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Although the stick-slip piezoelectric actuator has been extensively developed, its consistency in forward and reverse motions is still poor under the same driving voltage and frequency. To improve the consistency in forward and reverse motion, extremely precise adjustment of actuators is necessary. For achieving high consistency in forward and reverse motions with low difficulty in assembly and adjustment, a stick-slip piezoelectric actuator with the symmetric mechanism and optimized installation method was developed in this study. By means of the pseudo-rigid body method (PRBM), matrix-based compliance modeling (MCM) method and the finite element method (FEM), theoretical calculation and analysis of the designed symmetric flexure hinge mechanism (SFHM) were carried out firstly. Then, the effects of installation methods on the forward and reverse motion consistency were investigated by experiments, and accordingly, an optimized installation method was determined. With this method, output performances of the actuator were tested under various voltages, frequencies and external loads, and the consistency in forward and reverse motions were further compared and analyzed. The experimental results indicated that good consistency in forward and reverse motions had been successfully achieved by the symmetric mechanism and optimized installation method, and the ratio of difference λ was only 6.80% which showed the actuator had an extremely competitiveness. High bidirectional motion consistency will reduce the control difficulty of the actuator, which is beneficial to its application in the fields of precision instruments, aerospace and material mechanical performance testing. [ABSTRACT FROM AUTHOR]

Lower divertor, as the most critical part of experimental advanced superconducting tokamak (EAST), has functions of protecting the vacuum vessel, particles exhausting, and heat load handling. Doped graphite with SiC coating is adopted as plasma-facing material, which is bolted to active water-cooling heat sink by an M8 screw with a soft graphite sheet inserted between graphite tile and heat sink to improve the capacity of heat transmission currently. In order to guarantee excellent performance of lower divertor, every striking target, which contains 27th graphite tiles, must be inspected for its assembly quality before being installed in EAST device. This paper introduces a rapid nondestructive inspection method for EAST lower divertor by infrared (IR) thermography. The poor assembly quality, such as unevenness of contact surface of graphite tile or heat sink, overlap of the soft graphite sheet, and unqualified values of torque, can be detected qualitatively by comparison of the surface temperature evolution of graphite tiles in symmetric positions of the same divertor target when water flowing in the tube welded into heat sink is changed from hot to cold. The 3-D thermal finite-element analyses are performed to simulate the case of target with excellent assembly quality and defect-free tiles and as a reference for the experimental observations obtained by IR thermography eventually. [ABSTRACT FROM AUTHOR]

Indentation behavior of two-dimensional (2D) materials mounted on the substrates with varying stiffness is investigated using finite element method (FEM). The primary objective of present work is to understand the effect of the ratio of the elastic modulus of 2D-material to that of the substrate ( λ ) on the indentation deformation of the composite structure (2D-material/substrate). It is found that with the increase of λ , the deformations of both 2D-material and substrate become less localized; the contact area rapidly decreases with λ , which cannot be properly predicted by the classic indentation models. Therefore, for a large value of λ (e.g., λ  > 10 4 ), the existing indentation models are not able to properly describe the indentation response of 2D-material/substrate. In addition, due to an ultra-low thickness of 2D-material, the indentation behavior of 2D-material/substrate is mainly controlled by the substrate properties when λ is lower than 10 3 ; whereas the ratio of the strain energy of 2D-maerial to that of the overall strain energy rapidly increases with λ , which will reach the peak value of 1/3 at λ  = 10 6 . Therefore, for a high λ , it is possible to determine the elastic modulus of 2D-material from the overall indentation response of 2D-material/substrate by the inverse analysis with the help of FEM. [ABSTRACT FROM AUTHOR]

• A 2D theoretical model based on the bilinear CZM is proposed to characterize the debonding process of stiff film/compliant substrate systems. • The results of the present model are verified by the previous experimental data and the FEM results. • The present model can describe the full debonding process including the elastic, elastic-softening and elastic-softening-debonding stages. • When the film modulus increases, the remote strain corresponding to the debonding initiation first decreases and then stabilizes at a certain value. Interfacial debonding is one of the main failure modes of stiff film/compliant substrate systems, which are common in flexible electronics. In order to characterize their debonding process, we propose a theoretical model based on the bilinear cohesive zone model, where the stiff film acts like a membrane and the substrate is modeled by an elastic half-plane. The interfacial shear stress appears as a singular integral in the governing equations, and this term can be solved by expanding into the first-kind Chebyshev polynomials and further adopting the collocation method. The solutions of the present model are verified by the previous experimental data and the finite element analysis. The results indicate that the present model can not only capture the non-uniform deformation of the compliant substrate, but also describe the full debonding process including the elastic, elastic-softening and elastic-softening-debonding stages. Besides, the influences of film modulus, film thickness and interfacial properties on the debonding process are discussed. The present study can help us predict the debonding process of the stiff film/compliant substrate systems such as flexible electronics and guide the optimal design to prevent premature interfacial debonding. [ABSTRACT FROM AUTHOR]

Peen forming processing is widely used for shaping a large thin-walled component by introducing compressive stresses in surface layer. To predict the peening stress, expensive and time-consuming analyses were needed in experiments and numerical simulations. This paper is aimed to calculate the random peening effects based on the results of single and repeated impacts. Three kinds of finite element simulation models are adopted, including repeated impacts and two shots apart impacts as well as random peening models. With the repeatedly impacting simulations, the stress fields under different repeated numbers are obtained. With the two shots apart impacting simulations, the interactions of adjacent impacts are revealed and a size of isoeffect region of one impact obtained. Comparing the results of the repeated impacts and of random peening simulations, an expression is proposed to calculate random peening stresses with peening coverage less than 90% from the stresses of single and twice repeated impacts. Comparisons of the calculated and simulated stresses of random peening shows the same tendency and depth of compressive stress as well as the close magnitude of maximum compressive stress. The equivalent stretching force and bending moment of the calculated stress are in good agreement with the values of random peening simulation. The simulated results are verified with experimentally measured dimple sizes and resultant curvatures of peened plates. [ABSTRACT FROM AUTHOR]

Shot peening and peen forming are respectively used to strengthen and form a component by blasting numerous shots on the component. A large number of analytical and numerical researches have focused on revealing the effects of various peening parameters. The shot impacting positions are usually supposed as a regular or random distribution, but there is a lack of intermediate measurand to connect the regular and random peening effects. This paper is aimed to estimate the peening effects of different peening patterns with different measurands, such as peening coverage and impacting density. Two types of 3D finite element (FE) models with regularly and randomly distributed shots are developed with dynamic-implicit solver of Abaqus. A theoretical equation for calculating random peening coverage is developed to calculate the coverage within an area with symmetry boundaries. The simulation results reveal the evolutions of indentation size, peening coverage and stress field. The equivalent forces on the cross section of plate corresponding to the induced stresses of regular and random peening are compared under the same coverage and impacting density respectively. Peen forming experiments with strict boundary constraints are performed to verify the simulation methods and agreement is observed. [ABSTRACT FROM AUTHOR]