Yohei Takahashi

Position control of surface vessel with unknown disturbances

This paper describes dynamic position control of surface vessel with disturbances such as waves and wind. A smooth time-varying controller is proposed that performs both in presence and absence of disturbances. Using this controller, position of the vessel converges to neighborhood about zero that can be made arbitrarily small. In addition, if disturbance is small, orientation of the vessel converges to neighborhood about zero that is as small as possible. Effectiveness of proposed control law is demonstrated by simulation.

Phase Transformation of Ti-Ni Containing Platinum-Group Metals

Since the maximum shape recovery temperature of the binary Ti-Ni alloys is limited to be around 400K, the increase in martensitic transformation temperature ( M s ) of Ti-Ni should be done by alloying for the demand of high temperature applications. Although most of additional elements are known to decrease M s of Ti-Ni, substitutional elements having large atomic size are expected to increase M s . In this study, phase constitution, phase transformation temperature, lattice parameter of B2 phase and Vickers hardness were investigated for Ti-Ni alloys containing several platinum-group metals (PGM). The alloy systems investigated were the pseudobinary systems of TiNi-TiRh, TiNi-TiIr and TiNi-TiPt where the PGM atoms substitute for the Ni-sites of TiNi. The phase transformation and phase constitution were assessed by differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). It was found by XRD that TiNi can contain a large amount of the PGMs as Ti(Ni, Rh), Ti(Ni, Ir) and Ti(Ni, Pt). Lattice parameters monotonously increase with increasing amount of PGMs. With increasing Pt content, M s slightly decreases when less than 10mol%Pt while continuously increases as the rate of 26K/mol%Pt when more than 10mol%Pt. On the other hand, M s decreases and then disappears with increasing Rh or Ir content. Hardness ranges from HV180 to HV570 and the maximum values in the pseudobinary systems lie around 20–30mol%PGM, suggesting solid solution hardening caused by the substitution of PGMs.

EVOLUTION OF TEXTURE AND DISLOCATION DISTRIBUTIONS IN HIGH-DUCTILE AUSTENITIC STEEL DURING DEFORMATION

Fe-Mn-C austenitic steels exhibit outstanding high-ductile deformation in their plastic regions along with significant microstructural evolution. In this study, to characterize the microstructural evolution during deformation of these steels, line-profile and texture analyses were carried out using X-ray diffraction. The convolutional multiple whole profile fitting procedure was used for a line-profile analysis of 2 – diffraction data to evaluate variations of crystallite size, dislocation density, and dislocation arrangement during tensile deformation. A substantial refinement of the crystallite size proceeded at an early deformation stage. In addition, the dipole character of dislocations was enhanced with an increase in the tensile strain. Texture evolution was characterized by the analysis of orientation distribution functions. Three texture components grew with an increase in the tensile strain. According to the pole figure describing the full width at half maximum distribution of the 220 reflection, the nontextured grains had more microstructural defects than the textured grains. To evaluate the microstructural defects in detail, the 220 reflection observed at each texture orientation was analyzed by the single-line profile method. The crystallite size and dislocation density were almost comparable, irrespective of the kind of texture component. The crystallite size of the nontextured grains was also comparable to that of the textured grains, whereas the nontextured grains had a dislocation density several times that of the textured grains. Based on these microstructural data, the origin of the mechanical properties of the Fe-Mn-C steel was discussed.

Characterization of aging behavior of precipitates and dislocations in copper-based alloys

The growth of precipitates in a deformed CuNiSi alloy with an aging treatment and the rearrangement of dislocations were investigated using X-ray scattering methods. A small angle X-ray scattering (SAXS) method was used for characterizing the growth behavior of the precipitates with aging. The results showed that the precipitates grew gradually to a few nanometers in radius in the alloy aged under the condition that the alloy exhibited a maximum of the hardness due to precipitation hardening. The growth rate was prompted by the onset of the over aging, where the hardness starts to decrease. The line profile analysis of copper diffractions using modified Williamson-Hall and modified Warren-Averbach procedures yielded a variation in the dislocation density of the alloy as a function of the aging time. The dislocation density of the alloy before the aging treatment was estimated to be 1.70 15 m -2 , and its high value was held up to the peak-aging time. With the onset of the over aging, however, the dislocation density distinctly decreased by about one order, indicating that a large amount of the dislocation rearranged to release the alloy from the high dislocation-density state. It may be concluded that the massive rearrangement of dislocations was accompanied with coarsening of the precipitates.