A two-component Bose-Einstein condensate rotating in a toroidal trap is investigated. The topological constraint depends on the density distribution of each component along the circumference of the torus, and therefore the quantization condition on the circulation can be controlled by changing the miscibility using the Feshbach resonance. We find that the system exhibits a variety of dynamics depending on the initial angular momentum when the miscibility is changed.
Serious problems caused by bolted joint fatigue breakage still occur. This is because working load evaluation and durability strength evaluation have been insufficient in the product design stage, in the test stage of machine lifetime prediction, in the trial production stage, in the prototype machine test stage, and so forth. In this paper, we propose a method for measuring and analyzing the load on bolted joints used in a machine under actual operation. Working load measurement under actual machine operation and the results of its analysis are shown as load frequency diagrams. This is very important information for realizing the concept of simultaneous multiple design. An example of the measurement analysis method of the load (three types of the loads; axial force, bending moment, and the torsional torque) added to the bolted joint shank which comes out at the time of the actual machine operation is shown. The reliability of assessing the strength and durability of bolted joints is considered from the viewpoint of limited-lifetime (finite-lifetime) design using Miner’s rule with cumulative loosening damage models and fatigue limit (infinite-lifetime) design. As an example, we measured the working stress and evaluated the strength of a bolted joint of an actual machine to verify the usefulness of the proposed method. Also, examples of strength evaluation are shown to illustrate finite-lifetime and infinite-lifetime prediction. Moreover, the practical process and presumed example of fatigue life prediction are shown. It is considered as a contribution at the improvement of strength reliability and the load analysis method of the bolted joint of machine develop-ment stage and failure analysis stage. Our findings are also expected to eradicating accidents involving bolted joints in machines.
The calibrated wrench method is often used for tightening. When tightening bolted joints, it is important to apply high axial tension. However, since the axial tension is indirectly applied in this method, it varies and has a distribution in the case of tightening carried out in the production line of a factory, for example. However, the calibrated wrench method is still widely used because of the simple tool and easy standardization. In our previous papers, we analyzed and discussed the main points of this research by a theoretical approach as discussed below. Conventionally, this type of distribution has been considered to lie within a rhombus (more precisely, within a rectangular area). However, when considering the tightening torque and axial tension as independent random variables, the distribution becomes elliptical. The same idea applies to the relation between the tightening torque and the equivalent stress for a bolt axis based on shear strain energy theory. On the other hand, regarding the variation in the tightening torque (tightening work coefficient a) actually applied to a bolt, it was reported by Bickford, Kawasaki, and others that it can vary by 15% or more from the target (indicated) tightening torque. However, the torques for wrenches used at actual assembly sites or under lubricated conditions were not reported. Therefore, it is necessary to experimentally verify that the relation between the tightening torque and the axial tension (axial stress) and equivalent stress of a bolt axis is distributed in an ellipse. Furthermore, the screw-thread characteristics (torque coefficient, equivalent stress coefficient, coefficient of friction, etc.) during the tightening process should be clarified by an experimental approach and observation. Thus, in this study, in experiments under dry (as-obtained) and lubricated (Loctite 263) conditions, the tool (preset-type and dial-type torque wrenches) and bolt strength classification (8.8 and 10.9) were changed, and the screw-thread characteristics were observed during actual bolt tightening and the characteristics under different conditions were analyzed. It was clearly shown that the tightening torque and the axial tension (axial stress) of a bolt axis and the equivalent stress vary with an elliptical distribution rather than a rhombic distribution. Finally, the validity of the tightening theory based on the elliptical confidence limit method was also verified experimentally.
This paper presents a method for estimating the absolute lock effect in bolted joints during off-road vehicle operation. There is a good linear relation between axial tension decrease tendency (Loosening phenomenon) and the operation time (or mileage or number of operations) after the tightening on logarithmic coordinates. Based on this relation, this report leads to two estimating methods described below.1) Decrease of axial tension (self-loosening) is estimated accurately after long hours since tightening by measuring the initial axial tension behavior using the bolt loosening evaluation diagram.2) Method of Estimating the locking device availability (usefulness) on actual machine operation is obtained from laboratory loosening test results.
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