Seung-Muk Bae

Electrical/Mechanical Monitoring of Shape Memory Alloy Reinforcing Fibers Obtained by Pullout Tests in SMA/Cement Composite Materials

Self-healing is an essential property of smart concrete structures. In contrast to other structural metals, shape memory alloys (SMAs) offer two unique effects: shape memory effects, and superelastic effects. Composites composed of SMA wires and conventional cements can overcome the mechanical weaknesses associated with tensile fractures in conventional concretes. Under specialized environments, the material interface between the cementitious component and the SMA materials plays an important role in achieving the enhanced mechanical performance and robustness of the SMA/cement interface. This material interface is traditionally evaluated in terms of mechanical aspects, i.e., strain–stress characteristics. However, the current work attempts to simultaneously characterize the mechanical load-displacement relationships synchronized with impedance spectroscopy as a function of displacement. Frequency-dependent impedance spectroscopy is tested as an in situ monitoring tool for structural variations in smart composites composed of non-conducting cementitious materials and conducting metals. The artificial geometry change in the SMA wires is associated with an improved anchoring action that is compatible with the smallest variation in resistance compared with prismatic SMA wires embedded into a cement matrix. The significant increase in resistance is interpreted to be associated with the slip of the SMA fibers following the elastic deformation and the debonding of the SMA fiber/matrix.

Application of soft lithography to metal-induced lateral crystallization of amorphous Si thin films involving self-assembly monolayers and atomic layer deposition.

Micro-contact printing of self-assembly monolayers (SAMs), i.e., octadecyl-trichlorosilane (OTS) was combined with self limiting atomic layer deposition in order to fabricate the selective deposition of nickel oxide on amorphous Si thin films. The localized nickel species facilitated metal-induced crystallization (MIC) and at later stages, metal-induced lateral crystallization (MILC) in amorphous Si thin films at the elevated temperatures ranging from 500 °C to 550 °C. The uniform coating of SAMs onto amorphous Si thin films was monitored using physical/chemical characterization, i.e., atomic force microscopy, electron microscopy, and Raman spectroscopy. The crystalline feature was found to be superior to the counterpart solid-phase crystallization. The effectiveness of SAMs appears to provide the microscale patterning in addition to the sophisticated control against nickel-species.

Extraction of quantitative parameters for describing the microstructure of solid oxide fuel cells.

Digital quantification of a two-dimensional structure was applied to a GDC(Gd₂O₃-doped CeO₂)/LSM(La₀.₈₅Sr₀.₁₅MnO₃) composite cathode employed for solid oxide fuel cells. With the aid of high-resolution imaging capability based on secondary and backscattered electron images, two-dimensional electron micrographs were converted to digital binary files using an image processing tool combined with the line intercept method. Statistical analysis combined with a metallurgical tool was employed to determine microstructural factors, i.e., volume fraction, size distribution, and interconnectivity. The current work reports the quantification of the two-dimensional structural images of GDC/LSM composites applicable to solid oxide fuel cells, with the aim of obtaining the volume fraction, size distribution, and interconnectivity as functions of composite composition. The volume fractions of the solid constituent phases exhibit compositional dependence in cathodes; however, LSM interconnectivity increases gradually as a function of LSM composition, whereas that of GDC decreases significantly at 50 wt% LSM.