Toshihiro Kameda

Three dimensional dislocation-based crystalline constitutive formulation for ordered intermetallics

A three dimensional multiple-slip crystal plasticity constitutive formulation that is coupled to the temperature dependent evolution of mobile and immobile dislocation densities has been developed for a more detailed understanding of the deformation modes of ordered intermetallics. The predictive capabilities and accuracy of the constitutive formulation and the finite-element computational scheme have been investigated by simulating experimental results for single crystal nickel aluminide. There is good agreement between the computational and the experimental results. The use of the proposed constitutive formulation also resulted in accurate predictions of the increased strength of nickel aluminide as a function of increases in temperature. This is a strong indication that the dislocation based constitutive formulation and the finite-element algorithm result in accurate predictions of the deformation and strength response of monocrystalline nickel aluminide for the strain range and temperatures used in the experimental study. Based on these results, this dislocation based constitutive formulation will be used in future studies to investigate the effects of dislocation motion, interaction, and transmission on finite strain deformation and failure modes in intermetallic materials separated by high angle CSL and random GBs.

Intergranular and transgranular crack growth at triple junction boundaries in ordered intermetallics

Abstract Coincident site-lattice (CSL) and random grain boundaries (GBs) effects on intergranular and transgranular crack propagation paths in ordered intermetallics that are subjected to high rates of strain are investigated. A three dimensional dislocation density based multiple slip crystalline formulation and computational scheme are used for a detailed understanding and accurate characterization of interrelated deformation and failure mechanisms that can occur due to the generation, trapping, interaction, and annihilation of mobile and immobile dislocation densities that are generally associated with finite strain high strain-rate plasticity in L1 2 ordered intermetallics. Results from this study indicate that intergranular crack growth is along the GBs, normal to the stress-axis, and is due to the dominance of normal stresses in the crack-tip region. Transgranular crack growth is along slip-planes, and is due to the dominance of shear stresses in the crack-tip region.

AudioHaptics: audio and haptic rendering based on a physical model

In this paper, we propose a method for the synthesis of haptic and auditory senses that is based on a physical model called AudioHaptics. We have developed a haptic environment that incorporates auditory sensation. We achieved this by fitting a speaker at the end effecter of a haptic interface. The FEM (finite element method) was used to calculate the vibration of a virtual object when an impact is occurred, and the sound pressure data at the speaker position was then calculated based on the 2D complex amplitude of the object surface in real time. The AudioHaptics system can generate sounds originating from virtual objects, which can have arbitrary shapes, attributes and inner structures. Experiments for evaluation with real users demonstrated that this method is effective for rendering audio and haptic sensation.

Inelastic three dimensional high strain-rate dislocation density based analysis of grain-boundary effects and failure modes in ordered intermetallics

A three dimensional dislocation density based multiple slip crystalline formulation and computational scheme are introduced for a detailed understanding and accurate characterization of interrelated failure mechanisms that may occur on different length scales in intermetallics subjected to high strain-rates. This constitutive framework accounts for the generation, trapping, interaction, and annihilation of mobile and immobile dislocations densities that are generally associated with finite strain high strain-rate plasticity in Ll 2 ordered intermetallics. Coincident site-lattice (CSL) and random grain boundaries (GBs) effects on intergranular and transgranular failure at triple junctions are investigated. Results from this study indicate that intergranular cracks can nucleate due to dislocation pile-ups along the GBs, and that transgranular failure occurs on slip-planes that intersect the GB.

Elastic hysteresis in human eyes is an age-dependent value.

Background:  The elastic hysteresis phenomenon is observed when cyclic loading is applied to a viscoelastic system. The purpose of this study was to quantitatively evaluate elastic hysteresis in living human eyes against an external force.

Modeling of grain-boundary effects and intergranular and transgranular failure in polycrystalline intermetallics

A three-dimensional multiple-slip dislocation-density-based crystalline formation and specialized finite-element formulation were used to investigate dislocation-density transmission and blockage in nickel-aluminide polycrystalline aggregates, which were subjected to dynamic loading conditions, with a macroscopic crack and different distributions of random low-angle and coincident site lattice (CSL) grain boundaries (GBs). An interfacial GB scheme was developed to determine whether dislocation-density pileups or transmissions occur as immobile and mobile dislocation densities evolve along different slip systems. The three-dimensional dislocation-density-based crystalline formulation is based on inter-related mechanisms that can occur due to the generation, trapping, interaction, and annihilation of mobile and immobile dislocation densities that are generally associated with large strain-high-strain-rate plasticity in L12-ordered intermetallics. A crack-tip shielding factor was also formulated to delineate between transgranular and intergranular crack growth. The current results indicate that aggregates with a high frequency of Σ33a GBs would be susceptible to blunted transgranular crack growth due to high dislocation-density transmission rates and shear-stress accumulations, and that an aggregate with a high frequency of Σ17b GBs would be susceptible to sharp intergranular growth due to a large number of dislocation-density pileups and an accumulation of large normal stresses ahead of the crack tip.

Molecular Dynamics Based Observations of Grain Boundaries and Lattice Defects Functions in Fine Grained Metal

In order to study the characteristics of fine grained polycrystalline metals, it is important to recognize the function of grain boundaries (GB), crystal defects such as dislocation and/or nanoscale voids, since the fraction of GB increases as grain sizes decreases, the deformation process of these metals could be different from those in larger size grains. In this study, we first evaluate the hypothesis that GB behaves as dislocation source and sink during the deformation of fine grained metal, then compare the behavior between GB and a tiny defect from the view point of dislocation source and sink phenomena. Since continuous dislocation supplies could be considered as the key issue to improve the toughness of fine grained metals, this concept could be helpful to design next generation polycrystalline metals.

On the unstable propagation of a phase transition in a solid

Abstract To explore a possible mechanism of deep earthquakes, this paper analyzes the unstable propagation of a stress-induced phase transition which is initiated in a homogeneous stress field. This Stephen problem is formulated as an initial-value problem for the phase boundary, and the driving force of the boundary is computed by using the solution of the boundary-value problem for a partially transformed material. The propagation of the phase transition under uniform pressure is numerically simulated. It is shown that (1) under lower pressure, the transition is terminated at a certain size, but it can propagate unstably when an initially transformed region is sufficiently large; and (2) when the pressure attains a critical value, the propagation becomes unstable, and goes in a particular direction depending on the initial shape. These results confirm the possibility of the unstable propagation of phase transition, and provide a theoretical basis for the hypothesis that the phase transition of a mantle material can trigger a deep earthquake.

Elastic hysteresis in human eyes is age dependent value: Elastic hysteresis in human eyes is age dependent

Background:  The elastic hysteresis phenomenon is observed when cyclic loading is applied to a viscoelastic system. The purpose of this study was to quantitatively evaluate elastic hysteresis in living human eyes against an external force. Design:  Prospective case series. Participants:  Twenty-four eyes of 24 normal human subjects (mean age: 41.5 ± 10.6 years) were recruited. Methods:  A non-contact tonometry process was recorded with a high-speed camera. Central corneal thickness (CCT), corneal thickness at 4 mm from the center, corneal curvature, and anterior chamber depth (ACD) were measured. Intraocular pressure (IOP) was also measured using Goldmann applanation tonometry (GAT) and dynamic contour tonometer (DCT). Main Outcome Measures:  Energy loss due to elastic hysteresis was calculated and graphed. Results:  The mean CCT was 552.5 ± 36.1 µm, corneal curvature was 7.84 ± 0.26 mm, and ACD was 2.83 ± 0.29 mm. The mean GAT-IOP was 14.2 ± 2.7 mmHg and DCT-IOP was 16.3 ± 3.5 mmHg. The mean energy loss due to elastic hysteresis was 3.90 × 10(-6) ± 2.49 × 10(-6) Nm. Energy loss due to elastic hysteresis correlated significantly with age (Pearson correlation coefficient = 0.596, p = 0.0016). There were no significant correlations between energy loss due to elastic hysteresis and other measurements. Conclusion:  Energy loss due to elastic hysteresis in the eyes of subjects was found to positively correlate with age, independent of anterior eye structure or IOP. Therefore, it is believed that the viscosity of the eye increases with age.

Identification of Stress from Strain for Body with Not Fully Identified Constitutive Relations

This paper presents a new inversion method to identify a distribution of stress from a distribution of measured strain for a body whose constitutive relations are not fully known. The present method yields well-posed boundary value problems for unknown stress. Local constitutive relations are then determined from relations between the measured strain and the predicted stress. This procedure is different from an ordinary analysis of finding constitutive relations, which is usually formulated as the parameter identification by assuming a form of the constitutive relations. The rigorous formulation of the inversion method is briefly presented. Also, three examples to which the present method has been applied are shown. The validity and the usefulness of the method are discussed in view of the results obtained.