The correct evaluation of reliability for the system or components is very important for high quality and security. The traditional models take stress and strength as the static random variable without considering the effect of strength degradation. The effect of strength degradation on the reliability of a gear was studied in this paper. With the conditional reliability introduced, a reliability calculation model of gear with multiple failure modes is developed by using the stress-strength interference model, without the assumption that there was independent failure mode of gear. The reliability model of a gear under the strength degradation is developed based on the model. And the dependence of gear reliability on the strength degradation is studied. The result shows that the gear reliability decreases with the strength degradation due to fatigue, corrosion, aging and other factors.
Based on the finite element approach and the strain gradient (SG) theory, this paper produced a study on factors of size effect and minimum cutting thickness phenomenon in the micro-cutting process. Mechanisms of micro-cutting focusing on its characteristics that include size effect, tool edge radius and minimum cutting thickness has been studied. A new constitutive relationship based on SG theory is formulated to model the size effect of material properties at micro-scale. The new constitutive was implanted into the FEM, and size effect was investigated. From the result of simulation, it is indicated that size effect in micro-cutting could be well formulated by SG theory. The curve of material properties is approached to curve of JC with the depth cutting increased; when the rake angle is increased, the size effect is more obvious. The tool edge radius has a significant influence on the size effect. Result show that the cause of the minimum chip thickness is the tool edge radius.
This work presents the flexure-mechanism based decoupling design between high frequency piezoelectric ultrasonic transducers and their clamping connections to improve ultrasonic energy transmission efficiency. The ring, prismatic beam, and circular notched hinge based flanges were presented, and the crucial geometric dimensions of the transducers with the flexure decoupling flanges were determined. Finite element analysis (FEA) was carried out to investigate the dynamic characteristics of the transducers. Finally, experiments were conducted to examine and verify the effects of the proposed decoupling flanges. FEA and experimental results show that smaller frequency deviations and larger tip displacement amplitudes have been achieved by using the transducers with the flexure flanges compared with the transducer with a rigid ring-type flange, and thus the ultrasonic transmission efficiency can be improved through the flexure flanges.
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