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 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 , 10 and 100/s. As a result, it is shown clearly in Dual Phase steels that the dependence of strain rate on the Bauschinger effect exists. In addition, with the transformation of material into high strength, it is demonstrated that consideration of the influence of the Bauschinger effect becomes increasingly important; however, the need for consideration of the dependence of the strain rate and the influence of strength anisotropy on the Bauschinger effect decrease for a material model in a numerical simulation.
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