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Additive manufacturing (AM) of continuous fiber-reinforced thermoplastic composites (CFRTPCs) has become a hot area for both academia and industry. In this paper, a robot-assisted laser additive manufacturing (RLAM) technique is proposed, which involves utilizing a laser beam to heat the filament to a semi-molten state, followed by compacting it with a roller and bonding it layer by layer to create densely structured components. Firstly, an integrated framework of hardware, software, and control systems is presented. Then, the relationship between the processing parameters and the properties of the final specimens was examined. Finally, a process strategy was proposed to improve the forming accuracy. Due to the effective impregnation of continuous carbon fibers, the printed CFRTPCs using the LRAM process exhibit comparatively low porosity and superior mechanical performance. Specifically, the flexural strength, flexural modulus, and interlayer shear strength reached 584 MPa, 43.7 GPa, and 28.0 MPa, respectively. The prepared specimens boast a porosity of 0.19%, approaching levels achieved through autoclave processes. In addition, it was found that the dynamic offset of the yaw axis could be utilized to correct the deviation of the actual forming path due to the pultrusion force, thus making the position of the towpreg under the rollers controllable and improving the accuracy of the parts. This new method combines the advantages of industrial robotics and laser&roller-based continuous fiber additive manufacturing processes to enable high-performance additively manufactured large and complex CFRTPCs, which shows great potential for printing lightweight structures in the rail transit and aerospace industries. [Display omitted] • Laser assistance and roller pressure enhancement enable higher forming temperatures and pressures during the printing process. • Integrates hardware, software, control for rapid development of robot-assisted additive manufacturing. • High mechanical properties and low-porosity exceed nozzle-based 3D printing technology. • Dynamic yaw axis correction for pultrusion-induced deviations, improving forming accuracy. • RLAM increases design freedom of fiber paths, enabling AM of intricate CFRTPCs. Applications span aerospace and rail. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new method to generate the random distribution of fibres in the transversal cross-section of fibre reinforced composites with high fibre volume fraction. The algorithm, named random sequential expansion (RSE) algorithm by the authors, is based on the hard-core model, but overcomes the jamming limit of hard-core model and is able to generate random distributions for high values of fibre volume fractions. By adjusting the inter-fibre distance parameters, it can generate microstructures with different fibre volume fractions expediently. Statistical analysis is performed on the generated distributions and a good agreement with the completely spatial random (CSR) pattern is found in all statistics analysed. Finite element analysis (FEA) is conducted to predict the effective properties of the generated microstructures. The predicted properties show reasonable agreement with the experimental results. The present algorithm is simple, highly efficient and provides a useful alternative to generate random numerical models that can be used in micromechanical analysis of composites. [Copyright &y& Elsevier]

Abstract: The mechanical behavior of unidirectional fiber-reinforced polymer composites subjected to tension and compression perpendicular to the fibers is studied using computational micromechanics. The representative volume element of the composite microstructure with random fiber distribution is generated, and the two dominant damage mechanisms experimentally observed – matrix plastic deformation and interfacial debonding – are included in the simulation by the extended Drucker–Prager model and cohesive zone model respectively. Progressive failure procedure for both the matrix and interface is incorporated in the simulation, and ductile criterion is used to predict the damage initiation of the matrix taking into account its sensitivity to triaxial stress state. The simulation results clearly reveal the damage process of the composites and the interactions of different damage mechanisms. It can be concluded that the tension fracture initiates as interfacial debonding and evolves as a result of interactions between interfacial debonding and matrix plastic deformation, while the compression failure is dominated by matrix plastic damage. And then the effects of interfacial properties on the damage behavior of the composites are assessed. It is found that the interfacial stiffness and fracture energy have relatively smaller influence on the mechanical behavior of composites, while the influence of interfacial strength is significant. [Copyright &y& Elsevier]

We report magnetic alignment of single-crystalline microdiamonds with aid of superparamagnetic magnetite in polymeric composites and their material properties. The silicone composite containing aligned microdiamonds shows interesting properties in alignment direction, including enhancement of thermal conductivity, 250% higher than that of randomly dispersed counterpart at a low loading of 5.1 vol%. Composites with aligned diamond exhibited enhanced thermal conductivity and electrical insulation compared with matrix, and are attractive for application as thermal interface materials in the semiconductor industry, though the introduction of magnetite had part of negative effect on electrical resistivity of composites. A two-level model that accounts first-order interaction between particles to calculate effective thermal conductivity of composites with aligned microdiamonds, is found to fit accurately absolute value and tendency of thermal conductivity for composites with aligned particles. Utilizing the modelling procedure, the volume fraction of microdiamonds within chains is 0.3, which is smaller than 0.698 predicted for ideal body-centered-tetragonal arrangement of particles. This suggested that thermal conductivity of composites can be enhanced further by improving microstructures within particle chains. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA), as a biodegradable thermoplastic resin, has received extensive research and attention. However, PLA exhibits severe brittleness at room temperature, which will greatly limit its practical engineering application. Herein, five kinds of epoxy microspheres (EPs, 0.07–20 μm) with high surface reactivity were synthesized by the double emulsion method for toughening and reinforcing PLA. It is found that EPs efficiently improve the toughness of films while maintaining the high tensile strength and modulus. At only 0.5 wt% EPs, the elongation at break of PLA is increased to 19.5%, which is 4.9 times that of pure PLA. The efficient improvement in toughness is attributed to the reaction between surface epoxy groups of EPs and O–H of PLA. Toughening mechanisms mainly involve stress concentration, debonding cavitation, crazing growth and shear yielding plastic deformation. Meanwhile, due to the high rigidity of EPs, the tensile strength and modulus of PLA/0.5% 300 nm EPs film are 15.1% and 7.3% higher than that of pure PLA, respectively. This work exhibits a potential and promising application in toughening and reinforcing PLA. A series of epoxy microspheres (EPs) with large specific surface area, strong adhesion and high surface reactivity were synthesized by the double emulsion method for toughening and reinforcing polylactic acid (PLA). The stress-strain curves indicate that EPs can efficiently improve the toughness of films while maintaining the high tensile strength. The shear yielding of the PLA matrix is the main reason for achieving super toughness. [Display omitted] • EPs were successfully prepared by double emulsion method with buffer solution as the inner aqueous phase. • Compared with the general nano-toughening agent, EPs have excellent reactivity without any chemical modification. • At only 0.5% filling, the elongation at break of PLA/300 nm EPs film is 4.9 times that of pure PLA. • Debonding cavitation and crazing achieve initial toughening, while shear yielding bring super toughness. [ABSTRACT FROM AUTHOR]

Poly-ether-ether-ketone (PEEK) implants fabricated by laser powder bed fusion (LPBF) are promising candidates for bone tissue engineering because of the excellent biocompatibility of the material and the ability to realize personalized bone repair. However, the weak LPBF processability and biological inertness of PEEK limit the clinical application. In this work, bioactive glass (BG) is blended into PEEK and found to improve the LPBF processability and bioactivity. The results show that PEEK/BG composite powders exhibit better LPBF processability due to the wider sintering window (48.9%–79.1% wider) and higher thermal conductivity (5.7%–23.0% higher) compared with the pure PEEK as well as the crystallization inhibition during the cold powder spreading. The melting enthalpy and thermal stability of the composite reduce when the BG content increases, thereby leading to the decrease of the optimal laser power during the LPBF process. The modulus of PEEK/BG composites ranges from 2685.82 MPa to 3729.33 MPa, which can match the modulus of human cancellous bone. The variation of lattice constant c and cell volume with the laser power of the composites all show a similar trend to the mechanical properties. BG can promote hydroxy-carbonate-apatite deposition, suggesting that BG has great potential to promote osteogenesis. By varying the amount of BG incorporated, the PEEK composite implants can be applied to different regions in the body depending on the specific clinical requirements. [Display omitted] [ABSTRACT FROM AUTHOR]