Mechanical Engineering Letters
Online ISSN : 2189-5236
ISSN-L : 2189-5236
Volume 4
Showing 1-22 articles out of 22 articles from the selected issue
  • Yasuhiro NISHIKAWA, Hiroaki HOBARA
    2018 Volume 4 Pages 17-00452
    Published: 2018
    Released: January 11, 2018

    Athletes with lower extremity amputations need to clearly understand the mechanical stiffness of running-specific prostheses to select the most suitable one. However, manufacturers do not show the detailed stiffness data, and currently, there is no standardized testing method available. In this study, load-deflection behavior and mechanical stiffness of carbon fiber composite prosthesis were evaluated under a static compressive load. Fifteen testing conditions were employed by changing the position and length of adapter jig. The results of compression tests showed all load-deflection relations to be non-linear. The mechanical stiffness increased with increasing the applied load and decreasing the adapter jig length. Immediately after loading, the backward lateral force was applied to the prosthesis shank, and then, the forward lateral force was generated in continuing loading. By interaction of the adapter jig position and length, fifteen load-deflection diagrams were classified into seven tendencies. From the observation results of deformation behavior, the product of the adapter jig position and length was defined as the positional parameter, which quantitatively indicated the clamped condition. Consequently, the evaluation method of mechanical stiffness correlated with the applied load and the positional parameter was proposed.

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  • Takuro HONDA, Yuta NAKASHIMA, Hidehiko HIGAKI, Yoshitaka NAKANISHI
    2018 Volume 4 Pages 17-00590
    Published: 2018
    Released: January 15, 2018

    The lips of a shaft seal need to be lubricated to ensure its performance. Such seals are subjected to difficult conditions inside water pumps or underwater mechanical systems. Poor lubrication can cause high friction and wear of seal lips. A new shaft seal was designed to prevent water ingress with low friction and high wear resistance by adopting hydrophilic materials to seal rings. Hydrated composites for seal rings were developed with fibers to avoid excessive deformation. In experiments, cellulose nanofibers were most appropriate for reinforcement of the matrix material and the shaft seal exhibited its sealing performance at the speed of 5000 rpm under pressure of 0.8 MPa. This shaft seal will be useful not only for industrial pumps but also for generation systems driven by water flow, such as ocean current or streamflow.

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  • Shoko ARITA, Yasuyuki MIYAZAKI
    2018 Volume 4 Pages 17-00441
    Published: 2018
    Released: January 30, 2018

    Deployable structures are necessary for spacecraft to challenge advanced missions. It is important in designing the deployable space structures that they are easily deployable and reliably repeatable. Conventional study for improving the repeatability was conducted by investigating errors and its effect to the deployment. However, there was no general numerical method to evaluate the reliability efficiently and quantitatively, not estimating any errors. Therefore, the authors proposed an original numerical method to evaluate quantitatively the reliability of the deployment by detecting buckling in a dynamic analysis of FEM in 2016. In the recent study, we found a problem of false detection of the buckling by the conventional method, and we also found a method to solve the problem. The conventional method to detect the buckling in the dynamic analysis uses mode orthogonality to the rigid-body modal space and the eigenvalue. However, it was confirmed that the rigid-body mode is not discriminated correctly for the mixed modes of the rigid-body motion and the deformation. The cause of the problem is using the eigenvalue for the judgement of the buckling because it cannot be evaluate that the sign of the eigenvalue derives whether from the rigid-body motion or from the deformation. Therefore, this study proposes a modified method, not using the eigenvalue but using the work of the deformation for the judgement of the buckling. Finally, it was confirmed that the modified method enabled proper detection of the buckling for the mixed modes of the rigid-body motion and the deformation.

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  • Yuta MIZUMOTO, Hiroki ITOBE, Hiroi KANGAWA, Mika FUCHIDA, Takasumi TAN ...
    2018 Volume 4 Pages 17-00491
    Published: 2018
    Released: February 02, 2018

    Optical microcavities, which can confine light spatially, are important devices in the field of optics. Single-crystal calcium fluoride (CaF2) is one of the most suitable materials for optical microcavities. To manufacture a cavity made from CaF2, ultra-precision machining is an appropriate process. In the previous study, we have investigated the machinability of CaF2 and successfully manufactured a whispering gallery mode (WGM) CaF2 cavity. Although the manufactured cavity can confine light for a certain amount of time, it was found that the cavity performance could be unstable due to its negative thermo-optic coefficient. In this study, a novel CaF2-brass hybrid WGM microcavity was proposed and manufactured, which could stabilize the cavity performance. By using finite element method (FEM) simulations, it was shown that the proposed microcavity structure facilitates rapid heat diffusion from the cavity. A hybrid microcavity without a large brittle fracture was successfully manufactured by ultra-precision machining. Thermo-optic (TO) effects that cause an instability of the cavity performance are assumed to be suppressed during resonance.

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    2018 Volume 4 Pages 18-00038
    Published: 2018
    Released: March 09, 2018

    The Fukushima Daiichi Nuclear Power Plant accident showed a significant effect on the environment due to the release of a large amount of radioactive material. To prevent the damage of the reactor pressure vessel (RPV), an in-vessel melt retention (IVR) by external reactor vessel cooling is considered to be a key severe accident management strategy. For its success, investigation of the thermal-mechanical behavior of the RPV lower head is of importance. The main objective of this study is the development of a thermal structural calculation tool for simulating the failure process and the visco-plastic behavior of the RPV lower head wall during the late phase of a core-melt severe accident. OpenFOAM, an open-source toolbox for developing numerical solvers, was used for the calculation platform. Thermal behavior of the molten pool in the RPV lower head is simulated by the phase-change effective convectivity model (PECM). One of the LIVE (Late In-Vessel Phase Experiments) experiments was analyzed for an evaluation purpose and reasonable results were obtained. The solver was then extended to couple PECM with a structural analysis model that considers thermal expansion, plasticity, creep and material damage. Two FOREVER (Failure Of Reactor Vessel Retention) tests, each of which uses different type of steel, were analyzed: EC-FOREVER-2 with French RPV steel 16MND5 and EC-FOREVER-4 with American RPV steel SA533B1. The deformation and failure time agreed reasonably well with the measured data. In addition, the failure mode was also well predicted qualitatively. The numerical analysis showed that the developed tool has a capability of simulating the lower head thermal structural behavior.

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  • Yoshitaka NAKANISHI, Takuro HONDA, Keiji KASAMURA, Yuta NAKASHIMA, Hid ...
    2018 Volume 4 Pages 17-00654
    Published: 2018
    Released: March 26, 2018

    Power devices used for power control in electric vehicles have the drawback of high heat-generation, which can be effectively addressed by water-cooling. Their durability is affected by the performance of the seal lip in the coolant pump. The seal lip, in which a rotating shaft passes between liquid and gas phases, plays an important role in the separation of the two phases. To cool power devices, a specifically designed seal lip is required, as the seal lip is subjected to high pressure and temperatures of the water-based coolant and high-speed shaft rotation. A new type of seal lip has been developed by employing a biomimetic mechanism in which the hydrated lubrication mechanism found in natural articular cartilage is adopted. A fiber-reinforced PVF (polyvinyl formal) was employed as the hydrated and biomimetic seal lip material. The bio-inspired seal lip was attached to the shaft. Shaft rotation was controlled by a servomotor, which generated a speed of 5,000 rpm (revolutions per minute). An LLC (long-life coolant) was used as the coolant, which was diluted with distilled water at a concentration of 50%, heated to 75 °C, and pressurized to 0.3 MPa. Although the continuous leakage of LLC was observed, it was estimated that the bio-inspired seal lip might prevent the abrupt function failure in air-LLC separation. The frictional torque of the bio-inspired seal lip was lower than that of the conventional oil seal. These results suggest that the bio-inspired seal lip is a useful component in the water-cooling systems of high-power devices.

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  • Masao OGINO, Kaworu YODO, Ryuji SHIOYA, Hiroshi KAWAI
    2018 Volume 4 Pages 18-00088
    Published: 2018
    Released: March 28, 2018

    For post peta-scale supercomputers that have tens of thousands of cores, efficient parallel algorithms for finite element analysis (FEA) have been in great demand. The domain decomposition method (DDM) is a well-known technique for parallel FEA and the hierarchical DDM (HDDM) is an efficient implementation of the DDM on massively parallel computers. The HDDM has two-level parallelization and is expected to achieve highly parallel efficiency. However, the HDDM is essentially the same as the original DDM. Therefore, the number of subdomains may increase with an increase in the problem size, and then the DDM and HDDM would suffer from an increase in the number of iterations and reduction in parallel efficiency. In this study, for huge-scale FEA in the post peta-scale era, a two-level extension of the HDDM is proposed. The proposed method adopts the DDM for solving a linear equation in the interior of a subdomain, that is, a recursive algorithm.

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  • Yusuke HARA, Daisuke FURUKAWA, Souichi SAEKI
    2018 Volume 4 Pages 17-00656
    Published: 2018
    Released: April 09, 2018

    Although various apparatuses have been developed to assess the skin mechanical function, the spatial viscoelastic behavior of each skin layer including the epidermis and dermis is yet unclear. To resolve that lack of clarity, we built a handmade system combining a suction device with optical coherence tomography (OCT). OCT can visualize the vertical section of the skin with high spatial resolution and high acquisition speed. In addition, we developed an algorithm for time-dependent strain tomography, named Dynamic Optical Coherence Straingraphy (D-OCSA), which can analyze the changes in strain distributions over time in sequential OCT images. Using the system, successive OCT images of volar forearm skin were obtained after the suction release, followed by calculation of spatial distribution of creep recovery time as an index of viscoelastic behavior. As a result, we revealed that the creep recovery time in the dermis was significantly larger than that of the epidermis. This is the first report to provide evidence that there is a spatial difference in the viscoelastic behavior in the skin. Future application of our method would be beneficial to the diagnosis of skin mechanical function and the validation of cosmetic and medical applications.

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  • Tomoaki SATO
    2018 Volume 4 Pages 18-00082
    Published: 2018
    Released: April 16, 2018

    In this research, our goal is to create multimedia content for selected machinery, aiming to communicate to future generations the operating behaviors of these machines valued as items of technological heritage. Thus far, three devices registered as Japanese heritage machinery have been modeled in 3D-CAD form, digitally assembled as a virtual reproduction and then animated to complete the CGI content. The selected machinery is listed below. 1) The hauling machinery at the Kosuge Ship Repair Dock at the Mitsui Historical Shipyards Museum was selected as the preeminent piece of Japanese heritage machinery by the Japan Society of Mechanical Engineers; 2) the third-ranked piece of heritage machinery, Kaheji Ito's forged-iron treadle lathe (Meiji 8/1875) is preserved at the Meiji Village open-air museum in Aichi prefecture; 3) the fourth-ranked piece of heritage machinery is the land steam turbine (Meiji 41/1908, Mitsubishi Joint Stock Corporation). These completed projects have all been donated to their respective museums to provide enlightenment and guidance to visitors.

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    2018 Volume 4 Pages 18-00094
    Published: 2018
    Released: April 27, 2018

    In this research I focus on mobile robots that move to target location, and I developed a new brachiating robot with a simple mechanism. The robot uses a hook-shaped end effector for sustaining the robot itself to avoid the falling. I proposed a motion principle and a control strategy to perform brachiation motion. In particular, I suggested a simple motion planning method based on the motion principle (pendulum motion) of a rigid body. Then, I realized the brachiation motion by using the developed brachiating robot and the proposed motion strategy in downward and upward slopes' situations.

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  • Suguru UEMURA, Keisuke YASUDA, Yukihide ITO, Mutsuhiro ITO, Shuichiro ...
    2018 Volume 4 Pages 18-00053
    Published: 2018
    Released: May 08, 2018

    An adsorption heat pump system may make effective use of low-quality waste heat, but the system’s inadequate performance remains a critical issue. Improvements in efficiency and an understanding of the fundamental phenomena of water adsorption and desorption in a silica-gel particle are essential. X-ray transmission imaging was used to observe water adsorption/desorption phenomena in 3.7-mm-diameter silica-gel particles. Although previous studies did not conduct observations inside of the silica-gel particles, we were able to visualize the change in water distribution in silica-gel particles during adsorption and desorption using X-ray transmission imaging. When the silica-gel particles were cooled or heated, the adsorption or desorption proceeded gradually from the outer edge to the center, until the final equilibrium state of uniform water distribution was visible. A quantitative measurement of the water adsorbed in the silica-gel particles indicates that it took 20 min and 10 min to achieve adsorption and desorption equilibrium, respectively, in the silica-gel particle. In the silica-gel packed bed, all silica-gel particles desorbed at the same speed, but the adsorption slowed as the distance from the connection port increased.

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  • Takeshi OGAWA, Shota HASUNUMA, Yosuke INATOMI, Natsumi YASUKOCHI, Shoh ...
    2018 Volume 4 Pages 18-00134
    Published: 2018
    Released: May 25, 2018

    In the present study, the growth rate of optically dark area (ODA) was investigated for two types of bearing steels using a fracture mechanics approach. Ultrasonic fatigue tests were performed for the specimens with hydrogen pre-charging followed by exposing in the atmosphere for a week in order to investigate the effect of hydrogen trapped by inclusions on the growth of ODA. Together with the constant amplitude loading test, two-step and repeated two-step variable amplitude loading tests were performed in order to determine the fatigue crack growth rate by beach marks. The results revealed that fatigue strengths of the both materials were reduced by the hydrogen pre-charging. The size of ODA increased with decreasing the stress amplitude at fracture so that the stress intensity factor range at the end of the ODA growth became a constant value ranging between 4.5 and 5.5 MPa √m independent of the materials and the fatigue lives. ODA formation behavior is enhanced by trapped hydrogen by inclusions, which reduces the fatigue strength in the very high cycle fatigue regime.

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  • Shintaro FUKAYA, Toshinori AOKI, Yasuhiro KIMURA, Masumi SAKA
    2018 Volume 4 Pages 17-00604
    Published: 2018
    Released: June 01, 2018

    Cu, Cu2O and CuO nanostructures have characteristic physical properties, and are used in a variety of fields such as lithium ion batteries, solar batteries and gas sensors. Recently, various techniques for the nanostructures fabrication have been studied for these applications. It has been reported that electrochemical migration (ECM) causes insulation deterioration on the printed circuit boards in high-humidity and high-temperature conditions. Previous investigations of the suppression of ECM revealed that eluted Cu ions grew as dendrites. A considerable number of studies have investigated the suppression of ECM, but the beneficial use of ECM has not been studied extensively. The use of ECM has become the subject of increasing interest because ECM is a low-cost and green fabrication technique, and the reaction requires only DC voltage and water without any metal salts and hydroxides. Some attempts have been made to fabricate hybrid Cu-Cu2O nanostructures using ECM. However, it has been reported that the growth of dendrites between electrodes ceases because the dendrites create a short-circuit. Thus, proper fabrication has not yet been achieved. This study aimed to enhance the fabrication of hybrid Cu-Cu2O nanostructures using ECM. In this study, we changed the path length of the dendrites’ growth, and improved the fabrication process through evaluation of the results.

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  • Makoto KATOH
    2018 Volume 4 Pages 18-00062
    Published: 2018
    Released: June 26, 2018

    This paper presents a modeling based 2 links solid pendulum and the open loop simulation of an ornithopter like FESTO's smart bird after discovered the successful parameters. The elevation control of smart bird is not frequency control of faction like FESTO's smart bird but faction and gliding time like golden eagle or hawks. The forward control of smart bird is done by twist of root of wings. It is a difficult point that the range of the parameter in which it can fly is narrow at both solver of Simulink and Excell. Then, the balance value is different according to solver.

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  • Yoshihiko UEMATSU, Toshifumi KAKIUCHI, Megumi ADACHI
    2018 Volume 4 Pages 18-00213
    Published: 2018
    Released: July 05, 2018

    Electroless nickel plating was formed on A5052 aluminum alloy, and subsequently diamond-like carbon (DLC) was deposited on nickel plating to fabricate DLC/nickel plating hybrid coating. Cantilever rotating bending fatigue tests were conducted using the specimens with and without coatings. The fatigue strengths of the specimens with DLC or nickel plating single layers were higher than those of the substrate without coating. However, the specimens with nickel plating had large scatter in the fatigue strengths due to some cracking in the coatings. When DLC was deposited on the nickel-plating layer, the fatigue strengths were further improved compared with the specimens with DLC or nickel plating single layers. The observation of fatigue fracture surfaces revealed that fatigue crack initiated at the substrate just beneath the coating in the specimens with DLC or nickel plating single layers. However, subsurface fatigue crack initiation occurred in high cycle fatigue regime of the specimen with hybrid coating. It indicated that the improvement of fatigue strengths could be attributed to the suppression of fatigue crack initiation by coatings, where hybrid coating was more efficient than DLC or nickel plating single layers.

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  • Yao ZHU, Toshikazu FUJINO, Tatsuhiro JIBIKI
    2018 Volume 4 Pages 18-00177
    Published: 2018
    Released: July 20, 2018

    As the utilization of ocean resources continues to increase, the performance and reliability of equipment used in the marine environment will become more important. Many friction and contact parts in equipment used in the marine environment directly or indirectly contribute to the service life and efficiency of various equipment and structures. Therefore, materials used in sliding parts in contact with seawater need to have both superior corrosion resistance and superior wear resistance. To develop friction-resistant materials adapted to the marine environment, the surface of 18Cr-8Ni austenitic stainless steel was modified to add superior properties of corrosion and wear resistance. This stainless steel was modified with silicon powders or silicon carbide powders mixed with fine high-speed-steel particles, which acted as carrier particles in a friction reforming technique. After that, zinc anticorrosive coating was applied to the modified materials by surface pressing and rubbing of a zinc pin for sacrificial corrosion protection. Corrosion and friction testing was conducted in parallel in a 3.5% sodium chloride solution to simulate seawater under static and dynamic reciprocating motion conditions. The polarization curves and friction and wear characteristics of these modified materials were evaluated. As a result, the modified materials, especially stainless steel modified with mixed silicon and silicon carbide powders, exhibited better wear resistance than unmodified stainless steel in seawater. In addition, the corrosion rates of the modified materials and the substrate stainless steel were almost the same under the micro-reciprocating friction condition. Therefore, it was shown that the modified materials, especially stainless steel with mixed silicon and silicon carbide powders, exhibited excellent properties as friction-resistant materials in a marine environment.

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  • Ryuji TAKAHASHI, Nobuyuki TSUBOI, Takashi TOKUMASU, Shin-ichi TSUDA
    2018 Volume 4 Pages 18-00369
    Published: 2018
    Released: September 26, 2018

    We have validated the classical mixing rule (CMR) applied to the Soave–Redlich–Kwong (SRK) equation of state (EOS) as one of the van der Waals–type EOSs for the thermodynamic properties (pressure–volume–temperature relationship, specific heat at constant pressure) of oxygen–hydrogen mixture in supercritical state using molecular dynamics (MD) simulations. As for oxygen and hydrogen, effect of the intramolecular orientation on the intermolecular interaction is very small; therefore, we employed the Lennard–Jones (L–J) potential between each molecule. The intermolecular interaction between the different molecular species was given by modified Lorentz–Berthelot (L–B) rules, which improved the accuracy of the well–applied original L–B rules in accordance with the more accurate combining rules proposed for the L–J potential. We have validated the CMR applicability through the comparison of thermodynamic variables obtained by MD simulations with those obtained by CMR coupled with the SRK EOS. As a result, the thermodynamic variables by MD simulations corresponded with those from the SRK EOS employing CMR. Further, the relative difference in thermodynamic variables between the MD simulations and SRK EOS hardly increased against single–component fluids. Therefore, we conclude that the CMR can be applied to the oxygen–hydrogen mixture system in supercritical condition.

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  • Renta KASAI, Kazuhiko SASAGAWA, Kazuhiro FUJISAKI, Satoshi SAITO, Hiro ...
    2018 Volume 4 Pages 18-00257
    Published: 2018
    Released: October 12, 2018

    Touch panels are widely used to detect contact conditions between fingers and screens, as human interface devices. The touch sensor used in smartphones has been significantly developed in recent years, and the sensor can recognize not only contact position, but also changes in contact pressure. However, previously proposed touch panels have not been able to measure shear stress. Measurements of the shear stress can facilitate the realization of more sensuous and functional operations through the touch panels. Thus, a sensor for the contact pressure and shear stress measurements was fabricated in this study, in which a conductive polymer was used as a pressure-sensitive material. Sensing units were constructed from transparent materials and integrated to be a 4 × 4 array structure. The calibration tests were performed under combined stresses with the contact pressure and the shear stress in multi-axis loading. The sensor system can detect the distributions of three-axis stress components on surfaces. The stress components were simultaneously measured under several types of finger slide motions. The possibility of quantitative measurements of the stresses acting on touch panels was confirmed by considering transparency of the sensor.

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  • Moeto NAGAI, Kyohei TADA, Takayuki SHIBATA
    2018 Volume 4 Pages 18-00377
    Published: 2018
    Released: November 29, 2018

    The facilitation of access to rapid and low-cost microfabrication methods is essential for improving the development cycles of testing new chip designs and research ideas. A simple fabrication method of biocompatible microchannels with a height of 0.3 mm is significant for biological scientists to study animal and plant cells (∼0.1 mm). Microfabrication using a cutting plotter and a knife blade provides a rapid and low-cost technology. In a previous study, designed cut pieces were used as a channel mold, but they were easy to deform during handling, and therefore the large-scale production of channels was difficult. Moreover, it is required to characterize the cutting process of 0.3-mm-thick sheets with a low-cost plotter. Here, we report the development of an easy fabrication method of 0.3-mm-high polydimethylsiloxane (PDMS) microchannels based on a desktop cutting plotter (300 USD) and an engraved sheet as follows. 1) A 0.3-mm thick sheet of cast-coated paper or silicone rubber was used as a mold material and patterns were created with a cutting plotter. 2) It was pasted to a double-sided tape to make a master mold of a flow channel. 3) The mold was replicated in PDMS to make a negative mold. 4) This PDMS mold was again transferred to a final PDMS chip. 5) It was bonded to a glass substrate to form a PDMS flow channel. We characterized the pattern transition of rectangular shapes from an engraved sheet mold to a final PDMS channel, that is essential for the design of a channel using this method. I- and Y-shaped microchannels (height: 0.3 mm) were fabricated and fluorescent particles and 0.2-mm diameter Volvox were introduced into the channels to show their performances.

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    2018 Volume 4 Pages 18-00290
    Published: 2018
    Released: November 29, 2018

    In this study, we developed a method for obtaining high contributing whole body vibration behavior to the vehicle interior noise at the running condition by modified operational TPA method (OTPA with PC model). The original OTPA with PC model requires measuring all reference and response points simultaneously. However, if the number of the point is so much, applying this method becomes hard. Hence, the proposed method was made to increase the applicability of this method by realizing to obtain the high contributing whole body vibration behavior without the simultaneous measurement of all points. In the method, several operational tests are repeatedly carried out in each measurement group and high contributing vibration behavior of each group to the response point (interior noise) was obtained as the high contributing partial PC mode. Subsequently, the high contributing whole body PC mode was obtained by integrating the partial PC modes. For obtaining it, relationship between each partial PC and the response point and original phase and amplitude compensation method were utilized. As the result, the high contributing whole body PC mode could be obtained well with much more less measurement points by comparing with the original OTPA with PC model and the applicability of the method was increased.

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  • Nao FUJIMURA, Takashi NAKAMURA, Masahiro UENO
    2018 Volume 4 Pages 18-00437
    Published: 2018
    Released: December 26, 2018

    Recent studies on very high cycle fatigue (VHCF) have observed a unique fracture surface with a fine granular area around the crack origin that arises from long-term repeated contacts of fracture surfaces (over 107 cycles). A fine microstructure including nanocrystalline is known to form in the matrix just beneath the fracture surface. Focusing on these phenomena, this study devised a new surface modification technique, called Cyclic Press (CP), that creates a nanocrystalline layer using cyclic compressive loading. Repeated low-compression loadings were applied to the surfaces of SNCM439 high-strength steel and ADC12 die-cast aluminum alloy with an indenter for 5 × 107 cycles. Then, the surfaces and cross sections were analyzed by using a laser microscope, a scanning electron microscope, a scanning ion microscope, and energy dispersive X-ray spectrometry (EDS). As a result, a nanocrystalline structure very similar to that of the cross section beneath the fracture surface in the VHCF regime clearly formed in the surface layer of both materials. Additionally, an oxygen-rich layer formed at the surface of the CP-treated ADC12. This result was considered to be caused by diffusion of elemental oxygen in the atmosphere by a huge number of repeated contacts between the indenter and specimen. Overall, the results indicate that CP is a useful technique for forming nanocrystalline layers in metal surfaces and can also be expected as a new method for diffusing surrounding gaseous elements into surfaces at room temperature.

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  • Takayuki TOKOROYAMA, Toru KAMIYA, Nazeef Afifi Bin Hafiz AFMAD, Norits ...
    2018 Volume 4 Pages 18-00089
    Published: 2018
    Released: December 27, 2018

    Carbonaceous coatings such as Diamond-Like Carbon (DLC) are attractive candidates for reducing friction under boundary lubrication. However, the wear particles generated from the DLC are believed to form hard slurries that scratch surfaces like an abrasive, and they can shorten the lifetime of the DLC itself. Generally, in conventional automobiles, these wear particles are collected by oil filters. Modern engine bearings are required to reduce the friction coefficient to low levels so that low-viscosity lubricants are used to reduce resistance to flow. However, using a low-viscosity lubricant result in direct solid contact between surfaces, which disrupts the hydrodynamic lubrication and generates numerous wear particles. In this study, we carried out friction tests between DLC/DLC surfaces with kerosene as a boundary lubricant at room temperature. The friction tests were conducted over 12,000 cycles, and we replaced the lubricant after every 2000 cycles without changing the contact pair. Wear particles were collected from the lubricant using an electric field with the electrophoresis effect. The wear particles gathered near the positive electrode and fell onto a glass plate. Finally, after the kerosene evaporated, scanning electron microscope and laser optical microscope observations showed the relations between particle size and shape, the number of wear particles, and the friction coefficient.

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