Pure Ti and Ti-6Al-4V alloy show high specific strength, excellent fatigue strength and good corrosion resistance; however, their poor wear resistance limits potentially wider application. To improve the wear resistance of pure Ti and Ti-6Al-4V alloy, they were reinforced with two types of titanium carbonitrides (TiC1-xNx), TiC0.3N0.7 (N rich) and TiC0.7N0.3 (C rich). The composites with 2.5, 5.0, 7.5 and 10.0 vol.% reinforcement were fabricated by spark plasma sintering (SPS). Dry wear tests of the composites were performed against a 10 mm-diameter high-carbon-chromium steel ball under 23 N normal load, at a sliding speed of 100 mm/s and a sliding distance of 500 m using a ball-on-disk configuration. The pure Ti and Ti-6Al-4V alloy matrix composites with TiC0.3N0.7 showed good wear resistance compared to the composites with TiC0.7N0.3. For the TiC0.3N0.7 reinforcement, the pure Ti matrix composite showed better wear resistance than the Ti-6Al-4V alloy matrix composite. The specific wear rate of the pure Ti matrix composite containing 10 vol.% TiC0.3N0.7 was almost zero. The amount of nitrogen diffused into the titanium matrix was higher than that of carbon diffused into the matrix. The Vickers hardnesses of the composites with TiC0.3N0.7 were higher than those of the composites with TiC0.7N0.3, due to the solid solution strengthening of the nitrogen in the Ti matrix. Therefore, the dry sliding wear characteristics of the titanium matrix composites depended on the amount of nitrogen diffused into the Ti matrix.
Carbon fiber (CF) reinforced polyether ether ketone (PEEK) laminates are applied to the members of transportation structures exposed to severe conditions, because carbon fibers and PEEK have excellent heat-resistant and chemical stability. Therefore, it is important to ensure the long-term reliability of CF/PEEK laminates and evaluate the propagation of transverse cracks, which are generally the initial damage incurred by multidirectional laminates under fatigue loading. This study evaluated the detailed mechanism of transverse crack propagation toward the thickness direction in CF/PEEK quasi-isotropic laminates under fatigue loading. The transverse crack growth was observed using the replica method, and the energy release rate associated with the transverse crack propagation toward the thickness direction was calculated using a three-dimensional virtual crack closure-integral method. Thus, it was found that the transverse crack propagated in a stable manner until it passed through the 90° layer toward the thickness direction. Additionally, it was found that the crack growth rate increased in the range wherein the crack length was short, and maintained an approximately constant growth rate in the middle stage of propagation. According to Paris’ law, when the crack depth was relatively shallow, the experimental results are approximately consistent with the analytical evaluation results for the energy release rate associated with the transverse crack propagation toward the thickness direction. Finally, it is also concluded that the high ductility of the PEEK resin and good fiber/matrix interfacial property of the CF/PEEK laminates are important influencing factors for the stable and characteristic crack propagation observed in the experiment.
Functionally graded (FG) rods with three layers in the radial direction were fabricated by a spark plasma extrusion (SPE) process. The FG rods consisted of a pure Ti compact in the center, a 15TiB/Ti composite layer in the middle, and a 25TiC/Ti composite layer on the outside. Extrusion was carried out at a temperature of 1000 °C, at a pressure of 50 MPa with extrusion ratios (cross-sectional area before extrusion/cross-sectional area after extrusion) of 2.3 (from di = 15 mm to do = 10 mm) and 3.5 (from di = 15 mm to do = 8 mm). An FG rod with a length of over 40 mm and a high relative density could be obtained by the SPE process. The cross-sectional area ratio of the pure Ti layer after extrusion significantly decreased compared to the 15TiB/Ti and 25TiC/Ti composite layers due to the higher ductility of the pure Ti. On the contrary, the cross-sectional area ratio of the 25TiC/Ti composite layer increased after the extrusion, because the 25TiC/Ti composite layer had quite low ductility. Due to the sufficient material flow during the extrusion, the TiC particles in the 25TiC/Ti composite layer of the FG rod were uniformly distributed along the extrusion direction. Furthermore, during the SPE process, the TiB clusters in the TiB/Ti composite layer were transformed into TiB whiskers, and the TiB whiskers were mainly oriented parallel to the extrusion direction. The tensile strength of the TiB/Ti composite layer fabricated by the SPE process improved due to the transformation of the TiB whiskers and their orientation along the extrusion direction.
In this paper, the fracture problem of a functionally graded piezoelectric material strip (FGPM strip) containing a crack perpendicular to the interface between the FGPM strip and a homogeneous layer under an electric load is considered. Material properties are assumed to be exponentially dependent on the distance from the interface. The superposition technique is used to solve the governing equations. The stresses induced by the electric load in the un-cracked laminate are calculated, and the obtained normal stress is used as the crack surface tractions with opposite sign to formulate the mixed boundary value problem. By using the Fourier transforms, the electro-mechanical fracture problem is reduced to a singular integral equation, which is solved numerically. The stress intensity factors of the internal crack and the edge crack are computed and presented for the various values of the nonhomogeneous and geometric parameters.
Damage behaviors in cross-ply, [0/904]s cloth Carbon Fiber Reinforced Plastic (CFRP) laminates with different curing temperatures have been observed as a function of applied stress. Coupons manufactured by Vacuum-assisted Resin Transfer Molding (VaRTM) method with resin cured at room temperature and at 80-degree Celsius (post-curing temperature) were monotonically and cyclically loaded. Residual properties which are Young’s modulus etc. together with damage accumulation, have been recorded as a function of applied stress. DCB tests have been performed for matrix fractography purpose in this study. Significant differences can be observed in the mechanical properties, damage initiation, and progression in the laminates when the post-curing procedure is implemented. For room temperature cured laminates, matrix cracks initiated arbitrarily on the edge of the coupon with the influence of voids and other internal structures in the cloth laminates such as wefts, etc. without completely propagating in the thickness nor the width direction of the laminates. However, for post-cured laminates, cracks started at the edges and propagated through the thickness and width direction of the laminates. Matrix fractography results show that laminates cured at room temperature exhibit more plastic deformation which showed fewer brittle properties compared to laminates cured at higher temperatures as the matrix behaved in a more brittle fashion, which enhanced the tensile microcracking.
In recent years, studies on the fundamental principle of thrust vectoring using jets have been conducted to realize next-generation aircraft applications. Various methods for vector control of jet flow have been proposed, such as methods that achieve control via steady, continuous jets under the Coanda effect, steady suction flows near the Coanda surface, and synthetic jets from a neighbor slot as secondary jets. However, there are no studies on the flow direction control of jets using the secondary synthetic Coanda jet. In this study, the influence of synthetic jets near a circular cylinder on the flow characteristics of a primary jet was experimentally investigated. The main results obtained in the study were that the direction of the primary jet flow can be controlled using the secondary synthetic jet, and the degree of jet deflection depends on the frequency of the velocity oscillation for the secondary synthetic jet under an identical momentum ratio. Furthermore, when using the synthetic jet as the secondary flow, a controllable region larger than that obtained when using a steady and continuous injection or suction flow is expected. This is because secondary flow is generated using the ratio of the momentum between the primary jet and the secondary flow at the slot exit in conjunction with the dimensionless frequency of the synthetic jet based on the velocity of the primary flow at the slot exit.
It is important for the improvement of the performance and durability of solid oxide fuel cells (SOFCs) to clarify gas transfer phenomena in their porous electrodes. This study proposes two methods, an oxygen sensor method and an electrochemical impedance method, for the in-situ measurement of the effective binary diffusivity of an H2 – H2O system in the anode of an anode-supported SOFC, which is composed of a YSZ (Y2O3 stabilized ZrO2) electrolyte and an Ni-YSZ anode. By these methods, the effective binary diffusivity is determined based on Fick’s law by using hydrogen gas concentrations at two positions, the inside and surface of the anode. When the oxygen sensor method is used, a local hydrogen gas concentration in the anode is determined with a sensor made of a platinum wire coated with YSZ. On the other hand, when the electrochemical impedance method is used, a mean hydrogen gas concentration in the anode adjoining the electrolyte is determined by analyzing the measured electrochemical impedance spectra. The effective binary diffusivities determined by these methods are almost the same under the same conditions. And also they are in agreement with effective binary diffusivities calculated using the porosity and volume-averaged pore diameter obtained by analyzing the anode cross-section in an SEM image. Therefore, it is judged that both of these proposed methods enable the in-situ measurement of the hydrogen gas diffusivities in the anode when the SOFC is in operation. Furthermore, it is shown that nitrogen gas, including fuel gas, may work to inhibit the transfer of hydrogen gas.
There are three criteria typically used in the design of dynamic vibration absorbers (DVAs): H∞ optimization, H2 optimization, and stability maximization. Recently, interest has shifted to the optimization of multi-mass DVAs, but in fact, in even the most basic single-mass DVA, the effect of primary system damping on the optimal solution is still not fully understood with respect to the H∞ criterion. The author has recently reported an exact H∞-optimal solution for a series-type double-mass DVA attached to a damped primary system. This article presents the application of this H∞ optimization method developed for a double-mass DVA to the optimization of a single-mass DVA. In the H∞ optimization of the mobility transfer function, a highly accurate numerical solution was successfully obtained by solving a single sixth-order algebraic equation. In the case of the optimization of the compliance and accelerance transfer functions, it is shown that a highly accurate numerical solution can be obtained by solving ternary systems of simultaneous algebraic equations. It should be noted that the equations presented in this paper can be factorized into simpler equations when there is no damping in the primary system. It is also demonstrated herein that the factorized expressions yield the previously published H∞-optimal solutions.
Oil dampers are indispensable devices for vibration suppression, but their nonlinear behavior makes it difficult to theoretically determine their damping characteristics. For that reason, the damping coefficient for oil dampers has conventionally been handled by introducing an experimentally determined constant into theoretical equations. In other words, the characterization of oil dampers has ultimately relied on experimentation. Fortunately, if the damping oil is a Newtonian fluid, the Navier–Stokes equations are able to accurately describe its movement. In our previous study, the Navier–Stokes equations were solved using the finite difference method and the damping coefficient was accurately calculated for an annular-channel-type oil damper. In this paper, we report the damping and added mass characteristics of the commonly used oil dampers, the piston-hole-type and bypass-pipe-type dampers, obtained using the finite difference method as in the previous report. The most basic design formula indicates that the damping coefficients for these dampers are the same when the flow paths are equal in length; however, it was demonstrated in this study that the damping characteristics of these dampers differ greatly depending on the shape of the convective vortex generated in the cylinder. The immersed boundary method was used in the present numerical analysis because the boundary of the fluid to be analyzed is surrounded by fixed and moving walls.
In this paper, a new model of magnetically levitated (Maglev) vertical axis wind turbines (VAWTs) is presented for power generation purposes. The rotor is suspended by two permanent magnet attractive type passive magnetic bearings and one control coil; it is possible to rotate the rotor without any mechanical contact. The proposed model solves the most common problems which are found on the other Maglev VAWTs such as reducing the power consumption during the levitation to zero amperes by the zero-power control method and reducing rotation loss during rotation. In addition, the model has some main advantages consisting in the ability to avoid the resonance at the critical speed and increase the maximum rotation speed by changing the air gap between the rotor and passive magnetic bearings to adjust the radial stiffness of the rotor. The design of the passive magnetic bearings is investigated by the finite element analysis, and the optimum shape is discussed. The results of levitation tests are presented for the model to show the effectiveness of levitation current reduction and the adjustment of radial stiffness. The results of rotation tests show that the resonance can be avoided by changing the radial stiffness which also makes it possible to rotate the rotor over the critical speed. Moreover, the results of free-run tests show that the rotation loss of the proposed Maglev system is quite low.
Currently, cranes are used as transportation equipment in various industries such as construction, distribution and manufacturing. In the construction field, materials and products suspended from a crane hook are called suspended loads. Basically, the crane hook is a free rotation mechanism and lacks a rotating power function, so the suspended load under the crane hook rotates when exposed to strong wind and it remains extremely dangerous when working at high place. Accordingly, in this study, we have developed the suspended -load rotation-control device. Then, we focused on the characteristics of passive control that generate a large torque with respect to a short-term disturbance around the vertical axis of a uniaxial mechanical gyroscope. From this characteristics, a mechanical gyroscope is installed in a part of the device, and the suspended load is rotated by a motor-driven device hook. Then, the reaction torque generated when the suspended load is rotating is surpressed, and the suspended load is stopped at an arbitrary position. Actually, this device is applied to carry in materials and products at various sites. However, since several problems were found in the operation of this device, this study examined how to improve them. To shorten the offset time of the flywheel tilt angle, we examined two items. The first aspect of improving this device involves the study of a gyroscopic damper in which springs are added to the gimbal side of the mechanical gyroscope. The second item of the improvement method of this device involves controlling the posture using control by wind force. This paper introduces ways that improve the mechanical gyroscope offset function of this device. Next, to confirm the effectiveness of the gyroscopic damper and control by wind force are verified and the contents of the physical model created based on the verification test are also described.
In this study, unsteady aerodynamic forces induced by forced pitch and heave motions are measured and formulated to the unsteady aerodynamic coefficients by utilizing the 1/4-scale nearly actual vehicle model with wheels and wheel-houses and a system without unnecessary stings exposed to the flow. The unsteady aerodynamic lift forces are measured as input forces at front and rear axles in vehicle suspensions for each, and are expressed as the aerodynamic inerter, aerodynamic damping and aerodynamic spring coefficients which are equivalent in vehicle suspension property. These studies are conducted with less than 1.4 × 106 of Reynolds number and with less than 0.2 of non-dimensional frequency. From the results, it is observed the effect of front aerodynamic forces in proportion to motion acceleration which works as an inerter can be ignored in both of pitch and heave motion, but the effect of rear aerodynamic forces as an inerter must be considered in both motion, and the first-order lag must be considered additionally about the rear only in heave motion. Furthermore, the large difference of unsteady aerodynamic characteristics is obtained while comparing in different vehicle body shapes which are without and with a protrusion on the roof. Especially, the difference of unsteady aerodynamic forces of rear in pitch motion is much large. In the case without the protrusion, the aerodynamic inerter which restrains pitch motion is occurred. On the other hand, in the case with the protrusion, the effect of aerodynamic inerter decreases and other aerodynamic forces promotes pitch motion in opposite. The phenomenon of this difference is closely related to the behavior of flow velocities at near surface around the model. From the above, it is confirmed that the large difference of unsteady aerodynamic forces induced by motions occurs in the detail difference of body shapes at a nearly actual vehicle model, and can be expressed quantitatively as the difference of aerodynamic response.