The binary defocused fringe can overcome the nonlinear effect of an ordinary commercial digital projector and generate a good sinusoidal light field. In this paper, the binary fringe encoding method was chosen to complete the high-speed fringe projection using a DLP Lightcrafter 4500 model in dynamic Fourier transform profilometry, and then a camera was synchronously triggered to record the deformation fringes on the surface of a high-speed rotating radiator fan, whose time-changing 3D surface shape was reconstructed with Fourier fringe analysis. Further deformation analysis of the measured radiator fan blade and rotating shaft is helpful to improve the performance of the radiator. The experimental results on a tested radiator fan with the rotation speed of 4800rpm identified the validity of the presented setup, and this method can effectively expand the application of dynamic 3D shape measurement.
A procedure for identifying plastic constitutive parameters from measured displacement fields based on virtual fields is proposed in this paper. The displacement fields of the specimen surface are obtained through measurements using global digital image correlation. Then, material property identification is implemented by utilizing piecewise virtual fields. In order to identify the material properties from the displacement fields obtained at an instant, the total strain theory is used as the constitutive equation. The relations between the material properties, measured displacement fields, measured tractions, and virtual displacements are obtained from the principle of virtual work, and they are solved numerically to obtain material properties. The effectiveness of the proposed method is demonstrated by applying it to displacement fields obtained by an elasto-plastic finite element method and experimentally obtained displacement fields of a pure aluminum specimen. The results of the numerical validation show that the elasto-plastic material properties can be identified from a single set of displacement fields under proportional loading. Meanwhile, the results of the experimental validation show that the elasto-plastic material properties can be evaluated but the discrepancy between the inversely identified stress-strain curve and the directly measured one is observed.
The plateau stress of aluminum (Al) foam is an important mechanical parameter that is closely related to its energy absorptivity. An estimation method for plateau stress was proposed by simply assuming that when the mean true compressive stress on a maximum-porosity cross section perpendicular to the direction of compressive loading reaches the critical value, the nominal compressive stress becomes equal to the plateau stress. In this study, using commercial-purity A1050 Al, A6061 Al alloy and ADC12 Al alloy die castings containing a large amount of gases, uniform Al foam and two types of functionally graded (FG) Al foam were fabricated by the friction stir welding (FSW) route precursor process. The local porosity distributions for the fabricated Al foams were obtained from the observation of X-ray computed tomography (CT) images, then drop weight impact tests were carried out to evaluate the plateau stresses. Through the comparison of the test results with the results obtained by the estimation method, the applicability of the estimation method for plateau stress to impact compression tests on uniform aluminum Al foam and each foam layer of FG Al foam was examined. It was shown that the plateau stresses can be evaluated approximately within ±20% error when the proof stress is employed as the critical value.
It has been reported that when a high-speed projectile collides with aluminum foam, a unique crater with a narrow entrance and large cavity is formed, shaped like a turnip. In the case of a material with higher porosity, it is considered that a debris cloud is produced by the impact, and the crater is created by scattering the debris cloud inside of the target material. In addition, melting traces have been observed, and it is predicted that these are caused by the heat created by the impact. It is conceivable that the temperature of a plasma induced by high-speed impact is associated to indicate the temperature at impact, although this relationship has not yet been proven. Measuring temperature at impact point is difficult since the measuring device will have to avoid collision with the projectile. Therefore, it is essential to measure plasma apart from impact point and observe diffusion of plasma. In this paper, high-speed impact experiments in which plasma was measured with a triple probe and a high-speed camera was performed to confirm the above. The high-speed impact experiment was performed with a vertical gas gun at Ritsumeikan University's Impact Engineering Laboratory. The impact speed was 400 m/s, and the target material was A5052. The high-speed camera had a maximum frame rate of 1.4 Mfps and a minimum exposure time of 1.0 μs. Plasma signals were measured by the triple probe method, and at the moment of impact, the flash was recorded by the high-speed camera.
Temporal resolution and crosstalk of an ultra-high-speed image sensor operating at 1 Gfps are analyzed by using Monte Carlo simulation. An impulse response method is proposed to analyze crosstalk and to cancel large crosstalk involved in output signals of the sensor. The sensor is backside-illuminated (BSI) with multi-collection-gate (MCG) at central area of a pixel on the front side. Signal electrons generated by incident light near the back side travel to the central area of the pixel and are collected by the collection gates. The travel time and the path of a signal electron randomly distribute due to randomness in arriving spot on the backside of the sensor and penetration depth of an incident photon which generates the electron, and in the motion of the generated electron. The travel time is analyzed to define the temporal resolution of the sensor. A collecting gate is defined as one of the collection gates which is supposed to collect all the signal electrons at a certain time interval. However, due to the randomness, some of signal electrons migrate to other collection gates than the collecting gate, resulting in mixture of signal electrons at neighboring collection gates and/or pixels, causing crosstalk in time and space. The proposed impulse method is used to analyze crosstalk when the sensor operating at 1 Gfps. From the analysis, a cancellation method of crosstalk involved in output signals is presented and successfully applied in cancellation of crosstalk in an example of 2 dimensional images.
An image sensor with 300 kpixels operating at 20 Mfps is developed. Pixels on odd-number and even-number columns can be independently operated. The highest frame rate is 40 Mfps when a time shift of a half of the shortest frame interval is introduced to the operation of the odd and even pixel columns. The sensor is backside-illuminated one for high sensitivity to support the ultra-high-speed imaging with fewer photons. The concept, the structure and the operation scheme of the image sensor are presented. The pixel count and the highest frame rate of the prototype which was developed in 2011 were 165 kpixels and 16 Mfps. Therefore, the new image sensor achieved doubled performance. In-situ storage for 107 image signals is installed in each pixel. Simultaneous recording of image signals at all pixels makes it possible to capture consecutive 107 frames at a time interval for a signal packet to be transferred from the photodiode to the nearby storage element of each pixel. Video cameras equipped with these sensors are applied to imaging of high-speed phenomena such as electric spark discharge and sudden crack propagation for the performance test.
This paper reports an experimental result of expansion wave and cavitation bubble generation by underwater shock wave reflection at the interface for understanding of shock wave interaction phenomena related to the mechanism of shock wave human tissue damage. Underwater shock wave was generated by detonating a micro-explosive (silver azide pellet). The process of underwater shock wave reflection at the interface, expansion wave and cavitation bubble generation were visualized by shadowgraph method and recorded by an ultra-high-speed framing camera at high spatiotemporal resolution. The pressure time history near the interface in water was measured simultaneously by a needle hydrophone. High-speed shadowgraph sequential images show that a compression wave (shock wave) was reflected from a thin interface plate (Polystyrene, acrylic, Teflon, thickness of t=0.5 mm), and expansion wave was then generated in water by reflection from the air. In addition, a cavitation bubble was created behind the expansion wave. The simultaneously measured pressure history also shows that an expansion wave propagated behind shock wave. The negative peak pressure of expansion wave in the case of a thin plate shock wave interaction was larger than that in water surface interaction.
Dual-energy photon counting was performed using an energy-selecting device (ESD) and a cadmium telluride detector. The ESD is used to determine a low-energy range for computed tomography (CT) and consists of two comparators and a microcomputer (MC). The two threshold energies are determined using low and high-energy comparators, respectively. The MC in the ESD produces a single logical pulse when only a logical pulse from the low-energy comparator is input to the MC. To determine the high-energy range, logical pulses from the high-energy comparator are input to the MC outside the ESD. Logical pulses from the two MCs are input to frequency-voltage converters (FVCs) to convert count rates into voltages. The output voltages from the two FVCs are sent to a personal computer through an analog-digital converter to reconstruct tomograms. Dual-energy CT was accomplished at a tube voltage of 70 kV and a maximum count rate of 4.5 kilocounts per second, and two-different-energy tomograms were obtained simultaneously using iodine media.
The scanning laser-induced acoustic microscope (SLAM) has been developed as a tool for non-destructive observations of the defects in materials. It consists of the laser with modulation system, the function generator, the lock-in amplifier, the AE sensor which detects the longitudinal acoustic waves, the XY stage and a computer for signal processing. The cyclic chopping laser beam causes the thermal wave. Our own-built SLAM has successfully provided some nondestructive observations; the bonding boundary of the different materials and the small crack in the materials. Since the SLAM senses the local difference of thermal properties in the sample, it performs observing the boundary or the crack well. The scanning laser-induced acoustic image (LAI) is affected by the power and chopping frequency of the laser. We revealed that the laser power more than a certain value (105 mW) is required in order to obtain a clear LAI with our SLAM in the case of the observation of aluminum alloy. Moreover, the LAI is affected by the chopping frequency of the laser and the LAI becomes clearer as the chopping frequency becomes higher even if the chopping frequency is up to 15 kHz which is relatively low.
The fundamental study on the ultrasonic characterization of non-Gaussian rough surface of a material is carried out. In this study, a theoretical relationship among ultrasonic reflection coefficient at normal incidence, root mean square roughness Rq, and skewness Rsk (which is the measure of symmetrical level of a height distribution) has been derived. In the derivation, a Gaussian curve fitting to the non-Gaussian height distribution of a rough surface is effectively performed so that the Kirchhoff theory of wave scattering from a rough surface can be utilized. In order to verify the validity of the derived relationship, air-coupled ultrasonic pulse-echo measurements with normal incident configuration at center frequency of 0.35 MHz have been conducted to a series of sandpapers having various Rq and Rsk values. From the measured ultrasonic reflection coefficient of each sandpaper, the Rq values of the sandpapers have been estimated from the derived relationship with known values of skewness of the sandpapers and then compared to those measured by a mechanical stylus profiler. It is found that the Rq values estimated by the ultrasonic method and the stylus profiler almost agree with each other. Thus, the validity of the derived theoretical relationship is demonstrated.
The relation between strain and uniform elongation, and the effect of low-temperature annealing, were examined using an Al-Mg alloy (A5052) processed by accumulative roll bonding (ARB). Specimens were deformed by ARB for 1 to 7 cycles at room temperature, and then subjected to isochronal annealing for 30 min at temperatures ranging from 100 to 300 °C. Tensile properties, hardness, and grain boundary structure before and after annealing were investigated. The uniform elongation of ARB-processed specimens decreases with increasing ARB cycles. However, the elongation is improved by low-temperature annealing for specimens processed by ARB of 3 or more cycles. Higher strain in the ARB process results in higher uniform elongation after annealing, even though the specimens have the same value of 0.2% proof stress. This improvement of the uniform elongation by annealing is caused by annihilation of dislocations inside ultra-fine grains, which are developed by ARB of 3 or more cycles.
Displacement distribution in plate specimen of aluminum during tensile test was measured with digital image correlation method and strain distribution was derived based on the displacement distribution. Change of strain distribution was obtained during whole tensile test. Local concentrated strain starts to appear before proof stress and the local strain becomes larger as the deformation proceeds and strain at other area in the specimen almost does not change. In consideration of stress-strain relation, true stress derived from the conventional average stress in uniform area of the specimen decreases after proof stress with increase of true strain. True stress derived from the maximum strain in specimen increases with increase of true strain and it is found that work hardening exists. Stress-strain relation for aluminum was compared with the result for steel which the author already published. It was found that we have to measure strain distribution and consider local maximum strain to evaluate stress-strain relation accurately.
After a huge earthquake, it is important to evaluate additional plastic deformation induced by the disaster to identify damage to important structures such as nuclear power plants, tall buildings, or high-pressure hydrogen infrastructure. As residual magnetization takes on anhysteresis characteristics during plastic deformation, the “law of approach” based on the magnetomechanical functional property can be used as a non-destructive test, termed anhysteresis residual magnetization method, to determine additional plastic deformation beyond that of the last instance of magnetization or demagnetization. The mechanism of this property can be explained by the interactions between dislocations and magnetic domain walls. Furthermore, the experimental results of demagnetization under tensile or compressive stress are provided for the anhysteresis residual magnetization method under a non-magnetic field. The advantages and limitations of the method are discussed.
Drilling used to assemble carbon fiber reinforced plastic (CFRP) parts is employed widely in industries. With drilling of CFRPs microscopic damage like residual stress or interfacial debonding between fiber and matrix is accompanied prior to macroscopic damage like delamination or chipping. Although not only macroscopic damage but also microscopic damage is closely related with overall performance of composites, there is no effective method to evaluate microscopic damage. In the present study, quantitative evaluation of drilling-induced damage was attempted by measuring details of residual stresses in fibers for a unidirectional CFRP. Stress distributions along fiber located at the drilled-hole periphery were evaluated in μm spatial resolution by means of micro-Raman spectroscopy. At first, to clarify the dependence of drilling effect on fiber orientation and fiber location, residual stresses in fibers orientated at angles of 0°, 90° and 180° to cutting-edge were measured both on drill-entry and drill-exit side surfaces. As the result residual stresses in fibers caused by drilling were all compressive and showed considerable dependence on fiber orientation to cutting-edge of the drill. Residual stress in fibers at 90° arose firstly even in low feed speed. Difference was also observed between stress distributions of fibers on drill-entry side and those on drill-exit side. Next in order to decide the highest speed drilling without damage, interfacial stress distributions were monitored with increasing feed speed. Experiments of the same feed rate with different rotational speed were also conducted to examine the effect of rotational speed. Damage at the interface, i.e., interfacial debonding occurred between 30 mm/min to 150 mm/min feed. And higher rotational speed resulted in smaller residual stress even in the same feed rate a rotation. Such results show that evaluation using micro-Raman spectroscopy is well applicable to prove details of drilling-induced damage quantitatively.
Static experiments related to rapid crack bifurcation are conducted with PMMA plate specimens with Y-shaped notches. The bifurcation angle of the Y-shaped notch is changed from zero to 45 degrees. Tensile force is applied to the specimen, and a crack arises at one of the two branch notch tips. The crack propagation angle is measured, which is the angle between the crack and the branch notch. The measurement results say that the crack propagates in the same direction as the branch notch when the bifurcation angle is about 14 degrees. This angle is approximately the same as the bifurcation angle of fast propagating cracks. The crack propagation angle is also measured when the bifurcation angle approaches to zero. The crack propagation angle increases with decreasing the bifurcation angle and approaches 14 degrees as the bifurcation angle tends to zero. The experiments with two parallel notches are also carried out, and the crack propagation angle is measured. The crack propagation angle increases with decreasing the distance between the two parallel notches, and has the maximum value of about 22 degrees. When the distance between the two parallel notches decreases further, the crack propagation angle decreases. But the crack propagation angle does not approach zero but remain finite at 14 degrees as the distance of the two parallel notches tends to zero. These results explain why a crack bifurcates with the bifurcation angle of 14 degrees.
In this study, the effect of specimen thickness on the fatigue crack growth behavior of the friction stir welded (FSW) joints of 6063-T5 aluminum alloy was investigated. Generally, based on microstructure characterization of welded zone, three different zones have been classified, i.e., stir zone (SZ), thermo-mechanically affected zone (TMAZ) and heat-affected zone (HAZ). The crack growth behavior in the SZ was examined. In addition, the fatigue tests on the base materials (BM) of 6063-T5 aluminum alloy were carried out. The specimens with two different thickness were prepared for both the friction stir welded joints (SZ specimen) and the base materials (BM specimen). The fatigue crack propagated along the welding direction in the SZ specimen and the rolling direction in the BM specimen. Fatigue tests were conducted at the stress ratio R=0.1 under axial loading. The crack growth rate was accelerated as the specimen thickness increased and the thickness effect was more significant in the stir zone. In the SZ specimen, the crack growth rate of the thick specimen is approximately three times higher than that of the thin specimen except lower stress intensity factor range. In the BM specimen, the fatigue crack growth rate of the thick specimen is slightly higher than that of the thin specimen.
A new ΔK-decreasing test method of the metal film was developed. The film was adhered to a through elliptical hole in a base plate and was fatigued in accordance with the displacement constraint along the hole-circumference in the base plate subjected to a cyclic stress. Commonly, a stress intensity factor range was increased with a crack propagation under a constant stress amplitude but was decreased toward the hole-edge because of the difference in thickness between the film and the base plate in this ΔK-decreasing test method. The decrease in a stress intensity factor with a crack propagation was calculated by FEM analysis and the optimum aspect ratio of an elliptical hole was determined. Using the ΔK-decreasing test method, the crack propagation test was conducted for metal films. As a result, the fatigue crack propagation rate was decreased and was arrested near the hole-edge under the constant stress amplitude to the base plate. The threshold stress intensity factor ranges were obtained for some kinds of metal film and the accuracy of the testing method was discussed.
As drilling process for carbon fiber reinforced plastic (CFRP), gyro-driving drilling machine has been proposed. Recently, Cu-based diamond grinding wheels for this drilling machine have been fabricated by using centrifugal mixed-powder method (CMPM). However, because diamond abrasive grains in this grinding wheel are dispersed into pure Cu matrix, drop out of the diamond grains occurs due to low wettability between Cu and diamond. In this study, improvement of bonding force between Cu matrix and diamond grains in Cu/diamond composite fabricated by the CMPM is investigated. As improvement method, Ti particles are added into mixed-powder used for the CMPM. This addition of Ti particles forms thin TiC layer at interface between the Cu matrix and the diamond grain. Thickness of the TiC layer increases as the amount of Ti particles in the mixed-powder increases. As the results, the bonding force between the Cu matrix and diamond grains is improved by the addition of Ti particles. The bonding force is increased as Ti concentration in the mixed-powder increases up to 2 mass%. When the Ti concentration exceeds 2 mass%, the bonding force is saturated. Also, the Cu/diamond composite containing Ti makes larger worn groove on counter disc used for wear test comparing with the composite without Ti. Therefore, the addition of Ti particles into the mixed-powder can be expected to enhance grinding ability of Cu-based diamond grinding wheel fabricated by the CMPM.
Alternatively to conventional stress-strain hysteresis measurements in this paper physically based materials data such as specimen temperature, electrical resistance, speed of sound or generator power are used to describe the cyclic deformation behavior of metals in the high cycle (HCF) and the very high cycle fatigue (VHCF) regime. The mentioned physical parameters depend in a characteristic manner on the load and cycle dependent microstructure of metals. The change in temperature is proportional to the dissipated energy due to cyclic plastic deformation, the electrical resistance and speed of sound in metals depend on the individual dislocation and defect structure. Amongst others the generator power of ultrasonic testing machines is influenced by the internal friction of the material and consequently from the microstructure of a fatigued material. In analogy to the plastic strain amplitude all these data can be used to describe the cyclic deformation behavior and to calculate S, N-curves. The materials investigated are taken from technical components such as power plants, high speed trains and automotive industry to demonstrate that the presented methods and physical parameters can be used to describe the cyclic deformation and fatigue behavior of different steels with different microstructures. Related to the regarded materials and fatigues states SEM and TEM investigations were used to identify microstructural details such as slip bands, micro cracks, crack initiation sites and typical dislocation structures as well as phase transformations.
As a preliminary study, the effects of target temperature on ejecta size were examined at an impact velocity of 3.5 km/s with the goal of improving the ISO11227. At first, the size of each ejecta collected from test chamber, was examined by the image analysis software using a photograph of each ejecta (direct method). The cumulative number distributions of ejecta size were discussed. The effects of target temperature on ejecta size were small within a predictable range. After that, we compared the ejecta size distribution of the direct method with the results of the international standard method using witness plate (indirect method). The number of ejecta impact craters evaluated by the international standard method was very small at the high temperature. The results of international standard method using witness plate were easily influenced by temperature of target at the high temperature. It is highly possible that the international standard method underestimate the ejecta from target at high temperature.
In this paper the low-velocity and high-velocity impact damage in a carbon fiber reinforced plastic (CFRP) laminate with toughened interlayers was experimentally characterized. The low-velocity impact test was carried out by using a guided drop weight system while the high-velocity impact test was conducted by using a high-velocity impact testing machine. The damage in the laminate was then observed using optical microscopy and soft X-ray radiography. It was revealed from the observation that microscopic damage state and damage area varied with the impact velocity. The variation is ascribed to the fact that the low-velocity impact causes global deformation while the high-velocity impact energy is absorbed mainly by damage due to local deformation. Although the toughened interlayers suppress delamination for low impact energy, the high interlaminar fracture toughness sometimes causes the transition of interlaminar delamination to intralaminar one.
The main difficulty in conducting a high velocity experiment with a projectile accelerator is predicting the projectile velocity with great accuracy. This is of crucial importance in order to keep experimental conditions constant. During the design process of the single stage diaphragmless vertical gas gun installed at the Impact Engineering Laboratory in Ritsumeikan University, a theoretical formula proposed by Seigel was used to predict the projectile velocity for various ranges of gas pressure. However, the complexity of projectile dynamics such as frictional effects between the projectile and the launch tube, the aerodynamics of the projectile, temperature effects and pressure disturbances occurring during projectile acceleration are factors excluded from the theoretical formula, making it challenging to predict the actual velocity of the projectile. Hence, it was necessary to conduct a performance evaluation of single stage diaphragmless vertical gas gun. For the experiment, flat projectiles were used consisting of a brass impactor and a high-density polyethylene sabot. A neodymium magnet was placed inside the sabot for velocity measurement using Magnet-Coil method, and nitrogen and helium were selected as gas propellants. The experimental results were carefully analyzed, and found to show a similar trend with the theoretical solution. Fitting parameters were then introduced to make the final adjustment to the theoretical formula, showing good agreement with the experimental results.
The purpose of this paper is to investigate the micromechanical processes during impact as well as the related macro-mechanical restitution properties in a three body multiple impact system. Thereby, the microscale refers to the detailed processes during impact, while the macroscale refers to the overall dynamics of the impact system which is normally evaluated by rigid bodies. Specifically, this paper deals with numerical and experimental investigations of direct central collisions of three identical inelastic spheres. In the experiments the velocities of three spheres during impacts are measured by Laser-Doppler-Vibrometers. In the numerical simulation, finite element analyses are performed, where the material properties obtained from static and dynamic compression tests are used. In order to confirm the validity of the numerical model, the results from the finite element analyses are compared to the experimental results and show good agreement. Afterwards, micromechanical investigations of the impact processes are performed using finite element analysis. Thereby quantities such as impact force, deformation, and kinetic energy loss are investigated in detail. Then, the macroscale rebound properties of multiple collisions are derived using the simulation results on a microscale. In general, a single coefficient of restitution (COR) can be used to evaluate on the macroscale the restitution property in two body impacts. However, in instantaneous impact modelling this cannot be used for general multibody systems where multiple concurrent impacts occur. Therefore, a COR matrix is employed in this paper as measure of the macroscale restitution properties and the overall impact dynamics of the system. Finally, a rigid body simulation with continuous contact law is attempted as an alternative macro-mechanical model. It is shown for this specific impact system that this method can produce practical macroscale behavior of the colliding spheres if a simple single impact COR is used. This is shown by comparison with the COR matrix.
Many kinds of polymer foams are used in various situations. Especially, polymer foams are often used for shock absorber, therefore, there are many studies focusing on the effect of strain rate on the compressive properties, such as strength and absorbed energy. Since, most of them is produced from petroleum, they are not so environmentally friendly. Recent years, therefore, polylactic acid resin foam was developed that is a kind of plant-derived plastics with low environmental load. In this study, the effect of strain rate and temperature on the compressive property of polylactic acid resin foam was experimentally studied by carrying out the compression tests at various strain rates from 0.001 to 790 s-1. It was found that the flow stress of polylactic acid resin foam during compressive deformation increases with the increase of strain rates. It was also found that the flow stress of polylactic acid resin foam decreases with the increase of temperature. In addition, polylactic acid resin foam indicates brittle behavior near liquid nitrogen temperature and impact compression caused greater effects of brittleness than quasi-static tests.
In order to assess failure probability of cracked components, it is important to know the variations of the material properties and their influence on the failure load assessment. In this study, variations of the fracture toughness and stress-strain curve were investigated for cold worked stainless steel. The variations of the 0.2% proof and ultimate strengths obtained using 8 specimens of 20% cold worked stainless steel (CW20) were 77 MPa and 81 MPa, respectively. The respective variations were decreased to 13 and 21 MPa for 40% cold worked material (CW40). Namely, the variation in the tensile strength was decreased by hardening. The COVs (coefficients of variation) of fracture toughness were 7.3% and 16.7% for CW20 and CW40, respectively. Namely, the variation in the fracture toughness was increased by hardening. Then, in order to investigate the influence of the variations in the material properties on failure load of a cracked pipe, flaw assessments were performed for a cracked pipe subjected to a global bending load. Using the obtained material properties led to variation in the failure load. The variation in the failure load of the cracked pipe caused by the variation in the stress-strain curve was less than 1.5% for the COV. The variation in the failure load caused by fracture toughness variation was relatively large for CW40, although it was less than 2.0% for the maximum case. It was concluded that the hardening induced by cold working does not cause significant variation in the failure load of cracked stainless steel pipe.
Thermal barrier coatings (TBCs) on high temperature components in gas turbine engines are in some cases damaged by calcium-magnesium-alumino-silicates (CMAS) resulting from the ingestion of siliceous minerals at high temperatures exceeding 1200°C. An attempt to develop a non-destructive detection technique of CMAS damage on TBCs was carried out through an AC impedance technique in this work. The CMAS-affected TBC specimens were prepared by simulating the CMAS damage in laboratory, employing a synthetic CMAS product. The change in electric capacitance was measured by using an LCR meter. It was found that the capacitance of the ceramic top coat showed higher value at CMAS infiltrated areas, compared with that at the non-infiltrated ones. While the capacitance increased with increasing infiltration depth, the change in capacitance of the TBC specimen decreased when the CMAS enhanced the delamination damage of TBC top coat. Some discussion was made on the changes in capacitance using a simple condenser model, so that the present electric technique is applied to the CMAS damage detection and evaluation.
The strength against interfacial fracture nucleation from the free-edge of micro-scale bimaterial cantilevers consisting of silicon (Si) and copper (Cu) components is evaluated by using specimens with different free-edge shape. The fracture strength of Type A (90°/90° edge) specimens represented by the near-edge stress normal to the interface (σθθ) is significantly scattered. On the other hand, the fracture strength of Type B (135°/135° edge) specimens represented by the stress intensity factor of σθθ shows very good agreement. This indicates that the introduction of a sharp wedge at the free-edge is an effective measure for the evaluation of fracture strength that is unique to the interface. Such characteristics are also found to be unaltered by the plasticity of Cu component. The advantage of Type B specimen is then applied to the evaluation of the effect of gaseous environment on the fracture strength. There is no eminent reduction of strength value in hydrogen (H2)-containing gas, indicating that Si/Cu interface is relatively resistant against hydrogen embrittlement.
Various thermoplastic polymers have been spun to nanofibers by the electrospinning method, in which a polymer solution is ejected as a fine jet of liquid from the tip of the needle and is deposited on the collector by applying a high voltage to the polymer solution in the syringe. Due to special characteristics of nanofibers such as nanometer sized diameter, high surface area to volume ratio, and higher alignment of molecular chain, they have been used for a wide range of applications such as medical scaffolds and air filters. The morphology and diameter of electrospun fibers are dependent on a number of processing parameters that include the properties of the solution, the operational conditions and the surrounding conditions. The influence of the humidity on the fiber diameter of nanofibers in the electrospinning process has not been clarified yet. Polyamide 6 is an industrially important polymer thanks to its excellent physical properties, e.g. high fatigue strength, low coefficient of friction, and high resistance to chemicals. In this study, the influence of the humidity on the fiber diameter of PA6 in the electrospinning process was investigated by SEM observation and its mechanical properties were evaluated by tensile test. As the amount of humidity increased, the fiber diameters decreased. The tensile strengths of PA6 nanofibers nonwoven fabrics which were electrospun at 25 % and 65 % of humidity were 49±5 MPa and 71±12 MPa, respectively.
Carbon Fiber Reinforced Thermoplastics (CFRTP) have attracted attention in the automotive industry for their productivity and high specific strength and modulus. To guarantee the durability of CFRTP, it is important to understand the mechanical properties of CFRTP under practical service temperature. Since the mechanical properties of CFRTP are affected not only by reinforcement fibers and matrix resins but also by the fiber matrix interface, to reveal the fiber/matrix interface properties is one of the important issues to be solved. Among thermoplastic resins, polyamide (PA) is expected to be used for the matrix of CFRTP, owing to good interfacial adhesion to the carbon fiber, and good moldability. Although tensile tests of CFRTP under the high temperature environment were performed, the effects of temperature on the fiber/matrix interfacial shear strength have not been fully clarified. In this study, in order to evaluate the fiber/matrix interfacial properties at 25°C, 40°C and 80°C, single fiber pull-out tests, measurement of the thermal expansion coefficient of the resin, and analysis of the thermal expansion of the resin were performed. As temperature rose, resin expanded and interfacial shear strength of the CF/PA model composites decreased. This result suggests that the decrease of the interfacial shear strength by temperature rise is caused by the expansion of the resin.
Carbon nanotubes (CNTs) are highly resistant to deformation, and their electrical characteristics are also resistant to degradation at ambient conditions. The damage mechanisms of CNT loaded under high current density are considered to be the oxidation by Joule heating and migration of carbon atoms by high-density electron flows. In this study, the damage characteristics of single-wall CNT (SWCNT) network structures were investigated under accelerated condition with high current loading and heating. The semiconducting and metallic SWCNT network structure specimens of straight shape with 10 μm in width, and 50 μm or 100 μm in length were fabricated by means of photolithographic technique. A testing system applying high current density was constructed and accelerated tests of SWCNT specimens were conducted in the system. The changes of potential drop among the specimen under the constant current loading were recorded until damage occurrence in the SWCNT network structure. The damage characteristics of the specimens were discussed from the changes of microscopic structure and electric resistance under the different accelerated conditions. The disconnection of SWCNT structure was occurred at the cathode and center area of the straight shaped specimen and these were observed in three dimensional laser microscope and SEM images after current loading. There were two mechanisms based on oxidation of Joule heating and electromigration occurred in the SWCNT specimens under high density current loading.
For anode-supported solid oxide fuel cells (SOFCs), huge internal stress is generated in an electrolyte thin-film due to the difference of the coefficient of thermal expansion from an anode substrate. Micro-size defects are sometimes formed in the electrolyte thin-film during a manufacturing process, when the huge internal stress is released. The defects in the electrolyte thin-film cause cross leakage of fuel and air, which deteriorate the anode-supported SOFCs rapidly. The mechanical reliability of the electrolyte thin-film is important to prevent initial failure for cells and stacks. In the present work, the internal stress was evaluated by X-ray for planar anode-supported SOFCs with and without micro-size defects in an electrolyte thin-film. A compressive stress of 501-561 MPa was observed for yttria-stabilized zirconia (YSZ) electrolyte thin-film without micro-size defects on NiO-YSZ anode substrate sintered at 1350-1400 ℃. However, the stress was 188 and 453 MPa for the electrolyte thin-films sintered at 1200 and 1300 ℃, respectively, because of insufficient sintering. Many micro-size cracks and pores were observed in the electrolyte thin-films sintered at 1200 and 1300 ℃. Furthermore, the internal stress decreased by 50-100 MPa due to stress relief for the electrolyte thin-film with micropores, which were made during the actual manufacturing process, in spite of the sintering temperature of 1350 ℃. X-ray stress measurement has a potential to be applied as a non-destructive test method for anode-supported SOFCs.
If the shape memory polymer is applied to actuators, the novel intelligent shape memory actuators can be developed. The development of the functionally-graded shape memory polymer board was investigated for the development of the new actuators. The results obtained are summarized as follows. (1) Based on the shape recovery and recovery stress, the temperature-dependent multistep actuation can be obtained by using the shape memory polymer sheets and foams with various glass transition temperatures in the shape memory polymer actuators. (2) The functionally-graded shape memory polymer board composed of shape memory polymer sheets and foams, showing the similar indentation deformation property as a finger, can be applied to the elements coming into contact with body in the nursing-care robots or actuators.
Carbon Fiber Reinforced Plastic (CFRP) has high specific stiffness and its thermal deformation can be controlled by fiber orientation. Therefore, it is often adopted as a material of space observation systems. In this study, experiment, numerical and analytical calculation on thermal deformation of CFRP reflector models were conducted to investigate the characteristics of thermal deformation of CFRP reflectors (mirrors) for space observation systems. Two types of reflector models were manufactured, which were comprised of a quasi-isotropic CFRP laminate with and without an sprayed aluminum layer and a polyurethane layer on the top surface. The experimental results showed that the out-of-plane thermal deformation of the reflector model with the aluminum and polyurethane layers is considerably larger than that of the reflector model without the aluminum and polyurethane layers and maximum and minimum displacement were observed in specific directions. The result of the numerical calculation showed the same trend. Additionally, this trend was discussed analytically. Moreover, uncertainty of the structure and method of reducing out-of-plane displacement were discussed. When shape control to suppress thermal deformation of CFRP reflectors is considered, the result obtained in this work is important to determine the optimal placement of actuators.
The interaction phenomenon between shock waves and the DC-discharged plasma was experimentally investigated to aid future supersonic aerodynamic performance improvements. A shock tube was used to generate the shock wave. For the discharged plasma generation, a wedge type test model with electrodes (anode and cathode) connected to the power supply system was installed into the shock tube measurement section. The nominal shock wave Mach number in the experiment was 2.0. The plasma input power range was from 0 W to 35.7 W, where 0 W corresponded to the no discharge case. Schlieren photography was used for visualization, and the pressure histories were measured. From the visualization, due to the interaction with the discharged plasma, shock wave modulation with curvature was observed. However, from the pressure measurement, pressure histories in a plane parallel to the shock wave were nearly identical between the side-wall and the top-wall, despite the shock wave modulation. From these results―obtained from visualization and pressure measurement, the shock wave modulation observed in this study had a three-dimensional (3D) structure. In order to comprehend this phenomenon, a 3D simulation with a simple modulated temperature field was conducted. The simulation results also indicated 3D shock wave modulation. Therefore, experiment and simulation both support the 3D structure of the modulated shock wave due to the interaction with the discharged plasma.
Recently, with the appearance of the two-phase flow ejector in refrigeration air conditioning and heat pump systems, the efficiency of the cycle has largely been improved in comparison with that of conventional cooling and heating systems. We have been developing an ejector for the refrigeration cycle and fundamentally researching the behavior of two-dimensional expansion waves and oblique shock waves to clarify the characteristics of waves occurring during high-speed two-phase flow. In previous studies, it was revealed that an oblique shock wave is generated at the nozzle exit of the ejector and affects the flow field of the supersonic two-phase flow inside the mixing section in the ejector. This is because the speed of sound for a two-phase flow is low compared to that for a single-phase flow. In the present study, we elucidate the behavior of oblique shock waves and expansion waves of supersonic two-phase flow by experiments using carbon dioxide refrigerant. The angle of the oblique shock waves and the expansion waves were experimentally measured, and corresponded well with those calculated using a theoretical model.
Conservation of energy is becoming increasingly important for the protection of the environment. Improving the efficiency of a refrigeration cycle is a critical factor to achieve this goal. Recently, an ejector system was developed that reduces the energy requirements of the compressor in the refrigeration cycle. Two-phase-flow shock waves appear in the ejector under certain operating conditions and increase the pressure difference between suction inlet and outlet. Such shock waves play an important role in the ejector’s compression mechanism and thus merit a thorough investigation. In this work, we visualize the structure of a two-phase-flow shock wave in an ejector nozzle using a high-speed camera to monitor an optical beam transmitted through a refrigerant (hot water). As the pressure rises in the ejector outlet, the shock wave moves from the outlet to the nozzle throat and changes from an oblique shock wave to a normal shock wave. The shape of the output nozzle may modify the structure of the shock waves.
Heat exchangers are widely used for heating, cooling, evaporation, and condensation. There are many types of heat exchangers, shell and tube, fin tube, and double tube heat exchangers. Double tube heat exchangers show high performance, and several modifications have been made with regard to their pipe geometry to further improve their performance. A petal-shaped double tube with a large wetted perimeter is one such example. The working fluid of a heat exchanger for the evaporator and condenser of an air-conditioner or boiler may become a gas-liquid two-phase flow with phase change. In this study, the flow and heat transfer characteristics of air-water bubbly flow through a petal-shaped double tube with a large wetted perimeter are examined experimentally and compared with those of a conventional circular double tube. The experiments employed two petal-shaped double tubes: one with six petals and another with five petals. This study explains for single-phase water and two-phase air-water bubbly flows. The heat transfer characteristics are studied by measuring the temperature distributions in the inner and outer pipes by a thermo couple. The study also clarifies the effects of air bubbles on heat transfer performance.
An effectual thermal management is a very important issue in a light emitting diode (LED) floodlight because its performance and reliability decrease significantly as the junction temperature increases. A cooling device free of moving parts is suitable for lighting with natural convection. A very large heat sink is combined with a relatively small light source in high-power LED floodlights with everlasting miniaturization of microelectronic systems and highly developed high-density packing technology. Pulsating heat pipes (PHPs) lead to a breakthrough solution for passive two-phase flow spreading of LEDs non-radiant heat in case of a high-density mounting device. PHPs have little influence of gravity direction (floodlight attitude), high heat spreading performance, high reliability for long-term use, lightweight, low cost, and ease of production. This paper describes closed loop 8-turn, ethanol-charged PHPs with radial channels. The experimentally investigated PHPs have dimensions of 200 mm × 200 mm × 3 mm with central heating using a diameter of 38 mm heater. A copper plate is covered with polycarbonate plate for visual observations. A time-strip image processing technique has been applied to the flow videos to extract qualitative details of flow regimes concerning the liquid/vapor interface dynamics. Radial channel flow and thermal oscillation characteristics have been discussed using time-strip technique, Fourier power spectrum and autocorrelation function. The U-shaped vapor oscillates in the cooling section. The wall temperature-time histories fluctuate non-periodically.
From environmental point of view, natural refrigerants, whose Global Warming Potential (hereinafter GWP) is lower than commonly used refrigerants, have been considered in several industrial sectors. Refrigerated display cabinet that are installed in supermarkets and other small food stores such as Convenience Stores (hereinafter CVS) are commonly equipped with direct expansion refrigeration system using high GWP refrigerants such as HFC404A and HFC410A. Leakage rate and market stock of such high GWP refrigerants are the cause of global warming as a direct impact. Thus, natural refrigerants are considered as sustainable alternative refrigerants. Carbon dioxide (hereinafter CO2) is the most likely alternative refrigerant in the retail refrigeration sector because of non-toxicity and non-flammability. Furthermore, the efficiency level of refrigeration systems contribute to global warming as indirect impact. In these days, several refrigeration systems using CO2 refrigerant have been developed and installed in supermarket and CVS. New refrigeration systems using binary (cascade) cycle of CO2-CO2 refrigerant is developed for the refrigerated cabinets. In the early development, HFC404A refrigerant single cycle system and HFC-CO2 refrigerants cascade cycle system were usually used because the COP of CO2 refrigerant was low at high ambient temperature. Nevertheless, relatively high COP system could be constructed by optimizing the binary cycle using CO2-CO2 refrigerant. In this study, details of the system design and performance optimizations of the CO2-CO2 binary cycle will be discussed. Data of developed binary CO2-CO2 cycle system was compared with the data of current single HFC cycle and single CO2 cycle systems. As a result, it was confirmed that the energy efficiency of binary CO2-CO2 cycle became competitive to the current single HFC cycle. Moreover, some technical issues for enhancement of COP of CO2-CO2 binary cycle will be discussed in the literature.
Flame spread in the kinetic regime and eventual extinction have been studied for more than four decades for the implications on fire safety and flame instabilities. It is well known that the ratio between the residence time and the combustion time at the leading edge, the so called Damköhler number, plays a fundamental role in the blow-off extinction of a spreading flame. However, the role of the boundary layer, which may significantly affect the residence time at the flame leading edge, on the blow-off extinction has not been thoroughly studied. In this work we present new experimental data on blow-off extinction of PMMA (polymethyl methacrylate) fuels and establish an empirical relation between the boundary layer development length and the extinction flow velocity. Using a vertical wind tunnel it has been possible to carry on a large number of experiments over thin PMMA samples, for an opposed flow velocity range from 0 cm/s up to 100 cm/s. Furthermore, it was possible to rotate the wind tunnel to obtain results with a horizontal configuration, reducing the effect of buoyancy on the flame spread. The experimental data reveal that the extinction length, the distance from the sample leading edge at which the blow-off extinction occurs, is directly related to the opposing flow velocity. Using a simplified scale analysis previously proved to be reliable, the blow-off extinction appeared to occur at a constant effective velocity (defined inside of the boundary layer). This conclusion can have important implications in the definition of the kinetic regime and the quantification of an extinction limit for thin fuels.
Our goal for this study was to understand the cause of the differences in surface properties between surfaces processed using water jet peening (WJP) and shot peening (SP) and to examine the compressive residual stress introduction process with low plastic strain using SP. The dynamic behaviors of stress and strain in surfaces during these processes were analyzed through elasto-plastic calculations using a finite-element method program, and the calculated results were compared with measured results obtained through experiments. Media impacting a surface results in a difference in the hardness and microstructure of the processed surface. During SP, a shot deforms the surface locally with stress concentration in the early stages of the impact, while shock waves deform the surface evenly throughout the wave passage across the surface during WJP. A shot with a larger diameter creates a larger impact area on the surface during shot impact. Thus, SP with a large-diameter shot suppresses the stress concentration under the same kinetic energy condition. As the shot diameter increases, the equivalent plastic strain decreases. On the other hand, the shot is subject to size restriction since the calculated results indicate the compressive residual stress at the surface decreased and occasionally became almost zero as the shot diameter increased. Thus, compressive residual stress introduction with low plastic strain by using SP is considered achievable by using shots with a large diameter and choosing the appropriate peening conditions.
Pressure Retarded Osmosis (PRO) is expected to the new power generation system. The performance of the PRO module is closely relating to the permeation characteristics. In this paper, when fresh water flow rate is changed, 4 factors related to the reduction of permeation flow rate are researched with experiment. These 4 factors are concentration of solute in fresh water, salt leakage, concentration polarization, and dissipation of fresh water. The characteristics of the fresh water flow and permeation are studied for the hollow fiber membrane module used in PRO system. It is cleared that the dissipation of fresh water and the concentration polarization in hollow fiber largely influence to the reduction of permeation flow rate in the case of the low fresh water flow rate. Concentration of solute in fresh water, salt leakage influence to the reduction of permeation flow rate in the case of high fresh water flow rate.
In 2013, CO2 levels surpassed 400 ppm for the first time in recorded history. So, we are facing global warming due to the increase levels of atmospheric carbon dioxide (CO2). As a method of reducing CO2 emissions from the thermal power plants, there are carbon dioxide capture and storage (CCS) technologies. Oxyfuel combustion is one of the CO2 Capture technologies and IHI have developed it since 1989. Then, Callide Oxyfuel Project commenced to apply oxyfiring technology in an existing coal fired power plant and to demonstrate an oxyfuel power plant in March, 2008. Demonstration began in 2012 after existing boiler was retrofitted. During the demonstration for approximately three years, many tests were conducted and many data were collected for commercial use. As a result, we confirmed characteristics of oxyfiring such as total heat absorption, combustion characteristics, emissions of NOx, SOx, carbon-in-ash, operational flexibility from 15MWe (50%L) to 30MWe (100%L) and behavior of injected CO2 at the injection site. Total heat absorption of the boiler under oxyfiring was 2 to 3MW higher because of decreasing heat loss in flue gas and rising temperature of boiler feed water by a flue gas cooler. NO was decomposed in the furnace under oxyfiring because flue gas was recirculated. On the other hand, reaction between SO2 and absorbent such as Ca, Mg in ash was not so active regardless of high concentrated SO2 under oxyfiring. Carbon-in-ash was almost 40%~70% in oxyfirng compared with in airfiring because of longer residence time in the furnace. Operational flexibility is important to control oxyfiring operation and it was confirmed that oxyfiring can be operated as well as airfiring. In this paper, operational results are presented in Callide Oxyfuel Project.
Vibration suppressors are used to change the natural frequency of an elevator rope and prevent resonance. The displacement of the parts of the elevator rope at both the ends is small compared to that of the center part of the rope; therefore, it is not necessary to position the vibration suppressors in the parts on either ends. The elevator rope is generally modeled using a string, and linear string vibration is well researched. However, the vibration of the string equipped with vibration suppressors encounters geometric nonlinearity, and hence, its characteristics have been studied under a few conditions. Furthermore, in the case in which the vibration suppressor is located in the center part of the string, no exact solution has yet been obtained for the free vibration of the string. In this paper, an exact solution is presented for the free vibration of a string when the vibration suppressors are located in the center part of the string. In the analysis for determining the exact solution, the problem of free vibration with vibration suppressors is transposed to a problem of forced vibration. Further, to verify the validity of the exact solution, a finite difference analysis of the string vibration with vibration suppressors is performed. The calculated results obtained from the finite difference analysis are in good agreement with the results of the exact solution.
Nowadays, thin steel plates with high surface quality are required. However, the quality of steel plates is adversely affected by transport using the friction force generated by contact with rollers in the manufacturing process. As a solution to this problem, the non-contact transport of steel plates using an electromagnetic force has been proposed. When a steel plate has sufficient stiffness owing to its material or size, it can be levitated by a levitation system consisting of actuators installed in the vertical direction. On the other hand, it is difficult for very thin steel plates to levitate because of the deflection at locations where an attractive force is not applied. To improve the levitation performance of the conventional magnetic levitation system, we have proposed the addition of an electromagnet to control the horizontal displacement of the steel plate. However, there have been no detailed examinations of by how much the levitation stability of a steel plate is improved by the suppression of deflection. In this study, we obtained the shape of a levitated steel plate by electromagnetic field analysis and deformation analysis and evaluated the obtained shape of the steel plate. Furthermore, a levitation experiment was performed to verify the levitation stability of this system. The results show that the addition of an electromagnet in the horizontal direction is effective for achieving stable levitation.
Origami is a traditional Japanese craft that is based on the folding of the designed structure and can be widely used by industry. Origami folding is not a difficult task for human hands; however, folding by robot hands is such a challenge. In this paper, we suggest a novel approach for designing the origami-performing robotic systems. The main idea of the proposed method is to simulate the forming crease lines in origami models and folding behavior of a sheet of paper by robot end-effectors. The simulation approach becomes the main option in the real-world related with a robotic activity. Our investigation results show that many design parameters of a robot such as geometrical and topological, shape and configuration of the robotic arms, type of forces and their distributions, and others can be defined by the simulation of the folding origami structures. It means that the results of the simulation can be used as a basis of the final robot design without a series of experimental tests. Problems of the numerical simulation, including paper material structure, simulation origami model, the distribution and values of the applying forces, and others are considered carefully. The results of the design process of the robotic system based on the simulation of origami crease forming confirm our idea to use simulation approach with LS-DYNA solver to build the origami-performing robot for complex origami structures. The origami model “Star” was taken as an example to demonstrate the method for the different types of the creases in origami.
In this paper, we propose an entirely new manipulation strategy for dynamic manipulation of a rhythmic gymnastics ribbon, as one example of belt-like flexible objects, with a high-speed multi-jointed manipulator. The manipulation strategy involves manipulating the target object (rhythmic gymnastics ribbon) at a constant, high speed. Then, we can assume that the dynamic behavior of the ribbon can be obtained by performing algebraic calculations of the robot motion using the proposed strategy. Based on this assumption, we derive a simplified deformation model of the ribbon and suggest a simple motion planning method using the proposed model. Finally, we show simulation results and experimental results of shape generations (for example, circle, wave, figure-eight, and crack shapes) of a ribbon based on the proposed method, and we discuss quantitative evaluation of shape generations by image processing.
This paper deals with the active control of sound transmission through a rectangular honeycomb panel. The authors have proposed an effective control method using point force actuators and PVDF film sensors to suppress the transmitted sound power through a thin flexible panel in a low-frequency range before. With the proposed method, the frequency range in which the control effect can be obtained depends on the natural frequency of the panel since the method can control the lowest three odd/odd structural modes. Therefore, in order to make the control frequency range higher, a honeycomb panel, which has high strength-to-weight ratio, is used as a target panel in this study. However, when the honeycomb panel is used, the characteristics of sound transmission are totally changed and then the control effect decreases around even/odd, odd/even and even/even mode frequencies. Hence, in this study, active control method comprising both feedforward and feedback control is investigated theoretically and experimentally. The direct velocity feedback control is added to the previously proposed SISO feedforward control system in order to suppress resonances of the even order vibration modes. The results show that the feedback control can improve the control effect around even order structural mode frequencies and that the proposed control method using a honeycomb panel is capable of proceeding the significant control effect for improving the sound insulation property over a wide frequency range.
It is said that the parameters that characterize structural damping, i.e., the loss factor, are identical to the material of the specimen, but in actuality, the damping property is sometimes affected by specimen size or the frequency. In this paper, we investigated the effect of specimen size and frequency on the structural damping property. First, we showed a simple identification method for modal parameters when the damping property is modeled as the structural damping. Next, we identify the modal parameters of the freely supported thin steel beam using the method. We obtain the relationship between the natural frequency and modal damping ratio for specimen with the same thickness but different length, and for specimen with the same length but different thickness. Then we identify the parameters that characterize the damping property. The results showed that the modal damping ratio was high in the lower frequency ranges, though light and constant in the higher frequency ranges, that is, the damping property depends on the frequency, so that the damping property could not be expressed only by the loss factor. And the relationship between the natural frequency and the modal damping ratio was identical for specimen with same thickness, though it is not for specimen with the different thickness, that is, the damping property depends on the thickness. We conclude that the effect of specimen size and frequency should be considered when predicting damping property in actual design processes.