Jin-Yeong Choi

Mechanical and electrical properties of electrospun CNT/PVDF nanofiber for micro-actuator applications

Electrospun polyvinylidene fluoride (PVDF)-containing carbon nanotubes (CNT) were prepared for use in fabricating actuator materials. Actuating displacement was measured in an electrochemical environment. The electrospun nanofibers were arranged using a drum-type collector, and morphology was investigated using a field emission-scanning electron microscope. The uniformity of dispersion of CNT in the PVDF nanofibers was monitored by electron probe X-ray micro-analysis. Tensile strength and electrical resistivity results were used as an indication of the state of alignment. The electrospun CNT/PVDF nanofiber sheets exhibited better mechanical and electrical properties in the arranged direction. The efficiency and electrical capacities of electrospun CNT/PVDF nanofiber sheet were compared with those of cast PVDF sheets for use in actuator applications in electrochemical environments. The electrospun CNT/PVDF nanofiber sheets exhibited much better actuator performance than PVDF sheets, which are attributed to their superior electrical properties. Highlights (1) The interfacial durability of CNT/PVDF nanofibers was enhanced to increase contact area by reinforcing CNT. (2) The efficiency of CNT/PVDF actuators was improved due to interfacial properties. (3) Thin thickness drum-type collector was made to enhance nanofiber alignment. (4) The arranged CNT/PVDF nanofibers exhibited better mechanical and actuating displacements.

To improve interfacial and mechanical properties of carbon fiber–modified nano-SiC–epoxy composites using dispersion and wetting control

Significant improvements in mechanical properties (particularly stiffness) result from the appropriate addition of micro-carbon fibers in the nano and heterostructures of modified nano-SiC-filled epoxy matrix composites. The optimum dispersion conditions were found to be significantly dependent upon both the amount of nano-SiC filler and the sonication time. To investigate these dispersion effects, composites were fabricated with five different nano-SiC filler concentrations and compared to the untreated composite. Changes in electrical capacitance were used as a measure of the comparative degree of dispersion in these nano-SiC–epoxy composites. FE-SEM was used to observe the interfacial changes for the different surface conditions, and the mechanical damage was evaluated by inspection of fractured surfaces. Optimal conditions of dispersion, interfacial adhesion, and aspect ratio of the modified nano-SiC fillers were found to improve the composites’ mechanical properties.

Meso-scale finite element modeling of NomexTM honeycomb cores

NomexTM honeycomb core composite sandwich panels are widely used in aircraft structures. Detailed meso-scale finite element modeling of the honeycomb geometry can be used to analyze sandwich inserts, vibration response, and complex combined loading cases. The accuracy of a meso-scale honeycomb modeling technique for static load cases was evaluated. A rectangular honeycomb core was modeled with perfect hexagon honeycomb cells. Compression and shear tests simulations with linear and non-linear solutions were performed for four core densities. The simulated moduli and buckling strengths were recorded. These results were compared to property data published by honeycomb manufacturers. The simulated maximum honeycomb wall stresses at the manufacturer predicted core strengths were also recorded. The honeycomb walls’ first compression deformation mode shape was observed. Sinusoidal small imperfections were then introduced in the honeycomb geometry based on that deformation mode shape. These imperfections provided a better match to manufacturer compressive modulus data while having a limited impact on the shear moduli. The simulated properties did not exactly match manufacturers’ shear and compression data together for all the core densities. Modeling the honeycomb cells with rounded corners and with increased thickness at the cell junctions are potential strategies to improve the accuracy.

Improvement in mechanical properties of recycled GF prepreg with CNT reinforced composites using a spray coating method

Dispersion and shape of nanoparticles, as well as interfacial conditions, add significantly to difficulties in composite manufacture. In the work reported here, an innovative method of recycling composites using out-of-date prepreg was investigated in which the carbon nanotube (CNT) on the prepreg was optimally coated. Nanocomposites utilizing the out-of-date prepreg were coated with CNT and fabricated by a sheet molding method. CNT nanofillers were observed to be uniformly dispersed on epoxy prepreg by spray coating. The mechanical and interfacial properties of these CNT coated nanocomposites were improved over those of more conventionally manufactured carbon fiber/epoxy composites. The CNT nanofillers were embedded at the epoxy and fiber interface, as a result of etching of the epoxy prepreg surface by a CNT dispersion solution which enhanced interfacial reactivity.