Hideaki Katogi

Fatigue Behavior of Unidirectional Jute Spun Yarn Reinforced PLA

Abstract Natural fiber reinforced composites, which can be carbon-neutral materials, have been investigated for use as alternative materials to glass-fiber reinforced plastics (GFRP). The fatigue properties of natural fiber reinforced plastics are, however, not well known. In this study, uniaxial tensile fatigue tests of unidirectional jute spun yarn reinforced polylactic acid (PLA) were conducted in order to clarify the fatigue strength. The damage and fracture morphology of composite specimens were observed to elucidate the fatigue mechanism. Results show that the fatigue strength decreases concomitantly with increasing number of cycles. The fatigue strength at 106 cycles was 55% of the ultimate strength, which is an almost identical percentage to that of GFRP. The fatigue failure of composite specimens was probably caused by the breakage of jute filaments at the tips of fatigue cracks in PLA. This implies that the fatigue strength of the composite was strongly affected by the fatigue properties of PLA.

Effect of Surface Treatment on Creep Property of Jute Fiber Reinforced Green Composite under Environmental Temperature

In this study, effect of surface treatment on creep property of green composite under environmental temperature was investigated. Jute fiber was used as reinforcement. PLA (polylactic acid) was used as matrix. Surface treatments were conducted using 5 % solution of silane coupling agent and PVA (polyvinyl alcohol). The flexural test was conducted under 25°C environment. The flexural creep test was conducted for 50 hours at 25, 40 and 50°C environment. As a result, the flexural property of composite increased by the surface treatments. And the surface treatments affected the adhesion of fiber/resin interface. Creep strains of surface-treated jute fiber/resin composites were lower than that of virgin composite. The creep strain was decreased by the treatments. The effects are confirmed under various temperature conditions.

Mechanical Properties of Carbon Fiber Reinforced Plastics under Hot-Wet Environment

Water absorption behavior and flexural strength properties of carbon fiber reinforced plastics (CFRP) under hot-wet environment were examined. Those of epoxy resin were also examined for reference. Weight gains of CFRP and epoxy resin were measured after immersion in distilled water at temperatures under 90°C. Quasi-static flexural tests of CFRP and epoxy resin were conducted after immersion for 180 days. Weight gains of CFRP and epoxy resin increased with increasing water temperature. After immersion for 180 days at 90°C, weight gain of CFRP became 3.3times higher and that of epoxy resin was 2.3 times higher than that at RT, respectively. When CFRP and epoxy resin were immersed in distilled water at 90°C, weight gains of CFRP and epoxy resin increased and then decreased. Flexural strengths of CFRP and epoxy resin decreased in distilled water at temperatures less than 90°C. Flexural strengths of dried CFRP and epoxy resin after immersion recovered but were lower than that of virgin CFRP and epoxy resin. Debonding of fiber/resin interface and crack initiation in epoxy resin in distilled water resulted in the strength reduction.

Residual Tensile Property of Plain Woven Jute Fiber/Poly(Lactic Acid) Green Composites during Thermal Cycling

This study investigated the residual tensile properties of plain woven jute fiber reinforced poly(lactic acid) (PLA) during thermal cycling. Temperature ranges of thermal cycling tests were 35–45 °C and 35–55 °C. The maximum number of cycles was 103 cycles. The quasi-static tensile tests of jute fiber, PLA, and composite were conducted after thermal cycling tests. Thermal mechanical analyses of jute fiber and PLA were conducted after thermal cycling tests. Results led to the following conclusions. For temperatures of 35–45 °C, tensile strength of composite at 103 cycles decreased 10% compared to that of composite at 0 cycles. For temperatures of 35–55 °C, tensile strength and Young’s modulus of composite at 103 cycles decreased 15% and 10%, respectively, compared to that of composite at 0 cycles. Tensile properties and the coefficient of linear expansion of PLA and jute fiber remained almost unchanged after thermal cycling tests. From observation of a fracture surface, the length of fiber pull out in the fracture surface of composite at 103 cycles was longer than that of composite at 0 cycles. Therefore, tensile properties of the composite during thermal cycling were decreased, probably because of the decrease of interfacial adhesion between the fiber and resin.

Effect of Resin Particle on Interfacial Shear Strength of CF/MAPP after Immersion

Authors have reported that interfacial shear strength of Carbon Fiber (CF)/Maleic Anhydride grafted PolyPropylene (MAPP) was decreased by immersion for four weeks. As next stage, the purpose of this study is improvement of interfacial shear strength of CF/MAPP after immersion by adding resin particles around fiber. CF and resin particles added CF (RCF) were used as reinforcement. The major axis length of ellipse of resin particles was less than 5μm. In water absorption test, CF/MAPP and RCF/MAPP were immersed in distilled water for four weeks at room temperature. Micro debonding tests of CF/MAPP and RCF/MAPP after immersion were conducted. Fracture morphology of interface between fiber and resin was observed by using scanning electron microscope. As a result, following conclusions are obtained. In case of immersion for four weeks, the interfacial shear strength of RCF/MAPP was greatly increased (70%) compared with that of CF/MAPP. From fracture morphology of RCF/MAPP after immersion, some resin particles on CF surface were found after micro debonding test. Therefore, interfacial shear strength of CF/MAPP after immersion was increased by the effect of resin particles on CF surface.

Effect of Crystallinity on Mechanical Properties of Carbon Fiber Reinforced Polypropylene

In this study, effect of crystallinity on mechanical properties of carbon fiber reinforced thermoplastics (CFRTP) was investigated. Polypropylene (PP) and maleic anhydride modified polypropylene (MAPP) were used as matrix. The crystallinity of PP was controlled by using heat treatment after hot press molding of CFRTP. The range of crystallinity of PP and MAPP were from 26% to 40%. Flexural tests and izod impact tests of CFRTP were conducted based on Japanese Industrial Standard (JIS) K 7074 and JIS K 7110, respectively. As a result, flexural property and izod impact value of CFRTP using PP increased with an increase of crystallinity. However, flexural property and izod impact value of CFRTP using MAPP almost did not change with an increase of crystallinity.

Interfacial Shear Strength of Carbon Fiber Reinforced Polypropylene

In this study, interfacial shear strength of carbon fiber reinforced polypropylene were investigated. Two kinds of reinforcements are used. One is non-treated carbon fiber, another is acetone-treated carbon fiber. And two kinds of matrices are used. One is non-treated polypropylene, another is maleic anhydride-polypropylene. Three point flexural tests and micro debonding tests are conducted. As a result, following conclusions are obtained. Acetone treatment and maleic anhydride are effective to the adhesives on the surface between fiber and matrix. But simultaneous treatments are not effective. The shear strength is not dependent on fiber embedded length. The contact angle and fracture load are dependent on fiber embedded length. The interfacial strength is dependent on the contact angle. As the contact angle increases, the interfacial strength increases.

Effect of Water Temperature on Interfacial Shear Strength of Resin Particles Added CFRTP

In this study, interfacial shear strength of resin particles added carbon fiber/maleic acid anhydride grafted polypropylene under water temperature was investigated. Water temperature range was from room temperature to 80 oC. The maximum immersion time was 24 hours. Micro debonding tests of non and resin particles added composites were conducted. Fracture surface of resin particles added composite were observed by Scanning Electron Microscope (SEM). As a result, interfacial shear strengths of non particles added composite monotonously decreased with an increase of water temperature. Interfacial shear strength of resin particles added composite was higher than that of non resin particles added composite under all water temperatures except for 50 oC. From SEM observation, large resin particles on surface of carbon fiber after water immersion at 50 oC were found. And, many matrices and large resin particles on surface of carbon fiber after water immersion at 80 oC were found. Therefore, interfacial shear strength of composite was improved because resin particle addition prevented water penetration into the interface between fiber and matrix under water immersion less than 50 oC. And, interfacial shear strength of composite was probably improved by anchor effect of resin particle under water immersion at 80 oC.

Effect of matrix ductility on fatigue strength of unidirectional jute spun yarns impregnated with biodegradable plastics

Natural fiber-reinforced composites are carbon-neutral materials that are anticipated for use as an alternative to glass fiber-reinforced plastics. This study investigated the effects of matrix ductility on the fatigue strength of unidirectional jute spun yarns impregnated with biodegradable plastics. Polylactic acid (PLA) and polybutylene succinate (PBS) were used for the matrix. PLA is brittle, but it is widely used as a matrix of green composites. Because PBS has much higher ductility than that of PLA, it can be expected to have higher fatigue strength when subjected to the same strain amplitude as PLA. Fatigue tests were conducted with maximum stress set to 40–90% of the tensile strength. The stress ratio was set as 0.1. Results show that the matrix ductility strongly affects the fatigue strength and the fatigue mechanism of the composite. A matrix with better ductility was effective to improve fatigue strength.

Flexural Property and In Situ Observation of Carbon Milled Fiber Added Plain Woven Carbon Fiber/Epoxy Resin Composite

In this study, effect of Carbon Milled Fiber (CMF) addition on flexural fracture property of Carbon Fiber Reinforced Plastics (CFRP) was investigated. The CMF additive amounts to the epoxy resin were 0.5wt%, 0.8wt%, 1.0wt% and 1.2wt%. Static three point flexural test was conducted based on Japanese Industrial Standard (JIS) K 7074. The in situ observation of CMF added CFRP was conducted by using high-speed camera. As a result, following conclusions were obtained. In case that CMF additive amount was below 0.8wt%, flexural strength and flexural modulus of CFRP increased with an increase of CMF additive amount. In case of that CMF additive amount was above 1.0wt%, flexural strength and flexural modulus of the CFRP decreased compared with those of CMF 0.8wt% added CFRP. From in situ observation, crack initiation occurred at external layer on tension side of non CMF and CMF added CFRP. After crack initiation, delaminations of non CMF and CMF added CFRP were found. The delamination size of CMF 0.8wt% added CFRP was smaller than that of non CMF and CMF 1.2wt% added CFRP. Therefore, flexural property of CFRP was improved because delamination of CFRP was prevented by CMF 0.8wt%.