In the framework of mechanics of plasticity plastic instability has been taken up as the onset of ductile fracture. Hill established a sufficient criterion for uniqueness of boundary-value problem set by given velocities on a part of surface of a body and given nominal traction-rates on the remainder without any restriction placed on changes on geometry. Hill also obtained eigenstates intrinsic to the material and holding true at the collapse stages of uniqueness. The eigenstates demand work done in second order to vanish. We adopted the eigenstates as the concept of instability, and discussed here the onset of plastic instability occurred under simple and bi-axial tensions in uni-axially anisotropic (r value) plastic materials which are deduced from Hill's formulation. The anisotropy results in high formability with increasing of r value in many cases except for roughly negative strain rate ratio ε2 / ε1 < 0 . Superimposed pressure also gives high formability. We also showed the second order work done with respect to coordinate components at plastic instability.
This paper presents a re-formulation of the extended subloading surface model within the ‘unconventional plasticity’ concept applicable to cyclic loadings. The small strain theory is adopted in the model formulation. The rate-independent von Mises plasticity with nonlinear isotropic and kinematic combined hardening is adopted as a specific prototype model. A fully-implicit stress calculation algorithm based on the return-mapping scheme for the proposed anisotropic elasto-plastic constitutive model is also developed. In addition to the usual additive decomposition of the small strain tensor into elastic and plastic parts, we primarily make a kinematic assumption in which the plastic strain tensor is further additively decomposed into an energetic and dissipative parts. This idea is a small strain counterpart of the one recently adopted in finite strain models with nonlinear kinematic hardening based on the dual multiplicative decompositions of the deformation gradient tensors. The energetic part of the plastic strain is related to the back-stress for kinematic hardening via a hyperelastic-like constitutive equation. This enables the incorporation of Armstrong–Frederick nonlinear kinematic hardening into the model without using a rate-type evolution law for the back-stress. Based on a similar idea, we introduce another additive decomposition of the plastic strain, and thereby a nonlinear evolution for the elastic-core tensor, i.e. a key internal variable in the extended subloading surface model, which stands for a stress state where the material exhibits most elastic responses, can be introduced in a reasonable way. Fundamental property of the proposed model as well as the accuracy assessment of the developed numerical algorithm is demonstrated by numerical examples. A particular attention is focused on the accuracy of stress calculation in unloading and reverse-loading processes during cyclic deformation. An issue on convergence property in Newton-type iteration for the return-mapping scheme is also discussed, and an effective initial value for iteration is proposed.
To improve safety during automobile collisions, it is necessary to examine not only accident damage by the first collisions but also motion after the collision. However, it is difficult to specify the factor which affects the collision motion of the automobiles with various structures and mechanisms, though the theoretical and experimental analyses have been reported. In this study, in order to clarify factors which affect the automobile motion after side collisions, as the first step, the motion evaluation of the automobile subjected to side collision at front part was investigated by carrying out model collision tests, and fundamental theoretical analyses. Trajectory of automobile's center of gravity after the model collision test showed good agreement with the theoretical analysis result. In the future, influential factors are gradually considered in motion analysis by the fundamental theory and experimental approach by the model collision test used in this study, and the effect of their factors on the reconstruction of the collision accident is quantitatively clarified.
Fracture strength of cracked pipes made of moderate toughness materials is derived using J-integral value, which represents the driving force for fracture, and J-R curve, which corresponds to the material strength. However, in practical applications, it is not easy to obtain the J-integral value and J-R curve for the material of interest. Then, in the JSME Rules on Fitness-for-Service for Nuclear Power Plants (Codes for Nuclear Power Generation Facilities), the fracture strength is derived using the limit load divided by the Z-factor, which is given by equations in the code. Although Z-factor is largely influenced by crack depth, the current Z-factor equations do not include the effect of crack depth. Recently, new Z-factor equations, which took the effect of crack depth into account, were proposed. In this report, the validation of the proposed Z-factor equations was examined through a benchmark analysis for sample cases. The analyzed model was pipes with an axial or circumferential surface crack. The fracture stress due to ductile instability was calculated for an internal pressure or a bending load for various pipe and crack geometries. The analysis results derived by four organizations showed good agreement with the proposed equations and did not exhibit significant scattering. However, the new Z-factor equations were not conservative for all cases because the equations were derived by best-fit regressions. Then, in this report, revision were made on the new Z-factor equations so that the equations predict conservative fracture strength of cracked pipe of various geometries.
This study investigates the aerodynamics of an airfoil which passes close to an air-water interface with heaving motions by means of numerical simulation. Simulations are performed by solving the Navier-Stokes equation on a curvilinear coordinate system whose axes fit the moving airfoil surface in contrast to the conventional approaches which neglect the air viscosity. The air-water interface is captured by a CIP method. We show the crucial importance of taking the air viscosity into account for the successful prediction of the airfoil aerodynamics in heaving motions by demonstrating the observation of vortex separations near the leading edge of a NACA0012 airfoil at the Reynolds numbers of 50000 and 66138 based on the viscosity and the density of air and the translational velocity of the airfoil. It is found in this study that the existence of the water surface has a significant impact on the lift force on the heaving NACA0012 airfoil and the deviation of the lift coefficient from the one measured in the simulation conducted in the open space depends not only on the clearance between the airfoil and the water surface but on the mean angle of attack and the phase of the heaving. When the airfoil moves close to the surface, the surface effect on the airfoil-aerodynamics is emphasized due to the squeezed-film damping and the interaction of the separated vortices and the air-water interface. The importance of analyzing the fluid motion of both air and water phases is illustrated by showing that the kinetic energy of the moving airfoil transferred through the the air-water interface is rather significant.
Processes of the air entrapment in microstructures fabricated on walls of rectangular microchannels were visualized by a high-speed camera. Effects of the geometry of the microstructures on the formation and the shape of the liquid-gas interface in the microstructures were investigated with four channels having the same dimensions but different microstructure geometries at Re = 1. The microchannels were made of stainless steel and acrylic, and the microstructures were hydrophobized by triazinethiol. Water-ethanol mixtures with different mixing rate (ranged from 100:0 to 0:100) were employed as the test liquids, thereby effects of the wettability on the liquid-gas interface formation process was able to be investigated as well. Consequently, the following four types of the interface behaviors were observed: (a) complete air entrapment with concave liquid-gas interfaces in the microstructures, (b) almost entire part of the microstructures are filled with air with convex liquid-gas interfaces, (c) whole wall is wetted, while a little portion of air is left in the microstructures (the air phase is surrounded by the liquid phase), and (d) the microstructures are completely filled with the liquid phase. Type (a) was achieved only when the advancing contact angle was larger than the angle of the final shape of the liquid-gas interfaces, whereas Type (b), Type (c), and Type (d) showed dependencies on both the geometry of the microstructures and the wettability. The results will qualitatively help a strategy for the fabrication of the microstructures to obtain more proper shape of the liquid-gas interface for maximizing the slip length and the resulting drag reduction effect in microchannels.
Since the great east Japan earthquake in 2011, renewable energy is turned into importance. Hydro power is one of most important energies because it is not affected by weather condition and possible to generate steady quantity electric power, so it could be base load power. These days low head hydro power generation is going to increase, because it is easy to be set irrigation channel and agricultural waterway. We have developed water turbines appropriately for low head open channels to effectively utilize the hydro power energy. To improve the performance of the turbine, it is necessary to determine the free surface flow patterns around the turbine. We selected the undershot cross-flow water turbines which could apply to various sizes of channel and flow rate. Because we removed the turbine casing and guide vane, free surface flow patterns of the undershot cross-flow water turbine are very complex. We have researched free surface flow patterns around the turbines using both experiment and numerical analysis. We modified the apparatus system, and could measure mechanical friction loss of bearing. We introduced more precise computational grid of numerical analysis. So it was possible to specify more precise flow patterns near the runner. Time-averaged velocity distribution at inner or outer circumference of runner was almost consistent. As rotational speed increased, volume of cross-flow decreased and that of reversal flow increased. In generating torque and power of turbine, the most significant kind of flow was second stage cross-flow, and the most dominant component of flow was angular momentum. We estimated the torque and power of the turbine based on moment-of-momentum equation, and these results were consistent well with those of calculation.
The roughness sublayer beneath a turbulent boundary layer has been investigated analytically and experimentally, and the effect has been discussed on the mean velocity profile throughout the layer. The rough surface consists of two-dimensional square roughness elements. The roughness height is proportional to streamwise distance. It is one of conditions of an equilibrium boundary layer proposed by Rotta J.C. The roughness pitch ratio is 4. The measurement within/outside the roughness sublayer was made using LDV and CTA, respectively. The Reynolds number based on the momentum thickness is 6000. The roughness Reynolds number is 149 and the roughness is in complete rough regime. The analytical solutions of streamwise mean velocity and Reynolds shear stress profiles were derived from the space averaged Reynolds equation in the cavity region between roughness elements and the mixing length model. The solutions were well consistent with the experimental results. By use of the solutions and experimental results, the center height of drag moment and the constant of the roughness function can be represented as a function of the roughness pitch ratio for the equilibrium boundary layer. Also, from the momentum integral equation, Coles's wake law, solution and experimental results, the wake parameter will be given as a function of the friction parameter and relative roughness height. Finally, the local skin friction coefficient will be formulated with a function of the roughness pitch ratio and relative roughness height.
Unstable fluid force may be induced by rotor blade eccentricity in turbo machinery such as steam turbines. To develop a prediction method for unstable fluid force in turbine blade rows, we calculated the fluid force by using computational fluid dynamics (CFD) analysis, and the following conclusions were obtained. In this study, the unstable fluid force acting on the hub of the blade row is 0.8 to 1.2 times as large as that acting on the blades. Therefore, the unstable fluid force acting on the hub is not negligible. We developed a prediction method for unstable fluid force that uses blade tip gap sensitivity to the driving torque on a concentric blade row. The calculation error for the unstable fluid force was less than 11% compared with the CFD analysis. The maximum pressure location of the circumferential distribution of the perturbation pressure on hub is similar to that on tip seal. And the radial distribution of the perturbation pressure in front of the rotor blade row is uniform. The rotor surface region in front of the rotor blade row is the same as the hub. Therefore, the three dimensional flow is less influence to the unstable fluid force acting on the hub. And the prediction method by Benckert for unstable fluid force on the seal was applied to the hub. The calculation error for the unstable fluid force was less than 16% compared with the CFD analysis. The total calculation error for the unstable fluid force acting on the blade row was less than 13% compared with the CFD analysis.
In recent years, more than 10 million tons of industrial wastes are discarded annually. Those wastes are mainly composed of plastic, glass and metals which are the materials massively used in automobiles, electric and electronic products. It is well known that industrial waste contain precious metals like gold and have a great value of reutilization. Therefore, technology to properly separate the waste by their types of subject is very important for recycling industry. In this study, we have developed a new separation method by use of acoustic levitation phenomenon in a standing wave field. Unlike the conventional methods such as centrifugal particle separation or magnetic separation, this method enables to sort subjects by their densities, without relying on other material properties including size, magnetism and weight. First described in this paper is a theoretical analysis of levitation force exerted on an object to derive its trajectory in a standing wave field. It is found that the motion of the object is governed by its density and the strength of acoustic field. Based on this finding, we developed a prototype of separation system with twin-transducers and a belt conveyer. As a result of test to separate a mixture of SiO2 and Fe particles, 62wt% SiO2 is captured at node side while 72wt% Fe is captured at anti-node side. Finally, the prototype is used to repeatedly separate the chipped waste of actual OA equipment. Its density was increased about 150%.
This paper presents a three-dimensional flutter analysis of a rectangular sheet in an axial fluid flow. The unsteady fluid force acting on the sheet surface is calculated using Doublet-point method based on the unsteady lifting surface theory. The equation of motion of the sheet coupled with the fluid flow is derived employing the finite element method. The characteristic roots are obtained from the flutter determinant, and the stability of the system is examined with changing flow velocity. The flutter characteristics are clarified comparing the analytical results with wind-tunnel experiments. Lastly, the local work done by the unsteady fluid force on the sheet surface is shown, and the flutter mechanism is discussed.
Robotic technologies for supporting human activities have received much attention in recent years. The purpose of this study is to develop a wearable power assist device with a water-hydraulic artificial muscle actuator. This power assist device aims at helping wearer's elbow-joint movement. Since our power assist device is directly driven by tap water, it does not require pumps or compressors. Therefore, it needs much lower electric power than typical pneumatic and electric actuators. An artificial muscle actuator is used to actuate the power assist device because artificial muscle actuators are lightweight and highly flexible and would not hurt a person even in a collision, as this type of actuator consists of a flexible rubber tube surrounded by a braided-fiber shell. The control system of the power assist device comprises impedance control and amplification control. The impedance control is able to adjust the characteristics of dynamic interaction between the power assist device and a wearer, i.e. inertia, damping, and stiffness. The amplification control enables the power assist device to enhance torque exerted by a wearer. The power assist device developed in this study was worn by subjects and its effectiveness was examined based on surface electromyogram signals which reflect muscle activity. Experimental results demonstrated that our water-hydraulic power assist device leads to a decrease of muscle activity for all the subjects.
Karman vortex shedding occurs when the gas passes through a duct with a tube bank of the heat exchangers, such as gas heaters and boilers. Very high level sound in called “self-sustained tones” occurs due to the interference of the vortex and the sound field in the duct. In general, baffle plates are used to suppress the self-sustained tone. However, it is difficult to use them effectively, because insertion conditions have not been established yet. The purpose of this study is to clarify the effectiveness of the perforated plates for self-sustained tones. Then, perforated plates were installed in both sides of the duct to suppress the self-sustained tones. Because we thought that the perforated plate might have acoustic damping and resonance mode of the duct transverse direction to the flow might be suppressed by its damping effect, when the self-sustained tone occurred. Experiments were carried out to examine the suppression effect of the perforated plates installed. As a result, the suppression effect appeared in almost aperture ratio φ of perforated plate in case of φ > 0.01 (1%).
The dynamic buckling tests using cylindrical tubes with and without internal pellets were carried out to investigate the impact behavior. Various materials of cylindrical tubes and pellets were used to examine the buckling mode and the maximum loads at several impact velocities. In the case of low Young's modulus and low yield strength pellets, the influence of pellets was small because of the small load share of pellets, so the “W” shape of deformation shapes and the maximum impact loads were almost the same of those of empty tubes. On the other hand, the tubes with high Young's modulus and high yield strength pellets indicated different behaviors compared to the empty tubes because of the large load share of pellets. At low impact velocity, pellets with high yield strength caused the strengthening effect and increased the lateral stiffness for tubes. As a result, the pellets led to increase of impact load, decrease of deformation and change of buckling mode to the “S” shape. At high velocity, the strengthening effect of pellets made the tubes stiffer, but led to fracture by the constraint effect of pellets on plastic deformation. The deformation of tubes was compared to Euler's equation, and it was confirmed that the Euler's equation could be applied at the low impact velocity. However, it was not effective for the high velocity impact because of local deformation at the impact side. FEM analyses will be conducted to clarify the deformation shape, maximum load and the mechanism of fracture at high impact velocity as a further study.
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 reverse one, has a problem that the 1st natural frequency of the drive system may cause a backlash. For the problem, conventional methods with a notch filter were those to lower the gain of the 1st natural frequency. We employ a rate difference feedback method that feedbacks a signal in proportion to the difference between the forward direction motor velocity and the reverse one to the each motor torque, into the simulation and the experiment. Our method is able to improve the damping of the 1st natural frequency directly and suppress its vibration. We have shown through our analysis that the rate difference feedback gain acts to the damping factor of poles of the 1st natural frequency on the drive system. We evaluate our method in the non-linear simulation: 1) the vibration of the 1st natural frequency is remarkable where the motor velocity and the transmission torque is in the reverse phase, and backlash occurs in the transmission torque in a conventional method, 2) the vibration of the 1st natural frequency is suppressed where the vibration in the motor velocity and current is close to the same phase, and backlash does not occur in the transmission torque in our method. We have gotten the experimental results similar to the simulation.
This paper proposes a new shape optimization with robustness, and its application for disc brake squeal phenomena is shown. The disc brake squeal is known as self-excited vibration; the real and imaginary parts of the complex eigenvalue indicate the damping coefficient and natural angular frequency, respectively. The modes that have a negative damping coefficient cause disc brake squeal. For reducing brake squeal, non-parametric shape optimization has been applied for the modes that have a negative damping coefficient. However, in the non-parametric shape optimization, shape uncertainties of the brake system components are neglected. The uncertainties influence the robustness of the brake system for brake squeal. Therefore it is necessary to take into account the uncertainties on the non-parametric shape optimization to improve the performance of brake system with robustness. In this paper, component's natural frequencies are adopted as noise factor to express the influence of shape uncertainties. Since the shape uncertainties are non-parametric, it is difficult to measure and quantify the shape uncertainties in the actual design process. On the other hand, the component's natural frequencies are parametric and it is easier to measure and quantify the uncertainties than shape uncertainties. In this paper, a new non-parametric shape optimization with robustness which takes the component's shape as design variables (control factors) and the component's natural frequencies as noise factors is proposed. For a verification of the proposing robust shape optimization, a numerical example by using a simplified disc brake model is presented. For the result, it is shown that the standard derivation of damping coefficient monotonously decreases, satisfying the constraint for the mass of the brake pad at each iteration.
Vibration characteristics of a flying head slider in hard disk drives in proximity and asperity contact regimes attract much attention because head-disk spacing must be decreased to less than 1 nm in order to increase recording density. This study first elucidates head-disk interfacial (HDI) force as a function of static head spacing based on rough surface adhesion contact models and air-bearing force model. Then, selecting the most presumable surface force model which has a static unstable region at a thin lubricant thickness, microwaviness (MW)-excited vibrations of a single-degree-of-freedom slider model was simulated by the 4-th order Runge-Kutta method. It was found that the slider snaps-into a contact state from a proximity spacing state but the slider snaps-out to a flying state when the static head spacing is further decreased by increasing heater power. When MW amplitude is large, a drastically large spacing variation which contains various frequency components of less than 100 kHz appears in this unstable region. The spacing variation cannot be reduced to an allowable level even when the static unstable region disappears unless the minimum slider resonance is greater than about 100 kHz. It is discussed that these calculated results can explain the mechanisms of some experimental evidences reported in prior papers.
In a bathing environment, it is needed to evaluate an emotional effect quantitatively and continuously at stage of the product design for improving stress-relaxation effect. This study aimed to propose an index which can evaluate the comfort quantitatively and continuously on bathing. To search the physiological indices correlated to the comfortable feeling, we measured subjective evaluation of comfortable feeling in one-minute increments, with continuous measurement of physiological parameter before bathing, on bathing, after bathing. We analyzed the relationship between time-series data of the subjective evaluation and the physiological parameter. As a result, we proposed the evaluation index of comfortable feeling by using HF content obtained from spectral analysis of heart rate variability, and confirmed that the evaluation index can evaluate comfortable feeling quantitatively and continuously including the effect of personal preferences related to bathing.
In this study, we propose a shape optimization method of a frame structure for maximizing the elastic buckling load. The 1st buckling load factor is maximized under a volume constraint. The problem is formulated as a distribute parameter shape optimization problem, and the shape gradient function for this problem is theoretically derived using the Lagrange multiplier method, the adjoint variable method and the formulae of the material derivative. The derived shape gradient function is applied to the H1 gradient method for frame structures, a gradient method in the Hilbert space, where the optimal shape variation is calculated as the displacement field of the fictitious linear elastic of the frame structure. With the proposed method, the free-form, or arbitrarily formed frame structures with large scale design variables can be optimized without any shape parametrization. The problems of repeated eigenvalue and Euler buckling of each member are also considered and solved. The results show the validity of the proposed method to determine the optimal free-form of a frame structure for the elastic buckling design.
This paper describes a design method of the loading cam of the parallel shaft traction drive transmission which achieves high transmission efficiency. The geometrical profile of the cam which provides loading force in proportion to the transmitting force was determined with considering elastic deformation of components of the transmission. The loading force and transitional motion of the cam equipped on the prototype transmissions were measured and they agreed well calculations that shows the design method is proper. The required power of the ratio change actuator for the multi steps mechanism using the crank shaft was calculated. It was very small compering with transmitting power of the transmission that means effect on whole energy loss is small. Analysis on kinetic motion of the cam was executed by calculations and measurements have confirmed this system has potential which occurs self-excited vibration. Hydraulic circuit consisting of pistons and orifice is effective to avoid the vibration that was confirmed by calculations and measurements. Traction coefficient of the presented multi steps transmission decreases greatly at ratio change with large slip so that the transmission cannot execute power transmission. The shut off valve adding on the hydraulic circuit to fix transitional motion of the cam can transmit power to provide loading force with large slip at ratio change. Test result conducted the 2-speed transmission equipped with this mechanism achieves smooth and quick ratio change. This study shows the presented cam and its design method solve the most vital issue for traction drives which is how to provide suitable loading force.
Fretting wear in magnesium alloy AZ31 was investigated in order to understand the fundamental tribological properties in magnesium alloy. Ball on disc type fretting test was conducted, in which the cyclic tangential force was applied by rotating a gear pear with the weight. The ball specimen was made of SUJ2 bearing steel, and the disc specimen was made of magnesium alloy AZ31. Normal load was applied in the range between 1000 and 2000 N, and tangential force was 100 N. It is shown in the results that the contact surface was deformed plastically after the test under static condition, and the plastic deformation increases with time. It is also found that the contact surface after the fretting test shows that wear area was occurred at the edge of contact area. Chemical reaction film was formed on the wear area, and energy dispersive X-ray spectroscopy analysis results show that the film consists of magnesium and oxygen. Slip region at the edge of contact area increased with time, and the area depends on the tangential coefficient. The maximum depth of deformed dent in fretting test at 1000 N, was greater than that in the test under static condition, and the deformation depends on the tangential coefficient.
The objective of this study was to develop a motion analysis system to evaluate relations between the activation of the lower limb muscles, the pedal force and the movement of the lower limb during the pedaling motion. To confirm the effectiveness of the proposed analysis system, we analyzed the pedaling motion of nine cyclists to identify their pedaling skill. In the experiments, cyclists were instructed to perform their pedaling technique at two pedaling rates (80-90 rpm and 110-120 rpm). Surface electromyography (EMG) signals was recorded from tensor of latae (TFL), rectus femoris (RF), hamstrings (HAM) and gastrocnemius (GAS), and pedal force was measured by a power meter (Pioneer Corporation). Furthermore, the lower limb motion during the pedaling was measured using a 3D motion capture system to investigate the relations among measured data as mentioned above. The experimental results show that the proposed analysis system reveals the pedaling skill of cyclists and the relations between the EMG data, the pedal force and the movement during the pedaling motion. In this paper, firstly, the activation section of the lower limb muscles during the pedaling was determined quantitatively. Secondly, Tukey-Kramer test was conducted to determine whether there are significant differences (p < 0.05) between the pedaling effectiveness of the three groups (elite group, amateur group and beginner group). Finally, the pedaling skill of the cyclists was revealed based on the analysis results of the measurement experiments.