In the present study, the deformation-induced anisotropic mechanical characteristics and the strain distribution are evaluated from the specimens cut from the necking part of polycarbonate. First, large specimens are used to create deformation-induced anisotropy in the necking part via a uniaxial tensile test. Next, the small specimens are cut from the necking parts in an arbitrary direction with respect to the tensile direction of the large specimens. The anisotropic mechanical characteristics in the small specimens are evaluated by a uniaxial tensile test and the strain distribution is measured by the digital image correlation. The result shows that the stress-strain curve of the small specimen depends on the cutting angle to the tensile direction of the large specimens. The elastic modulus and the maximum stress of the small specimens are maximum in the tensile direction of the large specimen, and the elastic modulus and the maximum stress decreases with increasing the cutting angle. Therefore, the deformation-induced anisotropic mechanical characteristics in the necking part are observed. In addition, if the uniaxial tensile direction to the small specimen differs from that to the large specimen, a shear strain band appears in the small specimen and the longitudinal direction of the shear strain band is affected to the tensile direction of the large specimen. The test results indicate that the anisotropic elastic modulus and the anisotropic characteristics in the plastic region are expressed by the anisotropic elastic constitutive equation and the Tsai-Hill criterion, respectively. Moreover, the anisotropic strain hardening is revealed because the Tsai-Hill parameters depends on the plastic strain.
Ductile and brittle behavior during deformation and fracture for ice have attracted considerable research interest. The strength of ice has been reported to depend on the temperature, strain rate, and other factors. In addition, the tip shape of an object that comes into contact with ice is one of the important factors which influence the fracture phenomenon of ice. However, the associated fracture mechanisms have not been clarified. Therefore, in this study, a quasi-static indentation test was performed to investigate the deformation and fracture properties of pure ice. The displacement rate ranged from 0.002 to 2 mm/s, and the test temperature was approximately -10℃. Conical indenters with indenter angles (apex angles) of 90, 120, and 140° and spherical indenters with diameters of 10, 15, and 20 mm were used. In the case of the conical indenters, the maximum load at effective strain rates of 10-1 and 100 s-1 increased owing to the temporary stagnation of the cracks, caused by the negative rate dependence of the ice strength. In contrast, in the case of the spherical indenters, the maximum load at effective strain rates from 10-4 to 10-1 s-1 exhibited a trend similar to that in the uniaxial compression test: specifically, the maximum load peaked at 10-3 s-1 and then decreased with further increase in the strain rates. Furthermore, the contact radius when the ice fractured did not change considerably for different indenter shapes. This finding indicated that the internal deformation distribution caused by the indentation considerably influenced the deformation and fracture properties of ice. A larger indenter angle or diameter of the conical or spherical indenters, respectively, corresponded to a larger internal deformation distribution and a smaller displacement pertaining to the fracture.
Minimizing the retention of nuclear fuel materials in glove box components and curtailing the external exposure dose are desirable. Therefore, plutonium and uranium mixed oxide (MOX) powder adhesion-prevention technology involving nanoparticle coating of the acrylic panels of the glove box is developed. Surface analysis using atomic force microscopy showed that root mean square roughness value of the nanoparticle-coated acrylic test piece surface (75.8 nm) was higher than that of the noncoated surface (2.14 nm). The nanoparticle coating reduced the van der Waals force between alumina particles and the test piece surface through the formation of nanosized rugged surfaces. The coating reduced the minimum adhesion force (normalized by the particle diameter) between the uranium dioxide particle and the acrylic test piece surface. For the smallest particle (diameter: ～5 μm) associated with desorption, this minimum adhesion force decreased to ～5%. The nanoparticle coating also lowered the average adhesion mass per unit area of the MOX powder on the acrylic test piece to ～10%. The expectation is that this method will reduce the retention of nuclear fuel materials in the box, lower the external exposure dose, and improve the visibility of the acrylic panels.
One of the effective solutions to reduce CO2 emission derived from fossil fuels is the suppression of coal consumption in industrial boilers and power plants. Torrefaction is one of the promising treatments for reforming conventional solid biofuels, and torrefied solid biofuels have come to attract attention as an alternative to coal. When torrefied solid biofuels are utilized or produced, energy properties such as higher heating value (HHV) and energy yield of torrefied solid biofuels are quite important. In this study, to evaluate the energy properties for a given pyrolysis condition analytically, evaluation methods of HHV and mass yield of torrefied biomass based on isothermal pyrolysis kinetics are investigated for three biomass species, i) softwood; Japanese cedar, ii) hardwood; castanopsis and iii) herbaceous biomass; rice straw. There are two aims of the study. One is to present the HHV evaluation method by lumped-parameter pyrolysis kinetic models with high evaluation accuracy. The reduction in the mass yield due to torrefaction can be evaluated by the two-step pyrolysis kinetic model, and the HHV is provided with the mass fractions and heating values for constituent substances included in torrefied biomass of the two-step pyrolysis kinetic model. The other is to present the simple correlation to evaluate HHV without depending on three biomass species. From the comparison between the HHV evaluation method and experimental data, it is clarified that the proposed HHV evaluation method based on the two-step pyrolysis kinetic model can be useful to evaluate the HHV of torrefied biomass for three biomass samples with high evaluation accuracy, 5% or less. The linear correlation between HHV enhancement factor and mass yield of torrefied biomass is found regardless of three biomass species in the range of torrefaction mass yield larger than 0.6.
In recent years, many researchers have been attempting to optimize multi-mass dynamic vibration absorbers (DVAs) to improve the performance and robustness. To date, exact design formulas have been obtained for series-type double-mass DVAs, but for parallel-type double-mass DVAs, the optimal solutions have only been obtained in numerical form. Moreover, the expressions for calculating the numerical solutions were extremely long, making it impossible for the average user to obtain accurate design values. Another problem with the previously published expressions is that their length amplifies the rounding errors under certain calculation conditions, and sometimes makes the calculations impossible. In this paper, we propose an approximate design formula for a parallel-type double-mass DVA that is almost comparable to the exact solution in terms of accuracy. The deterioration rate of the damping performance has been confirmed as less than 0.015% in the typical use range of DVAs (mass ratio with the primary system of less than 0.2).
In most dynamic vibration absorbers (DVAs) used in practical applications, polymeric materials that have both restoring capabilities and damping effects are used instead of coil springs as spring elements. It is known that the damping force for such polymeric materials has hysteretic characteristics and varies in proportion to the relative displacement rather than the relative velocity between objects. This paper proposes an optimal design formula for a double-mass hysteretically damped DVA with two masses connected in series. For the design of the DVA in this study, the stability maximization criterion, which attenuates the free-vibration response of the primary system in the shortest time, was adopted. It was found that the optimal design expression for installing the series-type double-mass DVA on an undamped primary system can be expressed by a very simple formula. The maximized stability, which determines the speed of vibration convergence, of the double-mass DVA was 1.7 times that of the corresponding single-mass DVA. When there is damping in the primary system, the optimal design condition for the DVA cannot be expressed with such a simple formula, but an equation to calculate it is presented in this paper. The equation can be easily solved numerically, and the results show that the stability of the system is further increased compared to the undamped primary system.
Liquid crystalline epoxy resins have been reported to show superior mechanical and thermal properties. This high functionality is attributed to their meso- or macroscopic layered domain structure and their molecular scale ordering; hence, elucidation of the mechanism of layer formation during curing reactions is necessary for material development. In this study, the layer formation process has been investigated by the reactive coarse-grained molecular dynamics method. A mesogenic liquid crystalline epoxy and a typical non-mesogenic epoxy (diglycidyl ether of bisphenol A), mixed with a curing agent 4,4′-DDS (diaminodiphenyl sulfone), were considered. The results clearly showed that the mesogenic epoxy molecules formed a layer structure, whereas the non-mesogenic epoxy molecules remained as the amorphous structure even after the curing reactions. This difference was assumed to be caused by the straight structure of the mesogenic epoxy molecules and the strong attractive interactions between mesogenic parts. The interlayer spacing calculated by the simulation was in close agreement with the X-ray measurement. The details of the curing reaction process, e.g. the conversion and the molecular size in the mesogenic epoxy system, were also investigated. A large layer structure covered the simulation system after the stage in which the first reaction of the amine group was dominant, but the molecules were not large: the molecules were mainly attracted by the non-bond interactions. With the progress of the second reaction of the amine group, by which the tertiary amine was formed from the secondary amine, the molecular size became large and a rigid layer structure was formed over the whole simulation system. These results clearly indicated the role of the curing reactions: the first reaction produced small molecules from monomers and made them align in a layer form, and the second reaction connected them by cross-linking bonds and that produced rigid and large domains.
Quasi-Newton-based nonlinear finite element methods were extensively studied in the 1970s and 1980s. However, they have almost disappeared due to their poorer convergence performance than the Newton-Raphson method. An advantage of quasi-Newton methods over the Newton-Raphson method is shorter computational time even with a larger number of iterations. The speedup must grow as the number of degrees of freedom (DOFs) increases. Since computers and computational methods have been advancing steadily in the last 40 years, significant speedup can be expected at present. Therefore, we present a framework of a quasi-Newton-based parallel nonlinear finite element method consisting of a quasi-Newton method, implementation for parallel computing and a nonlinear material model. The advances of the present framework are a large number of DOFs and the use of a modern nonlinear material model. The number of DOFs exceeded 100 thousand in all analyses and reached one million in some analyses. This was enabled by the implementation of a quasi-Newton method for parallel computing and the use of a parallel sparse direct solver library. Note that, for more than several or ten million DOFs, an iterative linear solution method is generally preferred, resulting in the loss of the advantage of quasi-Newton methods. Furthermore, a modern finite-strain elastoplasticity material model with a realistic multilinear stress-strain curve was used in the present study, whereas an infinitesimal elastoplasticity model with a bilinear stress-strain curve was popular in the 1980s. Performance investigation of the present framework is given in the present paper. The quasi-Newton-based present framework achieved speedup of more than 30 times in modern large-deformation elastic-plastic analyses involving approximately one million DOFs, compared to the Newton-Raphson method.
Aiming at the problem of dislocation at the junction of metro carriages, a three DOF (degree of freedom) coupled vibration model of the junction of metro carriages was established. Then, the kinetic equation of vibration model was established by Lagrange method, the transfer function of the vibration model was deduced by Laplace transform, and the control system of vibration model was established by SIMULINK. In addition, the excitation signals such as the traction force, resistance force, lateral force and longitudinal force at wheel and rail were studied. Through simulation, obtain the coupling vibration characteristics under different parameters including traction force, spring stiffness and damping coefficient. The simulation results show that the amplitude differences ( x1 － x2 / y1 － y2 / z1 － z2 and x5 － x6 / y5 － y6 / z5 － z6 ) (Fig.2) at the junction of TC1-MP1 and MP2-TC2 (Fig.1) are more larger than other junctions. When the traction force is from 254 to 384kN, the larger the traction force, the larger the amplitude difference. When the parameters are: kx ≥ 3.5×107N/m, ky ≥ 1.7×105N/m, kz ≥ 2.75×105N/m, cx ≥ 4×105Ns/m, cy ≥ 1×105Ns/m, cz1 ≥ 3×104Ns/m， the dislocation is small.
Linkage mechanisms with 1 DOF composed of only lower pairs cannot generate the specified motion completely because of severe kinematic limitation of lower pairs. In order to relax the kinematic limitation and to generate the specified spatial trajectory completely, the authors have proposed the spatial rolling contact pair (SRCP), where two links in contact at a line roll relatively with generating the specified relative spatial trajectory completely, as a novel kinematic pair used for a spatial-path generator with 1 DOF. However, since it is a passive kinematic pair, it must be used in a closed-loop mechanism. Thus, the spatial-path generator with the SRCP cannot be simplified enough. In this paper, the ”active” spatial rolling contact pair (ASRCP), which is driven by several active elastic elements such as flexible linear actuators, is developed to achieve a simple spatial-path generator. Firstly, a design method to optimally arrange active elastic elements between two links of the SRCP based on a transmission index is proposed. Here, a method to use more than the minimum number of active elastic elements which are required to constitute force-closure state is described to design the ASRCP in order to achieve sufficient motion range. Besides, a control method of the ASRCP to generate the ideal rolling motion is proposed, where actuation forces of active elastic elements to get high stability between the links are calculated with the use of the actuation redundancy. As examples, the ASRCP driven with reeled-wires and the ASRCP driven with fluid-driven artificial muscles are designed and prototyped. Then, they are controlled with the proposed method, and their performances are investigated through motion capture experiments.
This paper presents a new structural design framework that incorporates the concept of topology optimization and genetic algorithms to improve the manufacturability and structural robustness of the optimal structure. The level set function is employed as a topological design variable to obtain clear structural boundaries, and the manufacturability of the structure is mathematically defined based on the manufacturing directions and the fictitious heat fluxes. To gain the manufacturable structure design, the optimization problem is formulated to find both the optimal shape of the structure and the optimal directions of the adjustable manufacturing tools. A level set-based optimization regarding manufacturability has been studied in previous papers, however, due to the influence of the manufacturing directions, the objective value tends to be captured in local optima as the structure becomes more complex. To cope with this issue, we decided to adapt a heuristic based approach, genetic algorithm, to the optimization method. Simultaneously, to reduce the computation time, we applied Design of Experiments for the initial population of the genetic algorithm. The initial population of the manufacturing directions is installed using Latin Hypercube sampling for both a good representation and computational efficiency. To demonstrate the effectiveness of the proposed method, several design examples are provided, and the differences from the optimal solution, derived by a previous gradient-based optimization scheme, are mentioned.