The fatigue life of solder alloys for the slow-fast cyclic loading condition is much shorter than that for the fast-slow cyclic loading condition, despite the two loading conditions having almost the same inelastic strain amplitudes. This means that the inelastic strain amplitude is not the best parameter used for estimating the fatigue life which shows the strain rate dependency. Then, the authors have previously proposed a fatigue life estimation method for Sn-3.0Ag-0.5Cu (SAC) solder using the creep strain amplitude obtained from the inelastic strain analysis using the stepped ramp wave (SW) loading. In this study, the fatigue tests for SAC solder under 16 loading conditions at RT and the SEM observations for the fatigue failure surfaces were conducted to give experimental supports to both the strain analysis method and the life estimation method. The inelastic strain analyses for all the tests showed that the analysis results were well correlated with the aspects of the fracture surfaces, and that the creep strain amplitudes obtained from the inelastic strain analysis were highly correlated with the strain-rate-dependent fatigue lives of SAC solder at RT. Also it was found that the relational expression between the creep strain amplitude and the fatigue life formulated at RT could be used for estimating the fatigue lives at 398 K.
Porous ceramics are expected to be applied as filters, catalysts, etc. in energy related structures, because they have higher heat-resistance and larger specific surface area. Even for such functional applications, their strength should be adequately evaluated to guarantee long-term durability with fulfilling the required functions. However, it is very difficult to investigate strength for porous ceramics with various pore characteristics experimentally. In this work, an analytical procedure was proposed for estimating strength in porous ceramics by taking account of the pore characteristics, such as porosity, pore density and pore radius. In the procedure, porous ceramics were assumed to have the same characteristics of crack distribution as those of pore distribution, and pores were presumed to be surrounded by virtual cracks. For several materials with different pore characteristics, numerical simulations based on the proposed procedure were carried out to estimate their strength and to clarify effects of pore characteristics on strength. It was reconfirmed that the strength of porous ceramics had a general tendency to decrease drastically as increasing porosity. It was also revealed that the strength of porous ceramics were affected by porosity, pore density and average pore radius, respectively. Based on the simulated results, it was suggested that porous ceramics with higher strength can be obtained by including many small pores in producing porous ceramics with a predetermined bulk porosity. In other words, for porous ceramics with the same bulk porosity, various strength characteristics can be attained by controlling the pore size.
Poly(lactic acid) (PLA) has attracted much attention for use in bone fixation devices, which are used for fracture treatment, because it degrades to nontoxic lactic acid through nonenzymatic hydrolytic degradation. However, the application of such device is limited to relatively low-load regions, because mechanical properties of PLA is poor than that of metal materials. The process of drawing PLA fibers has attracted much attention as an approach for improving the mechanical properties of PLA bone fixation devices. The mechanical properties and molecular orientation of drawn PLA fibers and films have been investigated. However, the optimization of drawing conditions in bulk processes in relation to bone fixation devices is difficult because a large number of potential drawing conditions exist. The purpose of this study was to analytically clarify molecular orientation behavior in drawn PLA billets. The molecular orientation obtained by extrusion in PLA billets was investigated using a combination of the finite element method (FEM) and a chain network model. As a result of the FEM, first principal plastic strain was generated, mainly in the tapered components during extrusion; this strain was in the axial direction of the rod. Radius strain distributions showed that strain in the center region was almost uniform, whereas strain peaked near the surface. The orientation function increased with extrusion ratio (ER), and the peak orientation function in the surface region increased with taper angle. Thus, the magnitude and distribution of the orientation function in extruded PLA billets may be controllable by ER and taper angle, respectively.
To develop an NH3/natural gas-fired gas-turbine combustor with minimal modifications to a natural gas-fired combustor, the effect of co-firing NH3 with natural gas on emission characteristics and combustion efficiency is investigated experimentally under atmospheric pressure. In this experiment, a lean premixed combustor that has basically the same structure and same size as those of an actual 2 MW-class gas-turbine combustor is used and the effects of equivalence ratio, NH3 mixing ratio, and NH3 injection method were evaluated. The results of NH3/natural gas/air premixed combustion show that NO emission shows a local maximum at a certain NH3 mixing ratio, when equivalence ratio is fixed. The NH3 mixing ratio where this maximal NO emission occurs shifts to higher ratios, when equivalence ratio is increased towards stoichiometric condition. At the same time, the maximal NO emission increases. The variation of NOx concentration can be explained by the change in the selective non-catalytic reduction (SNCR) effect, which depends on temperature and NH3 concentration in the flame. In particular, the influence of NH3 concentration on the SNCR effect appears to be stronger than that of temperature. On the other hand, concentrations of N2O and unburnt NH3 increase with increasing NH3 mixing ratio in the very lean case, when decreasing flame temperature approaches the lean flame blow-off limit. When NH3 is directly injected into the lean premixed flame of natural gas, NO and N2O concentrations are simultaneously reduced; this is attributed to the local increase of NH3 concentration and flame temperature. Finally, it is proposed to consider NOx as unburnt component in the calculation of combustion efficiency. When NH3 is fired, the enthalpy content of NOx is very high, and its influence on combustion efficiency cannot be ignored. It is also found that NH3 direct injection is effective in increasing combustion efficiency, achieving more than 99.6% of the combustion efficiency even if the enthalpy of NOx is considered.
This paper describes a new approach to improve compressor efficiency by using 1D CAE and 3D CAE. First, a 1D simulation model of a reciprocating compressor is proposed and the compressor efficiency is analyzed. Then, heat flow in the compressor is analyzed using a 1D thermal network simulation model and the heat receiving process of the refrigerant gas is investigated. Next, gas flow in the compressor is evaluated using 3D CFD and an improved compressor with a new structure is proposed. Finally, the effect of the improved compressor is evaluated through experiments. Results demonstrated that the proposed approach is very effective in actual development.
Model Predictive Control (MPC) is one of the control methods for discrete time systems. The optimal input is calculated by using Linear Quadratic Regulator (LQR). The weight matrices in the evaluation function for LQR are determined by a designer with professional experience and a trial & error approach. Therefore, even if the same system is targeted, the performance can differ depending on the designer. This paper proposes a new weight selection algorithm using Simultaneous Perturbation Stochastic Approximation (SPSA) for MPC. A new evaluation function is proposed for the selection algorithm. Numerical values of the overshoot and the settling time are directly applied as the user’s requirements in this evaluation function. The optimal weight matrices numerically satisfying those requirements can be selected by the proposed algorithm. Simulation study of a zero momentum spacecraft shows that the proposed method is effective for the weight selection with consideration of performance.
Six-pole active magnetic bearings (AMBs) have fewer poles than the more common eight-pole AMBs making it possible for them to be miniaturized and used in the development of small motors. In this paper, we propose a novel control method for the six-pole AMB, which switches between three-coil and five-coil modes. The three-coil mode excites three coils to generate a suspension force and reduce power consumption. In contrast, the five-coil mode excites five coils and can generate a larger maximum force than the three-coil mode. By switching between the two modes, it is possible to realize both an increase in the maximum suspension force and a reduction in power consumption. This paper derives the coil currents in the three- and five-coil modes, and introduces a switching method between them. The proposed method is verified with a test rig, and results show that the proposed method enables stable levitation with a lower current limit compared with the method that uses the three-coil mode alone. Moreover, a start-up procedure with a low current limit is proposed and experimentally verified.
This paper proposes a seismic analysis method based on nonlinear dynamic analysis to consider the fracture of steel frame structural members during earthquakes. The approach corresponds to real fracture mechanism, especially low cycle fatigue failure. The fracture judgment condition in the analysis method was determined using the shaking table test for steel frame structures. In the shaking table tests, fractures at the column-beam connection which were considered to be due to fatigue cracks, were observed. From a fractographic study of the fracture surface and the Finite Element Analysis study after the test, these fractures were confirmed to be a result of low cycle fatigue; therefore, a low cycle fatigue evaluation method was integrated into the proposed analysis method. By applying both the proposed analysis method and the ordinal method which does not consider member fracture, the effects of member fracture on the seismic performance of a whole structure were examined. The effects on factors such as whole stiffness, equivalent periods and damage distributions after severe ground motion were marked. It is preferable that these effects be taken into account in seismic performance evaluations for very severe ground motions in which the occurrence of structural component failure is suspected.
This paper presents the numerical simulation methods used to reproduce droplet retention and sliding on an inclined surface by using the Moving Particle Semi-implicit (MPS) method. The MPS method is useful for simulating free surface flows with highly deformed gas–liquid interfaces, such as the behavior of condensed water in an evaporator. However, the existing MPS method cannot correctly reproduce the behavior of a droplet retention and droplet sliding on an inclined surface. In the simulation of a droplet on a wall using the existing MPS method, the simulated droplet starts sliding as soon as the wall is inclined even slightly and falls down at a very high speed. In this study, the details of the forces acting from the wall to a droplet are considered, and the boundary condition models that contain the resistance forces acting on the contact line of a droplet are proposed. Droplet retention and droplet sliding on an inclined plate are successfully simulated by using the proposed models. Furthermore, the simulation results are compared with the experimental results reported in literature. The relationship between the droplet volume and critical sliding angle and that between the inclination angle of a slope and droplet sliding velocity are each compared using the experimental results and evaluated both qualitatively and quantitatively; they show good agreement with the experimental results.
We have studied the analysis method of interior noise in railway cars by means of a ray tracing method. Firstly, by using a point source as input, sound distribution inside a car was analysed and compared with the measurement result obtained by a loud speaker test. It was found that the analysis result of sound decay along the longitudinal direction of the car did not always match the measurement result. It is possibly because the wave character of the sound cannot be strictly simulated by the ray tracing method. However, for the purpose of analysing the sound distribution while the train is running, it may not be necessary to accurately simulate the sound decay in the longitudinal direction, because the sound sources are distributed everywhere inside the running car and therefore the importance of the sound decay along the longitudinal direction may be low. Based on this perspective, we have proposed the interior noise analysis method for the running condition by applying multiple sources inside the car. The amplitude of each source was estimated from the measured vibration of the interior panels as well as from the estimated radiation efficiency of each panel. Validation of the analysis was conducted by comparison with the measured data of the interior noise inside the running train, and it was confirmed that the level of interior noise reduction by the installation of passenger seats matched well between the analysis and the measurement.