The highly versatile fused filament fabrication (FFF) allows on-demand manufacturing of carbon fiber reinforced plastics (CFRP) structures with intricate geometries. However, the intrinsic low ...throughput and comparatively low strength of FFF have posed major hurdles for large-scale industrial applications. In this work, high strength PA6-CF composite parts containing up to 35 wt% CF are additively manufactured by directly feeding the composite pellets into a custom-designed screw-extrusion 3D printer. The effects of CF content on the rheological and mechanical properties of the PA6-CF composites are investigated in detail. Mechanical tests show that CF significantly enhances the strength of the 3D-printed composites. With 25 wt% CF, the tensile strength reaches maximum at 169.7 MPa, which is 3.2 times higher than the unfilled PA6, and is also among the highest for the 3D printed CFRPs reinforced by short fibers. In-depth microstructural characterization reveals the printed part retains long carbon fibers (average length over 200 μm) and has comparatively low porosity (2.93% at 25 wt% CF), which are conducive to achieve high mechanical strength. The mechanical strength also agrees reasonably well with the analytical model based on Kelly-Tyson equation.
Display omitted
•Successfully prepared PA6-CF composite pellets with three CF loadings (up to 35 wt%).•3D printing the pelletized composites with a screw-extrusion 3D printer.•The printed PA6-CF composites exhibit very high tensile strength, reaching 170 MPa.•The reinforcement saturation is identified around 25 wt% CF content.
The "Belt and Road" Initiative (BRI), i.e., the official Chinese term for the "Silk Road Economic Belt" and the "21st Century Maritime Silk Road", was proposed to share China's development ...opportunities with BRI-related countries and achieve common prosperity. Though the BRI itself conveys rich social and economic connotations, ecosystem health and the environmental problems in the Belt and Road regions are scientific issues. In this study, papers relating to the ecological issues of the BRI between January 2013 and December 2021 were collected and analyzed via CiteSpace. We found that some ecological issues were involved with the environmental challenges posed by the BRI, whereas others were, to a certain extent, subjective assumptions. Accordingly, we identified and classified the limitations and constraints of those environmental views about the BRI. By emphasizing that scientific data is key to explaining the ecological problems, we advanced four prospects for ecosystem health and environmental geography studies in the Belt and Road regions: (1) Spatial analysis and monitoring technology for the environment; (2) Clarification of the characteristics and mechanisms of the ecosystem and environments; (3) A focus on the interaction between the economy and the environment; (4) Specific and targeted strategies and solutions to different environmental problems.
Hard Cr–N and silicon doped Cr–Si–N nanocomposite coatings were deposited using closed unbalanced magnetron sputtering ion plating system. Coatings doped with various Si contents were synthesized by ...changing the power applied on Si targets. Composition of the films was analyzed using glow discharge optical emission spectrometry (GDOES). Microstructure and properties of the coatings were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and nano-indentation. The harnesses and the elastic modulus of Cr–Si–N coatings gradually increased with rising of silicon content and exhibited a maximum at silicon content of 4.1 at.% and 5.5 at.%. The maximum hardness and elastic modulus of the Cr–Si–N nanocomposite coatings were approximately 30 GPa and 352 GPa, respectively. Further increase in the silicon content resulted in a decrease in the hardness and the elastic modulus of the coatings. Results from XRD analyses of CrN coatings indicated that strongly preferred orientations of (111) were detected. The diffraction patterns of Cr–Si–N coatings showed a clear (220) with weak (200) and (311) preferred orientations, but the peak of CrN (111) was decreased with the increase of Si concentration. The XRD data of single-phase Si
3N
4 was free of peak. The peaks of CrN (111) and (220) were shifted slightly and broadened with the increase of silicon content. SEM observations of the sections of Cr–Si–N coatings with different silicon concentrations showed a typical columnar structure. It was evident from TEM observation that nanocomposite Cr–Si–N coatings exhibited nano-scale grain size. Friction coefficient and specific wear rate (SWR) of silicon doped Cr–N coatings from pin-on-disk test were significantly lower in comparison to that of CrN coatings.
This work demonstrates an effective and robust approach to regulate phase behaviors of a block copolymer by programming local features into otherwise homogeneous linear chains. A library of ...sequence-defined, isomeric block copolymers with globally the same composition but locally different side chain patterns were elaborately designed and prepared through an iterative convergent growth method. The precise chemical structure and uniform chain length rule out all inherent molecular defects associated with statistical distribution. The local features are found to exert surprisingly pronounced impacts on the self-assembly process, which have yet to be well recognized. While other molecular parameters remain essentially the same, simply rearranging a few methylene units among the alkyl side chains leads to strikingly different phase behaviors, bringing about (i) a rich diversity of nanostructures across hexagonally packed cylinders, Frank–Kasper A15 phase, Frank–Kasper σ phase, dodecagonal quasicrystals, and disordered state; (ii) a significant change of lattice dimension; and (iii) a substantial shift of order-to-disorder transition temperature (up to 40 °C). Different from the commonly observed enthalpy-dominated cases, the frustration due to the divergence between the native molecular geometry originating from side chain distribution and the local packing environment mandated by lattice symmetry is believed to play a pivotal role. Engineering the local chain feature introduces another level of structural complexity, opening up a new and effective pathway for modulating phase transition without changing the chemistry or composition.
Cr–N coatings were deposited using the ion-beam-assisted magnetron sputtering technique. The microstructure and mechanical properties of Cr–N coatings were found to be dependent on the ion ...bombardment energy. The microstructure of the coatings changes from columnar structure to fine and dense grains when the ion bombardment energy increases from 0 to 800
eV and to equiaxial grains for an ion energy of 1200
eV. The coatings average grain size, which is determined by the Voigt profile function, decreases from 20.3
nm at an ion energy of 0
eV to 8.8
nm at 800
eV and further increases to 21.5
nm at 1200
eV. Both the hardness and fracture toughness of the coatings are improved when the ion energy increases from 0 to 800
eV, which is related to the decrease of grain size. The grain size of the coating grown at an energy of 1200
eV is close to that of 0
eV, but the hardness and fracture toughness at 1200
eV are higher. This suggests that the improvement of hardness and fracture toughness is also related to the increased densification of the coatings caused by ion bombardment.
It is widely acknowledged that climate change has caused serious environmental issues, including drought, bushfires, floods, and heatwaves, and urban sustainability is currently seriously threatened ...as a result. Arden is one of the key urban regeneration areas set to experience dramatic residential changes under Melbourne's development blueprint within the next 20 years. The Arden Structure Plan (2022) outlines specific implementation steps but does not go into detail about the strategies and tactics used to address climate change and urban sustainability. Therefore, there are still problems with the plan, including a lack of information and time-bound development targets, ambiguous public engagement, little focus on urban crime, and insufficient climate change adaptation measures. The plan also considers affordable housing, a mixed-use development pattern that will significantly decrease environmental harm, and active transportation options, primarily walking and bicycling. Considering climate change, this plan will make Arden a suitable location for population growth. This paper aims to evaluate the Arden Structure Plan and make recommendations on how to improve the plan's urban sustainability and climate change considerations. Furthermore, it provides guidance on whether Arden is a suitable location for Melbourne's population growth in light of the climate change impacts anticipated to occur by 2100.
The additive manufacturing of continuous fiber reinforced thermoplastics (CFRTPs) paves way for the high‐strength, light‐weight components for variety of load‐bearing applications. In this work, the ...continuous carbon fiber reinforced PA6 (CCF‐PA6) composites was successfully printed from the prepreg filament. The prepreg filament was prepared in‐house by impregnating the heat‐and‐acid treated 1 K carbon fiber bundle with the molten PA6. The tensile strength of the prepreg filament, which contained with 40 vol% CF, reached 984 MPa. The unidirectional CCF‐PA6 specimens were subsequently 3D‐printed with the prepreg filament, and the mechanical strength of those 3D‐printed specimens were tunable by adjusting a set of printing parameters, such as layer thickness, hatch spacing and printing temperatures. The highest tensile strength of the specimen reached 555 MPa. Those specimens also exhibited outstanding mechanical strength at elevated temperatures, still reaching 184 MPa at 150°C. The mechanical strength of those specimens was dependent on the content of the fiber. This study can hopefully provide new insights for feedstock design and spur novel ideas in tailoring the mechanical properties of the 3D‐printed CFRTPs.
In this work, the continuous carbon fiber reinforced PA6 (CCF‐PA6) composites was successfully 3D‐printed from the prepreg filament. The printed specimens not only exhibit superior mechanical strength, but also excellent thermal stability, which pave ways for a variety of load‐bearing applications.
To improve the feature extraction ability of multipath signals and reduce the dependence on environmental information, this paper studies a method that combines multipath signal feature information ...mining and neural network in high-dimensional phase space instead of using the received complex acoustic pressure as the input of the neural network directly. Based on the phase space reconstruction (PSR) technology, we propose a hybrid model of the self-attention-based Transformer and convolutional neural network (CNN), named PSR-TransCNN. The covariance matrix of the reconstructed data is constructed as the input of the sparse auto-encoder (SAE). A transfer learning strategy is employed to obtain the optimal weight and offset value of SAE, which serve as the initial values of the PSR-TransCNN. Real-world experimental results demonstrate that the PSR-TransCNN significantly reduces the relative root mean square error (RMSE) by 0.006 compared with the matched field processing (MFP) method and exhibits outstanding generalization and practical application potential compared to other state-of-the-art (SOTA) methods. The PSR-TransCNN achieves an RMSE of 0.046 and an accuracy of 88.75%, successfully classifying sound sources with unknown labels. The proposed method effectively reduces the multipath effects and addresses the mismatch issue in sound source ranging (SSR) within an unexplored ocean environment.
Display omitted
•Investigating sound source ranging in simulated and SwellEx-96 actual ocean environments.•Phase space reconstruction is an effective data preprocessing method to alleviate multipath effects.•The generalization properties of different models trained using trial data are studied.•The effects of classifying sound sources with unknown labels are analyzed.
