Search Results (4)

Thermoplastic in situ Automated Fiber Placement (AFP) is an additive manufacturing method currently investigated for its suitability for the production of aerospace-grade composite structures. A considerable expense in this process is the manufacturing and preparation of a mold in which a composite part can be manufactured. One approach to lowering these costs is the use of a 3D-printable thermoplastic mold. However, AFP lay-up on a 3D-printed mold differs from the usage of a traditional metallic mold in various aspects. Most notable is a reduced stiffness of the mold, a lower thermal conductivity of the mold, and the need for varied process parameters of the AFP process. This study focuses on the investigation of the difference in mechanical and morphological characteristics of laminates produced on metallic and polymeric molds. To this end, the tensile strength and the interlaminar shear strength of laminates manufactured on each substrate were measured and compared. Additionally, morphological analysis using scanning electron microscopy and differential scanning calorimetry was performed to compare the crystallinity in laminates. No statistically significant difference in mechanical or morphological properties was found. Thus, thermoplastics were shown to be a suitable material for non-heated molds to manufacture in situ AFP composites. Full article

This study focuses on investigating the behavior of a thermoplastic matrix composite (Carbon Fiber-LMPAEK) under a bearing strength determination test. The specimens were subjected to a double-shear-bolted joint configuration tensile test, and the propagation of damage was monitored using extensometers. The research employs a technique that involves inelastic modelling and considers discrepancies in layer interfaces to better understand bearing damage propagation. In this context, cohesive modelling was utilized in all composite layers, and the Hashin damage propagation law was applied. The double-shear-bolted joint configuration chosen for the test revealed critical insights into the bearing strength determination of the Carbon Fiber-LMPAEK thermoplastic matrix composite. This comprehensive approach, combining inelastic modelling and considerations for layer interfaces, provided a nuanced understanding of the material’s response to bearing forces. The results of the study demonstrated that all specimens exhibited the desired type of bearing failure, characterized by severe delamination around the hole. Interestingly, the thermoplastic matrix composite showcased enhanced bearing properties compared to traditional thermoset materials. This observation underscores the potential advantages of thermoplastic composites in applications requiring robust bearing strength. One noteworthy aspect highlighted by the study is the inadequacy of current aerospace standards in prescribing the accumulation of bearing damage in thermoplastic composites. The research underscores the need for a more strategic modelling approach, particularly in cohesive modelling, to accurately capture the behavior of thermoplastic matrix composites under bearing forces. In summary, this investigation not only provides valuable insights into the bearing strength of Carbon Fiber-LMPAEK thermoplastic matrix composites, but also emphasizes the necessity for refining aerospace standards to address the specific characteristics and failure modes of these advanced materials. Full article

Ultrasonic welding is a fast and promising joining technique for thermoplastic composite parts. Understanding how changing the part thickness affects the process is crucial to its future upscaling and industrialization. This article presents an initial insight into the effect of the adherend’s thickness on the near-field ultrasonic welding of CF/LMPAEK thermoplastic composites. Different thicknesses of the top and bottom adherend were welded and analyzed using the output data of the welding equipment, temperature measurements, and other visual characterization techniques. Increasing the thickness of both the top and the bottom adherends showed to increase the power consumed during welding. An overshoot in the power needed at the onset of the welding process for increased thickness of the top adherend precluded welding beyond a threshold thickness of 4.72 mm. In the case of the thicker top adherends, there was also melting of the energy director and early fiber squeeze-out within the top adherend as a result of increased bulk heating. Increased bulk heating was hypothesized to be caused by increased hammering, as indicated by the amplitude readings for thicker adherends. Welding with a higher force, which is known to reduce hammering, corroborated this hypothesis as fiber squeeze-out within the top adherend was not observed. It is believed that hammering contributes to heating by causing an oscillatory impact excitation that is close to the natural frequencies of the system, which would result in amplification of the cyclic strain and subsequent increase in the viscoelastic heating in the adherend. Full article

Automated fiber placement (AFP) is a method to manufacture complex composite parts in an automatable and scalable process. Thermoplastic in situ AFP has received more attention in recent years for its use in high-performance, aerospace applications that use low-melting polyaryletherketone (LM-PAEK) composites. Although in situ AFP is a promising technology for the automated and economical manufacturing of composites, the production of a mold is still a considerable expense. Using large-scale additive manufacturing, molds can be manufactured in a short time frame for a fraction of the cost of traditional molds. By using polyamide 6 (PA6), a polymer incompatible with LM-PAEK, a bond can be created, which holds a laminate in the desired form during production and allows for demolding. Due to the thermoplastic nature of PA6, a mold can be manufactured using large-scale, extrusion-based additive manufacturing. This study investigates the suitability of 3D-printed molds composed of PA6 for the AFP of CF/LM-PAEK laminates. To this end, peel tests and shear tests were conducted to investigate the influence of the process temperature, the area of heating and the consolidation pressure on the bond of these incompatible polymers. A shear strength of up to 2.83 MPa and a peel strength of up to 0.173 N·mm⁻¹ were achievable. The principal suitability of PA6 as a mold material for the AFP of CF/LM-PAEK was demonstrated. Full article