It is well known that carbon nanofillers (CNFs) enhance the stiffness, electric conductivity and thermal conductivity of polymers. Alignment of carbon nanofillers in polymer is expected to increase the performances in the aligned direction. Several papers have reported that applying alternating electric field to a liquid suspension including CNFs causes alignment of CNFs in the electric field direction. Only a few papers have reported the fabrication of nanostructurally controlled composites by using AC field, but the conditions to let CNFs align have not been investigated. In this study, unidirectionally aligned carbon nanofiller/epoxy composite was fabricated under AC electric field, and the alignment of CNFs was in-situ observed during fabrication by using an optical microscope. Then, the effects of applied voltage, frequency and the weight fraction of CNFs on nanostructure were investigated. As a result, it is found that CNFs in uncured epoxy resin align in the AC electric field and form a chain-like network, and that in the end the network structure is hold with cured epoxy. It is also shown that the applied voltage and weight fraction affect the morphology of the network. Furthermore, the network morphology was quantified by using texture analysis. Local homogeneity in the longitudinal and transverse directions of the AC electric field was used. It is found that there is strong relationship between the changes of local homogeneity and network morphology.
An important thing of FRPs to use in structural member is to understand the visco-elastic behavior of them. In this study, creep behavior of glass fiber reinforced Polycarbonate (GFRPC) was researched. Before the creep test, GFRPCs were heated for various times at test temperature for aging treatment to research the effect of physical aging. The result shows that creep behavior of GFRPCs with various aging treatment could be able to make master curves of creep compliance on each aging conditions. And time-temperature shift factors with various aging conditions represented good agreement to time-temperature superposition principle of Arrhenius type plotting. To research the effect of physical aging quantitatively, it was compared with the master curves of various aging conditions. Therefore, the effect that the physical aging exerted on the visco-elasticity behavior was able to be understood including the existence of the fiber content.
Two kinds of cylindrical specimens of short-glass-fiber reinforced polybuthyleneterephthalate (PBT), the one with weld line at the center (W specimens) and the other with molding direction parallel to the specimen axis (MD specimens), were fatigued under axial total-strain-controlled conditions. The fatigue life of W specimens was slightly shorter than that of MD specimens when compared at the same range of total strain, although the difference was very small. When plotted against the stress amplitude or inelastic strain energy, the fatigue life was much shorter for W specimens. The tensile peak stress in stress-strain hysteresis loops decreased with the number of cycles. Unstable fracture took place at 30 to 40% reduction of peak stress in MD specimen, while in MD specimens a sharp decrease in the peak stress and the maximum in inelastic energy took place at the 40% reduction of the tensile peak stress. Unstable fracture did not occur in W specimens. The computerized tomography (CT) using synchrotron X-rays was applied to observe nondestructively the crack growth behavior in fatigued specimens. In W specimens, crack started from the surface and extended inward as a continuous long crack, while only many small cracks observed at the central region of the specimens until unstable fracture in MD specimen.
A CFRP scarf-repaired specimen is manufactured using the autoclave method on the assumption that it is a part of the repaired composite airframes. Such specimens are composed of a scarf joint and a step-lap joint. Though the in-plane mechanical properties of the scarf-repaired composites have been studied, few researches on out-of-plane behavior have been reported. Thus, the mechanism of the impact damages in the scarf-repaired composites was clarified through two kinds of experiments, the low-velocity impact test and the static indentation test. Through the low-velocity impact test, the damage configuration was observed and the influences of the scarf angle and stacking sequence on impact damage were investigated. As a result, the debonding at the interface between the adhesive layer and the repair laminate was observed in all the specimens. Moreover, damage growth was observed through the static indentation test. The indentation results indicated that the debonding at the interface between the adhesive layer and the repair laminate occurs at the intersection of the adhesive layer and the delamination of the repair laminate.
A galvanic corrosion-resistant carbon fiber-reinforced metal laminate (CFML) is created in this paper. Aluminum alloy 2024-T3 is selected as the metal layer. A surface treatment method of composite coating combining a sulfuric acid anodizing with a hybrid sol-gel coating for the aluminum alloy is developed. This composite coating is used to prevent CFML from galvanic corroding. Electrochemistry tests are conducted to evaluate the properties of electrochemistry of aluminum alloy treated by the present method. The test results prove that the composite coating can provide good protection for CFML against the galvanic corrosion. CFML consisting of carbon fiber-reinforced epoxy layer and the aluminum alloy sheet with composite coating is fabricated by autoclave cure processing. The cross-section of CFML is analyzed by scanning electron microscope (SEM) and electron probe micro analyzer (EPMA). Good thin interlayer consisting of composite films is formed between the aluminum alloy and carbon fiber-reinforced epoxy layer. Corrosion tests of CFML with and without composite coating are conducted and the CFML with composite coating shows excellent corrosion resistance.
Moisture absorption of GFRP degrades mechanical properties such as compressive and fatigue strength. Monitoring of moisture absorption of GFRP structures is useful to assure the structural integrity. Conventional moisture measuring methods for various materials is inappropriate for GFRP because of its inhomogeneity and low moisture absorption ratio. In this study, a new method is proposed to measure the moisture absorption ratio of GFRP laminates by using a polymer film capacitance sensor which is embedded between GFRP plies. The dielectric constant of the film (polyimide) depends on the moisture absorption ration of surrounding resin. The moisture absorption ration of GFRP is estimated indirectly from measuring the dielectric constant of the film. At first, the relationship between the moisture absorption ratio and the dielectric constant change of an ideal capacitive film sensor itself was investigated. Then, an epoxy specimen with a flexible print film sensor in the midplane was immersed in water, and the moisture absorption ratio of the specimen and the capacitance change of the sensor were monitored. As a result, it is shown that the moisture absorption ratio of GFRP laminates can be easily measured by the proposed method.
Laminated composite structures are increasingly used for aerospace structures, such as interstage structures of launch vehicles. For an optimal design of the laminated composite structures, both dimensions and stacking sequences of the structures should be optimized simultaneously since they affect each other. The stacking sequence optimization of composite laminates is a combinatorial optimization problem with some constraints. That makes the optimization of dimensions and stacking sequences a complex mixed problem that contains both combinatorial and continuous-discrete variable optimizations. Therefore, the design of the laminated composite structures has generally been carried out using a genetic algorithm (GA). GA inherently requires many evaluations of optimization functions during the process. It must be time consuming especially for composite structural optimizations, which needs a computationally expensive analysis for the evaluation of the functions such as stress and buckling load. Authors have proposed an effective and global optimization method of the composite structures. The method utilizes a kriging method for approximating expensive functions of the optimization. Using the kriging models makes it possible not only to reduce the computational cost to evaluate the functions but also to search for the optimal design globally with using multi-objective genetic algorithm (MOGA). In the method, fractal branch and bound (FBB) method is also adopted, which is a practical and low-cost stacking sequence optimization method. In the present paper, the proposed method is applied to a complicated design problem of a large-sized composite structure. A design of a rocket structure under combined load is addressed here. The result shows that the method is effective in the large-sized optimization problems.
For a new insight on the misfit dislocation networks in Ni-based superalloys, we investigate the structure and motion of misfit dislocations on two different semi-coherent interfaces between Ni and Ni3Al, Interface 1 and 2, by using molecular dynamics simulations. The former does not have Al atoms at the interface in the Ni3Al side, while the later does. Misfit dislocation networks are actually found on the interfaces along the <110> and <110> directions, as observed in experiments. Detail observation of the dislocation cores reveals that the network is basically composed of the edge dislocation ; however, Interface 1 also shows screw character at the intersections of the network. By applying the tension normal to the interfaces, many partial dislocation loops nucleate and propagate from the network on Interface 1, first in the Ni side then in the Ni3Al side. Partial loops are also originated from the network of Interface 2 into the Ni3Al side; however, they make dislocation locking with another partial on the conjugate slip plane, showing wedge-like stacking faults parallel to the network. Partial loops also nucleate and expand from the networks on both interfaces, only into the Ni3Al side under the compression normal to the interfaces. The dislocation locking is not found under the compression, while the partials originate a little faster from the network on Interface 1 than that of Interface 2.
This paper describes the relationship between Vickers hardness and the elastic-plastic material constants by using finite element analyses. The hardness increased with increasing yield stress and strain hardening coefficient, but it decreased with increasing strain hardening exponent. A new equation for predicting Vickers hardness was proposed as a function of yield stress, and of strain hardening coefficient and exponent. The hardness predicted by the equation agreed well with the finite element and experimental results. The fatigue limit and threshold of stress intensity factor were discussed in relation to the elastic-plastic material constants based on the proposed equation. The critical thickness of specimen for hardness testing was also discussed in connection with JIS and ISO standards.
To improve poor adhesion of Diamond-like Carbon (DLC) coatings on the steel substrate, Fine Particle Bombardment (FPB) using Cr based shot particles are combined with DLC coating process. The FPB treatment distributes diffused Cr elements onto the treated surface, creating a Cr-rich layer. The FPB treatment increases the surface hardness and roughness. Wear test was conducted to compare the tribological properties of the DLC coated FPB treated steels and that of the DLC coated non FPB treated ones with a special focused on the Cr-rich layer, surface hardness and roughness. The DLC coated surface, after FPB treatment, kept low friction coefficient, while the DLC coated non FPB treated ones showed a sudden increase indicating the delamination of DLC layer. This is because of Cr-rich layer, which increase adhesion between DLC coating and steel substrate.
In order to identify the mechanical parameters of the ground ahead of a tunnel face, a three-dimensional back-analysis method is newly proposed. The method consists of a three-dimensional finite element analysis and the secant method, and is based on an iteration procedure. The Poisson's ratio, the modulus of elasticity and the six components of the initial stress levels of the ground around a tunnel face are back analyzed from displacements obtained by field measurement, which are produced by one-step excavation of the tunnel face. Influence of measurement errors of field displacements on accuracy of the results identified is made clear through numerical calculation.
To improve the strength and wear resistance of Ti-6Al-4V alloy, which is widely used as a useful Ti alloy, a Ti-6Al-4V powder mixture was mechanically blended with Mo2C powder by the planet type rotating ball milling, and TiC dispersed Ti-6Al-4V alloy was produced by reaction sintering using SPS. The results of a study on the relationship between the structures and mechanical properties of this alloy prepared under various SPS conditions showed the following. When the raw powder of the Ti-6Al-4V alloy was mixed and stirred with 5 vol% Mo2C powder, the SPS reaction allowed for the preparation of a high-density TiC particle-dispersed Ti-6Al-4V alloy in a short period of time. For obtaining a uniform sintered material under 50MPa of pressure, sintering conditions including a temperature of 1373K or higher and a holding time of 0.3ks or longer were required. The matrix grain size and crystallized TiC particle size were 8∼9μm and 2.5∼3μm, respectively, under these conditions, and tended to increase with increasing sintering temperature and holding time. Although the grain growth was small up to a sintering temperature of 1373K, it was significant at 1474K. The TiC particles crystallized by the sintering reaction were effective in preventing the coarsening of the matrix structure and improving the yield stress and wear resistance. The additive material, Mo2C, on the other hand, caused a large reduction in the β-transformation temperature and an increase in the volume fraction of the β phase, leading to an effective improvement in ductility.
A highly concentrated aqueous solution of sodium borate in the range 5.24mol/kg (20°C)-24.1mol/kg (80°C), which is more than twice more concentrated than the most soluble known borate solutions, was prepared and applied to the fireproofing agent of wood. This high concentration is due to the formation of polyborate ions. Wood specimens of Japan cedar (Cryptomeria japonica) was pressure-impregnated with the solution at 120-190°C for 1 - 24h. The most appropriate temperature was 150°C (474kPa) and the treatment for 1h. was sufficient for the impregnation. Weight percent gains (WPGs) were increased with increasing the concentration of the borate solution, and this lead to the decrease of weight loss (WL) when heated at 750°C for 20min in air. The specimens pressure-impregnated for 1h. using the solution containing 24mol/kg of boron achieved the WPG of 124% and the WL of 38%. The fireproofing procedure was greatly simplified by using the new highly concentrated borate solution. The other kinds of wood showed lower WPGs than Japan cedar because of the high density or the much resin. SEM and EDX observation indicated that the sodium polyborate enrolled wood fiber by heating and intercepted oxygen and heat conduction. The polyborate foam and carbonized layer also intercepted the heat conduction. This technique is also expected to be applied to the fireproofing of laminated wood and particle board.
Health monitoring system equipped with blood extraction pump is one of the important problems for new medical technology to support the advanced age society. In this paper, a new piezoelectric actuator for blood extraction pump was proposed to increase volumetric change in pump. We devised the geometry of piezoelectric actuator with some slits that allows the stretching and contracting deformation in in-plane direction to create large deflection in out-of-plane direction. Focusing on a disc-type bimorph plate with some slits, the deformations under static electric load have been analyzed by finite element method with consideration of two geometric parameters, length l and width w of slits. The computational results indicated that the deformation of bimorph actuator changes from complex mode to single mode according to increase of slit length, and that single mode presents remarkable increase of deflection under surrounding-fixed condition. And then, a bimorph actuator with 4 slits l = 2.0, w = 0.5mm has been manufactured as an experiment. As a result, a developed actuator was proved to increase the deflection under dynamic electric load compared with a conventional bimorph actuator without slits.