The pencil lead drawing paper sensor (PLDPS) is a flexible and wearable sensing device, a new concept sensor that offers a tremendous potential feasibility for a variety of applications. Highly responsive, sensitive, low cost, easy-tohandle pencil lead graphite and paper made from cellulose pulp fibers extracted from wood, rags or grass, which are inexpensive, nature-friendly materials were used. The sensing effect on 3 different papers (Plane, Hwasun, and Han papers) based on the properties of PLDPS was compared via FT-IR, tensile test, optical observation and initial electrical resistance (ER). The interfacial and mechanical properties of epoxy and GF/epoxy composites were evaluated by damage sensing and ER mapping using PLDPS with impact, flexural, and interlaminar shear strength (ILSS) tests. The optimum type of paper used as the adherend for the pencil sensor was chosen as the plane paper. As glass fiber (GF)/epoxy composites were severely damaged, the large change in ER of PLDPS was observed distinctly.
Thermal conductivity of polyetheretherketone (PEEK) with fillers was investigated. By adding the hybrid fillers to polymer the thermal conductivity of composites was increased significantly. Thermal diffusivity of composites was measured using laser flash method. Synergistic filler effect between particulate SiC and carbon fiber (CF) was observed for thermal conductivity. In a PEEK based composite, thermal conductivity increased to 8.25 W/m-K for a 50 vol% hybrid filler (SiC+CF) system, whereas the thermal conductivity of 40 vol% CF was 3.1 W/m-K and 50 vol% of SiC was 2.4 W/m-K, respectively. The use of hybrid filler was found to be effective in increasing thermal conductivity of its composites due to formation of effective thermal conductive path. Experimental results of two-phase system were compared with Nielsen prediction.
Cure monitoring and stress-strain sensing of single-carbon fiber composites were nondestructively evaluated by the measurement of electrical resistance. The difference of electrical resistance before and after curing increased highest when gauge length of the specimen was the smallest. As curing temperature increased, the electrical behavior of steel fiber was different from that of semi-conductive carbon and SiC fibers. Residual stress built in the fiber was the highest at the fiber axis direction. Whereas residual stress built in the matrix was relatively high at the fiber circumference and radius directions. Residual stress calculated from the experiment was consistent with the results from the finite element analysis (FEA). The strain at low curing temperature was larger than that of higher temperature until the load reached maximum value. The apparent modulus of the electrodeposited composites was higher than that of the untreated composites due to the improved interfacial shear strength (IFSS). The electrical resistance was responded quantitatively with stress-strain behavior during the test. Electrical resistance measurement can be feasible nondestructive techniques to evaluate cure monitoring and stress-strain sensing in the conductive fiber composites.
Thermal properties of PEEK/silicon carbide(SiC) and PEEK/carbon fiber(CF) were investigated from ambient temperature up to 200°C measured by laser flash method. Thermal conductivity was increased from 0.29W/m-K without filler up to 2.4 W/m-K with at 50 volume % SiC and 3.1W/m-K with 40 volume % carbon fiber. Values from Nielsen theory that predicts thermal conductivity of two-phase system were compared to those obtained from experiment.
Sensing of dispersion and adhesion of PU type aircraft topcoat layer for LSP (Lightning Strike Protection) was evaluated by 2 dimensional (2D) electrical resistance (ER) mapping with different treatment times and multi-wall carbon nanotube (MWCNT) weight fractions. Conductive MWCNT was treated using hydrogen peroxide to improve dispersion in polyurethane (PU) type paint for several days. After treatment processing, MWCNT was dispersed in PU type coating solution using sonication dispersion method. CNT/PU coating solution was applied on the aircraft surface of carbon fiber reinforced epoxy composite (CFRC) using spray method. Static contact angle was performed using 4 types of solvents to calculate the work of adhesion between CNT/PU coating layer and CFRC surface. Surface ER of MWCNT added PU coating layer was measured to determine MWCNT dispersion. Visualization of MWCNT dispersion exhibited using 2-D ER mapping, whereas adhesion between MWCNT/PU coating layer and CFRC was evaluated via cross hatched cut test. The optimized condition of MWCNT treatment time and MWCNT weight fraction was found intensively.
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