A new microrobot manipulation technique with high precision (nano level) positional accuracy to move in a liquid environment with diamagnetic levitation is presented. Untethered manipulation of microrobots by means of externally applied magnetic forces has been emerging as a promising field of research, particularly due to its potential for medical and biological applications. The purpose of the presented method is to eliminate friction force between the surface of the substrate and microrobot. In an effort to achieve high accuracy motion, required magnetic force for the levitation of the microrobot was determined by finite element method (FEM) simulations in COMSOL (version 5.3, COMSOL Inc., Stockholm, Sweden) and verified by experimental results. According to position of the lifter magnet, the levitation height of the microrobot in the liquid was found analytically, and compared with the experimental results head-to-head. The stable working range of the microrobot is between 30 µm to 330 µm, and it was confirmed in both simulations and experimental results. It can follow the given trajectory with high accuracy (<1 µm error avg.) at varied speeds and levitation heights. Due to the nano-level positioning accuracy, desired locomotion can be achieved in pre-specified trajectories (sinusoidal or circular). During its locomotion, phase difference between lifter magnet and carrier magnet has been observed, and relation with drag force effect has been discussed. Without using strong electromagnets or bulky permanent magnets, our manipulation approach can move the microrobot in three dimensions in a liquid environment.

Hollow glass spheres (HGS) have many application areas in the field of composite production due to their lightweight property together with having a sufficient strength. This study has the focus on adding the HGS to epoxy resin in different concentrations. The surface of the glass spheres were modified with silane prior to resin casting. The material characterization of the HGS filled epoxies was based on the silane presence and the HGS addition. Dynamic mechanical analysis was applied to observe the mechanical properties depending on the temperature of the composites. Morphological investigations were made to determine the interfacial adhesion between epoxy and the HGS. As a result of these, it was obtained that the HGS addition enhanced the stiffness of the material without a sharp reduction in the ductility. Silane was observed to be successful in improving the storage modulus below the glass transition temperature (Tg). However, the reduction in Tg was observed in high amount of modified HGS loading due to their interfering effect on the crosslink system of the epoxy.

This research aims to develop a lightweight cementitious composite with satisfied mechanical and good thermal insulating properties. Two different types of hollow glass microspheres were used as lightweight aggregates and were substituted with fine aggregate by 10, 20 and 40% by volume. The rheological, physical, mechanical and microstructural properties of the resulting HGM-incorporated composites are investigated. The results showed that physical and mechanical properties of individual HGM particles plays a dominant role on the properties of lightweight cement mortars. HGM addition provided reductions up to 20% in the density and 45% in the thermal conductivity values of mortars compared to the reference. The optimum HGM ratio is suggested as 20%, which provides benefits such as reduced density and improved thermal insulation capability without causing significant reduction in compressive strength. It was concluded that HGMs can be used in the lightweight cementitious mortar production which have great potential in building applications to reduce the heating energy consumption.

PRECISE POSITIONING OF DIAMAGNETICALLY LEVITATED MICROROBOT

Protection of masonry structures is among the most important building groups around the world. Generally constructed of heavy materials such as stone and brick, these structures are highly seismically vulnerable. In large earthquakes, masonry structures that have not received adequate engineering services are usually heavily damaged or destroyed. To prevent damage to these structures, seismic hazard and risk analyses must first be conducted correctly. This study investigates the seismic hazards and risk distributions of historical masonry structures in Kocaeli, Türkiye. As a preliminary step, information and document collection studies on historical masonry structures were conducted in Kocaeli, Türkiye. Then, a detailed building inventory data set was prepared. Following that, a probabilistic seismic hazard assessment for the investigation area was conducted considering the different attenuation relationships. In the seismic hazard analyses, the hazard maps, hazard curves and response spectra were prepared based on the inventory data set at select reference points. After that, the seismic risk analyses were conducted to determine the structure distribution based on damage levels for the structures in the data set considering different fragility curves. Accordingly, historical masonry structures in Kocaeli province close to the North Anatolian Fault (NAF) Line have high hazard curves and spectrum values, whereas structures on the Black Sea coast have low values. According to the hazard maps obtained as a result of the analyses, Kartepe, Darica, Gölcük, and Başiskele districts have a high estimated hazard distribution, while Kandira has a lower estimated hazard distribution. Further, when the risk assessment is carried out by looking at the distribution of building groups based on damage levels, it was determined that towers, aqueducts, residential structures, and dome structures are the highest priority risk structures, respectively.