The integrity of railway axles is a critical aspect for ensuring the safety of a railway system. Therefore, non-destructive inspections such as ultrasonic testing and magnetic particle testing are conducted periodically. Some railway operators conduct ultrasonic tests directly on axles mounted on the train. However, the axles have to be disassembled for conducting magnetic particle testing. In the present study, the effects of variable amplitude stress acting on cracks and axle bending stress during ultrasonic test on ultrasonic response are discussed. An ultrasonic test was conducted using a full-scale axle specimen that had fatigue cracks and no artificial notches. The ultrasonic response was evaluated for the cracks whose lengths were 10 mm, 16 mm, and 19 mm. Under an unloaded condition, the ultrasonic response for the 16-mm-long and 19-mm-long cracks was approximately 4 or 7 times higher than that for the 10-mm-long crack, although the cross-sectional area of each of these cracks was approximately 2.5 or 3.5 times larger than that of the 10-mm-long crack. The obtained results indicate that the contribution of the reflection area to the ultrasonic response under a variable amplitude stress differs from that under a constant stress condition. Moreover, the influence of axle bending stress ranging between -50 MPa to +47 MPa on the ultrasonic response was investigated. A higher bending stress led to a higher ultrasonic response. However, the decreasing rate of ultrasonic response caused under compressive stress was lower than the increasing rate under tensile stress. For example, the ultrasonic response was approximately 2 dB lower than that under the unloaded condition at a compressive stress of -30 MPa; however, the ultrasonic response showed an increment of approximately 4 dB at a tensile stress of 30 MPa. A similar trend was observed in the crack of each length. The results denote that the crack position influences the precision of crack detection in ultrasonic inspection. However, considering that the maximum static bending stress of axles used in Japan is 30 MPa, its effect on inservice axle inspection is negligible.
The numerical analysis on the flight stability of the underwater projectiles are performed using computational fluid dynamics code which consists of gas/liquid phases analysis, 2D calculation method. The nose shape effect on the underwater flight stability is conducted. The ogival nose, the flat nose and the spike nose are used for the nose shapes. The static stability is determined by the direction of pressure on the projectile. The pressure on the flat nose makes projectile stable, although pressure on the ogival nose and the horizontal area of flat nose makes projectile unstable. The spike nose is statically unstable, however it is possible to increase the flight stability by changing the spike radius and the spike length. When the part of projectile gets out of the bubble and contacts with water, the water pressure acts as restoring force, which lead to improve the flight stability. This phenomenon is called ‘Tail slapping effect’. Tail slapping effect works most effectively when only backward of the center of gravity of the projectile contacts with water. The Effects is canceled as the angle of attack increases and the front of the projectile contacts with water. As a result, the improvement of stability due to the tail slapping effect is limited.
Wear of sliding surfaces in machinery is one of the major causes of mechanical failure. Thus, detecting wear on sliding surfaces is very important for preventing mechanical failure. Current diagnosis methods for detecting wear particles such as a spectrometry oil analysis program, particle count method and ferrography method are very useful for it. However, these methods need high cost, expertise and long time for the analysis. Moreover, the particle count method can only measure the size and the number of particles and it cannot indicate whether the lubricating oil is degraded by oxidation or solid particles. Therefore, the diagnosis method which can evaluate degradation cause and level of lubricating oil is required for effective maintenance. The authors have developed a new diagnostic method for lubricating oils by the colorimetric analysis of membrane patches. In the previous study, we reported that there is a good correlation between membrane patch color and contamination in lubricating oil. From the results of our previous study, it is possible to diagnose wear on sliding surfaces by using membrane patch color. The purpose of this study is to develop new wear monitoring method of sliding surface in machinery by using membrane patch color. First, we conducted filtration tests to investigate degradation causes of lubricating oil in actual machinery. The results showed that they are classified into solid particles and/or oxidation products. Secondly, we prepared oil samples which were artificially degraded by solid particles and/or oil oxidation products based on the filtration test, and we conducted wear tests in the degraded oils by using block-on-ring tester. The results presented that it is important to detect not only the number of particles but types of particles for the monitoring of wear on sliding surfaces. Finally, we investigated the relation between ISO cleanliness code and membrane patch color and we proposed a new parameter Ic using the ISO code. As a result, it is shown that it is possible to detect wear on sliding surfaces easily using Ic and membrane patch color.
In high speed turning, six kinds of materials, namely, Ti-6Al-4V, Inconel718, SUS304, S50C, Copper and Aluminum are machined with a ceramic cutting tool in order to investigate the influence of the cutting speed on the temperature of the cutting tool experimentally. The cutting temperature is measured by the two-color pyrometer with an optical fiber which is developed by the author. In cutting of Ti-6Al-4V and Inconel718 with Al2O3 ceramic tool, the cutting temperature increases with the increase of cutting speed and approaches to the melting points of the workpiece materials. The thermal conductivities of these difficult-to-cut materials are small, and Al2O3 ceramic has a small thermal conductivity and maintains a high strength even at the temperature of about 1000°C. In the cases of Copper and Aluminum, their thermal conductivities are much larger than those of Ti-6Al-4V and Inconel718, so that the cutting temperature increases so slowly with the increase of cutting speed that it is difficult to approach to the melting points of the workpiece materials.
Arterial endothelial function is known as a factor that correlates with progression of arteriosclerosis. This is measured by flowmediated dilatation (FMD) testing. This test is performed by measuring the brachial artery diameter with an ultrasound system or by measuring digital pulse volumes. Technical and cost-related problems have been pointed out for both methods. We came up with an idea to apply the near-infrared light-based vascular visualization to the measurement of changes in vessel diameter. So, at first, we investigated whether the FMD reaction can be detected with near-infrared transmission images. Next, we derived the estimated values that is considered to correspond to the FMD reaction from the vascular image change. We aimed to determine if these estimated values correlate with brachial-ankle pulse wave velocity (baPWV), which is related to arteriosclerosis. In 50 adult males varying in age, the right upper arm was compressed with a cuff at 200 mmHg for 5 min to cause the FMD reaction after the cuff release. In a 11-min period including time points before and after the cuff compression, near-infrared (wavelength: 850 nm) transmission images near the bilateral finger joints were taken with a CCD camera. The mean brightness was calculated from the images. While no major temporal changes in mean brightness were observed before cuff release, the mean brightness of the hyperemic finger sharply decreased after cuff release. This result suggested that the FMD reaction can be detected with near-infrared transmission images. When the brightness decrease ratio (BDR1) before and after cuff release were compared among age groups, BDR1 at age 50 over years group was significantly smaller than that at age 20-29 years group (p<0.05). BDR1 showed a significant negative correlation with baPWV (R=0.34). This measurement method is considered to have a possibility of estimating FMD reaction and arterial endothelial function.
The Impact damper with granular materials has a high damping effect for wide frequency range and it is used in many fields. Many researches have been made on the prediction of the damping effect of this damper on one degree of freedom spring-mass system. But it is more useful to be able to predict the damping effect when applied to a real complex structure. For this purpose, numerical modeling of damping effect of an impact damper is important for efficient design of structures set with dampers. In this paper, the granular materials are modeled as one mass point of restitution coefficient of zero that undergo displacement vibration excitation, and the motion of this mass point is theoretically analyzed for the case of vertical vibration and one side collision. From these results, we propose a method for obtaining the macroscopic damping effect of the impact damper with granular materials. This is obtained as a nonlinear equivalent mass ratio and nonlinear damping coefficient with amplitude dependence. Further the excitation experiment which identified the damping characteristic of the damper was carried out. Theoretical solution and experimental result show the good coincidence.
We propose curve contour detection algorithm for road white line detection based on Helmholtz principle. White line detection is widely used in driver support systems used mainly in highway or major arterial road. As the common road will be the target of operational area for autonomous vehicle, it is thought to be necessary to develop a new detection algorithm that can deal with various types of road. This paper proposes model-less algorithm that is constructed on a new edge feature inspired by Helmholtz principle through the analysis of the limit of Hough transform. This feature is basically same as Hough defined feature of edge count on the line except two remarkable points. The one is the restriction of count area and the other is the way of count which affords to detect curve line as well as straight line. Implementation by convolutional neural network is explained and the relation between tunable parameters and the detection performance as well as the processing time are discussed. Comparison between conventional methods such as Hough transform or machine learned contour detection algorithm BEL is explained for test image and images taken by on-board camera to show the superiority of proposed algorithm. We demonstrate that proposed algorithm that can apply to diverse road environments but is hardly affected by noise can be realized.
A reduction method of engine sound disturbance for on-board power spectral measurement of the tire sound is proposed and its validity is evaluated. The proposed method employs two microphones; one is mounted in the engine compartment, and the other in the wheel well of the vehicle. At first, the sound propagation characteristics between the two microphones are discussed. It is shown that the complex coherence between the engine sounds obtained with two microphones are very low. On the other hand, the power coherence takes about 0.4 within the frequency range from 0 to 15 kHz. These imply that the sound does not propagate linearly between the two microphones, but the power spectra of microphones correlate with each other. Next, the power spectra of the sound measured with each microphone are calculated and the power spectrum of the tire sound is extracted by the calculation with the two spectra based on a pre-identified transfer function between the two microphones. The calculated power spectrum of the tire sound depends on the driving conditions of the engine and its large variance is not acceptable. This may be caused by the error of the pre-identified transfer function. Then, the modified transfer function is determined and the power spectra are calculated again. As a result, the variance of the power spectra reduces from previous results and thus, the validity of the proposed method is confirmed.
Ball shooting machine (pitching machine) is used for practicing ball sports, and it is widely prevalent. However, there are few pitching machines that can throw a ball with a gyro spin, such as a football or rifle bullet, in which the axis of the ball spins in the same direction as the ball travels. In this study, a new ball shooting machine, which can throw in the ball in a wide range of speeds and all pitch types (no, top, down, side and gyro spin balls) was invented by introducing a launch mechanism using four rollers (two launch and two gyro rollers). The shooting machine is able to arbitrarily change the rotational speed of the four rollers and the crossing angle of both gyro rollers. Shooting tests were conducted using the prototype shooting machine to confirm the ability of its performance. From the experiment results, the prototype machine had a maximum ball speed of 42.5 m/s, a spin rate of exceeding 5000 rpm, and a ball of any pitch type could also be shot. In addition, the position accuracy (shot accuracy) at the targeted fall position in the opponent's court was high because the gyro spin and other pitch types (no, top and side spins) were less than 140 mm and 40 mm (the diameter of one table tennis ball), respectively. The prototype machine had the necessary launching performance for table tennis practice of a college student level.
When developing rehabilitation assist suits, safety consideration for patients is crucial. Computer-aided control techniques can improve their safety. However, when the computer breaks down, the assist suit may be dangerous for the user because of its unintentional motion. Therefore, assist suits with hardware-based safety devices are desired to guarantee safety even when the computers do not operate properly. In this paper, we present a new rehabilitation assist suit equipped with a velocity-based safety device and a torque limiter. The assist suit assists a patient's knee joint. The velocity-based safety device switches off the assist suit's motor if it detects an unexpected high joint angular velocity. The torque limiter cuts off the torque transmission if it detects an unexpected high joint torque. These safety devices will work even when the computer breaks down, because they consist of only passive mechanical components without actuators, controllers, or batteries. Firstly, we describe the features of the assist suit with the safety devices. Secondly, we introduce the structure of the assist suit. Thirdly, we explain the structure and mechanism of the velocity-based safety device. Fourthly, we show the prototype assist suit that we have developed. Finally, we present experimental results to verify the effectiveness of the velocity-based safety device installed on the developed assist suit.
This paper analyzes metal-mold polishing by human hands. The metal-mold polishing generally requires long experiences about polishing works. Although experienced persons have many excellent skills, it is a little difficult to evidently teach them to beginners in words because most skills are considered to depend on their physical and intuitive memories. Thus we attempt to bring out the characteristic skills about metal-mold polishing by human hands. This paper mainly discusses the difference of polishing skills between experienced persons and beginners. First, a new data acquisition tool is developed to obtain polishing data, which is designed similar to old tools used by experienced persons. The tool basically consists of a small grasping spatula, a grindstone chip, a force sensor, and a 3D motion sensor. Second, basic data acquired from the developed tool are explained, and the estimation method about some kinds of data is proposed, which are not directly obtained from the sensors attached to the tool. Third, the characteristics between experienced persons and beginners are carefully compared from the view of the tool angle, the polishing velocity, the pressing force, and the mean power of polishing. Then, we focus on the phase trajectories between the polishing position and velocity, and the resistant forces appeared in forward and backward polishing. In order to understand the interesting phenomena about the phase trajectories and resistant forces, a simple dynamical model is newly assumed, and the model evidently explains the phenomena. Finally, the main results and future works are summarized.
Recently, proceeding of the aging society has encouraged research and development of power assist systems. The authors' research group studies on the assist system control using an assist cart as a rollator. The merit of the proposed system is the aging people walk by themselves using the cart as the assisting tool and it helps anti-aging. Most serious problems of the proposed system are the avoidance of fallings and collisions without losing operability. To solve the problem, this paper proposes the remote control system taking operators' safety and operability into account. The remote control has a possibility of the establishment of the cost-effective multiple target control systems by reducing the requirement for each control target system. However, because of the limitation of communication data capabilities, the controller cannot grasp the state of the controlled object completely. To grasp the state and keep the safety, the authors apply an evaluator in the remote control system. It detects the effect of the uncertainty and keeps the controlled object safe. In addition, as an interface for the users to avoid the collisions, this paper applies the stiffness control. Introducing the virtual spring into the control system, the proposed system prevents the controlled object to collide the obstacle, without losing operability. Based on an application example for the one-dimensional assist rollator collision avoidance, this paper reveals the practicality of the proposed system by conducting experiments and the simulations. The result shows the proposed way is one of the effective ways for applying a remote control system to the assist system problem.
This paper describes a modeling method for predicting a walking route of a pedestrian in a stochastic manner. We consider one of the most typical situations where a pedestrian walks along to a sidewalk, and then some obstacle exists in front of the pedestrian. To represent the walking route of the pedestrian during the avoidance action, a stochastic model is suitable than deterministic one. The stochastic model is derived from the walking experiment where a pedestrian avoids some obstacle in natural walking. Based on the loci obtained from the experiment, the pedestrians walking speed and walking direction at any local area was approximated by Gaussian and Beta distribution function, respectively. As a result the walking route of a pedestrian can be represented in a stochastic manner. The estimated output of the model is examined by comparing with two real walking loci that were obtained from near-miss incident database. One examination scene is avoidance of a parked vehicle, and the other is of parked bicycle on the roadside. By the numerical simulation, we obtained the results that the both real walking routes are included within the 3-sigma ranges of the estimated output of 500 trials.
It is important to secure running safety of railway vehicles against wheel-climb derailment accidents. The safety is often discussed according to the value of derailment coefficients for the leading outside wheel of a railway bogie running on sharp curves. Therefore, the detailed force induced mechanism which influences the value of derailment coefficients should be clarified. One of the most dominant factors affecting the value of derailment coefficients is magnitudes of the coefficient of friction (COF) between wheel and rail. Since the gauge corner of the outer rail and the top of the inner rail are lubricated at some sharp curves, COF of wheels of a bogie are different from each other and show complicated variation. In this study, the effect of lubrication for the running safety of the railway bogie is investigated while considering the detailed force induced mechanism of the derailment coefficient increase utilizing both multibody dynamics simulations and experiments. Experiments and simulations are conducted with a roller-rig test equipment under various conditions of wheel/rail lubrication. In this research, a method to identify whether the bogie is in suitably lubricated condition in terms of running safety is discussed. The proposed method making use of the longitudinal force measurement with mono-link type axle supporting device is mentioned.
Horizontal moving body settling control mechanism which is mainly realized by momentum exchange, can be expected to save time of article transportation. Momentum exchange impact damper (MEID) is one of the mechanisms in order to solve shock response control problems. This paper proposes a novel hybrid mechanism consisting of passive MEID (PMEID) deceleration and active MEID (AMEID) rebound suppression for realizing rebound reduction of horizontal moving body colliding with a wall. In this method, all of the dampers are not released to the outside of the horizontal moving body but captured by soft springs to assume the actual usage condition. For the same reasons, the function to reduce the rebound and to extend the time in the state of zero rebound velocity is especially focused. The effectiveness of the proposed method is discussed by simulations and experiments. Simulations are conducted with both ideal and experimental conditions. Compared with the system with AMEID or PMEID only, the proposed hybrid MEID combines the advantages of each system and can realize settling control efficiently without releasing dampers out of the horizontal moving body. Ideal simulation results show that it is possible to reduce the rebound and the acceleration of moving body at the time of the collision, and reduce the active control input, simultaneously. These two advantages of the proposed method are also shown by the simulations with experimental conditions and the experimental results.
For hydrodynamic cavitation produced by a Venturi tube, cavitation bubble is collapsed at downstream of a nozzle and its intensity is influenced by upstream pressure and downstream pressure. In order to investigate the effect of the upstream pressure p1 and the downstream pressure p2 on aggressive intensity of hydrodynamic cavitation, an experiment measuring acoustic power by an AE sensor was conducted. Relationship between pressure conditions and acoustic power PA was studied. The higher the upstream pressure p1, the higher the acoustic power PA. Acoustic power had a maximum value at the upstream pressure p1 = 1.6, 2.1, 2.6, 3.1 and 3.6 MPa. At the upstream pressure p1 = 2.6 MPa and the downstream pressure p2 = 0.5 MPa, the aggressive intensity of hydrodynamic cavitation increased to be 36 times larger of the value corresponding to the atmospheric downstream pressure. While the optimum downstream pressure depended on the upstream pressure, the cavitation number was nearly constant for all upstream pressures. It was concluded that increasing the downstream pressure is an effective means to increase the aggressive intensity of the hydrodynamic cavitation without increasing the input energy.
Structure can get various mechanical characteristics by applying periodic structures as typified by lattice structures. Lattice structures are generally used inside the structural member in order to reduce the weight. One advantage of lattice structures is that we do not need to change the whole structural shape when we replace the solid part of a component with the lattice structures. Another advantage is the lightness of the weight, and hence it is important to design a high performance lattice shape with low weight. However, a framework for development of micro lattice structures considering both stiffness and weight has not been established. Thus, we propose a method for designing and producing micro lattice structures. We use a topology optimization method for a designing methodology. Topology optimization is an effective method in designing high performance lattice structure since topology optimization allows us to change the topology and to design a complicated shape. We use a metal additive manufacturing (AM) machine for producing the optimal lattice structures. AM allows us to produce a complicated structure which removal and forming manufacturing cannot produce. We use a bulk modulus as the objective function since it is one of the important mechanical characteristics in design. In this research, we use a homogenization method to compute the bulk modulus. Objective function was modified so that isotropy of the optimal shape is retained when the solution is updated. In addition, structures produced by AM need holes so that internal metal powder can be removed. Hence, we defined the design domain so that the optimal structure becomes open cell structure. Then, high bulk modulus shapes were derived using topology optimization. The lattice structures were produced by metal AM machine after being modified for production.
This paper describes that the film formation and shear properties of screw tightening lubricant PIB (Polyisobutylene) under the oil starvation condition. The point contacted pure sliding tests were conducted, and the film thickness was measured using the interferometry method with the spacer layer. The result showed that the starvation region occurred at the inlet of the conjunction becomes large with time. It was also shown in the initial time of the test that the film thickness decreases due to the oil starvation, however, the thickness is thicker than the value equivalent to surface roughness. The friction coefficient depended on the starved area, and that showed the constant value of 0.16-0.17 in the fully starved condition. The relationship between the friction coefficient and the shear rate suggested that the coefficient in the high shear rate condition is the constant value, that revealed the film may be changed to the solid like film with the high shear strength in the fully starved condition. The long term test showed that the breakdown of film is appeared at about 120 s and then the wear area expands in the remainder of the test. The test results suggested that the PIB lubrication film has the high shear strength and enable to protect the contact surface in the tightening screw from the direct contact and the wear.
Microgravity experiments of flame spread along a fuel droplet array were performed to examine the effect of ambient pressure on the flame spread speed. The purpose of this research is to investigate growth mechanism of group combustion of fuel droplets. A fuel droplet array was suspended by SiC fibers of 14 μm in diameter. The number of fuel droplet was varied from 6 to 10 depending on the droplet spacing. Nondimensional droplet spacing and ambient pressure were varied from 2 to 12.5 and from 0.10 to 0.60 MPa, respectively. To simulate flame spread through a 3D fuel-droplet-matrix, a fuel droplet array was placed on the axis of a rectangular optical cell. n-decane was employed as a fuel. The normalized flame spread speed decreased as the ambient pressure increased. For all ambient pressures, the normalized flame spread speed takes the maximum between 3 and 3.75 in the nondimensional droplet spacing. The dependence of the normalized flame spread speed on ambient pressure increases with the increase in the nondimensional droplet spacing. An empirical model equation which expresses the dependence of flame spread speed on the ambient pressure was proposed.
For the development of industrial heat pump systems supplying high-temperature heat source over 130 °C, experiments were carried out on cooling heat transfer of supercritical pressure HFO1234ze(E) flowing in a plate-type heat exchanger (PHE). HFO1234ze(E) with low Global Warming Potential (GWP) is expected as an alternative to refrigerant HFC134a. In the experiment, heat transfer coefficient data were obtained at different pressures including a near-critical pressure condition. To obtain the heat transfer coefficient, an integral method was used for evaluating the mean temperature difference between the refrigerant and cooling water in the PHE. Based on the measurements, characteristics of cooling heat transfer of supercritical pressure HFO1234ze(E) in the PHE were clarified. Generally, heat transfer coefficient showed considerably large values compared with tube flow, attributed to strong turbulence or agitation promoted by corrugated geometry of the PHE plate, and reached a maximum in the vicinity of the pseudocritical point. As the pressure approached the critical pressure, the peak of heat transfer coefficient became higher at lower bulk enthalpy, reflecting the pressure dependence of isobaric specific heat of the refrigerant. These results mean, even in the pseudocritical region where strong temperature dependency of physical properties appears, properties change in the flow cross section was small compared to the tube flow, although not negligible. The correlation developed in the previous study overestimated the measured heat transfer coefficient in the pseudocritical region for the pressure of the reduced pressure 1.01 very close to the critical pressure and also in the enthalpy region near to and lower than the pseudocritical point for the pressures of the reduced pressure about 1.1 or higher. For the better prediction, the necessity to consider the small but non-negligible properties change in the flow channel cross section was recognized.
The effects of environment temperature on initiation and multiplication of transverse crack in cross-ply carbon fiber reinforced thermoplastic (CFRTP) laminates have been investigated. Static tensile tests for the cross-ply laminates and the 90° unidirectional laminates were carried out at room temperature, 93 °C and 130 °C, respectively. The transverse cracks were observed by soft X-ray photography. The tensile strength and the failure strain in the cross-ply laminates and the 90° unidirectional laminates at high temperature decreased compared to the values at room temperature. It was also found that the behavior of initiation and multiplication of the transverse cracks in the cross-ply laminates was changed due to the environment temperature. The experimental results under different temperature were analyzed by Weibull distribution on the basis of probabilistic model. Next, the energy release rate was calculated due to formation of a new micro crack based on the Weibull distribution. The predicted transverse crack density by Weibull distribution was compared with the experiment result and the reasonability of using Weibull distribution to CFRTP cross-ply laminates under high temperature was verified. It was found that the critical energy release rate of CFRTP laminates has decreased at high temperature and the experimental results showed that the matrix strength was decreased at high temperature. Also, the fiber-matrix interfacial fracture on the fracture surface of the 90° unidirectional laminates was observed in some areas at high temperature whereas the matrix fracture was observed at room temperature. Therefore, it was suggested that the interface strength between polymer and fiber was decreased at high temperature.
The fracture toughness Jc of the material in the ductile to brittle transition temperature (DBTT) region shows test specimen thickness (TST) effect and temperature dependence, and apparently increases when compressive residual stress is applied. In this paper, as TST effect and temperature dependence, the fact that Jc apparently increases due to compressive residual stress is attributable to the loss in the one-to-one correspondence between J and the crack-tip stress distribution, and then, the fracture prediction of the specimen with compressive residual stress was performed using the T-scaling method proposed by the authors, and its validity was confirmed for high strength steel of 780 MPa class and 0.45 % carbon steel JIS S45C. In addition, it was suggested that the minimum of Jc with compressive residual stress can be predicted by requiring only the tensile test.
This paper presents numerical solution to two shape design problems of unsteady forced heat-convection fields to control temperature to a prescribed distribution. In the first problem, the square error integral between the actual temperature distributions and the prescribed temperature distributions on the prescribed sub-domains during the specified period of time is used as the objective functional. In the second problem, a multi-objective shape optimization problem using normalized objective functional is formulated for the temperature distribution prescribed problem and the total dissipated energy minimization problem in the unsteady forced heat-convection fields. Shape gradient of these shape design problems is derived theoretically using the Lagrange multiplier method, adjoint variable method, and the formulae of the material derivative. Reshaping is carried out by the traction method proposed as an approach to solving shape optimization problems. Numerical analyses program for the shape design is developed based on FreeFem++, and the validity of proposed method is confirmed by results of 2D numerical analyses.
We investigated differences in the hydrogen thermal desorption mechanism for Ni-Ti superelastic alloys following hydrogen charging by cathodic charging in a 0.9% NaCl aqueous solution and by immersion testing in a 0.2% APF aqueous solution. For the immersed specimen, the presence of corrosion products on the surface resulted in an upward shift of the hydrogen desorption peak by approximately 100 °C. When the total amount of desorbed hydrogen was almost the same for both specimens, a higher fraction was desorbed at temperatures below 200 °C for the cathodically charged specimen. Furthermore, a larger amount of hydride was formed for the cathodically charged specimen. These results indicate that the hydrogen thermal desorption mechanism depends on the presence of corrosion products on the surface and the amount of hydride formed.
There are many studies reported that a fatigue crack propagated in a tensile mode macroscopically and the fracture surface was mainly occupied by striations in many metals. Whereas, a unique fracture in which a crack propagated in a macroscopic shear direction accompanied by ductile facets was observed in some aluminum alloys under specific conditions. In the present study, fatigue tests of age-hardened Al alloys of extruded 2017-T4 and 7075-T6 were conducted in relative humidity environments of 25% and 85% under rotating bending and ultrasonic loading conditions to clarify the crystallographic feature of a shear mode crack and propose its growth mechanism. Many facets showing a feature of shear mode crack propagation with an equivalent size to the grain size were observed at the fracture surface under both conditions of rotating bending in high humidity and ultrasonic loading irrespective of humidity. In addition, it was confirmed that the angle between the loading axis and the growth direction of the shear mode crack composed a constant value, ~35°, relating to the marked texture in the propagation process of the macroscopic shear mode crack. However, a crack growth rate was lower in the ultrasonic loading than in the rotating bending in high humidity. Based on their differences in occurrence conditions of the shear mode crack, two mechanisms for this unique propagation were proposed as follows; that is, one was a shear mode crack occurred by the promotion of the slip deformation to one direction due to hydrogen generated by reaction of Al alloy with water vapor in high humidity, and the other was a crack by the suppression of the deformation to one direction due to re-welding of crack faces under ultrasonic loading.
A zirconium alloy cylindrical tube exhibited fracture under high-velocity axial impact load when high yield strength pellets were inserted as reported by Morishige et al., 2016. The fracture occurred after a crack was initiated at the tensile side of the bending tube. In this paper, FE analyses were conducted to clarify the fracture mechanism as well as the deformation behavior. At first, axial tensile tests using tubes with four slit-holes located at the center were performed in order to evaluate the fracture behavior of the tube. Then, digital image correlation (DIC) method was utilized to measure the local strain near the slit-holes. The results showed that the fracture displacement became smaller with smaller slit-holes’ radius. Also, the strain was concentrated at the slit-holes’ tips where cracks were generated before fracture. Subsequently, FE analyses of the tensile tests were conducted by LS-DYNA using the implicit method to obtain the fracture criterion. The load-displacement curve agreed well with the experiment. Then, the relationship between stress triaxiality and equivalent plastic strain near the slit-holes’ area were evaluated to define the fracture criterion. Finally, FE analyses of the axial impact tests using the dynamic explicit method were conducted to compare with the fracture criterion defined by the axial tensile tests. The results indicated that a localized stress and strain might occur at the tube boundary adjacent to pellets. This was caused by the interaction between tube and pellets’ edge which generated a tensile stress condition at the tube boundary when high yield strength pellet was applied. Under this condition, both stress triaxiality and effective plastic strain could increase and eventually lead to the fracture criterion.
A range sensor is known as one of sensors which are often installed in mobile robots. The range sensor can detect the distance to objects in the environment using laser beam. However, the measurement area of the range sensor is limited because the scanning plane of the sensor is single and parallel to the mounting surface. In this research, we developed a new range sensor capable of scanning in two directions. Using the periodic refraction of laser beam generated by the rotation of two acrylic prisms installed around the range sensor, two-directional scanning is realized. If this range sensor is placed at the front of the mobile robot horizontally, the robot becomes possible to scan both distant area and road surface. In addition, we devised a simple method for the classification and integration of two-directional measurement data based on a model fitting method. In this paper we describe the concept of the range sensor device and explain the method for the classification and integration of two-directional measurement data. Furthermore, we verified the range sensor's effectiveness through object detection experiments.
Vibration testing using a shaking table is a useful method to examine the vibration characteristics such as aseismic capacity of buildings for earthquakes and ride comfort of vehicles for vertical vibration. However, it’s necessary to design a controller which can reproduce the vibration such as earthquake waves accurately. Moreover, since there are various types of earthquakes such as a long-period earthquake and short-period earthquake, a controller with good tracking performance on wide frequency range is required in order to reproduce earthquake waves. Generally, a displacement feedback controller is employed in a control of the shaking table. However, almost all earthquake waves are saved as acceleration data. Therefore, an acceleration feedback controller is more proper to control the shaking table. The purpose of this study is to design an acceleration feedback control system with good tracking performance until high frequency range. However, it generates spillover caused by dynamics that is not included in plant model. As a result, the tracking performance of the controller degrades. So, we also proposed the method which can suppress spillover to solve this problem. The controller is designed based on Dual Model Matching method. Then, effectiveness of proposed control system is validated by experiments using 3degree-of-freedom shaking table.
Acoustic metamaterial can have arbitrary acoustic characteristics , and there is possibility to improve acoustic performance of any products dramatically. As metamaterial, many kind of types have been propounded and studied. It is mainly classified into resonance type and non-resonance type.Resonance type metamaterial can change acousic characteristics drastically, but frequency range is narrow. Non-resonance type’s acoustic characteristics range is less than resonance type, but it can be changed in broad frequency band. It is a great advantage to use. About non-resonance type metamaterial, it has been already studied to control transmitted sound, but it has not been studied about reflection sound. If reflection sound control become possible, effective method can be chosen to solve noise problem. For example, resonance frequency in a duct will be shifted by changing reflection direction from the wall. In this study, the design method of non-resonance type metamaterial to control reflection sound has been studied by using FEM and Transfer-function method, and to verify the design method, element test was conducted. Element test result correspond well with analysis result, and the design method of acoustic metamaterial has been verified in this study. In order to put into practical use, further study with actual product shape is needed to confirm manufacturability.
In order to clarify the mechanism of the vehicle body hysteresis affecting “rigidity feeling”, one of the driver's sensory evaluation in the driving test, the influence of friction acting on spot welding flanges on hysteresis, which is drawn by displacement - load diagram under static or relatively slow deformation of double-hat-shaped parts assembled by spot welding, is experimentally evaluated. By measuring the difference between loss energy of a specimen with strong contact on welding flanges and that of another specimen without contact, friction loss (energy dissipation generated only by friction excluding inevitable loss energy for measurement possessed by testing system itself) is calculated. The friction loss rising with increasing load amplitude and load rate confirms that friction hysteresis occurs in the structure even under the elastic deformation. In this paper, the load rate dependence and the extrapolation point to the zero load rate are evaluated as the dynamic and static characteristics of friction loss, respectively. As a result, the dynamic characteristic obtains a result proportional to the load amplitude, and the static characteristic is proportional to the square of the load amplitude. Additionally, a model with the reaction force as the sum of linear elastic resistance due to bending and shear deformation, Coulomb friction proportional to amplitude of displacement and viscous friction is proposed. Using this model, the prediction of static and dynamic characteristic of the friction loss shows good agreement with results of the experiment. Finally, the friction-induced hysteresis led from the model is quantitatively discussed.
In this paper, Dynamics stability analysis methods of a beam subjected to a confined annular axial flow is dealt with. Such structures are submarine resources production pipeline, reactor core structures of nuclear power plants, high-speed trains passing thorough a tunnel, a piping system in the field of ocean mining, and so on. The relation between the annular axial flow velocity and the unstable dynamics of structures are clarified. We have compared two analysis methods which can evaluate the dynamic instability of such structures. In first analysis method, the fluid is treated as viscous fluid, and is governed by the Navier-Stokes equation, and the beam structure is treated as the Euler-Bernoulli beam. This is called as the viscous fluid solution namely NS solution hereafter. In second analysis method reported by (Rinaldi and Paidoussis, 2012), the fluid is treated as ideal fluid. Then the viscosity effect is added to the equation of motion. This is called as the ideal fluid solution namely R&P solution hereafter. The complex eigenvalue analysis of the fluid structure coupled equation of motion is performed in order to clear up the dynamic instability. Performing the parametric studies, the comparison between both solutions is investigated. When the fluid viscosity becomes large, the difference in the critical velocity between the viscous fluid solution namely NS solution and the ideal fluid solution namely R&P solution is found to be generated. The destabilization effect appears due to the fluid viscosity force terms of the added stiffness of the fluid-structure coupled equation only in the viscous fluid solution.
In the steel/casting industries, a liquid container transport is carried out by an overhead traveling crane or a trolley. The operation of the overhead traveling crane is carried out both operation by the experience operator and operation by automated transportation in order to prevent quality deterioration due to the overflow and involvement in a hostile environment. In particular, the overhead crane transportation by the operator, which is allowed to select freely pathway, is needed from the point of freedoms of the operation. This paper presents a design of a liquid container transport control system with an overhead traveling crane, which is allowed to operate by an inexperienced operator easily. The presented control system is designed as to suppress both the rod vibration and the sloshing (liquid vibration) without measuring the sloshing. The presented control system is two DOFs controller, the feed-forward controller is based on two notch filter, and the feedback controller is based on the H2/H∞ controller design method using LMI. The derived controller is performed a controller order reduction in consideration with practical use. Some experiments are presented to show the effectiveness of the proposed design of control system.
A long flexible shaft such as a lance tube in a soot blower or a drill string in a rotary drilling system exhibits friction-induced vibration resulting in a whirling motion. This paper investigates the whirling motion of a long flexible shaft induced by frictional force and examines the effect of an intermediate support position on the whirling motion. The experimental apparatus investigated has a vertical shaft which rotates at a constant speed by means of an electric motor mounted at the top of the shaft. At the bottom end of the shaft is located a rubber ring so that frictional force acts on the tip of the shaft when the shaft is deflected. Comparing experimental and calculated results we clarify the vibration characteristics, such as whirling frequencies and amplitudes, at various rotational speeds and show the effective position of an intermediate support to suppress shaft vibration.
In industrial devices such as heat exchangers, fuel cells, and chemical reactors, the fluid flow enters the inlet manifold and streams into many branch passages. In order to improve the performance of these devices, it is important to obtain a uniform flow rate distribution in each passage. In the present study, an experimental investigation is performed for multiple-passage duct flows. The multiple-passage duct is a reverse flow type and consists of five branch ducts. The duct flows are investigated from the view-point of flow uniformity and pressure loss. Experiments are performed for Reynolds numbers ranging from 6.0 × 102 to 1.5 ×103, based on the bulk velocity and hydraulic diameter at the inlet duct. The aspect ratio (i.e., the ratio between the height and width of the branch duct) is varied as 0.6, 1.0, and 20. The effect of the outlet manifold volume on the flow distribution is investigated. The wall static pressure is measured, and the pressure loss and flow rate are evaluated. The velocity profiles are measured by a PIV system in order to clarify the effect of the increasing the outlet manifold volume. The results reveal that the flow rate changes only slightly with the aspect ratio. As the Reynolds number increases, the uniformity of the flow rate through each branch duct worsens. A uniform flow distribution is realized by increasing the volume of the outlet manifold. The flow uniformity is related to the reduction of the recirculation region at the inlet manifold.
The purpose of this study is to construct the automation technology based on the hammering task and its sound feedback with an industrial humanoid robot equipped with an integrated system of vision, sound and dual arm motion. First, we discuss a suitable flexible rubber stick to achieve the hammering task and developed the acoustic recognition system based on its hit sounds. Second, we confirm that the developed system is sufficient to investigate the task playing the glockenspiel, and also discuss the characteristics of motion based on dual arm motion. Third, we attempt to cooperate with hammering the bottle and pouring liquid into it based on estimating its hit sound. As a result, it can be seen that the proposed system using an industrial humanoid robot achieves sufficient motion accuracy. Therefore it is demonstrated that the proposed approach is found to be effective to construct the automation technology based on the hammering task and its sound feedback with an industrial humanoid robot.
Ti-Ni based Shape Memory Alloy (SMA) actuators have been used for robots because of their high power-to-weight ratios, easiness of simple ON-OFF driving, and flexibility. In addition, SMA actuators enable simultaneous self-sensing and displacement control of themselves by feedbacking their electrical-resistance values. Modeling of SMA actuators for servocontrol is not easy due to their characteristics such as nonlinearity, hysteretic behavior, and effect of temperature and stress. Most of past studies have not considered minor-loops in the hysteresis or simultaneous variation of temperature and stress; both are necessary to be considered when achieving a robust robot control with SMA actuators. This study proposes a novel SMA model for electrical-resistance feedback control, which enables to adapt load disturbance and easy implementation. Especially, in order to consider the stress and temperature variation and minor-loops of hysteretic behavior in the relation of temperature and strain, electrical-resistance model and phase transformation models were improved by considering phase transformations between three crystalline structures: austenite, twined-martensite and detwined-martensite. Displacement, stress, temperature and volume function of each phase can be calculated from applied voltage and electrical-resistance value, which are easy to observe. Model parameters were identified by applying several general experiments to the actual system. Through the verification experiments, calculation results of the proposed model from observed electrical-resistance values were confirmed to agree with the experimental results under complex temperature and stress variation. Subsequently, an electrical-resistance feedback control system with the proposed SMA model was developed, and the system showed to control the displacement successfully to a constant value with load disturbance.
Recently, the ultra-precision parts have become essential in many areas of advanced technology, including medical equipment, aircraft equipment, optical equipment and so on. These ultra-precision parts are required to have a high surface quality. Therefore, further precise machining and motion accuracy are required for the ultra-precision machine tools that machine these parts. Thus, the water-driven spindle, which is equipped with water hydrostatic bearings and a water-driven mechanism, was developed for ultra-precision machine tools. This spindle has higher stiffness than a spindle supported by aerostatic bearings. However, the heat generation due to fluid viscosity occurs at the bearings. If the temperature of each part in the spindle changes, undesirable deformation of the parts will occur. Deformation of the spindle during the machining process will then degrade the machining accuracy. In contrast, the water-driven spindle uses water as a lubricating fluid. Furthermore, water flow is supplied into the spindle in order to generate the driving power. Therefore, the water flow is an effective cooling medium for the water-driven spindle. Water cooling can be used to improve the thermal stability of the spindle because water has higher thermal conductivity and higher specific heat. In the present paper, the thermal stability of the water driven spindle is investigated experimentally. As a preliminary step, the changes in temperature of the water flow and the outer surface of the spindle are measured experimentally during spindle rotation at various rotational speeds. Furthermore, the influence of the power loss during spindle rotation on the temperature change of the water flow is investigated through calculations and experiments.
Multi-fidelity analysis has been used for reducing the calculation cost of evaluating the design solution, which is the most costly process in design optimization. In general, multi-fidelity analysis is applied to problems with continuous design variables, which are suitable to construct an approximate model of design space such as the response surface. On the other hand, combinatorial optimization problems, e.g., layout design, are difficult to apply the conventional multi-fidelity analysis, since the response surface cannot be constructed due to the property of the design variables. In this paper, we propose a multi-fidelity optimization method independent of the response surface and a simple analysis model for the method, and apply them to multi-disciplinary optimal layout design problem which is a complicated combinatorial optimization problem. The proposed analytical model, which adopts the concept of the explicit method, realizes for reducing the calculation time by simplifying the physical phenomenon. Then, the multi-fidelity optimization method is constructed by combining the proposed analysis model with the thermal network method which is a well-known thermal analysis method. We confirm that there is a strong correlation between the calculation result of the proposed analysis model and of a CAE software, and show that the proposed analysis model is suitable as a low fidelity model. The effectiveness of the proposed optimization method is demonstrated through numerical experiments.
This research presents an experimental investigation on the vision performance of a human body which is sitting on an automobile seat. Six subjects were selected from a panel for the experimental research and frequency exposes from 1 to 30Hz sine wave vibration to the subjects by the sweep for 240 seconds with the total amplitude of 2 millimeters. The subjects were measured a standard visual acuity test and a self-rated assessment for difficulties in visual perception every 2 Hz and two subjects of them were measured vertical acceleration for their head in the experimental investigation. From the experimental result, visual efficiency was declined to 49.55 % in the vicinity of the frequency range of 20 Hz. The cause of reduction of eyesight has been considered using the model eye of Gullstrand, and it has been found that the deformation of optic-axis length was 0.257 millimeters when the average eyesight of all subjects was reduced from 1.15 to 0.57. Some results are presented in the form of parametric graphs. The results are useful for improving vehicle ride comfort, maneuverability and safety driving.
The ball end mill is used as a tool for cutting the metal mold and some complicated shape lake a screw. The demand for the precise machining of the ball end milling is increasing. The ball end milling has the unavoidable problem of machining error by the elastic deformation of tool because of its low rigidity. So this report is set up the new method of the high precision machining used by the tool orientation control. The machining area at the point of the surface generation is changed depend on the tool orientation of the ball end mill. The geometric mechanism is analyzed and the relationship between the machining area and the tool orientation is clarified. And the cutting force and the machining error are measured by the machining test that the tool orientation has been varied. As the result, it is verified that the machining error becomes large at the point, which the machining area is large. And the machining error estimation index has been proposed and calculated about three dimensional surface.
A no-backlash drive control technique in which two motors drive a load axis, as one is for a forward direction and another is for a reverseone,hastwo problems :1)the drive system has a remarkable power loss, 2) the 1st natural frequency of the drive system may cause a backlash.For the former problem,weemploy a torque crossover method, in which a part of torque reference of the drive-side motor gives to the driven-side motor and the resulted torque reference of the driven-side one is reduced.For the latter problem,we employ a ratedifference feedback method that feedbacks a signal in proportion to the difference between the forward direction motorvelocity and the reverse one to the each motor torque.We have shown through our analysis thatthetorquecrossover does not affect poles of the 1st natural frequency, andthat theratedifference feedbackimproves the damping of the 1st natural frequency directly and suppress its vibration.We evaluate our method in the non-linear simulation andexperiment:1) it is preferable to increase the damping of the1st natural frequency with theratedifference feedback and then decrease the motor current with theratedifference in the control system tuning, 2) the torque difference between the two motors is required to some extent for no-backlash drive, so torque crossover should not be increased unnecessarily.We have gotten the experimental results that the total motor current has been reduced by 40%.
In recent years, the drill used to make holes is expected to exert both high machining accuracy and good processing capability. In order to meet those requirements, it is necessary to develop a new drill shape with good properties requested by designers. There is a strong need for a new system to shorten the drill fabrication time, to reduce material costs, and to create new drill configurations by predicting their characteristics. Current drill shape prediction systems cannot comprehensively and mathematically treat drill cross-section shape including the cutting edge, groove and so on. The prediction system would become more practical if the drill specification was mathematically formulated. This study reports the development of a system to predict not only the cross-sectional shape but also various parameters from the information of grinding wheels used in drill fabrication. Furthermore, this study proposes the new system to predict the most suitable grinding wheel setting from the grinding wheel shape and some drill specifications as the reverse process.
Recently, a titanium alloy has been as biomaterials that have stable mechanical property and superior biocompatibility. But the titanium alloy generally has higher young’s modulus in comparison with cortical bone, then bone resorption was occurred by stress shielding. For this reason β-type titanium alloy exhibiting super-elasticity and super-plasticity was developed. This alloy has high tensile stress and low young’s modulus too. However, the characteristics of this alloy is lost by severe heat environment and external force. Therefore, there is possibility that the advantageous characteristics may be lost during cutting. In this study, the effect of cutting temperature and cutting force on the affected layer was investigated by milling with small ball end mill tool in order to decrease the affected layer by cutting process. At the cutting speed of 16.0m/s, the thickness of the affected layer exceeded 2.5μm because of increasing of cutting temperature that approached to the neighborhood of transition temperature of this alloy. On the other hand, the affected layer was observed for the cutting condition of high cutting force by increasing feed rate of a tooth, depth of cut and pick feed, the thickness of the affected layer was 0.7μm .So, the affected layer was dominant by the influence of cutting temperature. To decreasing affected layer, the cutting temperature is able to decrease to decreasing feed rate of a tooth or depth of cut.
Response distribution of a SDOF linear system subjected to non-Gaussian random excitation is investigated. The excitation is modeled by a zero-mean stationary stochastic process prescribed by the non-Gaussian probability density and the power spectrum with bandwidth and dominant frequency parameters. In this paper, we use bimodal and Laplace distributions for the non-Gaussian distribution of the excitation. The excitation is generated numerically by using the Ito stochastic differential equation. Monte Carlo simulations are carried out to obtain the stationary probability densities^ of the system displacement and velocity. It is found that the shape of the response distribution changes depending on a difference in the shape of power spectral density between the excitation and the response. In order to evaluate the difference of the spectral densities quantitatively, a new index is defined. The correspondence of this index to the shape of the response distribution is shown. Next, we compare the present difference index of power spectra and another index which the authors used in the previous study to investigate the response distribution of a non-Gaussian randomly excited system. The comparison shows that when the present index is close to 0, the shape of the response distribution looks like the shape of the excitation distribution. For the index around 0.6, the response distribution becomes the middle shape between the excitation probability density and a Gaussian distribution. In the case of the index greater than 1.2, the response distribution is nearly Gaussian. The difference index of power spectra between the excitation and the response can be calculated readily from the frequency response function of a linear system and the excitation power spectrum, regardless of the excitation probability density function. This index enables us to roughly estimate the shapes of the probability distributions of the displacement and velocity responses without Monte Carlo simulation.
In minimally invasive surgery robots, force sensing is required to improve its manipulability. To perform delicate surgery, three-axis force sensing is desired. However, in general, the force resolution in the axial direction is worse than that in the radial direction owning to a slender shape of a forceps. This paper proposes a double diaphragm structure for forceps flexural elements. The distance between the two diaphragms can adjust the rigidity in the radial direction without changing the rigidity in the axial direction when the thickness of the diaphragm is constant. Thus, the thickness of the diaphragm adjusts the rigidity in the axial direction, while the distance between the two diaphragms adjusts the rigidity in the radial direction. A planar spiral cutting in the cross section of the diaphragm can reduce the maximum stress applied on it. Moreover, by adjusting the two spiral phases and direction, the crosstalk of the radial and axial forces can be reduced. In 5 mm forceps simulation, the rigidity of the axial direction is almost equal to that of the radial direction when the distance between the two diaphragms is 6.0 mm. We performed experiments of 10 mm forceps model and confirmed that the resolution of the radial direction is almost equal to that of the axial direction when the distance between the two diaphragms is 12.0 mm.
This research aims to develop capability of on-site staffs that can respond to beyond ‟design basis accident (DBA)” in the sophisticated socio-technical system, in which ensuring safety has been more complicated. Fukushima Daiichi nuclear accident is therefore considered as the actual case of “beyond DBA”. The authors focused on the actions to prevent the accident progression undertaken by on-site staffs, which were hardly evaluated in existing accident analyses and reports. With reference to the concept of resilience engineering, “Responding” of the four cornerstones was particularly analyzed. Based on the precedent studies, causal factors of modeling “Responding” where pointed out the importance of “Attitude” that is a new lesson learned from on-site response at the accident. In addition, new lessons learned on improvement of skills indicated the limit of the concept of risk removal type safety as a safety goal that human is defined as “a safety hazard element”. This led the necessity of the success expansion type of safety as a new safety goal that human is defined as “a resource necessary for system flexibility and resilience”. Focusing on “Responding” on-site enabled to deduce core competence by extracting causal factors. Thus, new lessons learned successfully derived introduced for human resource development of the next generation to lead technologies in the society.
Fatigue cracks in some aluminum alloys propagate not in a typical tensile mode with striations but in a macroscopic shear direction with ductile facets under specific conditions. In the previous paper, it was shown that this unique propagation of a shear mode crack occurred in high humidity under rotating bending fatigue and under ultrasonic loading fatigue irrespective of humidity. Two types of mechanism for the shear mode crack were proposed: one is a case that a slip deformation to one direction in cross slip in formation process of striation was enhanced by hydrogen generated in corrosion process of Al alloy in high humidity and the other is that a slip deformation of one direction was inhibited by the re-welding of crack faces in vacuum condition. In the present study, fatigue tests of Al alloys of extruded and drawn 2017-T4 and extruded 7075-T6 were conducted under rotating bending and ultrasonic loading conditions in relative humidity environments of 25% and 85% and in nitrogen gas, to verify the proposed mechanism experimentally and investigate influencing factors on the shear mode propagation. In addition, the effect of change in the testing condition on the propagation behavior of a crack was investigated. Although the microscopic shear mode propagation occurred within grains in both of the extruded and the drawn alloys, the crack propagated to a specific shear direction macroscopically in the extruded alloy related to the strong texture, and the crack propagated in a tensile mode macroscopically in the drawn alloy possessing no texture. These differences in macroscopic crack propagation mode, thus, were caused by the degree of texture. The proposed mechanism was verified by some experiments in various environments. Furthermore the effect of change in testing conditions influencing on the shear mode crack was explained by the results under the constant conditions.
Although bladed disks of turbomachinery are nominally designed to be cyclically symmetric (tuned system), the vibration characteristics of all blades on a disk are slightly different due to the manufacturing tolerance, the deviation of the material property, the wear during operation, and so on. These small variations break the cyclic symmetry, and split the eigenvalue pairs. The actual bladed disks with the small variations are referred to a mistuned system. Many researchers have studied mistuning, and main conclusions are while mistuning has an undesirable effect on the forced response, it has a beneficial (stabilizing) effect on the blade flutter (the self-excited vibration). Although such mistuning phenomena of bladed disks have been studied since 1980s, almost all studies focused on the amplification factor of the displacement response, and few studies researched the amplification factor of the vibratory stress response. Therefore, in the previous paper, authors studied the amplification factor expressed by the vibratory stress for the lower modes of the bladed disk, using the simple assumption. In this study, the mistuning effect expressed by the vibratory stress for the lower and higher modes are examined, using the reduced order model without any assumptions. First, formulation for evaluating the mistuning effect expressed by the vibratory stress is derived, using the reduced order model SNM (Subset of Nominal Modes). Second, the frequency response analysis of the mistuned simple bladed disk consisting of flat plates is carried out systematically. Finally, comparing the amplification factor of the displacement response with that of the vibratory stress response including the synthesized stress (Mises stress and the principal stress), mistuning phenomena expressed by the vibratory stress are clarified.
We investigated the damping mechanism of a granular material damping system applied to reducing vibration in structures that have a high natural frequency and small vibration displacement. Experiments were conducted under several conditions of total mass of granules. We also constructed a computational model of a single-degree-of-freedom vibration system with a granular material damper to study the mechanism of a granular material damping system. On the basis of the fundamental idea that the damping effect of a granular material damper is governed by the motion of the granules, we classified the granular materials as “relative motion mass” and “equivalent added mass” in the translational motion and as “rotating mass” and “not rotating mass” in the rotational motion and then considered the relationship of these mass classes to the damping characteristics. In this report, we examine the relationships of the motion of the granular materials, “relative motion mass” and “rotating mass”, and damping ratio by means of experiments and calculations for structures that have a high natural frequency and small vibration displacement.
This paper descries theoretical and experimental research on mechanical behavior of a cylindrical container which is divided into multiple space of an equal size into which one cylindrical rod of the same diameter and material is enclosed. It is clarified that an explanatory variable and a criterion variable which are governed rolling movement characteristics of the cylindrical container. A rotary dumping number that is a dimensionless parameter is defined. Theoretical formulas are introduced for the cylindrical container in which one, two and numerous cylindrical rods are enclosed in none divided space of the cylindrical container. Unfixed coefficients in the theoretical formula are properly identified from experimental results practiced more than one. As a result of investigation, we have found that initial velocity from which a rotary dumping number becomes maximum value exists for the cylindrical container in which numerous cylindrical rods are enclosed in none divided space. Some results are presented in the form of parametric tables and graphs.