Abstract: Three types of three-dimensional stitched carbon fiber reinforced silicon carbide composites (3DS C/SiCs) with 4, 9 and 16 Z-yarn/cm2 were fabricated by chemical vapor infiltration, respectively. Both iosipescu specimens without enough representative volume elements (RVEs) and ±45° tension specimens containing enough RVEs were tested to attain the in-plane shear properties of 3DS C/SiCs. The results showed that these two methods produced similar results. This demonstrated that the dimensions of iosipescu specimens were not necessary to cover enough RVEs for 3DS ceramic matrix composite in-plane shear testing. With respect to the shear modulus, both two methods would be regarded as the effective methods. However, in terms of the in-plane shear strength, iosipescu method would be a more reliable method.
Abstract: In this study, we investigated the effect of jute fiber’s thermal degradation on fiber strength and its polymer composite. First, we conducted a tensile strength test of a single jute fiber. Next, polyethylene and jute fibers were mixed by twin-screw extruder to make pellets. After making pellets, we used injection molding machine to make the test pieces. Tensile tests were conducted using injection molded sample. As a result, in the experiment of the single fibers, tensile strength of jute fiber monotonically decreased with increasing drying temperature. In case of composite, the tensile strength of molded sample increased with increasing control temperature in twin screw extrude in a range between 150°C ~ 220°C. When the temperature of twin-screw extruder was controlled above 300°C, pellets were burned black by thermal degradation and couldn’t fabricate the test piece.
Abstract: The fracture behavior and fatigue limit in notched specimens of C/C composites were investigated. Also, the effect of specimen thickness on fatigue limit was discussed. Two plates of different thicknesses of plates of C/C composites using fine-woven carbon fiber laminates with α=0°/90° direction were used for testing. α is the angle between the carbon fiber direction and specimen axis. The crack growth behavior and failure mechanism of specimens are derived from the shear damage in the fiber bundle and matrix. Slits of several sizes were cut on both sides of a test section and different geometries of the specimens were prepared. Specimens with slits and blunt-notches were used to compare the fatigue strength. The fatigue limit is related to the method of making the plate of carbon composites. Large sizes of voids are observed in the case of specimens of thinner thickness. The fatigue limit was related to the void fraction, and thinner specimens showed a lower fatigue limit.
Abstract: In this study, effect of thermal cycling after water absorption on flexural property of CFRP(Carbon Fiber Reinforced Plastics) was examined. Water absorption tests were conducted for 24 hours, 100 hours and 500 hours at 90°C. Thermal cycling test was conducted by using water absorbed specimen. The temperature range of thermal cycling test was from room temperature to-196°C. The static three-point flexural test of CFRP with freezing after water absorption was conducted based on JIS(Japanese Industrial standard) K 7074. Following conclusions are obtained. In case of immersion for 24 hours, flexural strength and modulus of CFRP with freezing after water absorption decreased with an increase of the number of cycles. In case of immersion for 100 hours and 500 hours, flexural strength and modulus of CFRP with freezing after water absorption did not change. The water absorption of CFRP was the phenomenon that the water penetrated into fiber/resin interface. So, in the case of immersion for 24 hours that the absorption time is not so long, damage progresses gradually in thermal cycling test. On the other hand, in the case of immersion for 500 hours is long, the damage progresses at the early stage of the thermal cycling test, and after that the damage does not almost progress.
Abstract: In this study, effects of water absorption and adding resin particles around fiber on interfacial shear strength of carbon fiber (CF)/maleic anhydride grafted polypropylene (MAPP) were investigated. In water absorption test, CF/MAPP specimen was immersed in distilled water at room temperature for four weeks. Micro debonding test of water absorbed CF/MAPP was conducted. Micro debonding test of Resin particle added Carbon Fiber (RCF)/MAPP was also conducted. The resin particle size was less than 5μm. Fracture surface of RCF/MAPP was observed by using Scanning Electron Microscope (SEM). As a result, following conclusions are obtained. In case of water absorbed CF/MAPP, the interfacial shear strength decreased 34% compared with that of virgin. The reason is thought that the interface between fiber/matrix was weakened by absorbing water. In case of resin particle, interfacial shear strength of RCF/MAPP increased 34% compared with that of CF/MAPP. From fracture morphology of RCF/MAPP, resin particles on CF surface were found. Therefore, interfacial shear strength of CF/MAPP was increased by the friction on the surface of carbon fibers.
Abstract: The development of nanocomposites promising a wide range of interesting properties such as mechanical, optical and electrical conductivity is under intense investigation. One key challenge towards practical applications lies in effective dispersion of nanofillers in the polymer matrices. An one-pot wet-chemistry synthesis approach was developed for successful fabrication of surface modified SiO2 nanoparticles@epoxy nanocomposites (1 wt%). Homogeneous nanofiller dispersion was obtained in SiO2-epoxide@epoxy. Importantly, the SiO2-epoxide@epoxy presented its enhanced mechanical properties with reference to pure epoxy, i.e., ~ 77% increase in maximum tensile stress and ~ 19% increase in Young’s modulus. This was attributed to the much improved dispersion of nanofillers and the optimized interaction between nanofillers and matrix. Further, SiO2-epoxide@epoxy prepared from master batch with 80 wt% SiO2 loading retained the good dispersion of nanofillers and enhanced mechanical properties. This demonstration allows future implementation of the developed approach for the surface modified SiO2@epoxy nanocomposites towards industrial applications.
Abstract: Particulate reinforced composites show viscoelastic behavior under various loading conditions. It is important to estimate mechanical behavior when this material is used for solid fuel on rocket motor. Cracks can be generated and propagated due to high combustion pressure in the service time. These cracks expand the burning area and lead to excessive combustion. Consequently, the rocket motor can cause malfunction or the performance deteriorated. In this study, edge cracked sheet specimen was used to perform the crack propagation tests. These tests were conducted in the range of temperature from -60°C to 60°C under 2.54 and 12.7 mm/min of strain rates. Based on the results, the stress intensity factors and the crack propagation rests were calculated. The crack resistance curves show the transition that stress intensity factors increases as temperature decrease. Also, fracture surfaces were investigated by scanning electron microscope to determine the fracture behavior under various temperatures.
Abstract: As oil & gas exploration and production is moving increasingly towards offshore and deeper water, and then the demand for lighter and stronger material for deep water structures is growing. Fibre reinforced plastic (FRP) is a potential alternate. However, such application has low tolerance for accidental impact loads. This paper presents an experimental investigation on the behaviour of hollow glass fibre reinforced plastic (GFRP) pipes subjected to transverse impact. Drop weight impact tests were adopted. The GFRP pipe specimens were simply supported at two ends. The variations of strain, deflection and impact force were recorded. Different failure modes were observed and the critical factors affecting the damage of GFRP pipes were discussed. Their structural performance under transverse impact was assessed.
Abstract: The mechanical strength of cellulose nanofiber-reinforced polyvinyl alcohol (PVA) composite films was evaluated by means of tensile test to explore the effect of fiber content and processing condition to the mechanical strength. Cellulose nanofibers were mixed with PVA resin at different weight ratios of 10, 20, 30, 40, 50, 60, 70, 80 and 90wt% and tensile tests were done on the composite films with thickness of 0.08~0.11mm. A set of samples for every respective weight ratio was hot-pressed at 180°C and 10MPa pressure and tensile tests were conducted to compare the failure behavior of the hot-pressed and the non hot-pressed composite films. The results showed that hot-pressed composite films exhibit a linear stress-strain curve as compared to the non-hot pressed composite films, which exhibited more ductile characteristic. For non hot-pressed specimens, tensile strength showed almost no significant increase from 0wt% to 50wt%, and finally a sudden increase especially from 50wt% to 70wt% fiber content where the highest average value recorded was 149MPa at 70wt%. As for hot-pressed composite films, the highest value of 167MPa at 60wt% was obtained without significant pattern of reinforcement effect with the change of nanofiber content. The reinforcement effect derived from cellulose nanofiber has shown favorable results which indicated an increase in the composite tensile strength of about 33.3% from pure PVA specimen, and hot-press process, though has reduced the ductile characteristics of the composite films, has increased tensile strength of the specimens up to 22% as compared to pure PVA specimens.