Yutaka Imaida

An Optimum Design Index of the Bottle with the Vacuum Insulation Structure

In this paper, we present an optimum design index of the bottle with a vacuum insulation structure. Thinner wall design is required to produce lighter bottles. When the wall thickness is too thin, the bottles crushed external pressure. Therefore it is necessary to provide the optimum design index of the bottle. We showed the factors that may affect on the deformation of bottles. We though the factors are classified into shape and material of the bottle. The factors in shape are length L, diameter D and thickness t of the bottles. And the factors for material are Young’s modulus and yield stress. The influence of each factor the critical deformation of bottles was verified by using FEM simulation. The nonlinear structural analysis LS-DYNA of the analytical software was applied. The analytical model simplified the base of the external cylinder is hollow cylinder model with shell element. Material properties for stainless steel (sus304), commercially pure titanium (Ti) and titanium alloy (Ti-6Al-4V). These each analytical model was loaded an external pressure by time steps. The pressure when the analytical model was transformed then was obtained. The result shows that the bottle’s strength has the definite relation from its shape and greatly influences the material rigidity.

High strain rate forming using an underwater shock wave focusing technique

Abstract This paper proposes an effective method for controlling the morphology of impulsive pressure waves in hydro-spark forming, making use of the technique of underwater shock wave focusing. Free forming experiments using ellipsoidal reflectors with two kinds of minor-to-major axis ratios b / a =0.6 and 0.8 are performed under several blank-setting conditions. The height of the formed product depends solely on the impulse of the shock wave, regardless of its focusing behavior, while the shape of the product is controlled by distribution of the applied pressure wave. It is demonstrated that the reflector having b / a =0.8 yields a wide range of pressure distribution, which can be estimated from the shock wave front distribution calculated considering the effect of non-linear reflection.

Impact compression behavior of FCC metals with pre-torsion strains

Abstract This paper investigates the effect of non-proportional pre-straining path on flow behavior of FCC metals at impact compression, where reversed torsion strain is introduced following 10% pre-torsion. Two kinds of FCC metals, Al and Cu, are employed to also examine the material dependency. Experimental results demonstrate that significant interaction exists between strain history and strain rate effects, which is strongly material dependent. The reversed torsion temporarily reduces strain history effect for Al. The trend is shown to be described qualitatively by analysis based on the crystalline plasticity theory where newly proposed back stress model considering piling-up behavior of dislocations is introduced.

A fundamental study of excimer laser ablation using experimental and MD simulation method

Abstract This paper focuses on the effect of pulse duration on ablation rate and behavior of plume in excimer laser ablation. Experimental results of laser ablation demonstrate that the 200 ns pulse laser exhibits a four to five times larger ablation rate than that with 20 ns pulse for the same laser fluence. CCD photography reveals that the plume velocity exceeds 4.5 km s −1 , corresponding to Mach 12. It is shown that these phenomena can be qualitatively explained by simulation results based on the molecular dynamics (MD) method. When the pulse duration becomes long, the number of ablated atoms increases accordingly under a constant laser fluence condition. The simulated results shows that the maximum velocity of expelled atoms ranges up to 20 km s −1 .

Study on the Bauschinger effect with increasing of tensile strength in dual phase steel sheets

The purpose of this study is to investigate the deformation property, under a high strain rate, of high strength steel sheets. The influence of strain rate on the Bauschinger effect is clarified, and the relation between the mechanical property and this influence is formulized. In this study, three kinds (590MPa, 780MPa, 980MPa) of high strength steel sheets of the Dual Phase type were applied. Both the rolling direction and the transverse direction specimens are created, and the compressive-tensile tests are conducted on three conditions of strain rate 7.0x10 -3

Improvement of mechanical properties of long jute fiber reinforced polylactide prepared by injection molding process

Natural plant fibers have recently been attracting attention as reinforcement for plastics due to their high specific mechanical properties and carbon neutrality. This study investigated the preparation process of long jute fibers reinforced polylactide acid (LJF/PLA) pellets by injection molding and explored the improvement of mechanical properties of molded LJF/PLA composites in relation to preservation of molecular weights of PLA matrix. LJF/PLA pellets containing 50mass% of jute fibers were prepared by an original pultrusion process developed for manufacturing long fiber reinforced thermoplastics (LFT), with excellent impregnation of resin into jute fiber bundles. Evaluation of injection-molded specimens from LJF/PLA pellets revealed that their tensile and flexural strength were dependent on molecular weights of PLA matrix, which correspondingly decreased with the moisture content of the original LJF/PLA pellets by the hydrolysis reaction. In the evaluation of chopped jute fiber reinforced PLA (Chopped-JF/PLA), prepared by the ordinary extruding method and injection molding, it was revealed that severe dehydration of jute fibers prior to compounding was proven to be effective for preventing the deterioration in the molecular weight of PLA, and that better fiber dispersion in ChoppedJF/PLA than in LJF/PLA contributed to attaining high mechanical properties in spite of shorter average fiber length remaining in the composites.

Improvement of Mechanical Properties of Semi-Solid Alloys by ECAP Processing

Recently, semi-solid processing is paid to attention in the field of the light alloys. By this method, it is improved ductility and fatigue strength. Although, because of those mechanical properties of the elongation and toughness is not excellent, the range that can be the application to parts is limited. On the other hand, it is reported that grain refinements cause improvement of ductility and appearance of super plasticity. Then, Equal-Channel Angular Pressing (ECAP) method is reported to be effective to the sample making of a bulk and ultra fine grain in various alloys in recent years. In this study, it tried to improve ductility and durability due to making ultra fine grain in AC4CH alloys by the ECAP method, and the influence of ECAP processing on the mechanical property of AC4CH was investigated. As the result, the ductility of AC4CH has improved by ECAP processing. However, the tensile strength of AC4CH declined along with the increase in the number of passes. So, for the purpose of additional improvement of tensile strength, ECAP-Back Pressure (ECAP-BP) method that was reported to be more effective for grain refinements than ECAP method was applied to semi-solid AC4CH and compared with ECAP method. As the result, the tensile strength of AC4CH was maintained by use of ECAP-BP. Moreover, both ductility and toughness of that have been also improved.

A Study On Preparation And MechanicalProperties Of Long Jute Fiber ReinforcedPolylactic Acid By The Injection Molding Process

Natural plant fibers have recently attracted attention as reinforcements for plastics due to their high specific mechanical properties and carbon neutrality. This study explored the preparation process for long jute fiber reinforced polylactic acid (LJF/PLA) pellets for injection molding and the mechanical performance of the molded composites. The originally fabricated pultrusion process for manufacturing long fiber reinforced thermoplastic (LFT) was capable of preparing LJF/PLA pellets, with the excellent impregnation of resin into jute fiber bundles. The incorporation of jute fibers of 50 mass% into PLA resulted in the improvement of flexural strength and modulus of injection molded composites. On the other hand, jute reinforcement was not effective for increasing the impact strength of the composite. Moreover, this study also investigated the influence of the moisture that had remained in jute fibers on the mechanical properties of the LJF/PLA composites. As the moisture content of jute fiber increased, the average molecular weight of matrix PLA in the LJF/PLA lowered due to the hydrolysis, and consequently the mechanical properties of the composites decreased. Eliminating moisture from jute fibers in the preparation process of LJF/PLA pellets was found to be important for preventing the deterioration in the molecular weight of PLA and the properties of the molded composites.

A Study On Preparation And Mechanical Properties Of Long Jute Fiber Reinforced Polylactic Acid By The Injection Molding Process

Natural plant fibers have recently attracted attention as reinforcements for plastics due to their high specific mechanical properties and carbon neutrality. This study explored the preparation process for long jute fiber reinforced polylactic acid (LJF/PLA) pellets for injection molding and the mechanical performance of the molded composites. The originally fabricated pultrusion process for manufacturing long fiber reinforced thermoplastic (LFT) was capable of preparing LJF/PLA pellets, with the excellent impregnation of resin into jute fiber bundles. The incorporation of jute fibers of 50 mass% into PLA resulted in the improvement of flexural strength and modulus of injection molded composites. On the other hand, jute reinforcement was not effective for increasing the impact strength of the composite. Moreover, this study also investigated the influence of the moisture that had remained in jute fibers on the mechanical properties of the LJF/PLA composites. As the moisture content of jute fiber increased, the average molecular weight of matrix PLA in the LJF/PLA lowered due to the hydrolysis, and consequently the mechanical properties of the composites decreased. Eliminating moisture from jute fibers in the preparation process of LJF/PLA pellets was found to be important for preventing the deterioration in the molecular weight of PLA and the properties of the molded composites.

Proposal Of Sheet Buckling Design Criteria ForHigh Strength Steel Under Impact Crushing

The purpose of this study is to verify the validity of sheet buckling design based on the effective width theory as an investigation of the impact crushing properties in high strength steel sheets. The need to make full cross-sections effectively without elastic buckling occurring is clarified and the application of the effective width theory under high speed deformation is considered. The findings of this investigation into the sheet buckling phenomenon are reported with numerical simulation by varying deformation strain rate, mechanical property of material and member configuration. The results demonstrate that the constant α used in the existing theory is function of strain rate  and material yield stress σY. With increasing crush speed, the cross section of a steel sheet becomes effective; the design based on the existing theory has provided enough evidence of safety. Furthermore, some criteria for limit buckling design are proposed.