マイクロガスタービンの翼振動に関する研究(ガスタービン技術の最先端 : 空力・構造,ガスサービン技術の最先端)

This paper demonstrates the investigations on the blade vibration of a radial inflow micro gas turbine wheel. Firstly, the dependence of Young's modulus on temperature was measured since it is a major concern in structure analysis. It is demonstrated that Young's modulus depends on temperature greatly and the dependence should be considered in vibration analysis, but the temperature gradient from the leading edge to the trailing edge of a blade can be ignored by applying the mean temperature. Secondly, turbine blades suffer many excitations during operation, such as pressure fluctuations (unsteady aerodynamic forces), torque fluctuations, and so forth. Meanwhile, they have many kinds of vibration modes, typical ones being blade-hub (disk) coupled modes and blade-shaft (torsional, longitudinal) coupled modes. Model experiments and FEM analysis were conducted to study the coupled vibrations and to identify the modes which are more likely to be excited. The results show that torque fluctuations and uniform pressure fluctuations are more likely to excite resonance of blade-shaft (torsional, longitudinal) coupled modes. Impact excitations and propagating pressure fluctuations are more likely to excite blade-hub (disk) coupled modes.

In this paper, the effects of shape and arrangement of inclusions on the effective Young's modulus of materials are considered by the application of the finite element method through examining a model, which has two groups of periodically arranged inclusions in a matrix. Here, two groups of inclusions A and B are considered, both having equally shaped equally arranged inclusions, which have the same elastic constants but different from the ones of the matrix. This model includes square and hexagonal arrays of inclusions as its special cases. First, the effect of shape of inclusions on the Young's modulus of composite materials is considered from the comparison between the results of rectangular and elliptical inclusions. Next, when the position of group A is fixed, the effect of location of group B is considered. Then. the effective elastic Young's modulus is almost independent of the location of group B if the projected areas of groups A and B are not overlapped. In conclusion, the volume fraction of inclusion and projected area fraction of inclusions are found to be two major parameters controlling the effective Young's modulus of composites.

The role of radial elastic properties in the development of aortic dissections

This study focused on modeling and optimization of the concentration of poly (vinyl alcohol) (PVA), cellulose nanocrystals (CNC), snail shell nanoparticles (SSN), and glycerol for the development of bioplastic films. The response surface methodology using Box–Behnken experimental design was used to investigate the effect of the independent parameters (additives concentrations) on the ultimate tensile strength and Young's modulus of fabricated bioplastic films. A varied ultimate tensile strength and Young's modulus with different component loadings was observed, proving the effect of nanoparticles loading effect on the mechanical properties of bioplastic films. The quadratic polynomial model experiment data provided a coefficient of determination (R2) of 0.795 for ultimate tensile strength and 0.732 for Young's modulus, evidencing the fitness of the models to pilot the optimization space. The optimum parameters were PVA (7.820%), CNC (1079%), SSN (1241%), and glycerol (2.657%). The ultimate tensile strength and Young's modulus of 27.2 MPa and 31.2 MPa were obtained for the developed bioplastic film with optimized concentrations of each component. The bioplastic films showed improved thermal stability and degradation. The scanning electron microscopy(SEM) imaging revealed a homogeneous dispersion of SSN and CNC in the matrix, which explained the improved properties observed.

For axially functionally graded beams with elastic modulus varying through the longitudinal directions, a measurement model for Young's modulus is presented based on the classic Euler-Bernoulli beam theory. When the force and deflection of cantilever beams are measured by the experiment method, the Young's modulus of axially functionally graded beams can be obtained by the measurement model. By the derivation rule of compound functions, the validity of the measurement model is proved. For the axially functionally graded beams with elastic modulus varying according to the power law and the exponential law respectively, the deflection is simulated by the finite element method. The simulated elastic modulus by the model is in accord with the theoretical value well.

When blending rubbers into polymers, different rubber distribution status and fraction due to different mechanical property. In this research, effective mechanical properties of rubber-toughened polymers with four blending fraction in six kinds of particle distribution status are simulated numerically by using finite element method. Rubber particle distribution model include four 2D models and two 3D models. Typical effective mechanical properties such as yield stress, Young's modulus, Poisson's ratio and stress-strain curve of each status are obtained. The Results show that all models Young's modulus and Poisson's ratio decrease with rubber particle volume fraction increasing. Young's modulus and Poisson's ratio of three-dimensional body-centered cubic and face-centered cubic models are in a close magnitude range, it means rubber particle volume fraction has less effect on 2D models and two 3D models. As we all known, Matrix yielding, crazing and interface debond. All play an important role in the toughening process of rubber-toughened polymers. So in this paper we also study on toughening mechanism using same models. Our simulation takes use of stress concentration factor, yield ratio and interface elements' strain difference which is related with matrix yielding, crazing and interface debond to study the toughening mechanism. Simulation shows that the maximum stress concentration factor increases with particle volume fraction. The shear yielding occurs first at the equator of rubber particle, and then yield region expands from the equator to the pole of the particle with loads increasing.

The possible mechanism of casein aggregation and micelle buildup was studied in a new approach by letting α-casein adsorb from low concentration (0.1 mg·ml(-1)) solutions onto the charged surfaces of polyelectrolyte films. It was found that α-casein could adsorb onto both positively and negatively charged surfaces. However, only when its negative phosphoseryl clusters remained free, i.e. when it adsorbed onto a negative surface, could calcium phosphate (CaP) nanoclusters bind to the casein molecules. Once the CaP clusters were in place, step-by-step building of multilayered casein architectures became possible. The presence of CaP was essential; neither Ca(2+) nor phosphate could alone facilitate casein aggregation. Thus, it seems that CaP is the organizing motive in the casein micelle formation. Atomic force microscopy revealed that even a single adsorbed casein layer was composed of very small (in the range of tens of nanometers) spherical forms. The stiffness of the adsorbed casein layer largely increased in the presence of CaP. On this basis, we can imagine that casein micelles emerge according to the following scheme. The amphipathic casein monomers aggregate into oligomers via hydrophobic interactions even in the absence of CaP. Full scale, CaP-carrying micelles could materialize by interlocking these casein oligomers with CaP nanoclusters. Such a mechanism would not contradict former experimental results and could offer a synthesis between the submicelle and the block copolymer models of casein micelles.

A schematic description of a stand based on a digital speckle interferometer with a diffuse reference wave is given, which makes it possible to determine the natural frequencies and vibration modes of the blades in real-time. In the frequency range of 100 ... 3000 Hz, an experimental study of the vibration characteristics of a turbine rotor blade of a gas turbine engine was carried out, under free boundary conditions, which were achieved by placing the blade on soft silicone racks. Blade dimensions: height along the trailing edge - 288 mm, a chord in the middle section - 88.5 mm. 7 modes of vibrations have been identified. The technology of creating a solid-state geometric model of a rotor blade based on a faceted body obtained by 3D scanning with an accuracy of 0.01 mm is presented. The finite element method, using the Lagrange variation principle, is used to calculate the values of natural frequencies and vibration modes of a blade based on the developed geometric model. Concerning the frequency range 100 ... 3000 Hz, using the Ansys Workbench software package, a series of calculations of the resonant frequencies of the blade, by the finite element method, in the range of variation of the values of mechanical properties was carried out: Young's modulus E = 200 ... 230 GPa; Poisson's ratio μ = 0.26 ... 0.3. The density of the material: ρ = 7830 kg / m³, determined experimentally, by the method of hydrostatic weighing. The final element used in the calculation is (tetrahedron) SOLID 187; the minimum element size is 0.6 mm. The total number of elements is about 1.5 ∙ 10⁶. Based on the two-dimensional spline interpolation of the calculated data, the dependence of the standard deviation of the calculated and experimental values on the adopted mechanical properties of the material of the rotor blade is built. In the range of values E = 215 ... 217 GPa and μ = 0.295 ... 0.3, the minimum standard deviation of the calculated frequencies from their experimental values is 0.73%. Provided the value of the standard deviation of frequencies is 1%, the range of values of mechanical properties will be: E = 211 ... 220 GPa and μ = 0.26 ... 0.3. It is shown that narrowing the studied range of values of Young's modulus and Poisson's ratio does not significantly affect the results obtained.

In order to improve the reliability of tire pressure monitoring system (TPMS), packaging design optimization is essential. In this paper, finite element method (FEM) is used to analyze the effect of packaging processes on the residual stresses of the sensor die and its packaging. The Young's modulus and thickness of the coating material, the dimension effect of the dies and the substrates on which the dies are attached are considered in this paper. Results show the thinner coating gel that has a lower Young's modulus generates lower residual stress and smaller zero offset as well as smaller temperature drift to the sensor. For a given coating soft gel, the thermal residual stress decreases with the thickness of adhesive layer decreasing, and the effect is not significant when the thickness of coating gel is smaller than 1.5mm. Therefore, this value can be decided as the technological parameter. Comparing stainless steel, Kovar and FR-4, the ceramic is more suitable for using as the substrate. The ceramic has lower CTE compared with steel, Kovar and FR-4, therefore the residual thermal stresses resulted from the CTE mismatch are much lower than that of steel, Kovar and FR-4. For a given coating soft gel and substrate, smaller dimension of the dies will benefit the sensor's performance on the residual stresses. For a given coating soft gel, the material of the shells has little effect on the residual stresses of the dies. The above simulation results can be used to guide the tire pressure sensor's packaging design optimization. Based on FEM results, the optimized die-attaching process parameters are proposed. The experiments indicate that the proposed pressure sensor has a stable output voltage and good linearity, and the zero offset and temperature drift of the sensors are also minor.

Capillary adhesion of microparticles was analytically calculated, modelled by finite element method (FEM) simulations and measured. The effects of elastic deformation and liquid adsorption were analyzed. By means of an atomic force microscope, we measured the force between a silica bead of 2 μm radius and a planar polydimethylsiloxane surface (Young's modulus E = 1 MPa) in the presence of ethanol at different vapor pressures. Results were compared to adhesion forces measured on a silicon wafer. Independent of the sample elastic modulus experiments showed a monotonous decrease of capillary forces with increasing ethanol partial vapor pressure for P/Psat > 0.2, where Psat is the saturation vapor pressure. However, adhesion forces on the soft surface were much stronger than on the rigid silicon wafer. In order to explain the experimental results, a previous developed theory (Soft Matter, 2010, 6, 3930) was extended to take into account vapor adsorption of ethanol. Analytical calculations were compared to results of FEM simulations where the detailed deformation of the elastic support close to the meniscus was explicitly taken into account.

Conventional material testing methods, such as tensile tests require the preparation of specimens and is not applicable for small-size coupons or on-site, in-situ testing. In this research, a method of determining material stress-strain curve based on spherical indentation is studied. Spherical-indentation process is analyzed by finite element (FE) method and a systematic analysis of relationships between indentation parameters and true stress/plastic-strain (sigmat- epsilonp) curve is performed for a range of material properties. A detailed methodology based on Tabor's empirical formula and Meyer's law is developed to determine the material strain hardening properties, Young's modulus and yield strength. It is noticed that Tabor's empirical formula is valid in the plastic region (deep indentation) with a small percentage error in the calculated values of yield strength. Based on the FE results, strain values have been predicted corresponding to which indentation gives satisfactory output. Steel and aluminum alloys, with same Young's modulus and yield strength but with different strain hardening coefficients, were selected for the simulation. FE simulation of 20 material models was performed. It is observed that the Tabor's constant is not equal to the value of 2.8 but takes different values for different materials. From the results it is concluded that the value of Tabor's constant decreases as the strain hardening value increases.

Predicting elastic properties of braided composites is useful in aerospace structures. In order to predict the properties precisely, fiber undulation and pores in the matrix must be considered during the calculation process. For pores in the matrix, they are considered as inclusions in a kind of isotropic material. Based on inclusion theory, the Mori-Tanaka method is used to predict Young's modulus of the pore matrix. Stiffness averaging method gives the estimated value of Young's modulus of the fiber parallel to the loading direction which contains undulation. Finally, the effective Young's modulus of the representative volume element (RVE) are obtained according to the mixture formula. In order to facilitate the finite element calculation, the RVE is divided into three kinds of sub unit cells. Finite element models of the three kinds of cells are established. And elements representing pores are used in the finite element models based on Python language. The error between analytical method and finite element method is small, which gives an excellent prediction on inplane tension Young's modulus of braided composites.

In this study, a high strain rate test method of a steel plate under blast loading from high explosive was designed and was conducted by a combined experimental/numerical approach to facilitate the estimation process for the dynamic stress-strain curve under practical strain rate conditions. The steel plate was subjected to a blast load, which was generated by Composition C4 explosive and the dynamic deformation of the plate was observed with a high-speed video camera. Time-deformation relations were acquired by image analysis. A numerical simulation for the dynamic behaviors of the plate identical to the experimental condition was conducted using a coupling analysis of finite element method (FEM) and discrete particle method (DPM). Explosives were modeled by discrete particles and the steel plate and other materials were modeled by finite element. The blast load on the plate was described fluid-structure interaction (FSI) between DPM and FEM. As inverse analysis scheme to estimate dynamic stress-strain curve, an evaluation using a quasistatic data was conducted. In addition, two types of approximations for stress-strain curve were assumed and optimized by least square method. One is a 2-piece approximation, and was optimized by least squares method using a yield stress and a tangent modulus as parameters. The other is a continuous piecewise linear approximation, in which a stress-strain curve was divided into some segments based on experimental time-deformation relation, and was sequentially optimized using youngs modulus or yield stress as parameter. The results showed that the piecewise approximation can gives reasonably agreement with SS curve obtained from the experiment.

Methods of analysing ropes. The extension–torsion method

The modal and the response during acceleration of high-g shock MEMS accelerometer were simulated using finite element method based on a practical packaging model. The modal frequency of the packaging structure increases with the Young's modulus of encapsulation resin. But the modal-frequency may be smaller then that of the packaging structure without encapsulation if the encapsulation resin is very soft. Under the 100 kG acceleration (1 G = 9.8 m/s/sup 2/), the simulated output voltage of accelerometer decreases slowly with the increase of Young's modulus or density of encapsulation resin. The simulated output voltages are close to the analytic results. They are also linear with the environmental accelerations.