Domain switching characteristics of a commercial lead zirconate titanate piezoelectric (PZT) ceramic at high temperature of 100℃ were investigated using an electron backscatter diffraction (EBSD) system. The PZT ceramic consisted of a tetragonal structure with grain size of about 5μm. To analyze the domain switching characteristics, the EBSD analysis was carried out in the same region of the PZT ceramic before and after the heating process. From this analysis, it appeared that each grain is formed by three different domains with different ratio. The area ratio of the domain was altered after the heating process because of the 90° domain switching. To understand clearly the 90° domain switching characteristics, the domain modes were categorized with the angle between the poling direction and c-axis of the tetragonal structure. Although the domain mode was categorized, no clear switching pattern was clarified, i.e., domain switching occurred randomly. Such domain switching mode was attributed to the complicated thermal stress in the PZT ceramic. In order to clarify the domain switching pattern under the heating process, the switching characteristics were investigated in details, in which the grain, having different stress distribution, was selected. The grain selected was constrained in the wide area by the other grains and some region was non-constrained due to the vacancy. From this analysis, severity of domain switching depended on the stress level, e.g., the higher compressive stress, caused by the thermal expansion of the other grains, made the strong domain switching.
With the development of spacecraft, the brittle materials like ceramics and glass have been used for significant components especially in optical and thermal systems. However, they are vulnerable to damage by hypervelocity impact of space debris and micrometeoroids. Against a backdrop of increasing number of space debris, impact-damage evaluation on brittle materials become a growing concern. In this study, a series of hypervelocity impact experiments has been conducted to evaluate internal damage propagation mechanism in a fused-silica-glass plate target by impacting a stainless steel projectile with 1-mm diameter in the velocity range around 2 km/s. Damage propagation behavior was observed from two directions simultaneously by means of in-situ shadowgraph coupled with an ultra-high-speed video camera. The observation concentrates on propagation behavior of lateral cracks and that of internal failure. The former is revealed to a mass of small cracks which were generated by passing of the surface stress wave. The latter propagation is affected by the longitudinal and transversal waves, the reflection of the spherical stress waves on the back surface of target. The failure propagates rapidly two times by the reflected waves: first rapid propagation was caused by tensile stress induced by the reflected longitudinal wave, the secondary rapid propagation was caused by shear-compression mixture stress induced by the reflected transversal wave, which was generated by mode conversion of the longitudinal wave.
Transluminal attenuation gradient (TAG) is expected as a noninvasive assessment of the functional significance of a stenosis, and has reported relatively high diagnostic performance. TAG measures the gradient of intraluminal radiological attenuation from the ostium at the first pass of the injected contrast agent; therefore, replacement of fluid by jet flow from a stenosis with gradually increasing contrast agent concentration should be investigated. We performed a phantom experiment and ALE fluid-structure interaction finite element simulation on pulsatile flow through a bifurcated flexible tube system with a stenosis. Experiment and simulation showed good agreement with temporal change of flow rate, pressure, and radius under 1 Hz square pulsatile flow. We varied Young modulus and rate of stenosis with 1 Hz sinusoidal input. Young modulus had little effect on the distribution of total flow, but a changed flow rate waveform and faster maximal velocity in the stenosis was observed with a smaller Young modulus. Then we simulated convection of particle tracers generated at the inlet, imitating a gradual increase in contrast agent with 80% and 95% stenosis. With 80% stenosis, axially symmetric flow resulted in reproductive tracer distributions; however, with 95% stenosis, the direction of jet flow from the stenosis and of subsequent helical flow varied every beat, suggesting this variation might lower sensitivity of TAG.
Tensile and fatigue tests were conducted on type 304 stainless steel plate-shaped specimens repaired by High Velocity Oxy Fuel (HVOF) spraying. Specimen surfaces were machined for repair into trapezoid with the same depth, the same length, and various slope angles (called here cutting angles). During tensile tests, damage evolution in the repaired part was continuously monitored under increasing load. Quantitative evaluation of the relationship between the strain gauge attached to the repaired part surface and the cross-head displacement was performed. In fatigue tests, influence of the repaired shape on damage evolution was studied, and obtained fatigue lives were compared between the cutting angles. According to tensile testing results, crack initiation strain values increase with cutting angles. At the same time, residual stresses were mostly compressive and almost independent from cutting angles, thus positively affecting the magnitude of fatigue strength. Fatigue test results indicated that specimens repaired with a cutting angle of 50°possess a superior fatigue life. The results showed that the HVOF spraying can potentially replace welding repair.
Fatigue crack in cast aluminum alloys subject to low-cycle fatigue is initiated mainly by the fracture of Si particles. To investigate the mechanism of Si particle fracture, we carried out the geometrical measurements and finite element analysis for a lot of Si particles in their actual geometrical configuration. The synchrotron X-ray CT was used for the geometrical measurement and the image-based finite element modeling. The fracture of Si particles were detected as a source of crack initiation from the CT images captured during the fatigue test. The large-scale voxel finite element model contains the outer surface, pores, Si and intermetallics. The number of elements was about 150 million. Two cycles of loading were calculated. The finite element analysis and its post-processing were performed on the supercomputers by the massively-parallel computing. The result of finite element analysis showed that the first principal stress was concentrated around the aligned or gathered Si particles, and the gradual increase by cyclic loading in the stress of the Si particles appeared near the outer surface and pores. Moreover, the result of geometrical measurements showed that the volume, shape index and adjacency index of each Si particle could be used to evaluate the likelihood of particle fracture. The probability of particle fracture was statistically evaluated with respect to those geometrical and mechanical parameters. The relationship between mechanical and geometrical parameters were also examined. As the result, the criteria of fractured Si particle was proposed by using the combination of geometrical and mechanical parameters.
The effect of stress ratio on through thickness fatigue properties of thick carbon fiber reinforced plastic (CFRP) laminates with toughened interlaminar layers was evaluated. The unidirectional (UD)  and quasi-isotropic (QI) [45/0/-45/90]11S laminates were formed using prepregs (T800S/3900-2B) with toughened interlaminar layers. The spool shaped specimens were cut from the laminates. Static tensile and compressive tests were performed. As the results of the static tests on both laminates, the through thickness compressive strength was more than five times higher than tensile strength. The fracture morphology under compressive loading was difference between each laminate. Fatigue tests were performed under the stress ratio of R=0.1,-1,-3 and -6 on both laminates. As the results of the fatigue tests on both laminates, the fatigue life decreased as the stress ratio was lower. On the other hand, the remarkable difference of the fracture surface was not observed under each fatigue test condition by both macroscopic and microscopic observation in this study. The fatigue life of UD and QI specimens was able to be evaluated by the proposed model, the modified H-κ model based on strain energy approach. The predicted fatigue life was good agreement with the experimental results.
The purpose of this study is to propose an effective model to estimate the effective thermal conductivity of compacts made from magnesium alloy particles, considering the effects of particle size, temperature and pressure. In order to investigate the influence of the particle size, six kinds of particles were prepared in which the cross sectional area was different. The test particles made from AZ91D were poured into a compression vessel and then a given pressure was applied to the piston of vessel for six hours under constant temperature condition. After compression, effective thermal conductivity of compacts were measured by steady state comparative-longitudinal heat flow method. The numerical calculation considering two-dimensional steady heat conduction was also conducted by using the actual cross section of compacts. Test results showed that the effective thermal conductivity of compacts were increased with increase of applied pressure and temperature elevation. Calculation results also revealed that by considering the actual cross section of compacts, the effective thermal conductivity could be well estimated when filling fraction is lower than 0.8. However, when filling fraction is exceed 0.8, the effect of thermal contact resistance between particles on thermal conductivity is not negligible. The experimental equation of effective thermal conductivity of compacts was determined to discuss the effects of cross sectional area of particles.
Residual stress measurements on pipe-shaped Ni-alloy, Inconel 625, were conducted. The pipes were made from a thin plate by roll-bend and weld along longitudinal direction of the pipe. Shot peening processes were performed to the outside surface of the pipes. The stresses were measured using X-ray stress measurement method. The residual stresses on the specimen before shot peening process were around 100 MPa toward longitudinal direction and around 250 MPa toward transvers direction to the welding direction. The residual stresses changed to 800 MPa in compressive by shot peening process. After thermal aging at 1173 K for 1 and 10 hour, the residual stresses changed to −100 MPa on the specimens with and without shot peening in both longitudinal and transvers directions. In addition, optical microscopic observation and the analyses of X-ray diffraction peaks were performed to reveal microstructural features due to welding, shot peening, and thermal aging. Equiaxed and columnar dendrites were generated in the center and the outer of fusion zone, respectively. The grains in the heat affected zone, between the fusion zone and base metal became larger. The grains near the surface even in welds became small by shot peening processes according to analyses of X-ray diffraction peaks. Even though induced compressive residual stresses were released during thermal ageing, refined grains had been smaller than before shot peening process.
We have established the torsion pin test method with tension to evaluate shearing delamination strength of thermal sprayed coating under tension-torsion combined stresses, recently. Apparent delamination strength depends on the diameter of the pin, so the stress distributions around the interface edge between the top-coat and the bond-coat have to be analyzed by using the finite element analysis based on the experimental results to see the real delamination strength. Before analyzing, the deformation properties of the thermal sprayed coating have to be known. In this report, macroscopic elastic deformation properties of the four kinds of porous thermal barrier coating (TBC) is investigated experimentally and analytically. First, the indentation tests are performed to obtain the loading and unloading-depth curves in various load levels, and secondarily Young's moduli are explored by using the unloading-depth curves, Hertz-contact theory and FEM analysis at several loading levels. It becomes clear that the obtained Young's moduli increase with increasing indentation load, which means that the obtained Young's modulus is an apparent modulus of the coating having some structural failure caused by indentation test. As the results, the real Young's moduli are determined at the very small load level with no structural failure for the four kinds of porous thermal barrier coatings.
In this study, the applicability of cumulative damage law for carbon steel, STS410, was investigated. In addition, prediction method of low cycle fatigue life based on small crack growth was researched. First, low cycle fatigue tests under two step variable loading condition were performed for STS410. Variation of cumulative damage UF at failure fell within general variation range, 0.7 to 1.4. The relationship between crack length and UF was corresponded under different conditions. Crack distribution was also corresponded under different strain range conditions. Therefore, cumulative damage law is available to evaluate the fatigue life of STS410. Next, crack initiation, growth and coalescence behavior of STS410 were modeled, and Monte Carlo simulation was carried out. Fatigue life and crack growth of simulation under strain range constant condition were similar to those of experimental results. In the case of two step loading simulation, simulation results show that UF at failure fell within variation range of strain range constant simulation. These results corresponded to experimental results. Crack length and distribution of simulation also corresponded to those of experiment. Therefore, good agreement can be seen in experiment and simulation, so low cycle fatigue lives of strain range constant and variable loading condition are able to be predicted using present model.
Peening is one of the mechanical surface modification techniques, which is used to improve the fatigue strength by the introduction of the compressive residual stress into the surface of specimen. Several peening techniques, such as shot peening, cavitation peening and laser peening have been proposed and demonstrated the improvement of fatigue strength. Mechanical properties on surface modification layer vary with the techniques because of the difference of mechanism of impacts and strain rate. Therefore, it is possible to improve the fatigue strength further by hybrid peening, which is a combination of different peening techniques, due to controlling the mechanical properties on surface modification layer. In this paper, in order to demonstrate the suppression of fatigue crack propagation by hybrid peening combining shot peening and cavitation peening or cavitation peening and laser peening, the fatigue crack propagation in duralumin treated by hybrid peening was investigated, and the crack propagation behavior of the specimen treated by hybrid peening and single peening method was compared. The relationship between the fatigue crack propagation and the mechanical properties was also evaluated. It was revealed that hybrid peening (former process: laser peening, latter process: cavitation peening and former process: cavitation peening, latter process: shot peening) was more effective to suppress the fatigue crack propagation than single peening method and the number of cycle to failure of the specimen treated by hybrid peening was the largest. The new indicator f(σR’, HV’, Rz’, β’) = σR･HV･β/Rz combined with four factors i.e. compressive residual stress σR, Vickers hardness HV, full-width at half maximum β and maximum height roughness Rz showed the effect of suppression of fatigue crack propagation by peening.
Aerodynamic noise generated around a step such as front pillars of automobiles, which is transmitted into the cabin through the window glass, can negatively affect the comfort of the passengers. For the reduction of this noise, it is necessary to clarify the acoustic source and process of the propagation of the acoustic waves from the step. To do this, direct aeroacoustic simulations were performed along with wind tunnel experiments for flows around a forward step in a turbulent boundary layer, where the freestream Mach number was 0.1 and the Reynolds number based on the incoming boundary layer thickness, δ, and the freestream velocity was 2.73×104. The computations were performed for the height of h/δ = 0.9 and 3.4, where the effects of the step height on the radiated sound were investigated. The radiated sound becomes more intense for the higher step of h/δ = 3.4 particularly in a low frequency range of St ≤ 1.5, where St is the non-dimensional frequency based on the step height and freestream velocity, due to the occurrence of the large-scale vortices in the separated flow. To elucidate the radiation of the acoustic waves, the pressure fluctuations were decomposed into non-radiating convective and radiating acoustic components by usage of two methods. One is utilizing wavenumber-frequency spectra and the other one is spatial Gaussian filtering for the fluctuations at each frequency, which is proposed in this paper. The results by the former method present that the level of convective components is larger than the acoustic components by 20 - 40 dB. Moreover, the radiating components by the proposed spatial filtering method show that the radiation occurs around the step edge and the reattachment point. It is indicated that the proposed method is effective for the investigation of the acoustic radiation for the pressure fluctuations composed of convective and acoustic components.
To increase thermal efficiency of internal combustion engine, lean burn and EGR (Exhaust Gas Recirculation) system have been developed with spark ignition coils generating larger discharge current and discharge energy than current mass production coils. Several researches clarified that larger discharge current increases discharge channel extension and decreases possibility of discharge channel blow-off and possibility of misfire. However, these investigations don't mentioned effect of larger discharge current and energy on air-fuel ratio and combustion period. Then purpose of this research is to investigate relation among air-fuel ratio, combustion period and coil specification in order to clarify control factor of air-fuel ratio of lean burn. In this study, five coils having different current profiles were evaluated under 2000 rpm and 0.6 MPa NMEP (Net indicated Mean Effective Pressure) at lean mixture condition by combustion test and in-cylinder optical measurement test with research single cylinder engine. The combustion test results showed a correlation between lean limit air-fuel ratio and initial combustion period. Moreover, optical measurement test showed that initial combustion period has a correlation with discharge energy before 1st restrike and discharge channel extension rate and variation of initial combustion period under stable control condition doesn't depend on discharge current.
In recent years, electronic control has become mainstream of pneumatic control systems. But pneumatic positioning systems have advantages such as explosion proof, operable even at power failure, simple structure, easier maintenance, and low price. Therefore, with fusion of mechanical feedback technology and latest technology, it is possible to realize an advanced system required for realize a safe and secure society, and it can be expected to be applied in a wide field in the future. In this study, we aim to develop advanced system incorporating pneumatic positioning systems with mechanical feedback, we propose a model of the pneumatic positioning systems with mechanical feedback, perform characteristic analysis using the model, and evaluate the effectiveness of the model by comparing with the experiment result. In this paper, step response experiments were carried out using three different sizes of cylinders, and the results of the step response experiment and the simulation were compared. As a result, except for high input pressure, the transient characteristics of both were in good agreement. Therefore, it proved that the proposed model is effective for analyzing the transient characteristics of the system incorporating pneumatic positioning systems with mechanical feedback. We also obtained the prospect that the characteristics analyzed using the proposed model can be used for developing new applications.
This paper proposes a novel controlled charge source circuit for synthetic admittance of piezoelectric shunt damping system. A design method for the proposed charge source circuit is also proposed. By analyzing the stability of the charge source circuit itself in consideration of the dynamics of the operational amplifier, this paper shows the conventional simple charge source circuit can be unstable because its minimum phase margin is extremely small. Moreover, we show that the minimum phase margin of the charge source circuit itself is greatly improved by the proposed method. In the case of the parameters of the experimental apparatus in this paper, the minimum phase margin is improved from less than 5 degrees to more than 75 degrees. Finally, we carry out the characterization of the developed circuit and shunt damping experiment in order to confirm the effectiveness of the proposed charge source circuit used as the synthetic admittance.
If damping alloy is used as structural material, a structure with high damping performance can be produced and its vibration and noise can be reduced. Damping mechanism of the damping alloy is to convert vibration energy into thermal energy. The damping performance of the damping alloy is not as good as it is used in a dynamic damper. This paper proposes a method of enlarging equivalent loss factor of a damping alloy spring by using a negative spring constant and it is confirmed that the equivalent loss factor of a damping alloy cantilever becomes large by the attraction force of magnet used as the negative spring constant. Optimal design of the dynamic damper which consists of the damping alloy cantilever and a pair of magnets is explained. The vibration suppression effect due to the dynamic damper is demonstrated by means of measuring the compliance and the time history response by impact excitation. The vibration suppression effect depends on the vibrational amplitude due to nonlinearity of the attraction force of magnet but can be sufficiently expected in comparison with the case without the dynamic damper.
Three-dimensional (3D) numerical simulation of incompressible, magnetohydrodynamic (MHD) flows under alternating-current (AC) magnetic fields are carried out, which takes into account the coupling with the electromagnetic fields in the solid and gas regions. A numerical scheme is constructed by combining the Galerkin finite element method and the edge-element based finite element method, which are applied to the discretizations of the Navier–Stokes equations and the electromagnetic field equations, respectively. The solution algorithm for fluid flow is based on an explicit fractional step approach and the simultaneous relaxation of velocity and pressure to satisfy the continuity equation. The electromagnetic field equations are formulated with the use of the magnetic vector potential which is defined on the edge elements. In the proposed numerical scheme, the advection term in the induction equation is not neglected, because the scheme needs to deal with the condition where the advection term is the same order with the diffusion term in that equation. The validity of the numerical scheme is verified through the analysis of the electromagnetic field under a direct-current magnetic field, and numerical simulations of the MHD flows under spatially uniform AC magnetic fields are carried out. It is confirmed that the spatio-temporal mean Lorentz force in the conducting fluid becomes weaker with the increase in the dimensionless frequency due to the skin effect. It is also shown that the flow pattern in a hexahedral closed domain is largely changed when the frequency is getting higher, which is associated with the change in the Lorentz force profile.
In this paper, a new formulation of three-dimensional J-integral for the evaluation of elastic-plastic fracture problem is presented. It is known that the J-integral represents the energy release rate per unit crack extension. The J-integral is a path-independent integral and can be computed on arbitrary integral path or domain. This property requires the assumption of proportional loading when an elastic-plastic material is considered. Because of this assumption, J-integral loses path-independent property under a non-proportional loading condition. We present a new formulation of three-dimensional J-integral representing the energy dissipation inside a small but finite domain in the vicinity of crack front. The dissipated energy includes the energy released by crack extension and the deformation energy that dissipates in the process zone. This formulation is the extension of the three-dimensional J-integral using equivalent domain integral method and derived without any assumptions on the deformation history. Therefore, it is possible to evaluate the J-integral for problems subject to any load histories. Finally, the problems of hyperelastic and large deformation cyclic elastic-plastic analysis using finite element method are presented. They show that the proposed method can be applied to non-proportional loading problem.
Recently the design of experiments is used to decide optimum processing conditions. However when the control factor interaction between the several control factors becomes large, the calculated accuracy using the design of experiments becomes very bad. Then everybody should check the results regarding the best and the worst conditions in the experiments. If differences between the calculated vale and the experimental value for the best and the worst conditions become large, the results using the design of experiments are never used. Therefore, in the previous research, we have developed the tool for easily finding the control factor interaction in the design of experiments. This control factor interaction between the several control factors action is large fault, an obstacle for innovation and disliked by everybody. However when the reaction between the several control factors becomes large effect which is surpassed the estimate, the control factor interaction becomes the synergistic effect which is liked by everybody, the synergistic effect finally brings large profit, excellent license and innovation. Therefore in this research, the tool for easily finding the synergistic effects between the control factors was developed and evaluated using the program in the previous research. The program was the tool for finding the control factor interaction in the design of experiments, it was improved for the easily finding the synergistic effects by using the new algorithm, and was evaluated by the several mathematical models and the experiment. It is concluded from the result that (1) the new program can clear the synergistic effects between the control factors, (2) the program also can clear the complex multiplier effects and (3) the program can clear the synergistic effects with innovative profit in the actual example.
The present paper describes edge contact analyses for power transmission gears using tooth-flank-film elements, which have been proposed for finite element analyses of tooth stresses. For edge contact analyses, the tooth-flank-film elements are placed not only on usable flanks but also over tooth edges. Finer elements on edge neighboring areas and on the parts of usable tooth flanks where tend to contact with mating edges enable the edge contact to be analyzed. Comparisons of calculated distributions of tooth contact stress with observed tooth flanks after a running test showed the validity of the proposed method for edge contact analyses.
Linkage mechanisms with 1 DOF consisting of links and lower pairs cannot completely generate the specified output motion. In order to solve that problem, the novel kinematic pair with 1 DOF is developed. This kinematic pair consists of two surfaces in line contact with each other and can generate relative rolling motion along the specified spatial trajectory. Thus, it is called the spatial rolling contact pair. The relative rolling motion along an arbitrary trajectory is specified so as to satisfy the kinematic condition of the spatial rolling motion. Rolling contact surfaces which can generate the specified motion are designed based on ruled surfaces of the instantaneous screw axis. Some norms to evaluate stability of rolling contact between designed pairing elements are introduced, and the pairing elements are constrained by many linear elastic elements so as to satisfy them. Some examples of the proposed kinematic pair are designed, and one of them is manufactured as a prototype. By some experiments, it is confirmed that the prototype generates the specified rolling motion and keeps rolling contact by designed elastic constraint. Finally, it is revealed that a spatial 4-bar mechanism with the spatial rolling contact pair can completely generate the specified output motion and can be synthesized more easily than the mechanism synthesized by conventional methods.
In sheet forming, the blank holder force (BHF) has a direct influence on product quality. A high BHF leads to tearing, whereas a low one results in wrinkling. For successful sheet forming, the BHF should be adjusted. Recently, the variable BHF (VBHF) that the BHF varies through stroke is recognized as one of the advanced sheet forming technologies. On the other hand, slide velocity (SV) that controls the die velocity is rarely discussed in the literature, and the SV should also be taken into account for the successful sheet forming. A high SV can achieve the high productivity, but wrinkling occurs. The VBHF trajectory and SV are unknown in advance, and the trial and error method is widely used. In this paper, design optimization approach using computational intelligence is adopted to determine them for achieving the high productivity. The processing time is taken as the objective function to be minimized for the high productivity. Numerical simulation in sheet forming is so intensive that a sequential approximate optimization using radial basis function network is adopted to determine the optimal solution. Based on the numerical result, the experiment using AC servo press (H1F200-2, Komatsu Industries Corp.) is carried out. Through the numerical and experimental result, the validity of proposed approach is examined.
Acupuncturists determine muscle stiffness by pressing their fingers down. To shorten the palpation time and minimize discomfort to the patient, a good palpation technique is required to determine the stiffness of the patient's muscles with as few presses as possible. However, palpation is dependent on the experience of the practitioner. Therefore, an investigation of human hardness discrimination characteristics is necessary to provide some quantitative guidance. In this study, to determine the relationship between different numbers of presses and the accuracy of discriminating hardness, we investigated the differential threshold of hardness for different numbers of presses (1, 3, or 5). We used 7 elastic test pieces, each with a different Young's modulus, as the presented stimuli. We conducted an experiment using the constant stimuli method to calculate the differential threshold of hardness as an evaluation index of hardness identification. In the experiment, the participants repeatedly pressed for either 1, 3, or 5 sets by using 2 presented stimuli and then distinguished the hardness of the stimuli. The results of the experiment showed that when the pressing forces were 5 and 10 N, as the number of presses decreased, the differential threshold of hardness increased. However, when the pressing force was 15 N, the differential threshold of hardness was small regardless of the number of indentations. This knowledge will be useful for the improvement of the palpation technique in acupuncture schools. For example, the index of the hardness discrimination characteristic used in this study may be used as a quantitative numerical target and for performance evaluation.
Spherical Acoustic Black Hole (ABH), a kind of acoustic metamaterial, has been made in the new configuration to control three dimensional propagation of acoustic wave and its characteristics have been investigated by experiments and numerical simulations. ABH is new sound absorber composed of shell and absorptive core. Shell guides the incident acoustic wave into the core and ABH traps acoustic wave. Moreover, shell matches the characteristic impedance to the medium around ABH at the surface, which can enlarge absorption area without reflection. The experimental model of spherical ABH is constructed by stacking urchin-like shaped layers made with a 3-D printer on the assumption that the sonic crystal theory (Torrent and Sánchez-Dehesa, 2006, 2007) is valid in new structure. To evaluate reflection and transmission of ABH quantitatively, sound pressure around ABH was measured and angle averaged reflection coefficient and angle averaged insertion loss (Elliott et al., 2014) were calculated. Also, Glass Wool Sphere made of the same material as core of ABH and Rigid Sphere made of the same material as shell of ABH were measured in the same way and ABH was compared with them. The results of experiment and finite element method analysis show spherical acoustic black hole can decrease reflection due to impedance matching. Moreover, it can change the propagation direction of acoustic wave due to refractive index distribution and a large acoustic ratio region caused by the small refraction was observed.
This study aims to develop an actively deformable space antenna system for radio astronomy around 100GHz. In order to reduce the thermal deformation in active control mechanisms composed of multiple materials, a method to cancel the mismatch of the coefficients of thermal expansion (CTE) is proposed and tested. The CTE mismatch between piezoelements and Super Invar structures is cancelled by adding another metallic part. For effective CTE cancellation, this study clarifies the cause of thermal deformation induced by the preloading mechanisms for a piezoelectric stack actuator. In addition, it shows the effect of the dimension tolerance of the piezoelements is significant, but still manageable by the proposed CTE cancellation method. The effectiveness of proposed method is validated by the use of finite-element analysis, prototyping models, and thermal deformation measurement experiments.