Search

This paper presents the first-principles investigation on interfacial adhesive strength between grafted polymer and cellulose. Focusing on maleic anhydride-grafted polypropylene, which is expected to be used in various applications including automobiles, a simple interfacial model was constructed under a local tensile loading condition. Then the stress–strain relation, deformation of molecular structure and breaking process were discussed. From comparison of mechanical responses among three chemically possible bonding configurations, it was clarified that the monoester bond exhibited higher interfacial strength than the diester bond. We also found that controlling the bonding configuration can improve the interface strength by about 50% compared to when primary OH groups react to form ester bonds. It was proved that this first-principles calculation model was effective for the definitive design and development of chemical modification of nanocellulose.

A multiscale numerical investigation into the origin of the magnetoelectric effect in multiferroic composite materials was performed. Specifically, a well-known but unconfirmed mechanism for generating a macroscopic magnetoelectric effect through transmission of mechanical strain between the ferroelectric and ferromagnetic phases in an inhomogeneous microstructure was quantitatively established through multiscale finite element simulations. An asymptotic homogenization theory was employed for scale bridging between the macrostructure and the microstructure. Focusing first on a polycrystalline BaTiO3/Terfenol-D composite, the relation between the physical properties and the ferroelectric-phase content was analyzed. A uniform magnetic field was then applied to the macrostructure and the mechanical strain in the microstructure was investigated. The specific strain component exhibited an off-centered distribution when divided into ferroelectric and ferromagnetic phases. The simulation revealed that the macroscopic magnetoelectric effect is determined by two factors, the shift of the average strain from zero and the homogenized piezoelectric constant. The macroscopic magnetoelectric effect increases as the product of these two factors increases. This conclusion is applicable to other inhomogeneous structures and it can explain the trend in the magnitude of the magnetoelectric effect for a random polycrystalline structure, a layered polycrystalline structure, and a layered single-crystal structure. The findings are helpful for the functional design of multiferroic composite materials.

A new actuator in which a metal cap is combined with a bimorph piezoelectric element was proposed, and the liquid transfer and mixing performance when applied to valveless microfluid devices was numerically verified. Especially to ensure high versatility, we aimed to be able to demonstrate sufficient performance with a general power supply of AC100V, 50 Hz in Japan. Two drive modes were considered: a single actuator applied only to the upper surface of the circular tank and double actuators applied to the upper and lower surfaces. In the liquid transfer performance test, it was found that the flow rate was improved by about 19 times in the single MC-BMP (Metal-Capped Bimorph) and about 82 times in the double MC-BMP compared with the conventional BMP (Bimorph). On the other hand, in the mixing performance test, it was found that the mixing index was improved about 2.3 times in the single MC-BMP and about 2.9 times in the double MC-BMP compared with the conventional BMP. Furthermore, protrusions were inserted into the flow path at the connection between the main flow path and the piezoelectric actuator, and the effect on the mixing performance was also verified. As a result, the mixing performance was greatly improved by inserting the protrusions, and finally, when two protrusions were inserted in the double actuation of the new MC-BMP, the mixing index reached 85%. From these results, we were able to verify the superiority of the proposed new MC-BMP, the usefulness and versatility that can be used with the general power supply of 100 V and 50 Hz. The findings can be expected to contribute to the design and development of pumps and mixers for various valveless microfluid devices.

To support the sustainable development of housing in a low-carbon society, this paper presents a multiscale simulation that connects material development at microscale, structural design of components at mesoscale, and evaluation of thermal insulation of the entire house at macroscale. The aim is the quantification of the correlation between local materials research and global goals. As one of important challenges, the constructed multiscale simulation was applied to a novel polycarbonate (PC) window whose surface is coated with scratch resistant resin containing hollow silica (HS) nanoparticles. The proposed PC window is one of the promising heat-insulated windows that is lightweight, has excellent light transmission, and is low in cost. The microscopic composite structure of HS particles dispersed in resin and the mesoscopic laminated structure of windows were analyzed, and the thermal insulating effect on an model room was clarified. In particular, the effects of thickness and HS content of coating layer were analyzed for the design of the window. HS particles reduced the thermal conductivity of the resin coating layer to 0.038 W/(m⋅K) or less with 3 wt%, and they also reduced the thermal conductivity of the single-glazing PC window to 0.167 W/(m⋅K) with 4 μm surface coating. Additionally, an evaluation experiment of thermal insulation was conducted in winter using a model house. The novel PC and a conventional glass windows were experimentally and computationally compared. As results, overnight in winter, the amount of CO2 emissions that could be reduced in one room was 0.048 gCO2 per window unit area.

A statistical investigation of the homogenized physical properties of polycrystalline $$\hbox {BaTiO}_{3}/ \hbox {CoFe}_{2} \hbox {O}_{4}$$ multiferroic composites is presented to detail the effect of how the representative volume elements for the microstructure are defined. The dependence on the number of microstructural orientations and the number of computational trials was analyzed, and the effective microstructural modeling condition was discussed based on the 95% confidence interval of the macrostructural homogenized physical constants. The computation reveals that the convergence of the homogenized physical properties is different between the diagonal and off-diagonal coupling constants. The homogenized magnetoelectric constants require more orientations and trials to achieve convergence. The influence of crystal orientation control through polarization treatment on the homogenized magnetoelectric constants was then investigated using the obtained effective microstructure model. The relation between the macrostructural homogenized physical properties and the microstructural orientations was discussed for multiferroic composites with different domain switching systems.

In this paper, the effective physical properties were numerically investigated for polycrystalline multiferroic com- posite materials consisting of ferroelectric BaTiO3 and ferromagnetic CoFe2O4 phases. An asymptotic homogenization theory was employed for scale-bridging between macrostructures and microstructures. The microstructural crystal orientations of both phases were assumed to be perfectly poled and the volume fraction of ferroelectric phase was changed from 0% to 100%. And then the homogenized physical properties of macrostructure, such as elastic stiffness, electric permittivity, magnetic permeabil- ity, piezoelectric and piezomagnetic stress constants, magnetoelectric constants, were estimated through the multiscale finite element analysis. Especially the local piezoelectric or piezomagnetic constants of each phase were virtually varied and their influence on the global magnetoelectric constant was discussed to understand ideal material combination.

This paper presents the first-principles investigation on the effect of a silane coupling agent on interfacial adhesive strength with metals. The challenge of this study is to relate atomic-scale phenomena on the interface to stress-strain diagram. Focusing on 3-mercaptopropyl trimethoxy silane (MPS), pure copper and aluminum were selected as the bonding metal. A simple MPS/metal interface model was constructed under a tensile loading condition. First-principles calculations show that MPS exhibits higher interfacial adhesion strength with pure aluminum than with cupper, qualitatively in agreement with the results of the single-lap tensile shear test. It was revealed that the concentrated increase in bond length between specific atoms corresponds to an atomic-scale necking and it forms nonlinear response and a maximum point of stress in a macroscopic stress-strain diagram. It was proved that this first-principles calculation model was effective for the design and development of silane coupling agents suitable for multi-materialization.

A multiscale optimization is presented for multiferroic composite materials to enhance magnetoelectric (ME) effect. The challenge of this study is to discover innovative microstructures beyond the conventional laminated structure which is the best of existing materials. The asymptotic homogenization theory was employed for scale bridging between the macrostructure and the microstructure. The homogenized ME coefficient of macrostructure was set to an objective function. The phase configuration and polarization directions in the microstructure were utilized as design variables. The computation yielded to an optimized microstructure, and found its macro homogenized ME coefficient is 21% larger than the conventional structure. The optimized microstructure consists of four rectangle regions and they are periodically repeated. Ferromagnetic and ferroelectric phases are alternately lined in each region and their polarization directions are determined by the special stated Euler angles. The computation successfully established that the optimal microstructure exists beyond the conventional layered structure. The findings open new avenues for enhancing physical properties of functional materials, and are expected to expand to digital fabrication by 3D printing.

This paper presents a computational and experimental study of a valveless pump driven by a noble piezoelectric composite actuator consisting of a bimorph piezoelectric plate and a metal cap. The superiority of deformation performance of the proposed composite actuator was demonstrated computationally through fi nite element simulation and was then verifi ed experimentally by defl ection measurements of a disc-shaped prototype under an alternating electric fi eld. The proposed composite actuator was applied to a valveless pump in a Y-shaped fl uid channel. The pump’s performance was estimated using a piezoelectric-fl uid interaction fi nite element simulation. The effect of the fl uid channel confi guration was investigated, and the liquid feed volume is discussed and compared with that of conventional actuators.

We presented a multiscale nonlinear finite element simulation to analyze domain switching behaviors in ferroelectric materials. We utilized an incremental form of fundamental constitutive law to consider changes in the material properties caused by domain switching. A multiscale nonlinear problem was formulated by employing the asymptotic homogenization theory based on the perturbation method and implemented using finite element analysis. The developed simulation was applied to barium titanate with a Perovskite-type tetragonal crystal structure. The 90° and 180° domain switching behaviors of a single crystal were computed for verification. The nonlinear behaviors of a bulk polycrystal with virtual microstructure were analyzed as a case study. The variation of the crystal orientation distribution in the polycrystalline microstructure was analyzed to reveal its influence on macroscopic hysteresis and butterfly curves.

In this paper, a two-step scale-up procedure based on asymptotic homogenization theory is proposed for hierarchical structures consisting of multigrains and multidomains in piezoelectric materials. Intragranular domains are modeled as a microstructure during the first-step homogenization. Then, in the second-step homogenization, an aggregate of randomly oriented grains is modeled by applying the first-step homogenized material properties of multidomains to every grain. A dual-domain structure consisting of positive and negative directional domains with a 180° orientation gap is computed for case study analysis. The three-dimensional electron backscatter diffraction-measured microstructure is employed for the multigrain structure. The effect of the domain configuration on the macroscopic homogenized material properties of polycrystalline piezoelectric materials is investigated through the two-step homogenization process. In particular, the material property changes caused by the piezoelectric effect, which cannot be estimated by the mixture law, are discussed for multigrain and multidomain structures.

From 1880’s discovery of piezoelectricity by French physicists Jacques and Pierre Curie, a huge number of piezoelectric materials have been developed and applied to the industrial equipment and scientific instrument. In the middle of 20th century, most widely used ceramic piezoelectric materials, BaTiO3 (BTO) in 1944, PbTiO3 in 1950, and Pb(Zr,Ti)O3 (PZT) in 1955, were discovered through “hermetic art approach.” It was not CAE driven material discovery. Actually, the experimental trial and error approach is inefficient way for the material discovery. Therefore a new CAE technique to develop a new high performance piezoelectric material under a short lead time is strongly required. It can analyze material characteristics, and design material structure and generation process simultaneously before actual production. This overall CAE technique for new material design and generation, which can be called as “process crystallographic simulation,” is discussed in this state-of-the-art paper, which will be able to establish a new concept of material and process design.

A computational approach based on electron backscatter diffraction (EBSD) measurement was proposed to estimate the effects of crystal morphology on the overall response of polycrystalline piezoelectric ceramics. EBSD-measured crystal orientations of a polycrystalline piezoelectric ceramic, barium titanate, were applied to a multiscale fi nite element simulation based on asymptotic homogenization theory. First, the orientation dependence of material properties, such as elastic compliance constants, dielectric and piezoelectric strain constants, was discussed for a single-domain crystal of tetragonal perovskite structure. The computation indicated that piezoelectric strain constants are more sensitive to crystal orientation compared with other properties. Then the single-crystalline material properties were introduced into multidirectionally oriented grains in the polycrystalline microstructure, the multiscale fi nite element analysis between macrostructure and EBSD-measured microstructure was performed. In this paper emphasis was placed on the diminution of microstructure. The authors discussed about the adverse effect on each component of macrostructural homogenized material properties, which is useful for micromechanics approaches.