Search

N, N, N0, N0 -Tetrapropargyl-p, p0-diaminodiphenylmethane (TPDDM) is synthesized and used to blended with 4,40-bismaleimide diphenylmethane (BDM) as propargyl compound in a molten state to obtain a TPDDM modified bismaleimide (BTP) resin. The BTP resins are cured under electron-beam (EB) irradiation as well as heat. The cure degree and reactions of BTP resins are studied. The thermal stability and mechanical properties of the cured BTP resins are further investigated. The results show that the BTP resins can be cured under EB irradiation and have over 82% degree of cure, which increases with the increase of EB irradiation dose. The cure reactions of EB-cured BTP resin are similar to that of heat-cured BTP resin. The temperature at 5% weight loss (Td5) and mechanical properties of the cured BTP resins are close analogies between EB and heat cure processes although the cure degrees of EB-cured BTP resins are lower. The glass transition temperature (Tg) and flexural modulus of the EB-cured BTP resin are higher than that of the heat-cured BTP resin. The Tg of the EB-cured BTP resin can reach over 385°C. The TPDDM-modified BDM is a candidate bismaleimide resin for the EB irradiation curing process in advanced manufacturing technology. [ABSTRACT FROM AUTHOR]

In this work, the hysteretic dynamics of a pseudoelastic shape memory alloy (SMA) spring is modeled and tested. A constitutive model of SMA spring is constructed by combining the theory of mechanical spring and the derived SMA constitutive relation. The SMA spring recovery force is modeled by employing the Euler-Lagrange equation based on a non-convex potential function. A macroscopic differential model is formulated to describe the hysteretic dynamics and the pseudoelasticity of the SMA spring. A theoretical method for estimating the equivalent stretch ratio at a specific temperature of SMA spring is given. Numerical simulations were presented in studying the influence of the stretch ratio at a temperature of 50, 70, and 90°C. The experimental tests are performed and presented together with their numerical counterparts. The comparison is made between numerical and experimental results to validate the proposed model for SMA spring. [ABSTRACT FROM AUTHOR]

Recently, a novel method for mechanical energy harvesting has been proposed, which is based on stress-induced polarization switching in ferroelectric materials. Compared with the traditional piezoelectric energy harvesters, a huge improvement in the output energy has already been theoretically demonstrated. In this article, the influence of different materials on the energy-harvesting performance associated with this new strategy is further studied. The state-of-the-art phase-field model is adopted to investigate the nonlinear hysteretic energy-harvesting process in two nanoscale ferroelectric energy harvesters, which are respectively based on two typical ferroelectric materials--single-crystal BaTiO3 and PbTiO3. In both cases, the effects of the bias voltage and bias resistance are carefully investigated and the optimum values are obtained. Later, the energy-harvesting process and energy flow details in both harvesters working at the optimum conditions are presented and carefully compared in the context of real applications. Furthermore, the energy-harvesting performance of a BaTiO3-based nanoscale piezoelectric energy harvester with equivalent material size is additionally simulated with the finite element method and compared with the corresponding results of the ferroelectric energy harvesters, where obvious advantages associated with the new strategy are demonstrated. [ABSTRACT FROM AUTHOR]

Abstract  The morphology and structure of the regenerated cellulose membranes prepared from its NaOH–urea aqueous solution by coagulating with 5 wt% H2SO4–10 wt% Na2SO4 aqueous solution with different temperatures and times were investigated. The pore size, water permeability and physical properties of the membranes were measured with scanning electron micrograph (SEM), wide X-ray diffraction (WXRD), Fourier transfer infrared spectroscopy (FTIR), flow rate method, and tensile testing. The SEM observation revealed that the structure and pore size of the membranes changed drastically as a function of the coagulation temperature. The membranes coagulated at lower temperatures tended to form the relatively small pore size than those at higher temperatures. On the contrary, the membranes coagulated at different times exhibited similar pore size. Interestingly, the mean pore size and water permeability of the membranes increased from 110 nm with standard deviation (SD) of 25 nm and 12 ml h−1 m−2 mmHg−1 respectively to 1,230 nm with SD of 180 nm and 43 ml h−1 m−2 mmHg−1 with an increase in coagulation temperature from 10 to 60C. However, the membranes regenerated below 20C exhibited the dense structure as well as good tensile strength and elongation at break. The result from FTIR and ultraviolet-visible (UV-vis) spectroscopy indicated that the relatively strong intermolecular hydrogen bonds exist in the cellulose membranes prepared at lower coagulation temperatures. This work provided a promising way to prepare cellulose materials with different pore sizes and physical properties by controlling the coagulation temperature. [ABSTRACT FROM AUTHOR]

Nonlinearities and hysteresis effects in a reciprocal PZT transducer are examined by use of a dynamical mathematical model on the basis of phase-transition theory. In particular, we consider the perovskite piezoelectric ceramic in which the polarization process in the material can be modeled by Landau theory for the first-order phase transformation, in which each polarization state is associated with a minimum of the Landau free-energy function. Nonlinear constitutive laws are obtained by using thermodynamical equilibrium conditions, and hysteretic behavior of the material can be modeled intrinsically. The time-dependent Ginzburg-Landau theory is used in the parameter identification involving hysteresis effects. We use the Chebyshev collocation method in the numerical simulations. The elastic field is assumed to be coupled linearly with other fields, and the nonlinearity is in the E-D coupling. We present numerical results for the reciprocal-transducer system and identify the influence of nonlinearities on the system dynamics at high and low frequency as well as electrical impedance effects due to tuning by a series inductance. It is found that nonlinear effects are not important at high frequencies (1 MHz) subject to high-input voltages, but they become important under high-voltage and off-resonance conditions. [ABSTRACT FROM AUTHOR]

Develops a backward poincare cell-mapping method for animating chaotic fluid mixing. Rotation of the secondary flow of incompressible fluids in a curved pipe; Methods for probing the chaotic fluid mixing. A Backward Poincare cell-mapping (BPCM) method has been developed for animating chaotic fluid mixing. The chaotic mixing field considered is induced by periodically rotating the secondary flow of incompressible fluids in a curved pipe. The pipe's cross-section is transformed into a cell space where each cell is initially assigned with a color code and mapped by integrating the velocity field forward in time. The mixing process is thus animated efficiently with each cell being painted with its color on a computer screen. We propose the backward Poincare cell-mapping instead of direct Poincare cell-mapping as a useful tool for probing the chaotic fluid mixing and for animating the phase deformation of nonlinear dynamical systems. [ABSTRACT FROM AUTHOR]

The fully coupled thermo-electro-mechanical properties of nanoscale ferroelectric actuators are investigated by a phase field model. Firstly, the thermal effect is incorporated into the commonly-used phase field model for ferroelectric materials in a thermodynamic consistent way and the governing equation for the temperature field is derived. Afterwards, the modified model is numerically implemented to study a selected prototype of the ferroelectric actuators, where strain associated with electric field-induced non-180° domain switching is employed. The temperature variation and energy flow in the actuation process are presented, which enhances our understanding of the working mechanism of the actuators. Furthermore, the influences of the input voltage frequency and the thermal boundary condition on the temperature variation are demonstrated and carefully discussed in the context of thermal management for real applications. [ABSTRACT FROM AUTHOR]

Different from the traditional piezoelectric vibration energy harvesting, a new strategy based on stress-induced polarization switching has been proposed in the current paper. Two related prototypes are presented and the associated advantages and drawbacks have been discussed in detail. It has been demonstrated that, with the assistance of a bias electric field, the robustness of the energy harvesters is improved. Furthermore, the real-space phase-field model has been employed to study the nonlinear hysteretic behavior involved in the proposed energy harvesting process. A substantially larger electric current associated with the stress-induced polarization switching has been demonstrated when compared with that with piezoelectric effect. In addition, the effects of bias electric potential, bias resistance, mechanical boundary conditions, charge leakage and electrodes arrangements have also been investigated by the phase-field simulation, which provides a guidance for future real implementations. [ABSTRACT FROM AUTHOR]