three-dimensional (3D) molds at a low cost and in a short time frame can facilitate TPC AFP adoption and entry into new markets requiring customized parts. The industry standard for mold manufacturing is milling or bending metal stock (typically invar, steel, or aluminum). This process can be costly and have lead times upwards of two months. Additive manufacturing can shorten the lead times significantly. Additively manufactured molds, to be used by TPC AFP, should withstand high temperatures and roller pressures. Current mold generation practices do not have a method of heating the mold surface necessary for dimensional accuracy of TPC tape-based parts. This paper investigates a process to create 3D molds via fused filament fabrication (FFF), a form of material extrusion additive manufacturing (AM), and high-performance materials that can withstand the temperatures and pressures of thermoplastic AFP application. FFF offers customized parts quickly and at a low cost. A laser-assisted AFP robot performed a layup over two heated FFF molds made of short carbon fiber reinforced polyetherketoneketone (CFPEKK), a flat plate and one with a one-axis curvature. These specimens performed well with no noticeable permanent deformation of the mold caused by either the roller or the laser demonstrating the viability of this mold generation process to create 3D molds usable with TPC AFP.

With the increasing demand for carbon fiber-reinforced parts in the aerospace industry, automated manufacturing methods such as automated fiber placement (AFP) are being established. To utilize AFP’s strong potential on multiple-curved surfaces such as chamfered sandwich structures, it is important to analyze and control emerging effects like gaps, bridging, and steering. An analytical relationship between path generation and effects of the AFP manufacture of chamfered sandwich structures have been found with good agreement to experimental tests. The deformation behavior of an industrially used compaction roller has been analyzed numerically and experimentally. The results show a nonuniform deformation behavior on flat and curved surfaces and the limited deformability of the compaction roller.

High-performance poly-ether-ketone-ketone (PEKK) thermoplastic (TP) composites, which are beginning to gain interest in the aerospace industry, require a joining procedure to integrate the individual parts. Amorphous TP bonding has been recently proposed to address the limitations of commonly used joining techniques for composites, such as mechanical fastening and adhesive bonding. In this study, we investigated the adhesive properties of a polyetherimide (PEI) film applied by hot press welding as an amorphous polymer interlayer of PEKK laminate. The temperature range of the bonding process was determined via differential scanning calorimetry analysis. The bonding strength was evaluated through single-lap shear tests. The effect of process temperature on the bonding strength was qualitatively analyzed via fracture surface morphology analysis. The interface between PEKK and PEI was analyzed via optical microscopy. The adhesive strength was as low as about 5 MPa up to the bonding temperature of 280[Formula: see text]C but then started to improve as the temperature increased, which is attributed to the interdiffusion of the PEKK matrix and PEI adhesive film. The maximum bonding strength of 23 MPa was confirmed at a bonding temperature of 340[Formula: see text]C. A mixed failure mode consisting of a relatively high ratio of fiber-tear failure to light-fiber-tear failure is observed at this process temperature. This failure mode can be attributed to the bonding temperature condition at which PEKK begins to melt.

In the last years, thermoplastic composites have been introduced as structural materials for high performance aerospace applications. However, these materials can present problems when exposed to moisture, temperature, and UV radiation, and besides it may occur as the synergy among the main degradation mechanisms. Among the thermoplastic composite materials, carbon fiber reinforced poly(ether-ketone-ketone) (PEKK) laminates have shown excellent balance of properties, including high glass transition temperature, high strength, stiffness and fracture toughness values, low moisture absorption, and good environmental resistance. The aim of the present work was to evaluate the influence of the environmental effect on the viscoelastic behavior and glass transition temperature of carbon fiber reinforced PEKK thermoplastic composites. In this work, the effects of environmental degradation on the viscoelastic properties of this composite material were studied by dynamic mechanical analyses. The most significant change was observed for the UV radiation accelerated weathering conditioning effects. A decrease of the storage modulus from 40 to 10 GPa and the Tg from 147 to 105℃ is observed, which decreases consequently the composite stiffness and the service temperature after exposed environmental effects. A synergetic degradation mechanism between UV radiation accelerated weathering test and hygrothermal conditioning is clearly verified.

To improve the physical-mechanical and thermophysical properties of polypropylene-based thermoplastic composite materials, we performed modification of a polymer matrix by reactive extrusion of polypropylene in the presence of benzoyl peroxide and polysiloxane polyols. Modified polypropylene was compounded with basalt, carbon, and para-aramide reinforcing fillers in a screw-disc extruder. It was established that the reinforcement of modified polypropylene by basalt fibers ensured a 110% increase in tensile strength. The reinforcement of modified polypropylene by carbon fibers allowed fabricating thermoplastic composite materials with tensile strength increased by 14%. The maximum reinforcing effect was observed by using para-aramide fibers as reinforcing fibers for modified polypropylene with tensile strength increased by 30% as compared with initial polypropylene. It was determined that the obtained thermoplastic composite materials based on modified polypropylene can be processed into products by the most productive methods (extrusion and injection molding). The developed materials exhibited improved thermal stability. The proposed ways of modification methods provide substantial improvement in physical-mechanical and thermophysical properties of modified polypropylene-based thermoplastic composite materials as compared with initial polypropylene. In addition, they ensure a significant increase in service properties of the products prepared from thermoplastic composite materials based on modified polypropylene.

Spring-in study of the aileron rib manufactured from advanced thermoplastic composite

Natural fiber-reinforced composites are becoming a growing trend because of their affordability, sustainability, abundant natural source, and minimal environmental effect. It has also shown to be an effective replacement of synthetic fiber, particularly in the transportation and construction sectors as ceiling, paneling, partition etc. In this study the jute fiber (Hessian Cloth) reinforced (10% to 50% fiber content by weight) Polypropylene (PP) and Polyethylene (PE) composite were made by compression molding technique to understand the effect of fiber loading on mechanical properties of two different thermoplastic composite materials. For jute fabric-reinforced thermoplastic composites, it was discovered that with 30 % fiber loading with PP and PE yielded the best results. It was found that the mechanical properties of the composites enhanced significantly with 30 % fiber content with PP and PE thermoplastic matrixes in contrast to 10% and 20% fiber content composites. However, increasing the fiber content over 30%, dramatically decrease the mechanical properties of the composite samples. The relationship between Tensile Strength (TS), Bending Strength (BS), Impact Strength (IS) and Tensile Modulus (TM), Bending Modulus (BM) was examined, along with water resistance properties for both composites. Additionally, the jute-reinforced polypropylene (PP) composite showed superior mechanical capabilities compared to the jute-polyethylene (PE) composite. This suggests that it could be a suitable replacement for the toy manufacturing, home or garden furniture, automotive and interior construction industries in the future.

This study investigated the pin-loaded tensile behavior, bearing strength, and failure mechanisms of thermosetting and thermoplastic composite materials. Specifically, the investigation focuses on carbon-fiber-reinforced polyetherketoneketone (CF/PEKK) and carbon-fiber-reinforced epoxy (CF/EPOXY). Notably, CF/PEKK exhibited a shear-out failure mode, surpassing CF/EPOXY with a 56.4% higher peak load. The absence of crack propagation in CF/EPOXY, attributed to the presence of yarn at a 90∘ angle, leads to bearing failure. In contrast, CF/PEKK demonstrates a significantly higher bearing strength, approximately 150[Formula: see text]MPa greater than CF/EPOXY. This discrepancy in performance suggests that CF/PEKK holds promise as a structural material for applications involving the fastening of thermoplastic composites, presenting a viable alternative to traditional thermosetting composites. The findings imply that the unique failure mechanisms and enhanced mechanical properties of CF/PEKK make it a compelling candidate for use in scenarios where thermosetting composites are conventionally applied. This study contributes valuable insights into the potential advancements and applications of thermoplastic composites in structural materials, paving the way for optimized and innovative engineering solutions.

Compared to thermoplastic processing chains based on conventional woven organo sheets, stamp forming of unidirectional fiber-reinforced materials offers opportunities such as enhanced part performance by tailored fiber architecture, or economic and ecologic benefits by scrap reduction. However, before stamp forming, stacks need to be built layer-wise from tape material and subsequently consolidated to a blank, which is cost-, time- and energy-consuming. Thermoplastic Automated Fiber Placement (AFP) technology is able to layup tape material and consolidate the laminate up to a certain degree at the same time. The aim of this study is to investigate the influence of the degree of consolidation obtained during layup on the part quality of formed parts, and compare these results to parts made from preforms that were consolidated in a separate step. Specimens were manufactured with a Coriolis AFP machine. Wedge-peel testing was performed to determine correlations between nip point temperature, feed rate, layup tool temperature and degree of bonding. Nip point temperature was found to govern the consolidation quality. Based on the results, parameter sets were defined to manufacture stamp forming preforms. The forming experiments were conducted with an infrared heating system and a hydraulic heating press, process parameters were kept constant. A 2D flat plate and 3D cone geometry were investigated. The processed parts were characterized by thickness measurements, optical 3D scanning and mechanical three-point-bending testing. Alongside, microsections were prepared and void content was measured at all processing states. After stamp forming, no significant differences were found between parts made from preforms with good and poor degree of bonding regarding the topology measurements and mechanical performance. However, differences were found regarding the obtained porosity values. Results prove the capability of this processing chain to produce high-quality parts from preforms that were layed up at high layup speeds, or that even show poor consolidation.