Determination and prediction of the dynamic properties of an O-ring for bearing support were performed. Utilizing O-rings as supporters of bearing is a promising way to suppress severe vibrations such as resonance and self-excited whirl experienced in high-speed turbo machinery. However, analytical prediction of the dynamic properties of O-rings has not been very successful so far because of its non-linear dependence on many parameters. In this study, focusing on the incompressibility of rubber materials, the isochoric shear viscoelasticity of an O-ring material was measured for high frequencies of up to 1 kHz. In measuring the viscoelasticity, a testing method developed by the authors was used. This method enables obtaining high-frequency shear viscoelasticity directly without assuming the temperature-frequency superposition principle. The obtained dynamic shear properties were modeled as functions of the frequency and hydrostatic pressure. Finite element models of squeezed O-rings were constructed with the material model assuming uniform property distribution, and dynamic analyses were conducted. The dynamic properties of O-rings were determined from the time-series data for the applied force and displacement. The data agreed with the experimental results of an actual O-ring. It was found that the dynamic properties of rubber components can be analytically predicted by considering the frequency and hydrostatic pressure dependence on the viscoelasticity.
In turbomachinery, such as turbine, pump, and valve, components damage caused by collapsing cavitation bubbles has been a critical issue that needs a proper solution. For this reason, investigation on the cavitation erosion behavior of materials as well as the life prediction techniques has been extensively conducted. Moreover, a number of repairing techniques, such as by a surface coating of polymeric materials, has been established. However, in real operation, cavitation is actually not the only load acquired by the components. Other external loads, such as centrifugal force and hydraulic pressure, may also affect the generation of damage. Therefore, its effect on the lifetime needs to be considered carefully. In this paper, the behavior of cavitation damage of epoxy resin specimens subjected to uniaxial tensile loading is reported. A self-developed testing device was used to conduct a cavitation test based on ASTM G32 while at the same time exerting a constant uniaxial tensile load to the specimen. Using this device, various levels of tensile stress effect on the cavitation damage was examined. As a result, besides erosion damage, we revealed that the specimens demonstrated fracture when a certain tensile load was applied. Furthermore, as the tensile load was increased, the time to fracture was shortened significantly, indicating the pronounced effect of tensile stress on the damage formation. The crack growth mechanism was then analyzed by fractography. The result indicated that the crack propagation under a mixed condition of cavitation and tensile loads was most likely driven by the combination of creep deformation and fatigue-like crack growth. Finally, a mathematical relationship between tensile stress and cavitation damage life was proposed. The relationship is important to enhancing the existing theory of cavitation damage evaluation in e.g. turbomachinery application.
Galling and wear have been a tribology problem in sheet metal forming of stainless steel. Although lubrication oil with chlorinated extreme pressure (EP) additives have been used, environmental and safety issues have demanded not to use chlorinated EP additives. For developing chloride-free oil for cold ironing of stainless steels, some commercial sulfur-based EP additives were evaluated by a cup internal ironing test. Moreover, the superior sulfur-based EP additive was combined with calcium- and zinc-base type additives in order to improve anti-galling performance. The mixture oil, as shown the high performance in the cup internal ironing test, successively passed a 10,000 shots practical process with severe ironing of stainless steel. After the 10,000 shots, it was found that no galling was observed on these 10,000 products. Based on the X-ray photoelectron spectroscopy (XPS) results, sulfide and calcium carbonate were formed on the surface of the products. This lubricating film seems to prevent galling in the practical process. The developed oil is an example of a chloride-free oil to replace the conventional chloride-containing oil.
The objective of this study was to solve the theoretically ideal arm stroke for a swimmer with hemiplegia by using the optimizing simulation. The method of optimizing simulation for non-disabled swimmers was extended to a swimmer with hemiplegia. In order to evaluate the arm strokes in the optimizing calculation, the swimming human simulation model SWUM was employed. As the design variables, the joint angles in the three time frames, in which the arm was performing underwater strokes, were used. The objective function was the swimming speed. Three constraint conditions including the maximum joint torque characteristics were imposed on the optimizing calculation. The swimming motion of an actual swimmer with hemiplegia was measured and put into the simulation as the original motion. In the simulation, significant increase in the swimming speed was obtained in the case of the optimized stroke with the actual swimmer's wrist motion at the slower stroke cycle. From the comparison between the optimized stroke and the actual swimmer's stroke, several differences were found as follows. First, at the entry phase in the fastest optimized stroke, the left elbow was more extended than the actual swimmer's stroke. Second, at the catch phase in the fastest optimized stroke, the forearm in the side view was more tilted with respect to the vertical line, while that in the actual swimmer was almost vertical. Third, at the pull and finish phases in the optimized stroke, the hand pushed the water sufficiently to the end, while that in the actual swimmer went out from the water earlier. Overall, it was found that the optimized stroke effectively utilized the joint torque at the shoulder and elbow to the maximum extent, by selecting the more natural positions and the slower stroke cycle.
We herein propose a liquid encapsulation method for a submillimeter-size polydimethylsiloxane (PDMS) membrane. We selected a magnetorheological (MR) fluid as the liquid to be encapsulated in the membrane, the stiffness of which is tuned by an external magnetic field. The proposed method consists of two steps. First, a PDMS bump was made to contact a MR fluid, and a MR fluid droplet was formed on top of the bump. Next, the droplet was dipped in a PDMS casting solution and fully covered with a PDMS casting solution layer. Finally, the droplet was encapsulated in the membrane after curing. We experimentally confirmed that the radius of the PDMS bump and the viscosity of the MR fluid were variable parameters that could determine the height of the structure. We also evaluated the stiffness characteristics of the structure. The calculated Young's modulus indicated that the stiffness varied from 70 kPa to 180 kPa in the presence of an external magnetic field. The results indicated that the structure could emulate relatively soft materials and could be applied to a tactile display used in palpation.
In this research, we investigated an energy supply system based on hydrogen derived from renewable energy. We modeled the energy flow and efficiency of a system using the MCH-toluene-hydrogen reaction cycle (MTHR) by methylcyclohexane (MCH, C6H11CH3) and toluene (C6H5CH3). Electric power storage by the MTHR and energy transport by a hydrogen infrastructure were investigated using numerical analysis. The energy flow of the whole system was investigated by cooperation of the numerical model of each component. The rate of input and output based on the calorific value of hydrogen defines the efficiency of each component and the system. When the electric power output of the renewable energy source was set to 100%, the maximum energy efficiency based on the calorific value of the hydrogen supplied from the hydrogenation facilities was 53.6%. Conversely, the electric power and thermal efficiency based on the rating of the dehydrogenation facilities were 29.9% and 6.8%, respectively. The maximum total power generation efficiency of the MCH-toluene-hydrogen reaction cycle was 16.0%; however, when thermal power was taken into account this rose to 16.7%. A case study was also conducted using a 1 MW wind farm combined with MTHR for Hokkaido in Japan.
A series of study is presented to develop a prediction method for pipe wall thinning in power plants in order to improve the maintenance management for piping system. In the first report, experiments for flow-accelerated corrosion (FAC) of carbon steel specimens were conducted and basic data of FAC rate were obtained by setting temperature from 50 to 150 ℃ and pH from 7.0 to 9.8 as main parameters. As this second report, the experimental data of FAC rate were compared with the prediction method. Effective mass transfer coefficient correlation was proposed and implemented into the prediction method considering combining effect of local average and turbulent velocity in the near-wall region calculated by computational fluid dynamics (CFD) simulation code. Fairly good agreement was confirmed between experimental and predicted FAC rate profile, quantitatively. Continuously, prediction method was applied to actual power plant piping systems, and some elbow components were chosen for evaluation in detail. Comparison of measured and predicted FAC rate also showed good agreement with data mostly evaluated conservatively in sense of maintenance management. As a whole, presented FAC prediction method including effective mass transfer coefficient was confirmed to predict measured FAC rate data of power plant pipe component with fairly good accuracy and reasonable conservatism, at least for the subjected temperature and pH conditions.
In recent years, due to its high specific stiffness and strength, fiber reinforced plastics (FRP) are being used in aerospace components, automobile components, sports equipment, and in various other applications. Especially since composite laminates have superior mechanical properties, there is a high demand for their use as structural materials. However, mechanical properties in the out-of-plane direction of composite laminates, specifically the interlaminar strength and fracture toughness, are much weaker than those in the in-plane direction. This study focuses on the needle punch techniques that aim to improve composite properties in the out-of-plane direction. This technique is typically used for fabricating non-woven fabrics. Fiber webs were punched by a plate containing many special needles with many barbs. A portion of fibers in the in-plane direction were aligned in the out-of-plane direction. In this study, the needle punch process is applied on chopped strand mats. Static tensile tests, fatigue loading tests, and residual strength tests are performed. Tensile properties, residual strength properties and fracture mechanisms of FRPs with needle-punched chopped strand mats are investigated.