Adhesive restorative composites have been used for dental clinical fields. So we examined the strength of adhesion between tooth substance and composite resin, used as restorative materials. Test method of adhesive strength, which simulated the force produced by mastication, was assessed by a push-out shear test, which is the new test method. The test specimens prepared ware then pressed to examine the adhesive strength of composite resin. The adhesive strength was highest for enamel, was lower for enamel/dentin and was lowest for dentin. The apparent adhesive strength, obtained from theoretical calculation, tended to show a constant relationship to the strength actually measured. This suggests that the effective adhesive area of the dentin is smaller than the area actually covered by the dentin. Furthermore, a gap, probably due to the effects of tensile stress, was observed in the adhesive interface between the composite resin and dentin. This gap seems to reduce the adhesive area, leading to a decrease on adhesive strength. Thus, the push-out shear test method appears to be useful in evaluating adhesive properties of composite resin.
A prediction methodology of fatigue strength of polymer composites for an arbitrary frequency, stress ratio, and temperature is introduced. The methodology is based upon the three hypotheses ; (A) Same time-temperature superposition principle holds for CSR (constant strain-rate), creep, and fatigue strengths, (B) Linear cumulative damage law is applicable under monotonic loading history, and (C) fatigue strength shows linear dependence upon stress ratio. The validity of hypotheses A, B, C, and the applicability of this prediction methodology were discussed. Finally, the future issues which should be solved for the practical use to the durability design are listed.
This paper deals with the geometric optimization for maximizing structural stiffness of 3-D arm-like variable geometry trusses (VGTs) subjected to an external static load. The 3-D arm-like VGTs are formed by joining several octahedral truss units, and their overall geometric configurations can be varied so as to change the mechanical characteristics of VGTs. The proposed approach to obtain the global optimum geometric configuration is based on the tunneling method. The numerical results obtained for two- and three-unit trusses agree well with those obtained by the parametric approach. Thus it can be concluded that the proposed approach is reliable enough to find the global optimum geometric configurations of 3-D arm-like VGTs.
In the present study, mechanical properties of a heat-resistant CFRP, G 40-800/5260, carbon/bismaleimide system are investigated experimentally. Laminate configurations are unidirectional 5and angle-ply [30/-30]S, [45/-45]S, [60/-60]S laminates. On-and off-axis tensile tests are performed on the unidirectional laminates. Tensile tests are conducted on the angle-ply laminates. The specimen size was 150 mm long and 10 mm wide. In order to investigate the effect of temperature on the mechanical properties, the tests are performed at the room temperature and 100°C. The temperature dependence of the mechanical properties is discussed. To model the nonlinearity in the stress-strain behavior of the unidirectional laminates, the one-parameter plasticity model is used. A master curve of the effective stress-effective plastic strain relation at each temperature is obtained which proves that the oneparameter plasticity model is valid for this material system. An attempt is also made to combine the one-parameter plasticity model and the classical lamination theory to predict the stress-strain relation of the angle-ply laminates.
In order to modify the toughness of epoxy resin, the blending method of multi polymer components was investigated. An epoxy resin based on diglycidyl ether of bisphenol A was modified with poly(ether sulfone)(PES) and poly (acrylonitrile-co-butadiene) rubber (NBR) and then cured with 4,4’-diaminodipheylsulfone. Morphology, dynamic mechanical properties, bending properties and fracture toughness of this ternary blend of were evaluated. Depending on the composition of PES and NBR, two distinct morphological states were observed, and the fracture behaviour varied from brittle to ductile with the change of morphology. From the morphology observation by various microscopes, the ternary blends that showed ductile behaviour have phase-inverted morphology in which the NBR-rich phase forms a continuous matrix, the epoxy-rich phase forms particles and the PES-rich phase also forms particles around the epoxy particles. Even at low loading level of PES and NBR which shows phase inversion, the storage modulus and Tg by dynamic mechanical analysis were as high as unmodified epoxy resin. And the bending properties were controlled by the loading level of PES and NBR, the kind of terminal functional groups and curing temperature.
GFRP has excellent corrosion resistance, so it has been employed widely such as acid tanks and drainpipes. However, in rare cases, GFRP products are failed by the stress corrosion cracking(SCC)of fiber under acid environment. It is considered that SCC is caused by degradation of interfacial strength, except for thermal stress between fiber and resin, or expansion and reduction due to the water absorption and discharge. In this study, interlaminar fracture toughness of GFRP whose fiber surface was treated with different agent was measured. Specimens were set up in acid solution bath with various temperature or time. As a result of experiment, in the case of the specimen of weak interfacial strength, fracture toughness KI decreased with increase of time or temperature. On the other hand, KI hardly decreased in the case of the specimen of strong interfacial strength. However, results of crack growth rate of both specimens were scattered at 323 K. It is considered that this scattering is caused by the change of damage mechanism, e.g., from single crack to multiple cracks, from interlaminar delamination to interfacial debonding and occurring of fiber bridging.
Silicon-carbide-coating is generally formed for the improvement of oxidation resistance of carbon/carbon matrix composites (C/Cs). Underneath a SiC coating thin conversion layer is often inserted to improve bonding strength between coating and C/C composite. The conversion treatment represents chemical reaction between the substrate carbon and gaseous Si. Two source materials, SiCl4 and SiO were examined to yield the conversion layer, and the mechanisms for the growth of a conversion layer were discussed, where the formation rate of a conversion layer was placed a special attention. Then, improvement of the interfacial shear strength of SiC-coated C/C composites by the conversion treatment was determined by a plunger method as a function of conversion time and treatment temperature, and the surfaces and cross-sections near the interface were observed by SEM and EPMA. These results indicate that the strengthening of the interfacial bonding by longer treatment time and higher treatment temperature is caused by so-called anchor effect due to the infiltration of CVD SiC in defects in a substrate C/C.
The effect of surface treatment of carbon black (CB) particles on the electrical conductivity of CB filled polymer is investigated in relation to the blending of matrix polymers. High density polyethylene (PE), polypropylene (PP), and the PP/PE polymer blend (weight ratio of PP/PE=40/60) are used as the matrix polymers. Silane coupling agents ; n-propyltrimethoxysilane (PS) and γ-aminopropyltrimethoxysilane (APS), are used for the surface treatment of CB particles. The following results are obtained from the electrical resistivity measurement of the composite : The percolation threshold ; the CB content at which the electrical resistivity of composite begins to decrease drastically, lowers by the blending of matrix polymers ; PP and PE. The percolation threshold of composite lowers by the surface treatment of CB with APS. The transmission electron microscopy (TEM) of the composites also shows the following results : CB particles in the PP/PE matrix preferentially dispersed in the PE phase. With increasing of the CB content, the PP phase which does not contain CB changes from continuous (the composite is insulating) to disperse (conductive).The threshold of CB content depends on the surface treatment of CB particles. The percolation threshold=1.5 phr is attained by the APS treatment of CB in the PP/PE and PE composites.
In order to develop the alkali resistance of anodic oxide film of aluminum, anodic oxidation aluminum was treated within the hydrothermal condition. And it is investigated that the effect of the hydrothermal temperature (80- 200°C) and anodic oxide film thickness on the alkali resistance time of the anodic oxide aluminum. The film thickness was controlled by changing the anodizing time from 0 min to 60 min in oxalic solution bath. By means of SEM observation of cross-section of film after hydrothermal treatment at 200°C, in the case of the thick film, then the film was composed three layers, outer cube structure layer and middle layer and inner columnar layer. In the case of the thin film, the columnar layer was disappeared. The alkali resistance time increased with increasing of the hydrothermal temperature. The alkali resistance time was effected the dense layer thickness which was calculated by the subtraction columnar layer thickness from film thickness. And, the value which was divided the alkali resistance time by dense layer thickness became 1.2 ks/μm between the anodizing time for 10 min and 35 min after hydrothermal treatment at 150°C, and became 5 ks/μm below 25 min at 200°C, respectively. Hydrothermal temperature was over 100°C, the value, alkali resistance time/dense layer thickness, of the anodizing film for 30 min was longer than the anodizing film for 60 min. Hydrothermal treatment at 80°C, then that value coincide the anodizing film for 30 min and 60 min.
Fiber Reinforced Plastic (FRP), which contains mainly Unsaturated Polyester (UP), has been developed as light and tough material. FRP is widely used for bathtubs, boats and automobiles. However, there is no useful recycling method for FRP wastes ; therefore most of them are landfilled. We investigated methods of decomposing UP into low molecular products without corrosion of recyclates. We examined various catalysts under ordinary pressure at 190°C for 4 hours, using various solvents. As a result, we found UP was decomposed and dissolved only alcohols with K3PO4・H2O as a catalyst not corroding glass after the examination of various solvents. Especially, high solubilities like 36% were shown in diethylene glycol monomethyl ether. The glass fiber and filler recovered from FRP waste by the method was tested as reinforcements for FRP. We found that the tensile and flexural strengths of the FRP using 100% recycled glass fiber were reduced to approximately 70% and 50% respectively, compared with the original FRP, while no significant deterioration in the strengths was observed for the FRP containing 100% recycled filler. We recognized that our newly developed method could be available for recycling glass fiber and filler in FRP waste.
A degraded GFRP stack was investigated and the degradation behavior was discussed. The fracture aspect were precisely observed not only mechanically,but also microscopically and chemically. Severe damages were found in the middle part of stack, and it is considered that the dew with high concentration acid was produced there and it attacked the GFRP. The lower part would be exposed both high temperature and low temperature environment, and thermal shock might be applied. Hence, the degradation behaviors varied with the position of the stack, because the each position is expected to different environment.