The additive manufacturing of continuous fiber composites has the advantage of a high-precision and efficient forming process, which can realize the lightweight and integrated manufacturing of complex structures. However, many void defects exist between layers in the printing process of additive manufacturing; consequently, the bonding performance between layers is poor. The bonding neck is considered a key parameter for representing the quality of interfacial bonding. In this study, the formation mechanism of the bonding neck was comprehensively analyzed. First, the influence of the nozzle and basement temperatures on the printing performance and bonding neck size was measured. Second, CT scanning was used to realize the quantitative characterization of bonding neck parameters, and the reason behind the deviation of actual measurements from theoretical calculations was analyzed. When the nozzle temperature increased from 180 to 220 °C, CT measurement showed that the bonding neck diameter increased from 0.29 to 0.34 mm, and the cross-sectional porosity reduced from 5.48% to 3.22%. Finally, the fracture mechanism was studied, and the influence of the interfacial bonding quality on the destruction process of the materials was determined. In conclusion, this study can assist in optimizing the process parameters, which improves the precision of the printing parts and performance between the layers.

To further improve the mechanical properties of thermoplastic resin in additive manufacturing (AM), this paper presents a novel method to directly and quantitatively place the short fibers (SFs) between two printing process of resin layers. The printed composite parts with SFs between the layers was reinforced. The effects of single-layer fiber content, multi-layer fiber content and the length of fibers on the mechanical properties of printed specimens were studied. The distribution of fibers and quality of interlayer bonding were assessed using mechanical property testing and microstructure examination. The results showed that the tensile strength of the single-layered specimen with 0.5 wt% interlayered SFs increased by 18.82%. However, when the content of SFs continued to increase, the mechanical properties declined because of the increasing interlayered gap and the poor bonding quality. In addition, when the interlayered SFs length was 0.5–1 mm, the best reinforcement was obtained. To improve the interfacial bonding quality between the fiber and the resin, post-treatment and laser-assisted preheating printing was used. This method is effective for the enhancement of the interfacial bonding to obtain better mechanical properties. The research proves that adding SFs by placement can reduce the wear and breakage of the fibers compared to the conventional forming process. Therefore, the precise control of the length and content of SFs was realized in the specimen. In summary, SFs placement combined with post-treatment and laser-assisted preheating is a new method in AM to improve the performance of thermoplastic resin.

Continuous carbon fiber reinforced poly‐ether–ether–ketone (CCF/PEEK) shows great potential in engineering applications attributed to superior mechanical properties together with excellent thermal and chemical resistance. In this study, a laser‐assisted additive manufacturing device was established to accurately collect and control the preheating temperature based on a coaxial infrared temperature measurement system. The influence on laser power consumption, interlaminar shear performance, and failure mechanism was investigated in condition of different preheating temperatures and printing speeds. Results indicated that the laser‐preheated specimens showed much higher ILSS with maximum values and increasing percentage reached 33.48 MPa and 157.0% compared to unpretreated specimens. With the increase of preheating temperature and printing speed, more laser power was consumed, while the ILSS and increasing percentage increased firstly and then decreased. The strengthening effect on the interlayer bonding was ascribed to promoting the penetration of PEEK molecular chain ends between adjacent layers, increasing the fluidity and enhancing the bonding effect between adjacent filament together with improving the impregnation behavior of the inner fibers. The proposed interlaminar strengthening method based on laser‐assisted preheating provides potential application prospects in aerospace and automotive industries.

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This work focuses on quantitatively investigating the relationship between creep and stress relaxation of 7050 aluminum alloy at ageing temperatures. The creep strain rates, creep exponent, n, and activation energy were extracted from both the creep and stress relaxation curves to explore the creep mechanisms. Results showed that higher applied stress promotes the creep and stress relaxation extents. The calculated creep strain rates from creep and stress relaxation curves located in similar ranges and share similar n values (n = 3.7 for creep and n = 3.5 for stress relaxation), indicating that both tests are dominated by the dislocation slip mechanism. Additionally, the n value for creep tests is a constant throughout the tests, indicating that the dominant creep mechanism is unchanged. However, the activation energy changes from 123 kJ/mol to 139 kJ/mol, possibly due to evolved dislocations. Such a new finding could provide a supporting mechanism for building constitutive equations depending on the evolved A value. Furthermore, compared to the single-stage creep ageing, no primary creep was observed in T74 multi-stage creep ageing while similar amount of total creep strains was achieved. This suggests an alternative loading sequence for creep age forming of 7050 aluminum alloy, i.e., loading at the second stage to avoid prolonged exposure to high temperatures, extend the tool life, and achieve similar amounts of inelastic deformations. Based on all the above studies, creep and stress relaxation have a certain relationship. This paper provides a theoretical basis for future research on creep ageing forming of 7050 aluminum alloy.

Advanced composite materials exhibit advantages of high specific strength, high specific modulus, and excellent designability. They are widely used in aerospace, rail transit, and other fields, and are strategic resources for industrially developed countries. Ensuring and improving the supply capacity of advanced composite materials and making breakthroughs in the design and forming, processing and assembling, testing and repairing technologies of large and complex composite components are of strategic significance in strengthening China's manufacturing sector. In this study, the current status and trends of precision manufacturing of composite components are analyzed, and the key technologies and equipment for precision manufacturing of composite components, including high-precision numerical control winding, automatic placement, preform forming, additive manufacturing, and high-performance carbon fiber production, are summarized. After specifying the key problems limiting the development of composite manufacturing technologies, we propose the development goals by 2035. Accordingly, suggestions are proposed including establishing national