This study describes a simulation-based estimation procedure of the structural failure probability using an “all quadrants sampling method” newly proposed, in which a sample called as a real sample is generated in an arbitrary quadrant of the basic variable space and then the coordinates of the real sample point is transformed into those of pseudo sample points over all of other quadrants by applying the previously proposed “inter-quadrant relational expression.” That is, once a real sample is generated in an arbitrary quadrant, and then pseudo samples are determined in all other quadrants concurrently. All of real and pseudo samples thus determined are used for the simulation to estimate structural failure probabilities. Numerical examples of various simulation methods combined with the proposed “all quadrants sampling method,” that is, “all quadrant sampling Monte Carlo simulation,” “all quadrant sampling directional simulation,” etc. are presented showing that the proposed method is effective for shortening simulation time.
Gigacycle fatigue properties of actual material of a storage cylinder, which had been used in a hydrogen station for verification tests, were examined in both longitudinal and circumferential directions. The storage cylinder was made of SNCM439 steel. Fatigue tests by using ultrasonic and servo-hydraulic fatigue testings were carried out on hydrogen-charged and uncharged specimens at stress ratio of R = -1. The specimen sizes were then not only φ3 mm but also φ7 mm. In the uncharged specimens, surface fracture was dominant in the longitudinal direction, while internal fracture occurred in the circumferential direction. On the other hand, the hydrogen-charged specimens showed internal fracture in both directions, and the fatigue strengths were lower than those of the uncharged specimens. The crack initiation sites of internal fracture were different in the directions: a single globular Al2O3 and a cluster of Al2O3 inclusions in the longitudinal and circumferential directions, respectively. With regard to anisotropy, the fatigue strength of the hydrogen-charged specimens was much lower in the circumferential direction than in the longitudinal direction. Concerning the size effect, the hydrogen-charged specimens showed clear size effects, i.e., the φ7 mm specimens showed much lower fatigue strength, revealing larger inclusions at the internal fracture origins.
Bivariate log-normal distribution analyses coupled with the cumulative hazard function method were conducted on the specific output class of 8 steam turbine units with components such as rotors, moving blades, nozzles, casings and other auxiliary equipment of high-, intermediate- and low-pressure turbines. The damage phenomena were classified into erosion, crack, deformation, corrosion, creep void formation and material degradation with corresponding components. Operation time and start up cycles for damage incidence in respective units were collected and statistically analyzed adding the non-failed data as well as failed data. After applying the bivariate log-normal distribution regression to those data sets, the prescribed failure probability was imposed to construct the equal probability ellipse contours as the quadratic function of operation time and start-up cycles. To determine whether the events were time dependent or cycle dependent, the shape and inclination of the contours were utilized. The order of event incidence was determined by using the lower end values of the major axis of equal probability contours. Although the order of event incidence could show variations according to the prescribed failure probability values, the examples for 90% probability ellipse contours were demonstrated here. The assessment results showed that the statistical analyses were effective for investigating the damage incidental scenario making and maintenance planning for actual plants.
A dual-phase magnesium alloy consisting of the usual α-Mg phase and a new LPSO (Long-Period Stacking Ordered Structure) phase has been developed and expected for a next-generation structural material owing to its excellent mechanical properties. Its materials strengthening is attributed to both the grain refinement of α-Mg phase generating in the process of dynamic recrystallization and a kink band formations in LPSO phase. In this paper, we develope a dynamic recrystallization model for HCP crystals by coupling the multi-phase-field (MPF) model and the dislocation-based crystal plasticity model through the dislocation density considering material properties of Mg/LPSO alloys. It is widely known that the pinning effect affects the grain refinement in α-Mg phase. Such effect is expressed by taking account of the grain boundary segregation of additional elements. In addition, some multiphysics analyses for Mg/LPSO alloys are carried out, and then nucleation along deformation bands such as kink bands and nucleus growth are numerically reproduced. Furthermore, on the basis of the obtained results, it is indicated that a kink band generates primarily around an α-Mg phase with orientation imperfection, a grain-refinement in α-Mg phase occurs secondarily along a deformation band as a prolongation of the kink band in LPSO phase.
The fracture toughness and toughening mechanism of six aluminum alloys, 5083-O, 6061-T6, 6066-T6, 7N01-T5, 7N01-T6 and 7075-T6, were examined in air and 115 MPa hydrogen gas. In both the environments, tentative fracture toughness, KQ, was about twice higher in 7N01-T5 and 7N01-T6 than in 5083-O, 6061-T6, 6066-T6 and 7075-T6. Stretch zone, dimples and inclusions at the dimple bottom were observed on the fracture surface by means of scanning electron microscopy. All the critical stretch zone width, SZWC, had a good correlation with tentative J integral, JQ, regardless of environments and materials. The dimple diameter was nearly equivalent in 6061-T6, 6066-T6, 7N01-T5 and 7N01-T6, although KQ was about twice higher in 7N01-T5 and 7N01-T6 than in the others. Among these four aluminum alloys, the existence probability of large inclusions (diameter ≥ 6 μm) at the dimple bottom was lower in 7N01-T5 and 7N01-T6, which had less impurity elements of Fe and Si. These results inferred that higher values of KQ were attributed to the delay in the initiation and growth of microvoids in 7N01-T5 and 7N01-T6. Taking into account the tentative fracture toughness in combination with slow strain rate tensile (SSRT), fatigue life and fatigue crack growth properties, a design by analysis of thick-walled cylinder was performed. The result suggested that 7N01-T5 and 7N01-T6 having higher KQ enabled the design of larger-sized cylinders with thicker wall.
Pure titanium thin wires have been used for medical fields. It is important to investigate the possibility of non-destructive inspection of pure titanium thin wires for the safety utilization of them. In order to investigate a fracture prediction method for a pure titanium thin wire, we performed tensile and fatigue tests and a finite element analysis to analyze the changes of direct current potential difference and diameter distribution of the pure titanium thin wire during tensile and fatigue tests. It was found that a direct current potential difference method may be available for evaluating the tensile and fatigue damages of the pure titanium thin wire. In the tensile and fatigue tests, the normalized direct current potential difference increased almost linearly with an increase in the nominal strain, and a sign of an increase of the normalized direct current potential difference was observed when the fatigue crack propagated. Therefore, the nondestructive inspection could be conducted by setting a tolerance value of the normalized direct current potential difference, or detecting a sign of an increase in the normalized direct current potential difference. In addition, a method of predicting the fracture location from the diameter distribution change of the pure titanium thin wire was studied. The method could be applied to tensile and fatigue fractures.
Non-contact manipulation of spherical micro objects using two facing glass micropipettes is proposed. One micropipette is on the left side of an object, and the other micropipette is on the right side. Each micropipette emits a jet of water and applies hydraulic pressure to the object. The center position of the object is always detected by microscopic image processing. For rotating the object, the micropipettes are arranged point symmetrically with respect to the center of the object and emit water jets. When the left micropipette is on the upper-left side of the object and the right micropipette is on the lower-right side, the object rotates clockwise. Exchanging the upper and lower positions of the micropipettes enables counterclockwise rotation. As the micropipettes come near the edge of the object, the object rotates faster. The micropipettes automatically keep the position relation of point symmetry even if the object moves during rotation; that allows continuous rotation. For moving the object, one or two micropipettes are used selectively according to the moving direction. When the moving direction is near horizontal, one micropipette is used. If the left micropipette is just besides the object and emits a water jet, the object moves right. As the left micropipette comes lower, the object moves in upper-right direction. When the moving direction is near vertical, the left and right micropipettes are used. If the micropipettes emit water jets at the both lower sides of the object, the object moves upward. In the same way, the object can be moved in all directions. The micropipettes automatically repeat rearrangement and water jet emission so as to compensate the error between the desired and actual moving directions. This feedback control enables the object to reach its goal position. The experimental results show that a glass bead with a diameter of about 120 μm can be rotated and moved to its goal position by the proposed method.
This paper proposes a method for sensorless tension control of shape memory alloy(SMA) actuators. Sensorless control has advantages in cost and size. Gated recurrent unit(GRU) was adopted to model complex characteristics of the SMA actuators. GRU is one of the machine learning technologies, which is evolved from the recurrent neural network. Modeling of SMA actuators are not easy due to their characteristics such as nonlinearity, hysteretic behavior, effects of temperature and stress. They are often responsible for control difficulties such as inaccuracy and instability. In this study, GRU is used to estimate the relation among the applied voltage(duty ratio), electrical-resistance, tension, displacement and room temperature. Two SMA models were created by GRU: the sensing model and the inverse model. Both models were trained with the original dataset obtained experimentally. A control framework for the sensorless tension control including the two SMA models was proposed. The sensing model which estimates the tension and displacement from the applied voltage, electrical-resistance and room temperature substituted for sensors. The inverse model which estimates the applied voltage canceled or reduced the effects of the hysteresis and nonlinearity as the feedforward controller. The results of experiments with the proposed control framework show that the actual tensions closely followed the target tensions without sensors.
Active noise control (ANC) is a technique used to reduce environmental noise in noisy places such as office or aircraft cabin. ANC reduces the overall input signal even when it has necessary information such as conversation as well as noise. In other words, conventional ANC has the disadvantage of reducing the required sound. On the other hand, there are scenes where conversation is desired even in a noisy environment. However, since the entire input signal is reduced, it cannot be solved even by using conventional ANC. We propose speech separation ANC system which separate announce and noise then control only noise component by ANC. To separate noise from the input signal, we focus on the signal separation method of spectral subtraction method and harmonic extraction method. These methods are simple and require a small computational load but have the disadvantage of leaving an estimated noise component. We also propose two signal separation methods which remain less noise component. In this paper, we verify the effectiveness of the proposed signal separation method while comparing it with the conventional signal separation method. Furthermore, the sound attenuation performance of the proposed method is confirmed by a control experiment in an anechoic room.
In the concept of the disposal of High Level radioactive Waste (HLW) in Japan, bentonite material such as the engineered barrier system is planned to backfill around over-pack in the disposal tunnel. For the barrier with sufficient performance, this bentonite density in this tunnel is very important factor to control the quality of the performance. In this study, the mixture of the technology between an actively heated system and a Distributed Temperature Sensing (DTS) using fiber-optic cable was applied with the aim to measure the density of the bentonite as this performance in order to take advantage of the character such as each density of bentonite under same water content has different heat conductivity. Specifically, to define the density of bentonite, the heat conductivity in an unsteady state continuously was measured. Moreover, we performed to measure a density using Optic-fiber cable to improve the measurement performance instead of the existing measurement sensor. 1) High resolution measuring a temperature system which has multi-point measurement 2) The usage of reference box which have some fixed density of bentonite in the container beforehand and connect them on the measurement same line of fiber-optic cable. Before the In-situ performance, we conducted this system at our laboratory in order to check the handling of a measurement procedure and improve the evaluation method about the temperature data.
This paper describes vibration characteristics of a cantilevered flexible sheet under the periodic aerodynamic excitation. In the experiment, movable plates(exciter) are set at the upstream side from the sheet in a wind-tunnel. Moreover, a theoretical model for calculation of a frequency response (amplitude ratio between the movable plate and sheet) subjected to aerodynamic excitation by the movable plate is developed. Fluid force acting on the sheet surface is calculated by the Doublet-point Method based on the unsteady lifting surface theory. Finally, the local work done by the fluid force acting on the sheet surface under aerodynamic excitation is determined theoretically and the region in which the exciting fluid force acts is clarified.
Soft actuators are attracting attention as safe driving sources suitable for robots coexisting in human living environment. As one of the promising actuators, a fishing line artificial muscle has been proposed. It is manufactured by twisting nylon fiber into coil shape. It expands and contracts in response to temperature change. By using conductive nylon fiber as a material or winding a nichrome wire, it is possible to drive electrically by Joule heating. The actuator is able to control by simple driving circuit and feedback control method; however, a squared nonlinearity due to Joule's law exists in response characteristics. In this research, we apply a linearizing compensation by PWM drive and simple feedback control with unti-windup method. The proposed method is investigated through experiments.
In this study, we applied a path control method using nearest-point search in a ball-and-plate device and performed an experimental verification with an actual machine. In this method, a path is input to a computer as a sequence of points with high affinity and path control is performed by separating the path in the direction of movement and in the direction of path error, based on the nearest point obtained. In conventional path control, the target point is assumed to be given in advance in the direction of movement. However, depending on the target application, the path response may be disturbed when there are multiple nearest points or when a large disturbance is applied. Therefore, in this paper, we propose a method for determining the target point by using the relation between the nearest point and the target point in the direction of movement so that it is suitable for the path control of the ball-and-plate device. We applied this method to a new ball-and-plate device that moves the plate stably using four synchronously controlled linear motors. The effectiveness of the method was verified through an experiment in which various disturbances were applied.
Many researches have investigated the gait generations and adaptation mechanisms of animals. It is well-known that a decerebrate cat can change and adapt its gait on split-belt (velocity of left-fore belt is faster than others) treadmill. In our previous study, we showed that the leg controller as a model of CPG (Central Pattern Generator) using leg loading/unloading for the leg phase transition can integrate rhythmic motion control and posture control using a quadruped robot Kotetsu. We intend to make a physical model of split-belt adaptation of a decerebrate cat at cerebellum through experiments employing this CPG model. For such experiments, we need to construct the system keeping legs of the robot touching down on each belt. In this study, we develop the system measuring the position and orientation of the robot in the horizontal plane using a camera above the treadmill. The visual navigation system adjusts the trajectory of joints using such visual information. But adjustment of hip roll joint angle in the swing phase might conflict with touch down angle control for stable posture in the roll plane, and make the robot fall down. On the other hand, adjustment of hip roll joint angle in the stance phase is not concerned with touch angle control, does not disturb the posture in the roll plane, and makes the robot keep walking on the split-belt treadmill. As the results of experiments, we confirmed those characteristics, and realized the split-belt walking of the robot. Spec. and movies of Kotetsu can be seen at http://www.robotlocomotion.kit.ac.jp/kotetsu/index-j.html.
The in-situ blocked force approach is suitable for estimating noise radiation from a mechanical system by component tests of its active subsystem because blocked force is a specific characteristic of the active subsystem and independent from the passive subsystem or supporting structure of the component test bench for the active subsystem. However, it is reported that the in-situ blocked force approach is a methodology for estimating structure borne noise and cannot be applied to airborne noise. In this research it was found that the in-situ blocked force approach can be approximately applied to airborne noise in eigenfrequencies of the mechanical system. Therefore it was proposed to employ the in-situ blocked force approach to estimate airborne noise as an approximate method at eigenfrequencies of the mechanical system in the previous paper. In this paper the proposed estimation method was verified by numerical analysis of noise radiation from a cantilever rectangular plate. Eigenfrequencies and vibration responses of the cantilever rectangular plate were obtained by FEM and sound pressures at an observed point were calculated on the assumption that point sound sources are distributed at the all FE nodes on the whole plate surface. Furthermore, a means based on discarding small singular values in the inverse matrix method was proposed in order to reduce the estimation error which is increased in the peak frequencies of blocked forces.
This study provides a theoretical investigation on shear stress distribution inside a steel roller with a nanostructured surface, manufactured by the severe plastic deformation and induction heating processes, under a rolling contact fatigue testing, mainly focusing the effect of friction coefficient on a shear stress range and mean stress. By using the finite element method, the stress profiles were estimated at several depths from the roller surface, and it was observed at all the depths considered that the reduction in the friction between two sliding rollers can reduce the mean shear stress which probably affects the fatigue life under the rolling contact. This result may support the hypothesis that the friction reduction induced by grain refinement prolongs the rolling-contact fatigue life of the steel material.
In numerical analyses based on unstructured meshes represented by the finite element method, quadrilateral and hexa-hedral meshes are used for a two-dimensional and a three-dimensional analyses, respectively, from the viewpoint of calculation accuracy and computation time. However, a method for automatically generating quadrilateral and hexahedral meshes has not been established thus far; in addition, a considerable amount of effort is required to perform manual mesh modifications. Mesh generation based on the frame field method is an effective technique to extract high quality quadrilateral and hexahedral meshes through the optimization of the posture of a frame with rotational symmetry. This method needs to solve a mixed-integer programming (MIP) problem while extracting the quadrilateral and hexahedral mesh using integer grid maps. When solving an MIP using a greedy method, solving a simultaneous equation is required approximately O(M) times, where M is the number of integer constraints. In this study, we propose a method to obtain a quadrilateral mesh by solving a simultaneous equation approximately O(1) times. In this method, the frame field is calculated using finite element discretization, and the finite element mesh is appropriately remeshed to be aligned with the integer grid resulting from the frame field optimization. The proposed method can reduce the amount of computation required to obtain integer grid maps for mesh extraction, without impairing the mesh quality. The proposed method is evaluated with respect to by mesh quality using the aspect ratio and the scaled Jacobian. Numerical examples demonstrate that the mesh quality is comparable to or better than that produced by conventional methods and manual procedures.
In the 21st century, as it is important to produce products with care for protecting the earth, a producer must be careful to conserve energy, save resources and reduce waste which pollutes environment. On the other hand, in case of a machine tool, much quantity of lubricating oil was used for smooth drive, electrical energy of forced cooling was used for high accuracy and much cutting oil was also used for lubrication and cooling. This is large problem for protecting the earth. Therefore the nozzle with the optimum specification was developed and evaluated for an environmentally-friendly. The calculation model for heat transfer coefficient regarding the mist of the strong alkaline water was firstly estimated. Then the nozzle with the optimum specification was developed by using the calculation model. The cooling properties of the forced cooling using the nozzle with the optimum specification was finally investigated and evaluated in several experiments. It is concluded from the results that; (1) Mist of strong alkaline water was very effective for forced cooling, (2) The optimum condition regarding the mist of strong alkaline water for forced cooling was cleared, (3) The nozzle with the optimum specification has very high heat transfer coefficient and is effective for long tool life.
Rzeppa constant velocity joints are mainly used as outboard joints in the drive-shafts of front wheel drive vehicles. This type of joint transmits driving torque through balls provided in the joint. The ball force that transmits this torque fluctuates periodically when a joint angle exists between the two transmitting axes. Ball force fluctuation must be reduced since ball forces affect joint performance aspects such as strength and durability. This paper proposes a mechanism and method for reducing ball force fluctuation. The reduction mechanism for ball force fluctuation is based on the theory that ball forces are balanced with the secondary moment related to the driving torque and joint angle, which suggests that increasing the percentage of the axial ball force content of the secondary moment might be an effective method of reducing fluctuation. To validate this proposed mechanism, a detailed analysis model of a Rzeppa joint was constructed based on a multibody dynamics approach, including the contact and friction forces acting on multiple parts of the joint. Computational results using this model showed that the proposed reduction mechanism is valid. This reduction mechanism was used to formulate a method of reducing ball force fluctuation based on a specific ball groove arrangement. Finally, the effectiveness of the reduction method was validated by computational results using a detailed analysis model.
The Japan Electric Association code, JEAC 4206-2016 specifies a procedure for assessment of a reactor pressure vessel integrity against pressurized thermal shock (PTS) events which postulates a semi-elliptical flaw (10 mm in depth x 60 mm in length) beneath the cladding. JEAC 4206-2016 prescribes a simple method for calculating stress intensity factor of the flaw, taking into account the effect of yielding of cladding which has been originally developed in France. However, since this method is a rather conservative in comparison with that obtained by elastic-plastic finite element analysis, JEAC 4206-2016 also allows to calculate the stress intensity factor by converting the J-integral obtained from elastic-plastic finite element analysis. Since the J-integral is only defined for a linear or nonlinear elastic behavior material, the J-integral cannot be determined for an elastic-plastic behavior material during the unloading phase of PTS events. In addition, the residual stress and plastic strain induced by clad welding and joint welding needs to be considered in calculating the stress intensity factor. In this paper, the calculation procedure for a stress intensity factor of a fully circumferential flaw beneath the cladding during PTS events using finite element analysis is investigated.
Manufacturing industries have tended towards high-mix low-volume production in recent years. As a result, there is always strong impetus to shorten the manufacturing lead time of mechanical products. Computer aided process planning (CAPP) has been studied to automate process planning in the field of machining. It has been noted that feature recognition is considered as a key technology to develop CAPP systems. In previous works, machining features have been usually recognized based on geometric information such as surface, volume, and so on. However, those machining features never satisfy designer’s intents due to the recognition without dealing with design information such as geometric tolerances and surface roughness. Therefore, in this study, machining primitives having common design information are combined into one machining primitive and the combined machining primitive inherits the design information from the target shape. Then, the same machining sequence is allocated to some machining primitives which have the same design information. Moreover, machining feature is recognized for plural machining primitives by assuming as one generated surface when generated surfaces consist of the same plane or cylinder. From conducted case studies, it is confirmed that the developed CAPP system enables to recognize machining features by referring design information such as geometric tolerances and surface roughness.
By attaching a cycle unit to a general-purpose wheelchair, the authors have developed wheelchair cycles that can provide various riding positions. Many reports have described studies of high workloads for athletes examining the relation between a bicycle riding position and kinetics such as joint moments. Nevertheless, few reports describe low workloads in studies targeting people with weak muscles or people with lower limb disability. This study was conducted to elucidate the joint moment for a cycling motion under a low workload with wheelchair cycles having various heights of bottom brackets (BBs), which are defined as the crankshaft center of a cycle. Lower limb trajectory and pedaling force shown by five healthy men were measured when they used wheelchair cycles with BB heights of 260, 500, and 580 mm. Pedaling velocity of 50 rpm was assumed for a 10 W workload. A pedal type force sensor was developed to obtain a change in pedal reaction force during cycling. The joint moment was obtained from the inverse dynamics procedure. For evaluation, to compare waveform characteristics for each BB height, the flexor and extensor moments of the lower limb (hip, knee, ankle) that most contribute to the pedaling exercise were investigated using the average value and amplitude of the joint moment. For lower BB height, low muscle strength is suitable for initial training. For higher BB height, aggressive muscle strength is suitable for training. Particularly for people with weak muscles, a BB height lower than the seat is desirable for rehabilitation.