Lin Xiao

Supercritical CO ₂ (sc‐CO ₂ ) was widely used in CO ₂ flooding projects to enhance the recovery efficiency recently owing to its amazing dissolving capability and permeability. Fiber reinforced pipe (FRP) has exceptional properties that may be widely used in the petrochemical sector for transportation of corrosive fluid in CO ₂ flooding projects. In this research, a system was designed to simulate the transport behavior of fluids containing CO ₂ which can reaches the supercritical state by the adjustment of pressure and temperature. The fluid penetrates into the resin interior through the pores and gathers in the cavities at 65°C and 8 MPa. When the temperature and pressure are below the critical point, the CO ₂ volume expands dramatically, causing inter‐layered micro‐crack. When the environmental conditions repeatedly change above and below the critical point, these cracks will continue to propagate along the fiber arrangement direction, resulting in the fracture progressively grow into the delamination. At the same time, the fluid corrodes the resin in some areas of the surface, generating pitting and a 0.66% loss in resin content. The composition of elements and groups altered after corrosion revealed that a chemical interaction occurred between fluid and epoxy resin. Finally, due to physical and chemical processes produced by penetration, expansion, and dissolution, the stiffness of FRP fell by 3.53% during treatment. Highlights: In the present work, a reactor coated with polytetrafluoroethylene (PTFE) was built to model the corrosion of FRP in delivery fluids containing sc‐CO ₂ . The corrosion mechanism was shown as a combination action by chemical react and physical behavior comprising penetration, expansion and dissolution. The physical corrosion mechanism of fluid containing sc‐CO ₂ was investigated. The fluid containing sc‐CO ₂ penetrated the FRP via pores and accumulated in cavities. The quick expansion of sc‐CO ₂ causes delamination while the ambient circumstances remain below the critical threshold. The pitting and resin loss can be linked to the epoxy resin solution in supercritical CO ₂ . The chemical process, known as hydrolysis, took place on the interior surface of epoxy resin and a fluid containing supercritical CO ₂ . This finally resulted in molecular structural modification.

To enhance the ductility of carbon fiber‐reinforced polymer (CFRP) composites, a variety of nacre‐inspired structures with discontinuities were constructed based on the ratio of overlapping length to CFRP laminate thickness. The damage mechanisms and tensile characteristics of discontinuous laminates were elucidated using finite element analysis and experimental investigation. To anticipate the mechanical behavior of the CFRP laminate, an improved Chang‐Chang failure criteria was devised. Moreover, a model adopts the Benzeggagh‐Kenane criterion on cohesive surfaces for delamination initiation and propagation. The predicted stress–strain values are validated using experimental data under tensile stress. Furthermore, a mathematical model accurately predicted the relationship between the tensile performance of nacre‐inspired laminate and overlapping length. According to the findings, the longer the overlapping length (more than 19.5 mm) is, the lower the pseudo‐ductility. Meanwhile, the shorter the overlapping length (less than 17.5 mm) is, the lower the tensile strength. Furthermore, the laminate exhibits some pseudo‐ductility as well as little decrease in tensile strength when the overlapping length is approximately 18.5 mm.Highlights: A mathematical model for predicting the tensile properties of various nacre‐inspired laminates was established. The relationship between the discontinuous structure and the pseudo‐ductility of the nacre‐inspired laminate was revealed. Compared with other similar structural laminates, the laminate with an overlapping length of 17.5 mm has better overall performance. Proposed an improved Chang‐Chang progressive failure criterion that was utilized to simulate and analyze the mechanical response and damage of the nacre‐inspired laminates under tension.

Carbon fiber‐reinforced polymer composites (CFRPs) are widely used in many fields because of their excellent mechanical properties; however, they are very sensitive to low velocity impact. A new‐type biomimetic structure, which has a “bricks‐and‐mortar” arrangement of nacre from mollusk shells, was designed and manufactured for enhancing the impact resistance of the CFRPs. The impact response and absorption of impact energy of this structure were also investigated. Impact damage forms of the biomimetic structure were analyzed based on the surface and internal morphologies. The results indicate that biomimetic structure can decrease the impact damage of the CFRPs. Two damage behaviors of the biomimetic structure were observed under relatively higher impact energy. The discontinuous structure reduces the damage using a smaller load for the first damage and a larger deformation for the second damage, which improves the impact resistance of the CFRPs. The discontinuous structure restrains longitudinal crack propagation to a certain extent, effectively reducing the damaged area of the CFRPs. Thus, the proposed structure can increase the strength retention rate of the material by about 5%. In addition, the compression after impact damage modes of CFRPs with three types of structure are summarized and classified originally.

As a promising alternative to traditional prepreg, carbon fiber/poly(ether ether ketone) (CF/PEEK) hybrid composites have attracted wide public interest for their flexibility and conformability. However, modification methods focused on the hybrid premix have not been previously studied. In the present work, the interfacial strength of the hybrid composite was improved by treating the carbon and PEEK fibers together in a radiofrequency (RF) plasma containing one of the following gases to achieve surface activation: air, Ar, or Ar–air. After plasma treatment, the increased roughness of CF and the grafted chemical groups of CFs and PEEK fibers were propitious to the mechanical interlocking and interfacial strength. Significant interfacial shear strength (IFSS) enhancement was achieved after Ar 1 min, air 1 min plasma treatment. This study offers an alternative method for improving the interfacial properties of CF/PEEK composites by focusing on the boundary layer and modifying and controlling the fiber–matrix interface.

Blends of cyanate ester and phthalonitrile–polyhedral oligomeric silsesquioxane copolymers were prepared, and their cure behavior and properties were compared via differential scanning calorimetry (DSC) analysis, thermogravimetric (TG) analysis, dynamic mechanical analysis, Fourier-transform far-infrared (FTIR) spectroscopy, and rheometric studies. The copolymer blends showed high chemical reactivity, low viscosity, and good thermal stability (TG temperatures were above 400 °C). The glass-transition temperature of the blends increased by at least 140 °C compared to cyanate ester resin. The blends are suitable for preparing carbon-fiber-reinforced composite materials via a winding process and a prepreg lay-up process with a molding technique. The FTIR data showed that the polymerization products contained triazine-ring structures that were responsible for the superior thermal properties.

Continuous carbon fiber (CF)-reinforced poly (ether ether ketone) (PEEK) composites have excellent mechanical properties, but their processing techniques are limited. Therefore, we promoted a braiding method based on the hybrid fiber method by hot-compacting CF/PEEK plain weave fabrics to solve the problem of difficult wetting between CF and PEEK. Four parameters—melting temperature, molding pressure, crystallization temperature and the resin contents—were investigated for optimized fabrication. After studying the melting range, thermal stability and the contact angle of PEEK under different temperatures, the melting temperature was set at 370 °C. An ultra-depth-of-field 3D microscope was adopted to investigate the effects of molding pressure in the melting stage. The tensile strength or modulus along and perpendicular to the carbon fiber direction and crystallinity under different crystallization temperatures were analyzed. As a result, the sample crystalized at 300 °C showed an excellent tensile properties and crystallinity. The increased mass ratio of PEEK ranging from 50.45% to 59.07% allowed for much stronger interfacial strength; however, the higher resin content can lead to the dispersion of CFs, loss of resin and the formation of defects during processing. Finally, the optimal resin mass content was 59.07%, with a tensile strength of 738.36 ± 14.49 MPa and a flexural strength of 659.68 ± 57.53 MPa. This paper studied the optimized processing parameters to obtain better properties from CF/PEEK plain weave fabrics and to further broaden the specific applications of CF/PEEK composites, demonstrating a new direction for its fabrication.