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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.

The purpose of this study is to develop automotive frictional parts, especially continuously variable transmission (CVT) blocks using a composite material made of thermoplastic resin and fiber. CVT blocks were used at about 100oC under high pressure and friction conditions; nylon 9T, otherwise named PA9T, was used. PA9T has a high melting point which is higher than the maximum temperature at the state of slip. To apply composite materials to the manufacture of CVT blocks, material properties such as high strength, modulus of elasticity and fatigue strength are important. Therefore, the aim of this study is improvements in mechanical properties by adding fillers to PA9T under various compounding and molding conditions. PA9T and carbon fibers were mixed using a twin screw extruder. After compounding, dumbbell specimens were made using an injection molding machine. Bending, fatigue and abrasion tests were conducted. Moreover, the transmission capacity of CVT belt made of PA9T composites was evaluated and slip tests were conducted. According to the results of tests, PA9T with CF38.8 vol% achieved desired values for CVT application. The CVT belt has a torque capacity of 40 Nm under an axle load of 2.0 kN.

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.

The purpose of this study is to develop automotive frictional parts, especially continuously variable transmission (CVT) blocks by using a composite material made of thermoplastics resin and fiber. CVT blocks are used at about 100oC under high pressure and friction condition. So, we have used nylon 9T, PA9T. PA9T has high a melting point that is higher than maximum temperature of the state of slip. To apply composite materials to CVT blocks, the material properties such as high strength, modulus of elasticity and fatigue strength are important. Therefore, a purpose of this study is improvements of mechanical properties by adding fillers to PA9T with various compounding and molding condition. PA9T and CF were mixed by using twin screw extruder. After compounding, dumbbell specimens were made by using injection molding machine. Bending, fatigue and abrasion tests were conducted. Moreover, we evaluated the transmission capacity of CVT belt made of PA9T composites and conducted slip test. According to results of tests, PA9T with CF38.8 vol% achieved desired values of CVT. The CVT belt has 40 Nm of torque under 2.0 kN of axle load.

The mechanism of strain rate dependence on the Bauschinger effect in dualphase type high strength steel sheets is investigated and the influence of mesostructure differences on spring-back is estimated in this study. Compression-tensile tests at a strain rate from 0.007/s to 100/s is conducted. To differentiate between the multiphase structure-induced effect and the matrix properties, the same tests are also conducted for ferrite single phase steel. As a result, the Bauschinger effect on dual phase steel is not associated with the matrix properties independently. Moreover, it is revealed that a multiphase structure-induced effect acts a dominant function for deformation characteristics through experiments and micro observations.

A bottle with a vacuum insulation structure is generally called a thermos bottle. It has a dual structure with inner and outer cylinders and a vacuum layer between them. The bottle with the structure maintains the heat and cold. It has been found useful for many years as a container that carries drinking water. Recently, the lightweight design of a vacuum bottle has been required to meet consumer demand. However, the bottle's wall collapses during the process of drawing a vacuum if the stiffness of the cylinder is not enough. To construct the design guide that can prevent the collapse of a double-structured bottle induced by the pressure difference, a numerical simulation was performed. The critical thickness tc, which is the thickness of the bottle when the bottle starts to deform under 1 atm, was defined. tc depends on the length and diameter of the bottle. The index to dertermine tc from the length and diameter of the bottle was suggested. To evaluate the validity of the analysis, vacuum bottles were prepared and experiments were conducted. The index we suggested showed good agreement with the experimental results. The shift of index within the increase of Young's modulus can be formulated.

The continuous ECAP process which can provide three-dimensional strain was developed in this study. A die with tri-axis crossed channels having channel angle φ of 90° and curvature ψ of 0° was created. As a result, continuous ECAP process via route Bc for AC4CH aluminium semi-solid alloy could be performed at 573K at pressing speed of 0.5mm/sec using the developed die. The continuous method cut the processing time in half compared to the non-continuously conventional method. The grains became fine from 100μm to approximately 2μm. Workpiece processed 8 passes exhibited four times higher toughness than as-cast alloy.

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.

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