The characteristics of silver inkjet printing were intensively investigated with control of surface energy and substrate temperature. A fluorocarbon (FC) film was spincoated on a silicon (Si) substrate to obtain a hydrophobic surface, and an ultraviolet (UV)/ozone (O 3 ) treatment was performed to control the surface wettability of the FC film surface. To characterize the surface changes, we performed measurements of the static and dynamic contact angles and calculated the surface energy by Wu's harmonic mean model. The surface energy of the FC film increased with the UV/O 3 treatment time, while the contact angles decreased. In silver inkjet printing, the hydrophobic FC film could reduce the diameter of the printed droplets. Merging of deposited droplets was observed when the substrate was kept at room temperature. Substrate heating was effective in preventing the merging phenomenon among the deposited droplets, and in reducing the width of printed lines. The merging phenomenon of deposited droplets was also prevented by increasing the UV/O 3 treatment time. Continuous silver lines in the width range of 48.04-139.21 µm were successfully achieved by inkjet printing on the UV/O 3 -treated hydrophobic FC films at substrate temperatures below 90 • C.
The objective of this research is to provide flexural test results that are applicable to the actual strengthening design of reinforced concrete (RC) beams by investigating the flexural capacities of RC beams strengthened with unbonded high-strength bars. The advantages of the proposed strengthening method are the speed and simplicity of installation. Additionally, it is possible to acquire strengthened performance without skilled workers. A set of ten laboratory tests on RC beams strengthened with high-strength bars and unstrengthened RC beams as the control group were performed. The main test parameters are the diameter of high-strength bar and the ratio of tension reinforcement. The equivalent tension reinforcement ratio of the high-tension bars to the strength ratio of rebars is also considered. The test result indicates that the maximum strain of the high-strength bars pretensioned with 40% yield strain exceeds the nominal yield strain of high-strength bars. The deflection ratio of the strengthened RC beam within the serviceability limit state was less than 54% in comparison with that of unreinforced beams. Thus, it is possible to simplify the design equation by using the equivalent tension reinforcement ratio.
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