Natural fiber-reinforced composites are now finding extensive uses in various fields from household articles to automobiles. These composites can score high compared to common synthetic fiber-based composites, notably glass fiber-reinforced composites, in areas such as occupational safety and health, and impact on environment. The current research work is motivated by the need for exploring jute fibers as replacement for glass fibers for various engineering design applications including more demanding impact protection applications as in automotive body structures. In the current work, detailed mechanical characterization of jute-polyester (JP) composite laminates till failure has been carried out for tensile, compressive and flexural loads by varying volume fraction of jute fibers. The effect of fiber volume fraction on mechanical properties is shown. Because of the potency of closed thin-walled components as structural energy-absorbers, a comprehensive experimental study has been performed, for the first time, comparing the behaviors of various geometric sections of JP and glass-polyester (GP) composite tubes under axial quasi-static and low velocity impact loading. Additionally, for jute-reinforced plastic panels to be feasible solutions for applications such as automotive interior trim panels, laminates made of such materials should have adequate perforation resistance. Thus, a detailed comparative study has been carried out for assessing the performance of JP laminates vis-a-vis GP plates under low velocity impact perforation conditions. As high-end product design is heavily driven by CAE (Computer-Aided Engineering), the current research work has also focused on the challenging task of developing reliable modeling procedures for explicit finite element analysis using LS-DYNA for predicting load-displacement responses and failures of JP composites under quasi-static and impact loading conditions. In order to extend the applications of JP composites to structurally demanding applications, hybrid laminates made of jute-steel composites and jute with nanoclay-reinforced polyester have been investigated and the considerable enhancement of mechanical properties due to hybridization is shown. Furthermore, a comprehensive study has been conducted on the behavior of JP laminates for varying degrees of moisture content until saturation, and the efficacy of hybrid laminates in this context has been shown.

従来型の繊維強化プラスチック(FRP)に対し環境負荷の少ない「グリーンコンポジット」の実用的な成形プロセスの確立が切望されている。本研究では、天然繊維およびポリ乳酸を原料とする長繊維強化樹脂(LFT)ペレット製造および射出成形による複合材製造法を対象に、複合材の力学的特性に対する繊維の含有水分や熱劣化の影響、繊維分散の効果等を把握し、高い特性を発揮させるための成形プロセスおよび諸条件を提示した。 / 'Green Composites' have been attracting attention due to their high sustainability and carbon neutrality. This study investigated the preparation process for composites of long jute fiber reinforced polylactic acid by LFT-pellet manufacturing method followed by injection molding. The author explored effect of several factors, such as moisture in fiber, heat decomposition of fiber at processing and the level of fiber dispersion in matrix resin, on mechanical properties of composites. The author eventually proposed the optimized process and operating windows for attaining higher mechanical properties of composites. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University