The objective of the present study is to carry out in situ observations of deformation and annealing of aluminum (Al) single crystals using a synchrotron radiation X-ray at SPring-8. Al single-crystalline samples having a 〈111〉 orientation parallel to the longitudinal direction were grown by the Bridgman method. The samples were deformed in tension to a nominal strain of 8% at room temperature using an in-line tensioning apparatus. Post-deformation annealing at 480 °C was subsequently carried out in the same apparatus. A two-dimensional detector was used to detect multiple diffracted beams from the sample during deformation and annealing. The volume irradiated by the X-ray beam was found to be composed of three regions having small orientation differences attributable to the subgrain microstructures of the sample. Detailed analyses of diffraction spot intensity showed that the subgrain microstructures were surpassed by dislocated microstructures as the tensile strain increased. During post-deformation annealing, diffraction spots from a recrystallized grain first appeared at 180 s after the temperature reached 480 °C. The coexistence of diffraction spots from the deformation matrix and recrystallized grains lasted only about 22 s in the irradiated volume. The migration rate of the boundary between the deformation matrix and the recrystallized grain was estimated to be on the order of several micrometers per second.
A modified perturbation method, in which the applicable range of a small parameter ε for the solution is extended larger than that by the conventional perturbation method, is applied to two simple heat transfer problems with temperature-dependent thermal properties. The main procedure of the modified perturbation method is: (1) A perturbation parameter ε is assumed to be included in the nonlinear term of the differential equation. The solution θ is expressed by θ = φ + θf, where θf is an initial approximation of the solution and φ is θ − θf. (In the example problems of this paper, we assume that θf is a constant.) (2) θ = φ + θf is substituted into the differential equation and the nonlinear term is split into linear and nonlinear terms. (3) ε which is not in the nonlinear term is replaced by a newly introduced variable ε’. (4) An asymptotic expansion of φ in powers of ε is assumed for the solution of the differential equation, from which we obtain the perturbation solution of φ including ε’ and ε’. (5) ε in the perturbation solution of φ is replaced by ε. Then we obtain the perturbation solution of θ. By solving the two example problems, it is made clear that the solution by the modified perturbation method is more accurate than that by the conventional perturbation method. It is also made clear that the modified perturbation method extends drastically the applicable range of the perturbation parameter in comparison with the conventional perturbation method. The modifications of the perturbation method help reduce the contribution of the nonlinear term, which drastically improves the convergence characteristics of the solution. The reason for the good convergence characteristics of the modified perturbation solution is discussed.
Conventional remote operation of an excavator has low work efficiency comparing with on-site operations. This is because it is difficult for an operator to recognize the excavator status and surrounding environments. Moreover, there are restrictions such as a limitation on the amount of information that can be transmitted, delays in communication, and harsh environments that cause sensor failure. Therefore, we have developed a semi-autonomous control system that consists of autonomy and human manipulation. This paper proposes (1) a bilateral control system based on variable admittance and (2) an autonomous control using nonlinear dynamics that has attractors with stagnation and trajectory-bifurcation. (1) In the proposed method, the admittance parameters are changed based on the difference between the leader and follower position. We implement the proposed method into a prototype of excavator and verify the operation with two types of external environmental forces: free movement and contact with a rock. (2) The attractor’s stagnation is designed as a sink of vector field converging to an arbitrary point on the trajectory. A stagnation is placed at a trajectory’s bifurcation point, and the operator selects the next operation by adding a force to the leader system, which is measured through a force sensor. We design two types of bifurcating attractors and conduct an experimental verification of the proposed semi-autonomous control system.
Living machines have microactuators and are suitable for further miniaturization of microsystems, and their potential as autonomous microrobots has been investigated. The key motion of micromechanisms is self-oscillation, which has been achieved by the synchronized motion of cardiomyocytes. Pulsatile flows play an important role in a variety of microfluidic applications. The advantage of Vorticella is that a single cell generates several micrometers of displacement and can actuate a microsystem. Self-oscillation of Vorticella has yet to be used for a purpose other than actuating microstructure. This paper reports the extension of previous works to develop a self-oscillating microvalve and improvement of the sealing properties of a calcium-responsive valve actuated by Vorticella. V. convallaria was introduced into a microfluidic chamber and used to make a self-oscillating cellular microvalve. We demonstrated a self-oscillating cellular microvalve actuated by live Vorticella. While the extension of a stalk of live Vorticella sealed the opening of a channel and stopped a flow, the contraction moved the zooid and the flow resumed. The performance of a cellular valve was studied and we obtained the minimum transition time, tMIN = 2 s, and the valve efficiency, ηmax = 98.7%, by switching the fluid between the contraction and extension motions. The changes in Vorticella cell properties after the permeabilization treatment were studied to investigate improvement measures to a calcium-responsive valve. Fluid was also switched by manipulating the Ca2+ concentration using a stalk of membrane-treated Vorticella. The permeabilization conditions of 0.1 wt.% saponin solution at room temperature (RT) for 5 min and 0.01 vol% Triton X-100, 0°C for 30 min gave better valve efficiency than 0.15 wt.% saponin at RT for 10 min.
Among uncertainties that should be considered in the validation of numerical simulation, this study focused on the manufacturing process-induced geometrical imperfection. As one of the newly developed manufacturing process, the additive manufacturing by selective laser melting is studied. Dumbbell type tensile specimens with circular hole were additively manufactured using nylon with different building directions, and the distorted circular hole was modeled as an elliptic shape. Representative geometrical parameters were defined and statistically measured. It was found out that the width of the manufactured specimens and the length of the shortest ligament linearly depended on a sine function of the building direction. The database constructed from geometrical measurement could be interpolated with respect to the building direction. Using the interpolation of the database, probabilistic finite element models successfully predicted before manufacturing the upper and lower bounds of the mechanical behavior. The proposed method was verified by image-based analyses of real specimens, then it was applied to the same specimen but with unexperienced building direction as well as to an S-shaped component with seven circular holes.