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In this study, the moisture related hygroscopic characteristics and mechanical properties of polymer–clay nanocomposites (PCNs) were investigated using molecular dynamics (MD) simulations and experiments as a function of the weight fraction of nanoclay. The hygroscopic and mechanical properties including the moisture saturation amount, moisture diffusivity, work of adhesion, and elastic modulus of the PCNs were studied using MD simulations and compared to experimental results as a function of the nanoclay content. It was demonstrated that the proposed MD simulation technique can be successfully used for the prediction of the effects of the nanoclay on the moisture diffusion characteristics as well as mechanical improvements of PCNs. It is expected that the simulation technique applied in this work can be widely used to evaluate the performances of nanocomposite materials. [ABSTRACT FROM AUTHOR]

Abstract: Copper nano-ink with a drop-on-demand (DOD) piezoelectric inkjet printing method was introduced. The printed electrodes were thermally sintered to ensure high-quality electrical and mechanical performances. To check the reliability of the printed electrodes on a polymer layer, resistance changes were measured under static loading. The electrodes with various widths and thicknesses were used to find the optimal dimensions. A multifunctional composite laminate which can harvest and store a solar energy was fabricated using printed electrodes. An amorphous silicon solar cell and a thin film solid state lithium-ion battery were adhesively joined and electrically connected to a thin flexible printed circuit board (PCB). Then, the passive components such as resistor and diode were electrically connected to the printed circuit board by silver pasting. The integrated PCB was co-cured with a carbon/epoxy composite laminate by the vacuum bag molding process in an autoclave. The structural and functional performance of the final energy harvesting/storage composite laminate was tested under mechanical loading. [Copyright &y& Elsevier]

Abstract: The cure kinetics of a thermally mendable polymer based on Diels-Alder (DA) and retro-Diels-Alder (rDA) reactions, mendomer 401, was investigated using dynamic differential scanning calorimetry (DSC). The resulting behavior was modeled using a conventional cure kinetic model for thermosetting polymers. A composite panel with two layers of carbon fabric and mendomer 401 was fabricated following the cure cycle suggested by the cure kinetics model. Micro-indentation tests were performed to investigate mechanical properties and dynamic mechanical thermal analysis (DMTA) was conducted to study thermal behavior and to find the trigger temperature for healing. Self-healing behavior of the carbon fiber/mendomer composite was demonstrated using electrical resistive heating over the glass transition temperature. [Copyright &y& Elsevier]

Abstract: In this work, cure control system using dielectrometry for co-cured metal/composite hybrid structures was devised to reduce the fabricational thermal residual stress of the bonding layer between metal and composite material. The cure kinetic model of carbon fiber epoxy composite materials was developed by curve fitting the differential scanning calorimetry (DSC) data. The relationship between start of cure and gelation points of epoxy resin and the dissipation factor were investigated. The degree of cure was obtained by comparing the dissipation factor from the dielectric properties to the degree of cure from the DSC. Also, the curvature experiment of co-cured steel/composite strip and the static lap shear tests of the co-cured steel/composite lap joints were measured to investigate the effect of cure cycle on the thermal residual stress of the co-cured hybrid structures. From these results, the cure control algorithm using the dielectrometry for reduction of thermal residual stress was devised and verified under various temperature profiles. [Copyright &y& Elsevier]

Abstract In this work, damage sensing and self-healing of carbon fiber polypropylene (CFPP)/carbon nanotube (CNT) nano-composite were performed based on addressable conducting network (ACN). To increase damage sensing resolution of CFPP/CNT nano-composite, through-thickness electrical conductivity was improved by adjusting press condition and spraying carbon nanotubes (CNT) between prepregs. From the results, electrical resistivity in thickness direction was reduced to 19.44 Ω·mm under 1.0 MPa and 1.0 wt% of CNT condition. Also, self-healing efficiency was examined with respect to the temperature and time via resistive heating of CFPP/CNT nano-composite. As a result, the optimized fabrication and self-healing condition exhibited high resolution of damage sensing with outstanding self-healing efficiency (96.83%) under fourth cycle of repeated three-point bending test. [ABSTRACT FROM AUTHOR]

The terahertz time-domain spectroscopy (THz-TDS) imaging technique was used to detect the weld line defect of an injection-moulded short glass fiber-reinforced composite. To determine the effect of the weld lines on tensile strength, tensile tests were conducted with the specimens fabricated with NORYL (amorphous blends of polyphenylene ether resin and polystyrene) having a short glass fiber content ranging from 0% to 30%. The time delay phenomenon of the THz waves was observed with respect to the weld line and short glass fiber contents. The interaction between the THz waves and structural characteristics of the weld line, such as density and fiber orientation, were studied and different time delay phenomena of THz signal were observed owing to the different refractive index of the weld line defect. The refractive index of THz wave was also obtained by an analytical calculation and compared with the experimental results in order to determine the correlation between degradations of tensile strength and changes in the reflected THz wave caused by the weld line. Finally, the weld line defect of the specimens was successfully detected and identified using a THz-TDS imaging technique, showing that this technique is a nondestructive inspection method that can be utilized to evaluate the reliability of injection moulded short glass fiber-reinforced composite structures. [ABSTRACT FROM AUTHOR]

The electrical resistance change method (ERCM) is a promising method for structural health monitoring (SHM) of composites. In this work, copper (Cu) nano-ink was printed and successfully sintered on carbon-fiber-reinforced polymer (CFRP) substrate for damage sensing via a flash light sintering method. Before printing, surface-polished CFRP substrate was flash light treated to remove remnant epoxy between carbon fibers. Then, Cu nano-ink was formulated and printed on the CFRP substrate, and the printed Cu nano-ink patterns were sintered within a few milliseconds using a range of flash light irradiation energies. A two-step flash light sintering method to reduce contact resistance between the Cu electrode and CFRP interface was further investigated. Fabricated Cu electrodes were characterized using scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Using a two-step sintering approach, we fabricated Cu electrodes on CFRP with low contact resistance (0.93 Ω), high durability, and no mechanical degradation of CFRP substrate. [ABSTRACT FROM AUTHOR]

Thermoplastic differs in crystallinity depending on the manufacturing conditions such as temperature and cooling rate, which affect the mechanical properties of the thermoplastic-based composites. In this work, the crystallinity of polyethylene terephthalate (PET) was varied according to the cooling rate to investigate the mechanical properties of PET matrix-based carbon fiber (CF)/PET composites. The thermal characteristics and crystallinity were analyzed through the differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis. The mechanical behavior of CF/PET composites with different degrees of crystallinity was studied with varied temperature conditions. The failure modes of the fractured CF/PET composites were observed by using a digital microscope and scanning electron microscope (SEM). As a result, the crystallized CF/PET composites were improved 11.6 times higher in in-plane shear (±45° laminated) strength and 3.78 times higher in shear modulus than that of amorphous CF/PET composites at high temperature. [Display omitted] [ABSTRACT FROM AUTHOR]