Most of polymers used as structural materials are crystalline polymers that are mixtures consisting of glassy and crystalline phases. In this paper, we propose a material model representing the deformation behaviors of both crystalline and glassy phases by use of a unified manner based on crystal plasticity theory. A homogenization method is introduced into the above model in order to carry out deformation analysis connecting macroscopic specimen and microscopic unit cell. Then a further multiscale simulation bridging three hierarchical material structures, i.e., molecular chain scale, lamellar crystal scale and practical macroscopic scale is conducted for a polypropylene plate subjected to tensile load. It is tried to reproduce formation and propagation of shear bands and to visualize directly orientation of molecular chains inside the macroscopic structure. The relationship on deformation behavior between macroscopic plate and unit cell is investigated. Moreover, an inelastic response law based on a probabilistic theory considering change of local free volume is adopted as a hardening law of glassy part so as to express characteristic mechanical properties, i.e., nonlinear viscoelastic response before initial yielding, strain softening after initial yielding and nonlinear strain recovery in unloading process in crystalline polymers.

抄録全体を表示

Polymers show peculiar mechanical responses that are not observed in metals, such as remarkable strain rate dependency and ductile fracture caused by craze which is an assembly consisting of micro-voids and fibrils. In the design process for polymeric products, we attempt generally to predict the fracture position by commercial FEM solvers. However, we can not precisely reproduce the fracture behavior of polymers, because a material model that can express an accumulation of craze is not installed yet on the current commercial solvers. Therefore, so as to predict fracture on the basis of craze behavior, we proposed a constitutive equation with craze effect, the craze evolution equation that can express propagation and growth cessation of craze, the evolution of mean normal plastic strain and criterion for craze initiation with strain rate dependency in our previous work. In this study, our craze evolution equation is extended to an enhanced type covering wide range of strain rate and is proposed as a material model by combining with non-coaxial elastoviscoplastic constitutive equation and the evolution equations proposed in the previous work. Then, numerical uni-axial tensile tests in which applied strain rate is given at five levels between 0.01s^-1 and 100s^-1 are conducted on a commercial FEM solver LS-DYNA to which the present material model is added via user subroutine. Furthermore, we predict computationally the fracture positions under the condition of wide range of strain rates by using the criteria of craze concentration and fibril strength.

抄録全体を表示

This paper describes a stochastic multiscale stress analysis and failure probability analysis of a particle reinforced composite material via the stochastic homogenization analysis. In order to validate a numerical result based on the computational methodology, the importance of the probabilistic analysis in computational mechanics has been noticed in recent. In particular, we focus on the computational procedure for estimation of uncertainty propagation through the different scales in a heterogeneous material, and the influences of a microscopic random variation of elastic properties of component materials on the microscopic stress field and microscopic failure probability are investigated. The Monte-Carlo simulation and the perturbation-based approach are employed for the stochastic analysis, and the homogenization-theory based finite element analysis is employed for the multiscale stress analysis. With the numerical results, the influences of the microscopic random variation of the elastic properties are investigated, and applicability of the perturbation-based approach is discussed. From the results, the importance of the presented multiscale stochastic stress analysis and the failure probability analysis considering the microscopic random variation for a heterogeneous material will be illustrated.

抄録全体を表示

On four kinds of silicon nitride ceramics, the statistical properties of bending strength and fracture toughness were investigated. On these properties, universal estimation based on Weibull statistics and local fracture model was attempted. And the influences of microstructure on statistical properties of bending strength and fracture toughness were studied. In the analysis based on Weibull statistics, the equations which universally evaluate bending strength of smooth specimen and fracture toughness of pre-cracked specimen by means of Weibull stress were derived. According to this analysis, if it is assumed that the fracture of pre-cracked specimen occurs from crack front or defect in front of crack tip, it is predicted that Weibull modulus of fracture toughness equals to 4 independently of materials. However, fracture toughness and its Weibull modulus predicted by Weibull stress differed from the measured values, and their correlation was different among materials. The reason may be that aforementioned assumption is not consistent as suggested by the observation of fracture surfaces. On the other hand, in the analysis based on local fracture model, the intrinsic strength of grain boundary was estimated with the use of bending strength, defect size and grain diameter by means of point stress model in which the fracture depends on intrinsic strength of grain or grain boundary. Then the fracture toughness of pre-cracked specimen was predicted by the intrinsic strength of grain boundary. As a result, the predicted fracture toughness showed a tendency to be proportional to grain diameter in good agreement with experimental results.

抄録全体を表示

A single-cycle bending test of polycrystalline pure titanium was carried out using a rectangular specimen with a pair of parallel grooves. The plastic deformation in a long part between these grooves was observed at every quarter cycle of back-and-forth bending. Before the test, multiple square marks of gold were made at the lattice points having a mutual distance of 12.5 μm in the region of interest by ion-coater. The strain and rotation during the test were evaluated based on the displacement of these gold marks. The following results were obtained: (1) The region of interest between grooves showed plastic deformation during bending, and the deformation was mainly caused by slips. Twining was also observed in some grains. (2) The strain and rotation during the bending were not uniform grains to grains. The shearing strain was small compared with the normal strains and rotation. (3) The region, which showed a larger normal strain at the first quarter cycle, continued to show a relatively large strain at the following quarter cycles in an opposite direction. Rotation showed a similar behavior. (4) Crystal orientation analysis was performed for grains with clear slip lines. The plastic deformation of these grains seemed to occur mainly by the prismatic slip.

抄録全体を表示

Fibrils were isolated from rat tail tendons and tensile tests of the fibrils were performed in the air (dry) condition or in the physiological saline solution (wet) condition. After the fibrils were immersed in the physiological saline solution for 3 and 30 minutes, the fibrils were stretched to failure. There were no significant differences in the tensile properties between 3 and 30 minutes. These results indicate that the fibrils were sufficiently hydrated by the immersion of 3 minutes. The fibrils immersed for 3 minutes showed the tensile strength of 111±31 MPa (Mean±S.E.), strain at failure of 32.1±4.5 %, and tangent modulus of 350±53 MPa. Next, the fibrils were stretched to failure in the air. The dry fibrils showed the tensile strength of 702±137 MPa, strain at failure of 30.4±8.5 %, and tangent modulus of 2720±840 MPa. The tensile strength and tangent modulus of the dry fibrils were significantly larger than those of the wet fibrils. There were no significant differences in the strain at failure between the dry and wet fibrils. These results point to the great importance of water for the tensile properties of collagen fibrils.

抄録全体を表示

To investigate the deformation behavior of multi-layered ceramic capacitors (MLCCs) during production press process is very important to reduce over all MLCC size and increase the capacity of the MLCC through the enlargement of the electrode area. In the previous paper, the deformation of MLCC blocks in the uniaxial compression test was observed and the filling mechanism was clarified based on the measurement results. In this study, the non-frame press tests of MLCC blocks were carried out to realize the high precision press, in which the lateral compressive stress was given in addition to the longitudinal one. The deformation process was clarified based on the results of cross-sectional observation. In the edge part of the MLCC block, the interlayer space in Side-Gaps L and W was decreased by longitudinal strain and the lateral strain, whereas, at the central part of the MLCC block, the interlayer space in Side-Gaps L and W was decreased only by longitudinal strain. Since the difference in the deformation behavior between the central part and the edge part generated variations in the thickness of MLCC block, the width of the internal electrode part and the width of the Side-Gap, it was concluded that non-frame press was not suitable for high precision press of MLCC block.

抄録全体を表示

Methods of evaluating the one-sided tolerance limit (A- and B-basis values) of unbalanced sample sets are derived. The A- and B-basis values are statistically calculated numbers that respectively indicate that at least 99 and 90 percent of the population is expected to equal or exceed the statistically calculated value with a confidence of 95 percent, and they are often used as strength tolerance limits in aerospace designs. The A- and B-basis values tend to be underestimated when the sample size is small and the conventional methods are used. Our novel methods improve the basis values by combining multiple sample sets from normally (Gaussian) distributed populations. We extended analysis of variance (ANOVA) to evaluate the A- and B-basis values by using non-central t-distribution under the condition of equality of variances. In addition, we derive coefficients for the basis values under the condition of non-equality of variances by using a Monte-Carlo method. Numerical examples show that both methods, i.e., equality and non-equality of variance cases, increase the A- and B-basis values.

抄録全体を表示

When a porous solid is subjected to both gas infiltration and heat transfer, thermal stresses are generated in such a solid. In the previous repot, fundamental theory for a porous solid under such a complex situation was developed. In this study, a thermal stress problem for a porous solid with a flat boundary surface, which is generally called a semi-infinite space, subjected to a concentrated point loading is investigated. A method of solution based upon displacement potential and Fourier integral transform techniques is applied to solve the problem. Closed form solutions of the gas pressure, solid temperature and thermal stress fields in semi-infinite porous media are presented. It is shown that the thermal stress solution for the problem includes only a free expansion term caused due to the gas pressure and external pressure at the free boundary surface. Numerical results reveal that the thermal stress increases with the gas permeability (^κ/_ζ).

抄録全体を表示

In the present study, we apply an Arbitrary Lagrangian-Eulerian (ALE) finite element method, which can rationally solve the interaction behavior between the fluid flow and the nonlinear solid deformation, to the simulation of indentation process of lubricated elastoplastic plates by the ball collision. As have been reported by numerous experimental works, it is also shown by the present numerical approach that the characteristic of lubricant affects indentation profiles. For instance, the indentation profile represents the conical shape due to viscous property of lubricant, while the profile represents the bowl-type shape under the dry condition. Based on the systematic numerical investigation, it is confirmed in the case of lubricated condition that the indentation is formed through the pressure of a fluid. Then, a squeeze effect of viscous flow and a shut-up of lubricant, which is caused by velocity of lateral flow, are observed. Furthermore, it is understood that the conical shape of indentation profile is formed at an initial contact stage, and then its size similarly grow up during loading. Thus, it is confirmed that the ALE finite element method is one of effective methods for the examination of impact problems on lubricated surfaces.

抄録全体を表示

Electronic components, such as semiconductor devices are required for the optimum design of material properties, manufacturing process and structural dimensions when they become smaller and thinner. The finite element analysis and the viscoelastic analysis based on a linear viscoelastic theory are generally used to calculate the thermal stress and the warpage which generate in semiconductor devices. But these analysis methods are very complicated to calculate the thermal stress and the warpage of devices. For these reasons, in this paper, the simplified predicting formulae were derived by approximating the properties such as the modulus of longitudinal elasticity and thermal expansion coefficient into two domains, that is, the glassy zone and rubbery zone by the glass transition temperature of plastic materials. And it were derived by using the simple expressions based on the mechanics of materials in common use.Two-layered laminated bodies consisting of the epoxy resin and steel, printed wiring board were used for the experimental and theoretical studies of residual warpage. As a result, it was clarified that the residual warpage calculated by using the simplified prediction equations derived here was in good agreement with the experimental values and theoretical values, and these simplified prediction equations derived here were useful and available for optimum designing the electronic devices.

抄録全体を表示

Many cracks are initiated at a production facility of cars. So, stop-holes are drilled at crack tips to reduce the stress concentration. However that method does not work to prevent the crack growth. That facility will be renovated next year, so some other method of arresting crack growth should be found before the renovation. Because of this situation, we investigate a method of preventing crack growth by using a crack arrester. Before installing the crack arrester in the production facility, we carried out experiments in a laboratory. It was confirmed that the crack arrester works well to prevent crack growth. Then, the crack arrester was used to prevent crack growth in the production facility. In this paper, the experimental results in the laboratory are introduced, and the effectiveness of the crack arrester to prevent fatigue crack growth is shown.

抄録全体を表示

We proposed an electroformed mold for thermal imprint of borosilicate glass in this paper. The mold was made of Ni-W electrodeposition film that was superior to heat-resistance and removing glass. The resist pattern for electroforming was fabricated with SU8-10. Ni-W solution for electroforming was developed by mixing nickel sulfamate, tungsten sodium and citric acid. The minimum pitch and the height of the pattern on Ni-W electroformed mold were about 40 μm and 3.8 μm, respectively. The thermal imprint for borosilicate glass carried out with Ni-W electroformed mold. The shape of the Ni-W electroformed mold was printed on the borosilicate glass by thermal imprint. The borosilicate glass was removed from the Ni-W electroformed mold easily.

抄録全体を表示

Shape memory gels (SMG) are one kind of functional materials that can be deformed plastically and fixed the deformed shape at lower temperature. At higher temperature, SMG can return their original shape. A novel transparent SMG (SA-DMAAm gels) was developed from crystalline monomer stearyl acrylate (SA) and amorphous monomer N,N-dimethylacrylamide (DMAAm). We had succeeded in improving its mechanical properties. In this work, the aim is to develop conductive SMG by adding carbon black into SA-DMAAm gels. The molar ratio of SA to DMAAm was 1:3, and the weight ratio of carbon black to DMAAm was 1/100. The shape of prepared conductive SMG (SA-DMAAm/Carbon gels) is possibly controlled by Joule heat. This feature has quite promising applications in the field of new devices. The mechanical, shape-memory and conductive properties, as well as crystal structure of SA-DMAAm/Carbon gels were characterized.

抄録全体を表示