Key Engineering Materials Vols. 471-472

Abstract: The study involving utilization of agricultural residue is gaining attention. This is an attempt to investigate the possibility of producing composite panels from rice husk (RH), an abundant source of agricultural residues. Composite panels were produced by mixing 1mm of rice husk with a commercial binder called urea formaldehyde at different density levels namely 650kg/m3, 700kg/m3 and 750kg/m3. Two types of resin content (10% and 12%) were used. Mechanical strength tests were performed on the panels conforming to British Standard (BS EN 310). Results obtained indicated that the modulus of elasticity (MOE) increased up to 1753.98MPa at 750kg/m3 density level with 12% resin content. Similarly, modulus of rupture (MOR) increased up to 8.08MPa with increase in panel density and amount of resin content. Thus, the potential of producing reasonably good composite panels from rice husk for specific end usage is very promising.

Abstract: In this study, wastes of wood cutting mills (wood flour) as well as wastes of textile industry (granules of polypropylene) were used in manufacturing wood-plastic composites. Hence, wood flour with weight percent of 30, 35 and 40 was mixed with corresponding amount of polypropylene and coupling agent, polypropylene grafted maleic anhydride in amount of 6 percent was used in whole compounds. Production was done by batch method and with employment of hot press and after preparation and cutting of specimens physical and mechanical properties of them was studied. The results showed that with increase of wood flour up to 35 percent, MOR, MOE, water absorption and thickness swelling increases but further than it mechanical and physical properties decreases. Besides, increase of wood flour up to 40 percent increased the hardness of the specimens.

Abstract: Lead-free solder paste printing process accounts for majority of the assembly defects in the electronic manufacturing industry. In the stencil printing process, the solder paste must be able to withstand low and high shear rates, which results in continuous structural breakdown and build-up. The study investigates the effect of nickel additional to the thixotropic behaviour of lead-free Sn/Ag/Cu solder pastes using the structural kinetic model. A hysteresis loop test and constant shear test is utilized to investigate the thixotropic behaviour of the pastes using parallel plate rheometry in temperature 30 oC. In this study, the shear rates were increased from 0.01 s-1 to 10s-1 and the second curve was a result of decreasing shear rate from 10s-1 to 0.01s-1. For the constant shear test, the samples were subjected to two constant shear rates of 0.1s-1 and 1s-1. The constant shear rate test was designed to study the structural breakdown and build-up of the paste materials. From this investigation, hysteresis loop test was shown to be an effective test method to differentiate the extent of structural recovery in the solder pastes. The results of the structural parameter values obtained from the kinetic model showed a good correlation to the breakdown and build-up of the paste structure.

Abstract: This study presents the results of immediate and long-term deflections of reinforced concrete beams strengthened with carbon fiber reinforced polymer (CFRP) laminates under sustained loading The test parameters were sustained load and different degrees of strengthening scheme for both cracked and un-cracked sections of beams. The applied sustained load was 56% and 38% of the ultimate static capacities of the un-strengthened beams for cracked and un-cracked section respectively. The long term deflections of CFRP strengthened beams at six month were on average 1.42 times the immediate deflections for un-cracked beams and 1.45 times the immediate deflections for cracked beams. The experimental results indicate that the long-term deflection of cracked beam shows significantly higher value compared to that of un-cracked beams. A comparison of time dependent deformation between analytical and experimental results shows closer agreement for the un-cracked beam sections. More conservative theoretical estimation is observed in the case of cracked beam section in spite the inclusion of tension stiffening effect. Finally, factors affecting the long-term deflection of strengthened beams are discussed to get better understanding on the long term behaviour of strengthened beams.

Abstract: In this paper, experimental study is carried out to evaluate the flexural performance of reinforced concrete beams strengthened with different ratios of carbon fibre reinforced polymer (CFRP) laminates. Four rectangular reinforced concrete beams strengthened with different reinforcement ratios of CFRP laminates are tested to failure under transverse bending on a simply supported span of 1.9 m. The increase of ultimate strength provided by the bonded carbon fiber is assessed and failure mode is identified. The results indicated that the flexural capacity of beam was significantly improved as the layers of laminates increased. It is concluded that the attachment of CFRP laminates has substantial influence on the performance of CFRP strengthened beams. However, de-bonding of CFRP laminates from the concrete surface is still a concern for the case of multi-layer strengthening of beam. Based on the observed results, recommendations are made to prevent the premature de-bonding failure of strengthened beams.

Abstract: The purpose of this study was to determine some physical and mechanical properties of sandwich panels manufactured from the core of Paulownia wood and surfaces of multilayer of fiberglass and resins. Paulownia was selected among Hardwoods because of its s low density (0.26 g/cm3) and high strength/weight ratio. Eight treatments were used for experiments: Two kinds of fiberglass (needle and combination of the needle and curtain type), two various resins (polyester and epoxy) and two core thicknesses (9mm and 19mm). Physical properties including density, resistance to water absorption, Dimensional stability, and Mechanical Properties such as internal bonding, compressive and bending strength of panels were measured following ASTM Standard. The results indicated that panels with 19 mm thick core had lower density (0.5g/ cm3) compared to the 9mm thick panels (0.7g/cm3). Bigger volume of wood in the core of panels with higher thickness was the main reason of this result. The experimental results showed that thickness of wood was effective on the modulus of rupture, modulus of elasticity, and compressive strength, significantly. Epoxy resin presented higher internal bond compared to the polyester resin. The two kind of fiberglass (needle one and the combination of needle and curtain type) didn’t have noticeable differences on mechanical properties. It also was found that Paulownia is a promising species for manufacturing sandwich panel.

Abstract: The aim of this study was to manufacture wood based particleboard by using wood particles and agricultural residues of walnut and almond shells that have no economical value other than being used merely as low grade fuel and fodder and evaluating of its performance. This study was done at two stages; first determination of optimum press condition of producing boards from mixture of wood particles and walnut/almond shells and second stage was evaluation of the effect of different ratios of walnut/almond shells (10 and 30%) and the shell mesh size (≤ 0.7 and ≥ 2 mm) on their mechanical (modulus of rupture and modulus of elasticity and internal bonding) and physical (thickness swelling and water absorption) properties. The result of first stage of the study showed that of press pressure of 2.5 and 5 MPa, press temperature of 150 and 180 °C and press time of 5 and 10 minutes, optimum press condition of producing boards from mixture of wood particles and walnut/almond shells are press pressure of 2.5 MPa, press temperature of 180 °C and press time of 5 minutes. The result of second stage of the study showed no meaningful difference between mechanical and physical properties of composite boards containing 10 percent of walnut and almond shell with reference one (board A). Besides, the range of used almond and walnut mesh size had no meaningful differences.

Abstract: Porous Ag-Bi2O3 composite cathodes on stainless steel (SS) substrate, an excellent mixed-ionic conductor that can be used as cathode material for the intermediate temperature solid oxide fuel cell (IT-SOFC) has been developed using the slurry painting method. Characterisation of the composite cathode includes the thermal analysis, morphology, and porosity of the porous cathode. Thermal analysis of the dried slurry was conducted in order to determine the heating schedule for eliminating the organic components using thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). The TGA and DSC analyses confirmed the organic vehicle was fully decomposed below 418oC and the formation of composite cathode oxide phase took place beyond 600oC. The microstructure of the thermally treated cathode was analysed using SEM and XRD. The SEM results showed that the grain size of the cathode increased with the increase of temperature during thermal treatment and the X-ray diffraction (XRD) analyses confirmed the presence of δ-Bi2O3 phase on the cathode. Porosity was obtained using the Archimedes method. The Ag2O3-Bi2O3 cathode on stainless steel substrates was found to have a porosity of 53%, 51%, 39% and 28% upon 1, 2, 3, and 4 coatings, respectively, as well as thermal treatment at 800°C for 1 hour.

Abstract: It is well known those two popular methods of testing; destructive testing based on fracture mechanics and non-destructive testing (NDT) which does not make any damage in the specimen. NDT was first used for military purpose but nowadays it is used widely in many fields such as composite materials, medical purposes, fire safety, laser welding, food safety and quality and characterization of materials. The aim of this paper is to review the recent advancement of thermography non-destructive methods especially in testing a quality of bio-composites materials. The review reveals the advantages and disadvantages of pursuing any of the available methods in NDT on bio composite materials.

Abstract: The injection molding of polymer composite is one of the promising and practical methods in the manufacturing of bipolar plates in mass production. Graphite filler with higher loading concentration is mainly used for this purpose. The particle size and composition (wt. %) of graphite filler material influences on the mechanical properties and electrical conductivity of composite materials. The main challenge is the reduction of flow ability during injection of high load filler material. Flow ability of feedstock material is an important factor in the process of injection molding. This paper presents a development of the rheology approach on the effect of particle size in material flow ability occurs in the injection molding process. Polypropylene (PP) as polymer matrix and graphite as conductive filler mixed together with different size to form feedstock material. Graphite purchase from local Asbury Graphite Mills, Inc, grade 3243 with particle size in average after sieve of ≤40, ≤100, and ≤150 μm. Proportions of polymer matrix and graphite at (PP / G) 25 / 75 wt. %. Mixing of graphite in PP matrix is done using an internal mixer (Thermo Haake) at 50 rpm, temperature at 200 oC. Rheology behaviors of graphite composite were measured using a capillary rheometer type Shimadzu CFT-500D, with a diameter 1 mm and length 10 mm. The fracture surface morphology was examined using scanning electron microscopy (SEM). The electrical conductivity of composite materials was measured by the four point probe. The hardness property measurement of conductive material composite was performed using a Dynamic ultra micro hardness tester using a Vickers typed diamond indenter. The results indicate that the level of viscosity and shear rate on all eligible mixed particle size capable of injectable. The properties of composite materials is the highest in three mix particle size (40/100/150 μm) for the electrical conductivity of 9.13 S.cm-1 and hardness at 34.3 HV. Viscosity of 56 Pa.s at a temperature of 200 oC and shear rates generated in 3231 s-1. The highest electrical conductivity for a single particle size is 49.2 S.cm-1 at 150 μm and hardness of Vickers to 47.2 HV at 100 um. The highest electrical conductivity and hardness due to the packing density and reinforcement different particle size.