Materials Science Forum Vol. 1107

Abstract: Polyamide (PA) nanofibers (NFs) interleaves have been inserted as a continuous non-woven mat between prepreg plies of a carbon fiber reinforced (CFR) laminate during lamination. Hybridization has been made by mixing two different material scales, being the micro-scale and the nanoscale of the CFs and the NFs respectively and two different polymer types being thermosetting the matrix and thermoplastic the NFs. Final composite laminates have been produced by vacuum bagging and autoclave molding according to the consolidated industrial procedure of aeronautic parts. Traditional square CFR laminates with 20 plies have been also manufactured using the same unidirectional (UD) CFR prepreg tape with 0/90 stacking sequence for comparison. Rectangular specimens were finally extracted from the manufactured plates. Dynamic mechanical analysis (DMA) and three-point bending tests were carried out. The reduction of the glass transition temperature T_g revealed the achieved interaction among PANFs and the resin matrix. Moreover, bending strength increased up to 9% for hybrid laminates revealing that nanostructures can add functionalities to traditional composite laminates without affecting their mechanical performances.

Abstract: A 3d printer has been prototyped for additive manufacturing of carbon fiber (CF) poly-ether-ketone-ketone (PEKK) composites. The machine consisted of a SCARA robot, equipped with an extrusion device. The nozzle was designed to allow the deposition of thin unidirectional (UD) tapes without affecting the fiber continuity. An elastic connection between the robot end-effector and the extruder was used for allowing tape agglomeration during manufacturing. Deposition tests were carried out at the extrusion temperature of 400°C and the rate of 130 mm/min, for a maximum number of 3 layers on a CF-epoxy laminate as substrate. The good agglomeration of the 3d printed parts and their adhesion on the composite substrate are shown by the resulted final thickness, and the ability to machine them by end milling. Results show the feasibility of using this technology for the manufacturing of composite shims in the aeronautic sector.

Abstract: Flexible sensors and actuators have broad applications in the fields of wearable electronics for health, sports, functional textiles, robotics and cobot applications. Graphene-or graphite-based polymer nanocomposites are promising materials for the development of soft sensors and actuators. This study investigates strain sensing properties of silicon rubber with various graphene filler concentrations (8wt%-12wt%). Current-voltage characteristics have been measured under various strains. We obtain that the sensor’s electrical resistance, for a given voltage, can be approximated by a linear fit of the logarithmic resistance as function of the extension ratio of the sensor. The obtained mechanically induced logarithmic resistor behavior of the polymer nanocomposite is highly promising for the development of electronic sensing and control. Furthermore, thin film graphite layers were investigated on highly stretchable silicone membranes.

Abstract: The ARB (Accumulative Roll Bonding) method is greatly watched as a new severe plastic deformation process that uses only a conventional general rolling machine. The ARB method is a preparation method of ultra-fine-grained, high-strength thin metal and alloy sheets by repeated rolling. The purpose of this study was to clarify the effectiveness of the ARB method as a metal matrix composite manufacturing process. At first, alumina particles and short carbon fibers were used as dispersoids, and pure aluminum was used as the thin plate. Then, the dispersoids were deposited on a pure aluminum plate to 2 vol.% dispersoids. Six of these aluminum sheets were stacked to form a multi-layer composite sheet, which was then cold rolled at a rolling reduction of 67%. After rolling, the sheet composites were cut in half, overlapped, and rolled again. The composites were obtained by repeating this process. When the repetition exceeded 6 times, the dispersoids tended to disperse in the aluminum matrix. In addition, uniform dispersion progressed through further repeat rolling. By repeated rolling, the tensile strength of the composite sheets was greatly improved. In addition, the tensile strength of the composites was higher than that of the ARB-processed monolithic aluminum sheet. The improvement in strength was caused by the refinement of aluminum grains rather than the particle dispersion.

Abstract: In previous research conducted by the authors, a new vibration-damping steel sheet was developed using a new method employing friction stir forming (FSF) to create a laminated composite sheet in which steel sheets and superplastic alloys are laminated in layers. However, the details of the bonding mechanism have not yet been clarified. The present study investigates the relationship between the pressure during the process and the weld interface in the creation of the mentioned superplastic composite sheet. More specifically, a 0.5mm thick perforated steel plate is inserted between two Zn-22Al superplastic alloys and the FSF is applied to the top layer of Zn-22Al. The probe of the FSF tool passes directly above the perforated steel plate, the material stirred by the probe plastically flows into the hole and is joined to the underlying Zn-22Al interface by superplastic diffusion bonding (SPF/DB). It was revealed that the process parameters (rotational speed and tool feed rate) must be perfectly adequate to produce adequate heat input and pressure leading to a proper plastic flow of the material and the occurrence of superplasticity in Zn-22Al. In this study, as a first step to clarify the detailed joining mechanism, the amount of pressure applied to the specimen during the process is measured. While changing the process parameters, the pressure was measured at three points, under the probe of the friction stir process tool and, on the advancing, and retreating sides, to investigate the relationship between the parameters and the pressure at the joint interface.

Abstract: Hybrid composites are gaining increasing interest in the development of aluminium metal matrix (AMCs) for various industrial applications owing to their ability to integrate multiple functionalities within a single material matrix with enhanced physio-mechanical properties as opposed to single-fibre reinforced composites. Green plantain peel ash (GPPA) is an agricultural waste with potential for reinforcement purposes. However, no study has investigated GPPA natural filler as a reinforcement for AMCs. This study, therefore, aims at assessing the influence of variations in GPPA particles and alumina as reinforcements in the fabrication of hybrid composites using Al-Mg-Si alloy as a matrix. This study also reassessed the chemical composition of the GPPA particles and investigated their mechanical properties. However, enhanced mechanical properties, including hardness, tensile strength, and ductility, were observed at varying weight ratios. Results obtained in this study suggest a promising potential application of GPPA particulates as complementing reinforcements in the production of lightweight, strong, and high-performance AMCs well-suited for engineering, aerospace, construction, and packaging applications.

Abstract: Harmonic structure has a heterogeneous microstructure consisting of bimodal grain size together with a controlled and specific topological 3D distribution of fine and coarse grains. These microstructural features of the harmonic structure materials lead to unique mechanical properties. In this study, harmonic structure was designed using the severe plastic deformation powder metallurgy process at room and cryogenic temperatures on pure nickel. There is no difference in appearance between mechanically milled (MM) powder at room and cryogenic temperatures. The compacts of the MM powder show the harmonic structure with a network fine grained area and the dispersed coarse grain area. The MM at cryogenic temperature affects the compact of the MM powder milled for 86.4 ks and its effects include an increase in shell fraction and a decrease in core grain size. Moreover, the harmonic structure materials show a synergy extra hardening in Hall-Petch relation. It is noteworthy that the harmonic structure materials exhibit a higher Hall-Petch coefficient than the homogeneous compacts despite of the same material.

Abstract: The high-temperature deformation behavior and microstructural changes of harmonic structure composites with WC-Co alloys and high-speed steel (HSS) were investigated in detail. A harmonic structure composite was fabricated by consolidating the mechanically milled powder having WC-Co and HSS powder. The harmonic structure composite demonstrates the microstructure composed of network area (WC-Co) and dispersed area (HSS). The harmonic structure composite shows a sufficient compressive strength in the compression tests at 773 K, but the compression strength decreases at temperatures of above 873 K. The 0.2% proof stress at high temperature almost unchanged even if the network area fraction changed. Furthermore, the network area plays an important role in the high temperature deformation of harmonic structure composites. These results suggest that the formation of voids for WC-Co boundary sliding and poor sintering is an important factor in stress reduction in the high-temperature compression of harmonic structure composites.

Abstract: Diffraction contrast tomography using ultrabright synchrotron radiation X-rays was performed on an austenitic stainless steel with a bimodal harmonic structure in which a network structure of fine grains (Shell) surrounds a coarse grain structure (Core). Then, not only were the shape and position of each grain reconstructed, but the change in excess dislocation density during the fatigue process, Δρ, was also measured. The results show that Δρ depends on the diffraction plane, Schmidt factor, and grain size, and that the change in Δρ during the fatigue process of a harmonic structured material is less than that of a conventional material. This result indicates that the network of fine grains in the harmonic structure supports microdeformation and suppresses the deformation of coarse grains. Furthermore, it was found that Δρ of grains unrelated to crack initiation increased continuously with the number of cycles, whereas that around the crack initiation site decreased with crack initiation.