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In this work, a novel mechanical amplification structure for a MEMS vibratory gyroscope is proposed with the aim of improving their sensitivity. The scheme is implemented using a system of micromachined V-shaped springs as a deflection amplifying mechanism. The effectiveness of the mechanism is first demonstrated for a capacitive fully decoupled quad mass gyroscope. A proof of concept vertical-axis mechanically amplified gyroscope with an amplification factor of 365% has been designed, simulated and fabricated, and results from its evaluation are presented in this paper. Experimental results show that the natural frequency of the gyroscope is 11.67 KHz, and the full scale measurement range is up to ±400°/s with a maximum nonlinearity of 54.69 ppm. The bias stability is 44.53°/h. The experiment results show that this quad mass gyroscope's performance is a very potential new way of reaching the navigation grade in the future. [ABSTRACT FROM AUTHOR]

In the sheet forming process, the final bending angle is mostly determined based on experience rather than based on a reliable theoretical framework. Furthermore, the local bent areas tend to decrease in thickness. Thus, it is difficult to control the quality of the final products. In this study, we developed an optimized bending angle function by combining segment boundaries to improve the final sheet forming quality and reduce the local thinning defects. The finite element submodel method was used to establish a high-definition thickness-sensitive numerical model for the bottom bending area of the hat-shaped part. This method accurately simulated the thickness variation law of the bending area of roll forming and analyzed the optimization function of the bending angle of the segment boundary as well as the process parameters for local thinning. Finally, roll-bending experiments were conducted to analyze the bending angle distribution conditions and the change law with respect to the process parameters of the cap-shaped parts in case of local thinning defects to verify the accuracy of the finite element simulation process. The results showed that the local thinning defect in the bending area of the hat-shaped part was smaller during roll bending, and the forming quality obtained was better than that obtained using other previously reported methods. The experimental data were consistent with the simulation data, verifying the accuracy of our proposed approach. Moreover, the thickness of the thinning defect was influenced by the process parameters; the plate bending radius and yield strength increased, and thickness thinning gradually decreased. Furthermore, the local thinning defects increased with the increasing plate thickness. [ABSTRACT FROM AUTHOR]

We investigate the MEMS resonant cantilevers for high-performance thermogravimetric analysis (TGA) of chemical decomposition, featuring high accuracy and minimized thermal lag. Each resonant cantilever is integrated with a microheater for sample heating near the free end, which is thermally isolated from the resonance excitation and readout elements at the fixed end. Combining finite element modeling and experiments, we demonstrate that the sample loading region can stabilize within ~11.2 milliseconds in response to a step heating of 500 °C, suggesting a very fast thermal response of the MEMS resonant cantilevers of more than 104 °C/s. Benefiting from such a fast thermal response, we perform high-performance TG measurements on basic copper carbonate (Cu2(OH)2CO3) and calcium oxalate monohydrate (CaC2O4·H2O). The measured weight losses better agree with the theoretical values with 5–10 times smaller thermal lags at the same heating rate, compared with those measured by using conventional TGA. The MEMS resonant cantilevers hold promise for highly accurate and efficient TG characterization of materials in various fields. [ABSTRACT FROM AUTHOR]

Composite concrete structures are designed to integrate various concrete types at different levels, thereby improving their shear properties. In this paper, the effects of the interfacial keyway, reinforcement ratio, and pouring sequence on the shear strength of concrete-coal gangue concrete interface are studied by experiments and analyses. A total of 10 specimens were made, and the push-off test was carried out. Nonlinear finite element simulation was carried out using ABAQUS, and the influence of keyway angle on crack development was studied based on the extended finite element method (XFEM). It is found that the remarkable tensile and crack stability of engineered cementitious composites (ECC) has a positive effect on the shear strength of the ECC-coal gangue concrete interface. The ultimate shear strength of the interface and the ductility of the interface under shear load are significantly improved by interfacial shear reinforcement. The introduction of an interfacial keyway improves the shear strength of the concrete interface, and the number of keyways has the most significant effect on the interfacial shear strength. The angle between the crack propagation direction and interface will increase with the increase of keyway angle, the simulation results are in good agreement with the experiments. [ABSTRACT FROM AUTHOR]

Understanding water transport in partially saturated concrete is of great significance for the durability assessment and service life prediction in engineering practice. In this paper, the three-dimensional (3D) unsaturated transport in concrete under capillary suction, hydraulic pressure and gravity force is simulated by the finite element method (FEM). A three-phase mesoscale model containing mortar matrix, coarse aggregates and interfacial transition zone (ITZ) is utilized, in which the zero-thickness interface element is employed for simulating thin ITZ structure. As the most important parameters for unsaturated mass transport analysis, the hydraulic diffusivity and unsaturated permeability are rationally estimated from the physical experiments. The cumulative mass of water penetration, as well as the penetration depth, obtained from the numerical modeling shows reasonable accordance with the experimental results. Moreover, main characteristics of the unsaturated transport (e.g., pore water pressure development, flow velocity distribution and the dynamic movement of wetting front and phreatic surface) are well captured by the simulation. [ABSTRACT FROM AUTHOR]

With the uncertain fractures involved in the water-rock interaction in the enhanced geothermal system (EGS) taken into account, numerical simulation of heat extraction is challenging to implement, especially in the situation where the EGS is conducted in a complex fracture network. In this study, a discrete fracture network (DFN) modeling procedure based on finite element method (FEM) is proposed to simulate the uncertainty of heat extraction performance in the fractured hot dry rock (HDR), in which the rock matrix and fractures are discretized into triangular elements and zero-thickness elements, respectively. To verify the effectiveness of the established numerical model, the simulation results are compared with the analytical solution and a good agreement is reached. Further, Monte Carlo simulation (MCS) method is adopted to probabilistically study the production performance of EGS considering the randomness of the fracture network. According to the MCS results, heat production performance, i.e., outlet average temperature, EGS lifetime, output thermal power, heat extraction ratio, and levelized cost of energy (LCOE), are statistically analyzed. The study results indicate that the heat extraction performance can be more effectively assessed by the probabilistic analysis, and the uncertainties involved in the heat extraction process cannot be ignored. • Fracture uncertainty should be taken into account in water-rock interaction in EGS. • Single deterministic simulation might be insufficiently accurate. • MCS method is adopted to probabilistic study the production performance. • Probabilistic analysis provides guidance for geothermal exploitation in EGS. • Performance assessment parameters data have statistical distribution feature. [ABSTRACT FROM AUTHOR]

Concrete is modeled on the mesoscale as a heterogeneous three-phase composite consisting of mortar, aggregates and the interfacial transition zone (ITZ). By exerting a steady state flow in the concrete sample, the effective permeability is estimated using finite element method (FEM). Extensive Monte Carlo (MC) simulations for more than 1000 concrete samples are carried out. The effects of the mesostructural parameters (i.e., the shape, gradation and volume fraction of aggregates and the thickness and permeability of ITZ) on the permeability of concrete are comprehensively investigated. For a specific set of mesostructural parameters, the size of the representative volume element (RVE) for concrete permeability is suggested in terms of the expected errors by numerical and statistical analysis. It shows that computational homogenization for estimating the effective permeability of concrete in three dimensions (3D) is absolutely necessary since the two dimensional (2D) results are less representative. [ABSTRACT FROM AUTHOR]

Durability of concrete depends largely on its water permeability, which is dominated by the composition and difficultly evaluated. This paper presents a three-dimensional (3D) FE algorithm to investigate the water transport performance in concrete. This FE model possesses three-phase mesostructure consisting of coarse aggregates, mortar matrix, and the interfacial transition zone (ITZ) which is practically modeled by the zero-thickness interface element. A series of numerical tests with regard to concrete samples containing different volume fractions of coarse aggregates are conducted. The calculated permeability coefficients are in reasonable accordance with the physical experiment data. Effects of aggregates and ITZ on the concrete permeability are also quantitatively studied by the numerical test. It is proved that the proposed algorithm is capable of modeling the permeable characteristics of concrete which is affected greatly by its heterogeneous mesostructure. [ABSTRACT FROM AUTHOR]

Numerical investigation on stability of the rock slope with densely distributed fractures is still challenging. To overcome the large computational requirements caused by the fracture representation, material heterogeneity and mathematical nonlinearity, an efficient discrete fracture network (DFN) based modeling scheme is developed in this paper. With DFNs stochastically generated according to the statistical distributions of the fractures for resembling the natural fractured rock slope, finite element method (FEM) based strength reduction analysis is conducted for locating the critical slip surface and assessing the factor of safety, where the rock blocks are discretized as solid elements while discrete fractures are practically modeled by frictional contact interface elements. The effectiveness of the proposed approach is validated by comparison against analytical and several numerical solutions. A case study is further performed to evaluate the effects of DFN realization number and geometrical configuration on the stability of the fractured rock slope. It shows that 20 DFN realizations are sufficient to obtain a statistically convergent mean of the factor of safety. The predicted critical slip surface displays to be non-circular but linear or broken line morphology along the fracture network. The proposed numerical scheme shows to be useful and promising in investigating the deformation response and sliding failure mode in highly fractured rock slope. Massive fractures disorder the displacement distribution of the slope and influence the overall factor of safety, and the estimated factor of safety decreases with the increase ofslope height and angle, indicating the fracture distribution and slope geometric features as the prominent influential factors. [ABSTRACT FROM AUTHOR]

Tracking the crack propagation in concrete at the mesoscopic level is of great importance for revealing the crack pattern and failure mechanism, due to the huge threat of cracking to structure safety. This paper develops a phase field modeling scheme with mesostructure of concrete composite to investigate its crack propagation behavior. With the classical phase field model and the staggered algorithm implementation by three-dimensional (3D) finite element method (FEM), crack propagation within concrete's mesostructure composed of coarse aggregate, mortar matrix, interfacial transition zone (ITZ) and initial defects including micropores and microcracks is modeled. The proposed modeling scheme is tested on single-aggregate samples and complex mesostructured concrete samples subjected to uniaxial loading, showing reasonable accordance with the experimental observation and common failure modes of concrete material. The results indicate that mesostructural configurations are important factors affecting the crack pattern of concrete. The presence of coarse aggregates is prone to initiate and induce interfacial cracking in the ITZ effect, but also exerts the blocking effect on the crack growth. And the initial defects (micropores and microcracks) are also the important influential factor on crack initiation, propagation and the formation of the major crack. It is found that the higher the volume fractions of aggregates and initial defects, the cracking of concrete initiates earlier, propagates faster and penetrates more easily when subjected to the same loading condition. [ABSTRACT FROM AUTHOR]

This research investigates the air drag damping effect of the micromachined cantilevers in different resonance modes on the quality factor, which are operated in ambient air. Based on a simplified dish-string model for air drag force acting on the resonant cantilever, the air drag damping properties of the cantilevers vibrating in different modes are analyzed with theoretic vibration mechanics, which is complemented and further confirmed with finite-element simulation. Four kinds of integrated cantilevers, which resonate in the first flexural mode, the second flexural mode, the first torsional mode, and the second torsional mode, respectively, are designed and fabricated by using micromachining techniques. Finally, biomolecular sensing experiments are carried out to verify the theoretical results obtained before. From both the modeling and experimental results, it can be seen that damping characteristics of the torsional cantilever resonators are generally better than that of the flexural ones, and quality factor of the cantilever resonator in a higher-frequency mode is always superior to that in a lower-frequency one. Among the four kinds of microcantilever resonators operated in our experiments, the one operated in the second flexural modes exhibits the highest Q factor and the best biomass sensing performance. [ABSTRACT FROM AUTHOR]

• Coupling behavior of groundwater flow and solute transport in fractured rock mass was simulated by a 3D FE algorithm. • Fractures were modeled practically by the zero-thickness elements. • The proposed approach was validated with various means including analytical, experimental and numerical methods. • Solute concentration field in fractured rock was evaluated, along with its influencing factors. Understanding of water and mass transfer in fractured rock mass is essential to the safety and environmental problems associated with rock engineering. It is still challenging to precisely predict the transport behaviors of water and solute in rock mass due to the large computational requirements when considering the presence of massive fractures and the mass exchange between rock matrix and fractures. Based on the discrete fracture network (DFN) model, a three-dimensional (3D) numerical approach is proposed to investigate the coupling behavior of groundwater flow and solute transport in fractured rock mass. Utilizing a stochastically generated fracture-matrix system, numerical simulation for groundwater flow and solute transport is implemented for both rock matrix and fractures with finite element method (FEM). With rock matrix discretized as tetrahedral elements and discrete fractures represented by zero-thickness elements, the modeling complexity is significantly reduced. The proposed approach is validated with various means including analytical, experimental and numerical methods. It is further employed to simulate the mass transport process in rock mass containing large-scale fracture network, predict the solute concentration distribution and estimate the dominant factors influencing the solute field. From the results, the main features of mass transfer in fractured rock mass are captured. Water convection in fractures could greatly affect the distribution of the solute concentration, indicating that the discrete fractures play an important role in accelerating the mass transport. The diffusion coefficient of the rock matrix also alters the overall transport characteristics of solute species, which should not be ignored for a precise prediction. The findings of this study could provide a direct reference for optimizing the pollutant treatment plan and the construction design of the radioactive waste repository. [ABSTRACT FROM AUTHOR]

Abstract: To enhance the stability of packaged high-g MEMS accelerometers with double cantilevers positioned asymmetrically, the dynamic shock responses of components versus impurity concentration of piezoresistors at various working temperatures have been probed by using Finite Element Method (FEM). Results indicate that the dynamic output responses of component are actually the superposition of the forced vibrations with dynamic shock and those of cantilevers in their eigenfrequency. The dynamic responses of components are sensitive to the working temperature. With the increase of working temperature, the inherent frequency vibrations of the cantilevers are depressed gradually. Moreover, the larger the difference between the working temperature and reference temperature, the more obvious the impurity effect of piezoresistors is. The difference between the peak output voltage of response under 1×1018 cm−3 and that under 1×1021 cm−3 varies greatly from −2.2146mV at T =0°C to 8.6609mV at T =100°C, of course, is partly due to the characteristic variation of damping media under various working temperatures. Therefore, to improve the stability of component and further weaken the impurity concentration effect and the temperature effect of piezoresistors on the performance of components, it is necessary to increase the impurity concentration of piezoresistors and keep the components working at relatively lower temperature only if the electro-performance of component is satisfied. [Copyright &y& Elsevier]

Abstract: In this paper, the study on silicon nano-mechanical electro-thermal probe array used for high-density storage has been performed. After the introduction of structure and working principle of the NEMS probe, the design of component followed by using both theoretical analysis and finite element analysis (FEA). By using advanced (micro-) nano-machining technology, the piezoresistive sensor and the resistive heater have been integrated on the silicon micro-cantilever and the component has been fabricated. Subsequently, the electro-thermal performance and sensitivity have been tested agreeing well with those simulated. About 31.6Gb/in2 surface data-writing density was realized successfully on thin PMMA film by using AFM equipment with optimized thermal writing parameters. [Copyright &y& Elsevier]

When the structures or parts are subjected to fatigue damage, its nonlinear characteristics will be characterized sensitively. The nonlinear characteristics of the system can be well described by the nonlinear output frequency response function deduced by the Volterra series. The nonlinear output frequency response function is the collection of frequency functions of various orders which contain different nonlinear information about the system. In other words, it is not intuitive when it is used directly for the detection of fatigue damage to structures or parts. Therefore, how to build an intuitive detection index will be the key to the application of the nonlinear output frequency response function in engineering practice. In this paper, based on the concept of information entropy, complexity and divergence, 4 detection indexes were proposed and the definition and estimation methods were given. Fatigue tests were carried out on the specimens by a fatigue test machine, and a series of specimens with different fatigue cycle times were obtained. The nonlinear output frequency response function was estimated by using the data of the hammer excitation measurement. The detection effect of 4 detection indexes and traditional detection index Fe was analyzed and compared. The results show that the proposed detection indexes are more sensitive and effective for detecting fatigue damage before microcracks formed. [ABSTRACT FROM AUTHOR]

In this work, finite element simulation has been applied in frequency-domain and time-domain analyses for a packaged accelerometer used in high-G environments. In order to understand the effect of the adhesive material, which is filled in the gap between the sensor chip and the package bulk, on the output signal of accelerometer, a simplified packaged structure has been adopted in this analysis. The results from simulations show that the Young’s moduli of seal adhesive has important influences on the mode shapes of the packaged accelerometer and a small Young’s modulus will bring in strong distortion of output signal of accelerometer. As the Young’s moduli increased, the waveform of accelerometer output signal became better after digital filtering. The seal adhesive with Young’s modulus like molding compound in IC packaging would not induce significant problems in signal distortion. The frequency and averaged amplitude of output signal of the packaged accelerometer were not affected by Young’s modulus of seal material. The accelerometer output was linearly dependent on the input of acceleration impulse and the response was very well when the input of the acceleration amplitudes changed. The simulations for a practical packaging structure defined in this work showed that the results were similar to the simulations for the simplified structure of accelerometer with packaging, and the simulation results from the simplified structure could serve as a basis for design of high-G accelerometer packaging in a certain degree. [Copyright &y& Elsevier]