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2020 Vol. 41, No. 5 Published: 2020-10-28

	391	Advances in Topology Optimization of Piezoelectric Smart Structures

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2020.034
		Piezoelectric materials have been widely used in precise driving, vibration control, precise positioning and other fields due to their high deformation accuracy, fast response, and easy fabrication into miniaturized devices. Changing the position, size, and shape of piezoelectric components in piezoelectric smart structures can effectively improve the mechanical properties of the system, which has attracted the attention and research of many scholars and engineers. Topology optimization, as a powerful automated design tool, has been successfully applied to the optimization design of piezoelectric smart structures. In this review, the research background and significance of the topology optimization of piezoelectric smart structures are firstly surveyed, then the analysis and active control methods of piezoelectric smart structures are briefly outlined. Afterwards, recent advances are systematically reviewed in the optimization of piezoelectric smart structures for static deformation control and vibration control, and design and optimization of piezoelectric energy harvesting devices. Finally, several important issues for future studies in topology optimization of piezoelectric structures are identified.
		2020 Vol. 41 (5): 391-408 [Abstract] ( 340 ) HTML (1 KB) PDF (0 KB) ( 178 )

	409	Microstructure evolution-based plasticity model for V5Cr5Ti alloy

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2020.026
		In order to accurately describe and predict the plastic deformation of V5Cr5Ti alloy, a microstructure evolution-based constitutive model was established. Miniaturized specimens of V5Cr5Ti alloy are used to carry out a series of uniaxial tensile tests by pulling up to different strain levels. Microstructural evolution analyses are then performed in order to capture the physical mechanisms and dominating its plastic deformation. It is found that the evolutions of dislocation density and second phase are the main factors affecting plastic deformation behavior of V5Cr5Ti alloy. Based on these observations, the equations of dislocation density evolution and that of flow stress which involves non-thermal stress, thermal activation stress and dispersive phase strengthening stress are developed, using microstructure evolution information. The new model is then numerically implemented using finite element method through an implicit stress update algorithm. The validity and prediction accuracy of the model are finally checked and verified by comparing to the experimental results and that of other conventional constitutive models.
		2020 Vol. 41 (5): 409-420 [Abstract] ( 240 ) HTML (1 KB) PDF (0 KB) ( 182 )

	421	CONSTITUTIVE MODEL OF LOW TEMPERATURE RATCHETING EFFECT OF S30408

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2020.015
		S30408 austenitic stainless steel is widely used to make the inner container of LNG and other cryogenic tanker due to its excellent mechanical properties and low temperature resistance. The inner container of this type of tank can not only bear constant stress caused by internal pressure, but also bear alternating stress caused by inertial load at its supporting part, which is prone to gradual plastic strain accumulation, i.e. ratcheting.However, there is still a lack of constitutive description to effectively predict the low temperature ratcheting effect of S30408. The ratcheting strain of low temperature S30408 austenitic stainless steel is simulated by sevseral more advanced constitutive models. It is found that this several constitutive models have the the disadvantages of low-prediction in the early cycles and over-prediction in the late cycles. And this difference will increase with the number of cycles. Based on the Ohno-Wang II model, this paper associates deformation martensite content with isotropic and kinematic hardening rule, and gives the evolution rule of martensite limit content dL, and then proposes a cyclic plastic constitutive model containing martensite transformation. The dL of the martensite limit content in this paper can better describe the variation rule of martensite limit value with the accumulated plastic strain. Through the simulation of low temperature S30408 austenitic stainless steel by sevseral more advanced constitutive models and the new constitutive model, it is found that the model can effectively improve the situation that the predicted value is too low in the initial cycles, and can also well describe the situation that the material reaches ratchet stability in the later cycles.
		2020 Vol. 41 (5): 421-432 [Abstract] ( 268 ) HTML (1 KB) PDF (0 KB) ( 173 )

	433	INVESTIGATION ON CONTRAST INVERSION IN BIMODAL AMPLITUDE MODULATION ATOMIC FORCE MICROSCOPY

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2020.016
		Bimodal amplitude modulation atomic force microscopy (AM-AFM) is widely used in micro/nanoscale mechanical imaging. However, the contrast inversion which probably appears during imaging makes it difficult to understand the imaging results. Combining the finite difference method and the in-phase and quadrature method, the influences of the selection of probes with different force constants, the mechanical properties of the sample components, and the settings of the imaging parameters on contrast inversion of the amplitude and phase of the second mode are investigated numerically in bimodal AM-AFM. Results show that for a stiff probe, the contrasts of the amplitude and phase of the second mode for components with different viscosity coefficients would not reverse with increasing elastic moduli. The contrast of the amplitude of the second mode for components with different moduli would be inverted with increasing viscosity coefficients, while contrast inversion of the phase of the second mode will not occur. For a soft probe, the increase of the elastic moduli or the viscosity coefficient would result in the transition of the interaction regimes, giving rise to discontinuous jumps of the response. For a soft cantilever, the contrast of the phase of the second mode for components with a higher modulus and different viscosity coefficients or the contrast of the phase of the second mode for components with a small viscosity coefficient and different moduli is lower compared to that of a stiff cantilever. The contrast of the amplitude of the second mode for components with different elastic moduli will reverse as the free amplitude of the second mode increases. However, the contrast at different viscosity coefficients does not reverse. Furthermore, the smaller the free amplitude of the second mode, the higher the contrast of the phase of the second mode to the elastic moduli or viscosity coefficients of the components. The amplitude or phase contrast of the second mode may be inverted in different interaction regimes and the interaction regime should be kept in the repulsive regime to achieve a higher imaging contrast.
		2020 Vol. 41 (5): 433-443 [Abstract] ( 189 ) HTML (1 KB) PDF (0 KB) ( 189 )

	444	Thermo-electro-mechanical properties of piezoelectric nanoplates with flexoelectricity

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2020.025
		Abstract：Flexoelectric effect, which is induced by inhomogeneous strain (or strain gradient), is a size-dependent electromechanical coupling effect. Based on the Kirchhoff plate hypothesis and the theory of flexoelectricity, the differential governing equations of the piezoelectric thin plates under temperature and voltage are derived. The influence of nonlinear terms in governing equations is quantitatively analyzed. For clamped piezoelectric nanoplates, the governing equations are solved by adopting Ritz’s method, and the bending and vibration behaviors of the piezoelectric nanoplates are numerically investigated. To study the influence of temperature and flexoelectricity on the coupling characteristics and mechanical behavior of thin nanoplates, we consider the material coefficients of the piezoelectric nanoplates being independent on temperature and linearly dependent on temperature, respectively. For case studies, we choose PZT-5H as the structural material and investigate the influence of flexoelectricity and temperature on the transverse displacement and resonant frequency of the nanoplates. Results show that flexoelectric effect has a significant influence on the mechanical behavior of piezoelectric nanoplates and is size-dependent. In addition, the thin nanoplate is sensitive to the temperature change. Therefore, we can utilize flexoelectricity and temperature to tune the multi-field coupling characteristics and mechanical behavior of piezoelectric nanoplates , in this way，the performance of piezoelectric nanoplate based electronic devices such as sensors and actuators in NEMS/MEMS could be optimized.
		2020 Vol. 41 (5): 444-454 [Abstract] ( 285 ) HTML (1 KB) PDF (0 KB) ( 191 )

	455	Application of Deep Learning in Debris Cloud Simulation

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2020.029
		With the rapidly development of deep learning technology, various models based on data-driven have been widely studied and used in Computational Solid Mechanics and computational fluid dynamics. Based on the deep learning method, this project proposes a data-driven model for debris cloud generation. By the combination of Conditional Variation-Auto-Encoder model and numerical simulation results of SPH method, a deep learning model for simulating hypervelocity impact debris cloud was constructed. Before training deep learning model, some data preprocessing steps are needed to improve the data distribution law, such as spatial grid division and quality aggregation, which are conducive to improving the training speed and generalization performance. Experimental results show that the deep learning model can make a good prediction and interpolation in the range of training data set and also showed this ability just near training data. It provided to be a potential way to realize the comprehensive utilization of existing experimental data and numerical simulation results. And also maybe a potential way to improve the accuracy of debris cloud model.
		2020 Vol. 41 (5): 455-469 [Abstract] ( 252 ) HTML (1 KB) PDF (0 KB) ( 189 )

	470	A structural reliability analysis method based on convex set-probability hybrid model

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2020.028
		Because the reliability method under probability theory cannot consider the problem of convex set model under incomplete information, this paper establishes a reliability analysis method under convex set-probability hybrid model based on sample sampling and Laplace progressive integral method. Two different types of convex set models are considered, including ellipsoid model and interval model. Latin hypercube sampling is used to generate sample points in standard space, and then transformed into convex set space by matrix transformation, and the sample points of convex set variables are obtained. These sample points are substituted into the limit state equation, so that the hybrid reliability model is transtormed into the probabilistic reliability model. Laplace progressive integration method is used to solve the failure probability of each limit state equation. The maximum and minimum values of the results are calculated, and the upper and lower bounds of the failure probability are obtained. The coefficient of variation of the failure probability is used to describe the stability of calculation result. The accuracy is verified by three examples, the influence of the number of sample points of convex set variables on the results is discussed and the comparison calculation is carried out by Monte Carlo method under hybrid model. The research shows that the method proposed in this paper has high accuracy and efficiency, it is also applicable to the reliability problems with small failure probability. When the upper and lower bounds of the convex set variables are the same, the results obtained by the interval model and the ellipsoid model are different. In order to stabilize the results, the ellipsoid model requires more convex set sample points than the interval model. If the interval model is used, the number of sample points should be above 3000. If the number of sample points in the convex set is the same, the coefficient of variation of the failure probability calculation result of the ellipsoid model is small, and the stability is higher than interval model. The method proposed in this paper can provide a new idea for the reliability analysis of hybrid model.
		2020 Vol. 41 (5): 470-484 [Abstract] ( 162 ) HTML (1 KB) PDF (0 KB) ( 185 )

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