High-temperature water stress corrosion cracking has high tensile stress sensitivity, and its growth rate has been evaluated using the stress intensity factor, which is a linear fracture mechanics parameter. Stress corrosion cracking mainly occurs and propagates around welded metals or heat-affected zones. These regions have complex residual stress distributions and yield strength distributions because of input heat effects. The authors previously reported that the stress intensity factor becomes inapplicable when steep residual stress distributions or yield strength distributions occur along the crack propagation path, because small-scale yielding conditions deviate around those distributions. Here, when the stress intensity factor is modified by considering these distributions, the modified stress intensity factor may be used for crack growth evaluation for large-scale yielding. The authors previously proposed a modified stress intensity factor incorporating the stress distribution or yield strength distribution in front of the crack using the rate of change of stress intensity factor and yield strength. However, the applicable range of modified stress intensity factor for large-scale yielding was not clarified. In this study, the range was analytically investigated by comparison with the J-integral solution. A three-point bending specimen with parallel surface crack was adopted as the analytical model and the stress intensity factor, modified stress intensity factor and equivalent stress intensity factor derived from the J-integral were calculated and compared under large-scale yielding conditions. The modified stress intensity was closer to the equivalent stress intensity factor when compared with the stress intensity factor. If deviation from the J-integral solution is acceptable up to 2%, the modified stress intensity factor is applicable up to 30% of the J-integral limit, while the stress intensity factor is applicable up to 10%. These results showed that the modified stress intensity factor can be applied even when the yielding scale exceeds the small-scale yielding criterion.
To effectively use micro or nano materials and create advanced materials systems from them, welding techniques for such small scale materials are vital. For this purpose, the tips of two thin wires were welded together with Joule heat and the conditions required to achieve it was discovered experimentally. In this paper, the Joule heat welding of thin wires to thin films deposited on substrates is described. To derive the conditions required to achieve this, a heat conduction model for a cylindrical element in the film located at the contact between the wire and the film is considered and the critical thickness of the film above which the welding conditions are independent of film thickness is derived analytically. The validity of the heat conduction model was experimentally verified by welding 0.8 μm diameter Pt wires onto thin Pt films on electrically-insulated substrates. The experiments are performed for various combinations of the length of the wire and the thickness of the films. The current required for welding the wires onto the films having the thickness over the critical thickness are investigated and the conditions required for the welding are found to be coincident with those for welding the tips of two wires with Joule heat.
A new type of anode incorporating the proton conductor BaCe0.8Y0.2O3-α (BCY) was fabricated and proposed for a high-power solid oxide fuel cell (SOFC). The most striking feature of these anodes was that the power density of the SOFC with an anode consisting of 50% Ni, 35% Gd2O3-doped CeO2, and 15% BCY was almost twice that of the SOFC with an anode of 50% Ni and 50% GDC. Thermal desorption spectroscopy revealed that a large amount of hydrogen was adsorbed on the surface of the BCY particles, and the adsorption energy decreased when the BCY particles were in contact with the nickel particles. Consequently, the BCY particles were thought to play an important role in the enhancement of the adsorbed hydrogen supply via the anodic reaction around the triple phase boundary.
In this paper, a tracking control problem for discrete-time linear systems with actuator saturation is addressed. Firstly, a design condition of a controller parameterized by a single scheduling parameter is introduced. The proposed controller includes an integrator to achieve the zero steady-state error in the case where a step reference signal is applied. Then a gain-scheduled control algorithm that guarantees closed-loop stability and makes the tracking error converge to zero in the case of a step reference signal is proposed. In the proposed control algorithm, the scheduling parameter and the state of the controller are determined on-line so that the tracking control performance is improved. The scheduling parameter and the state of the controller are computed simultaneously by solving a convex optimization problem with a linear matrix inequality constraint. Two numerical examples are provided to illustrate effectiveness of the proposed control algorithm.
A finite element procedure for vibration analysis of multi-span functionally graded material (FGM) beams subjected to a moving harmonic load is presented. The material properties of the beam are assumed to vary continuously in the thickness direction by a power-law distribution. The finite element formulation is derived by using the exact solution of the governing differential equations of an FGM Timoshenko beam segment to interpolate the displacements and rotation. The shift in the neutral axis position is taken into account in the formulation. The dynamic response of the beam is computed with the aid of the Newmark method. The numerical results show that the proposed formulation is capable to give accurate dynamic characteristics of the beams. A parametric study is carried out to highlight the effect of the material heterogeneity, number of spans and loading parameters on the dynamic response of the beams. The influence of the aspect ratio is also studied and highlighted.
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