Bamboo (Phyllostachys pubescens) fibers obtained by using a steam explosion method were hot pressed under various molding conditions such as temperature and pressure in this study. The effects of these molding conditions on the bulk density, tensile strength, and flexural strength are examined. Furthermore, the effect of the heating temperature on the mechanical properties of bamboo fiber bundles is also examined. The experimental results reveal that the bulk density increased with the molding temperature up to 130°C and was saturated at a constant value above 130°C due to decreases in the void content. This is because of the plastic deformation of parenchyma cells of bamboo fibers as the molding temperature rises. The tensile and flexural strengths of the unidirectional composite depend on the molding temperature. These strengths increased with the molding temperature up to 130°C as well as with the bulk density. These increases in the strengths were achieved by improved adhesive property. However, the strengths of the composite decreased above 130°C due to the decomposition of the bamboo fiber by heating. Thus, it was clarified that the optimum molding temperature was approximately 130°C. In addition, it was confirmed that the molding pressure has less effect on the bulk density, the tensile strength, and the flexural strength of the composites.
Current paper proposes an effective technique to improve mechanical properties of bamboo fiber reinforced PLA (Poly Lactic Acid) by fibrillation on the surface of bamboo fibers (BFs). To improve the interfacial properties between bamboo fibers and matrix, the surface of alkali treated bamboo pulp was fibrillated by milling machine. The bamboo pulps were milled under 3 different conditions (Fibrillated Alkali Bamboo fiber : FAB). Degree of fibrillation (D.F.) was defined as water retention of the bamboo fiber. Four types of bamboo fiber were prepared in this study ; the D.F was 0 (pulp), 3.5, 4.3 and 4.8. The FAB/PLA composites were injection molded after fibrillated bamboo fibers were mixed into PLA. The effect of fibrillation on mechanical properties of BF/PLA composite was investigated. The viscosity of melted FAB/PLA was increased and the rate of crystallization decreased when the bamboo fiber was processed with large number of (D.F.). The bending strength and interfacial shear strength of FAB/PLA composites was significantly increased in comparison to that of the original bamboo pulp/PLA composite when the D.F. was selected to 3.5, compared to that of un-fibrillated AB/PLA composites. Long pull-out of the fiber with smooth surface was observed on the fracture surfaces of un-fibrillated AB/PLA composites. However, the bending strength of FAB/PLA composites was decreased when the D.F. was 4.3 and 4.8. The discussion in the paper showed that the decrease in strength of fibrillated bamboo fiber and change of fiber orientation should degrade the bending strength of FAB/PLA composite when the fiber was excessively fibrillated. This paper mentioned the optimum condition was there to enhance interfacial properties between bamboo fiber and PLA matrix.
Effect of alkali-treatment on the mechanical properties of a ramie plied yarn reinforced green composite was investigated, using NaOH solutions with various concentrations. The composites reinforced with NaOH-treated yarns decrease in strength and Young's modulus if the concentration of the solution is equal to 12wt% or more. It was proved from X-ray diffraction analysis that these decreases were closely related with a decrease in the index of crystallinity and a crystalline transformation from cellulose I to cellulose II of the yarns. On the other hand, fracture strain of the NaOH-treated yarn composites increased largely, as compared to that of the untreated yarn composite. In this study, furthermore, the effect of liquid ammonia (NH3) treatment on the mechanical properties of the green composite was investigated. The results showed that the NH3-treated yarn composites showed higher tensile strength and fracture strain, as compared to those of the untreated yarn composites, but their Young's modulus decreased. It was considered that such changes were concerned to a change in the yarn structure, as well as a crystalline transformation from cellulose I to cellulose III and the less index of crystallinity.
In recent years, development of environmentally friendly materials including relatively high mechanical properties is demanded by various industrial fields. Especially, composites consisting of plant-based natural fibers and biodegradable resin, so-called fully green composites, are one of the most promising environmentally friendly materials for practical use. The purpose of this study is thus to explore the effects of fabric density and yarn twist on the mechanical properties of the composites reinforced with ramie woven fabrics, and clarify a difference between mechanical properties of the composites and reinforcing fabrics. The results show that tensile strength and Young's modulus of the composites are substantially different from those of the fabrics, because of the stress transfer mechanism of the matrix resin. In addition, the effects of fabric density and yarn twist on the tensile properties of the composites are discussed from results of a finite element analysis.
In the present paper, the fatigue damage behaviour of fibre metal laminates based on a titanium alloy and glass fibre-reinforced polymers (Ti/GFRP) as Ti/FRP system was investigated in detail. Static tensile tests and tensile-tensile fatigue tests were conducted on open-hole specimens of these laminates that were assembled by bonding Ti alloy sheets and GFRP plates. The fatigue damage modes of the Ti/GFRP during the tests were observed. From the experimental evidence, the dominant damage modes were identified as cracks in the Ti layer, delaminations between the Ti layer and the adhesive layer, transverse cracks in the 90° layer and 0°/90° interlaminar delaminations in the GFRP layer near the open-hole. A finite element model that represents these fatigue damages in the laminates was developed based on the damage observations. The model predictions were compared to experimental results for the stiffness degradation. The model was able to capture the stiffness reduction trends for the Ti/GFRP. This result indicated that this model could be considered to be available to predict the mechanical properties of the Ti/GFRP. Then, the stress intensity factor at the crack tip in the Ti layer was also evaluated by using this finite element model. The calculated stress intensity factor at the crack tip of the Ti layer of the laminates kept almost constant with the crack growth. From these results, it was shown that the stress concentration at the crack tip was reduced by the GFRP layer, and then, the cracks in the Ti layer exhibited the stable growth by following the Paris's law relationship.
Phenolic resin has originally advantages of heat proof, fire resistance and less smoke during burning. The FRP with phenolic resin having these advantages is one of suitable materials in structures of vessels and railway carriages. However, in the case of the resole type of phenolic resin, the water owing to condensation reaction and to fabrication method remains in the matrix and this water evaporates and becomes voids in curing process. As a result, fine matrix can not obtain. In this paper, a method of fabricating new phenolic FRP composed of Novolak type of phenolic resin as a matrix and glass fabrics as a reinforcement is shown. In order to prevent the movement of glass fibers in the fabrics during resin injection, a resole coating to the fabrics is executed before installing in the die. Furthermore, mechanical properties of the phenolic FRP are compared with those of the conventional FRP with unsaturated polyester resin. As a result, the phenolic FRP shows the high performance and it has a possibility to be employed as the structural members in the vessels and carriages.
Two pitch based high modulus type carbon fibers with oxidative surface and sizing treatments and without any treatments are used in the present work. These fibers are made under the same process derived from the same precursor. Unidirectional carbon fiber reinforced carbon composites (C/C composites) are prepared from two kinds of these carbon fibers and four kinds of carbon matrix precursors, two thermosetting resins (phenolic and furan resins) and two pitches, (coal-tar and petroleum pitches). The tensile test of the strand specimen of the composites heat-treated at different temperatures is carried out by following JIS R7601. Effects of oxidative surface and sizing treatments of carbon fiber on tensile properties of the composites derived from different matrix precursors are discussed. In the case of high modulus type pitch based carbon fiber, it is found that there is almost no effect on the strength of composites by the surface oxidation and sizing treatment of the carbon fiber, except for showing different fracture morphologies of graphitized composites derived from the thermosetting resins between the treated and the untreated fibers.
A simple method for the fabrication of silica/polypropylene (PP) nanocomposites was investigated, whereby silica particles of 190nm in diameter without any surface modification were dispersed uniformly through mechanical breakdown of loosely packed agglomerates of silica nanoparticles with low fracture strength in a kneaded PP melt during direct melt-compounding. The method consists of two stages. The first stage involves preparation of the loosely packed silica agglomerate by destabilizing a colloidal aqueous solution of nanometer-size spherical silica via pH control and KBr addition, and the second stage involves melt-compounding of an isotactic PP with the silica agglomerates. The pore structure and strength of the silica agglomerate prepared in the first stage were found to control the dispersion state of the silica nanoparticles in the silica/PP composite, and the use of loosely packed silica agglomerates with numerous large pores was shown to be effective for achieving a uniform dispersion of isolated primary silica nanoparticles in the PP matrix. Non-isothermal differential scanning calorimetry (DSC) analyses of the fabricated composites revealed that the crystallization temperature of the PP matrix phase shifts towards higher one with decreasing dispersion size of silica and increasing content of distributed nano-silica. A DSC analysis may be a potential candidate for useful method to evaluate the dispersion characteristics of the inorganic nano-fillers in crystalline polymer-based nanocomposites.
The effects of strain rate and temperature on compressive properties of a biodegradable plastic made from oil were examined. Stress-strain curves of the biodegradable plastic were measured over a wide range of strain rates from 10–5 s–1to 104 s–1, using a quasi-static compression testing machine and a split Hopkinson pressure bar (SHPB) system. The strain rate slightly affected Young's modulus and considerably increased yield stress. In addition, the effect of temperature on Young's modulus and flow stress was also examined in a range from 3°C to 61°C. Young's modulus and yield stress decreased with increasing temperature. Empirical equation of yield stress for each temperature was derived for the strain rates from 102 s–1 to 104 s–1. A master curve of yield stress, reduced to 24°C, was made using these empirical equations. The values of activation energies related to the α and β relaxation processes were respectively estimated from the master curve of yield stress and from the best fit of equations based on Ree-Eyring theory and Bauwens' treatment. Temperature measurement of specimens was also made using thermocouples during dynamic compression. The ratio of the temperature rise to the mechanical energy of plastic deformation was calculated at a strain rate of 660 s–1 and 820 s–1.
We have investigated the force closing and compression strength of mandible to clarify the relationships between the material quality and the elastic property of the mandible among various termite species. The compression tests of mandibles have carried out coating with the epoxy resin. For example, the maximum load of Zootermopsis nevadensis is about 4.8N and that of Monchamus alternatus is 20N. We analyzed the buckling stress using the Tetmajer's formula, because the parameter λ' (= 1/√nI/A) was smaller than 100. The calculated result showed that the critical load was equal to the maximum compressive load. The elastic modulus were the range of 2–7MPa. The forces of closing of the mandibles with applying the air pressure were measured in various termite species. The air pressure of Z. nevadensis is about 0.7kPa, and that of M. alternatus is about 1.63kPa, whereas we have improved the measuring system with a load cell, and the force of closing mandibles of Z. nevadensis were about 4–5mN.
Increase in quality and decrease in cost of products have been needed in the industrial market. It is necessary to reduce the cost in die-casting products as well that the concept of “Net Shape” becomes popular in light of reductions in machining costs. However, the present technology tends to minimize machining operation instead of completely omitting machining. Thus, the least deformation is desired after the die-casting. Here, we investigate the method to obtain the optimum condition by using orthogonal array and monitoring system for casting condition by SOM (Self Organizing Maps) in order to maintain the optimized casting condition for minimizing deformation. First, the relationship between deformation volume and temperature difference in casting products is found. Through these analyses, we distinct that the products with less temperature difference had less deformation, and obtain the optimum condition by orthogonal array. Next, we suggested a scheme for preparing a basic SOM based on the analysis. It is found that the SOM monitoring system contains effective characteristics to obtain optimum condition for least deformation and monitoring.
This paper presents the results of laboratory investigation on the corrosion of oil alkyd-coated steel plates with unpainted defects under marine environment. Oil Alkyd paint-coated divided steel plates, (30mm × 30mm) composed of 9 pieces of 10mm × 10mm steel elements with different types of defects, were submerged in 3% NaCl solution after which the corrosion behavior of the steel plates was investigated for a period of 4 months. Macrocell corrosion, polarization resistance and double layer capacitance were measured in the laboratory in order to assess the corrosion behavior of paint coated steel plates with defects. The test results show that the presence of defects enhanced the degradation at the surrounding sound portion of the coated steel plates by causing a reduction in its polarization resistance while enhancing the increase in double layer capacitance. Furthermore, macrocell corrosion occurred between the painted part which acted as cathode and the defect part which acted as anode. Macrocell corrosion was seen as a contributor to the delamination of the surrounding painted portions paving way for the generation and progress of microcell corrosion at the surrounding painted parts.