The occurrence of deterioration in concrete structures due to salt damages is increasing rapidly, making its maintenance problematic. Although cross-sectional repair and surface coating methods are implemented as counteractive repair measures of deteriorated structures, there is still the problem of re-deterioration. Conversely, while cathodic protection has been undertaken as a repair measure, it was not popular because it was a newly introduced technology at that time. However, since many of the actual structures in which cathodic protection was applied have sustained a high anticorrosion effect even after more than 20 years, its application in recent years is increasing. In this study, we investigate the interpretation and maintenance method of the different characteristics of cathodic protection from the environment on the basis of the exposure test data and the actual structure data.
Dissolution and Repassivation during and after passivity breakdown of four kinds of metallic biomaterials in simulated body fluid were examined using rapid straining electrode test. The materials were pure titanium, Ti-6Al-4V alloy, Type 316L stainless steel and Co-Cr alloy. Rapid straining was applied for electrodes of these materials that were immersed in a simulated body fluid containing proteins for 1 day, 1 week or 1 week with cell culturing prior to the test, then changes in strain, stress and anodic current were observed simultaneously. The maximum anodic current density during rapid straining was observed for pure titanium. However, maximum charge density generated after rapid straining until 100 s from the termination of rapid elongation was observed for Type 316L stainless steel. These results suggest that the amount of dissolution of metallic biomaterials with passivity breakdown depends on the equilibrium potential of metal substrates and repassivation rate. The charge densities generated on the samples immersed for 1 week in the simulated body fluid prior to the rapid elongation and covered with cells was larger than that generated on the sample immersed for 1 day in pure Ti, Ti-6Al-4V alloy and Type 316L stainless steel. The highest increase rate of the charge density was confirmed in the sample covered with cells of Type 316L stainless steel.
Corrosion of the inner surface of steel pipes around the insulating joints under cathodic protection not to corrode the outer surface of their buried pipes was experienced for the pipelines of a district heating and cooling system supplying a high-temperature and high-pressure water. In order to prevent such interference corrosion induced by the protection current flowing out to the supplying water, the single insulating joints were replaced by the double insulating joints at both ends of titanium short pipes and the thick steel pipes (STPG) for anodic side. The performance of these countermeasures for 14 years’ service was studied by inspection of materials collected from the field and laboratory tests. The localized corrosion of STPG pipes at anodic site has been suppressed as low for service of 20 years. The titanium short pipe also does not exhibit no distinct corrosion damage at anodic part, nor hydrogen embrittlement at cathodic part. Furthermore, the resistance at insulating joints can be predicted by a simple numerical model based on electrochemical parameters obtained by laboratory tests simulating the behavior of titanium and steel in the high-temperature and high-pressure water.
Cathodic protection is being applied to buried steel pipelines and polarized potential of pipelines is kept less noble than the protection potential criterion, -0.85 V vs. Cu/CuSO4. However, instantaneous anodic current has been infrequently observed in some fields even though polarized potential of pipelines is kept less noble than the protection potential criterion. In this study, the influence of instantaneous anodic current on corrosion protection of buried steel pipelines under cathodic protection was evaluated and the oxidation reaction causing anodic current was investigated to some extent. As a result, it was found that most of the anodic current was not attributed to corrosion reaction and the maximum value of corrosion rate of steel was as little as 1.8 μm/year. Therefore, it was considered that there was no matter on buried steel pipelines even though the instantaneous anodic current occurred under the protection potential criterion. It was estimated that some part of the anodic current was attributed to the oxidation reactions of components in soil and of rust on the steel surface.
In order to evaluate the effect of carbon fiber reinforced thermoplastic (CFRTP) forming temperature on the flexural strength in a non-destructive inspection, the relationship between the flexural strength and the hardness using pendulum hardness tester was investigated in the CFRTP laminated sheets molded at some different temperatures. Carbon fiber of plain weave and acrylic resin (PMMA) were used as reinforcement and matrix, respectively. The laminated sheet was formed by hot pressing. As a result, the flexural strength increased with increasing forming temperature. The new damping hardness (HDH) measured by the pendulum type hardness tester showed a good correlation with the flexural strength. In the laminated sheet formed at low temperature, the damping hardness measured at different position exhibited large deviation. This variation is due to the random array of fiber bundles. Therefore the homogeneity and the mechanical properties of CFRTP can be estimated in a non-destructive testing by the damping hardness measured at a number of positions.
In this study, we clarified relationship between the interfacial average stress and the non-dimensional intensity of stress singularity for aluminum bonded joints. In experiments, delamination tests were carried out by changing thickness of the adhesive layer, and the delamination force for each thickness of the adhesive layer was obtained. In addition, the intensity of stress singularity for each bonded joints model was computed by results of stress analysis based on the FEM using Akin singular element. Consequently, the relationship between the delamination force and the intensity of stress singularity could be obtained. However, this relation can't be directly applied to evaluate the delamination force, because the value of the order of singularity is different at each target problem. Therefore, in this study, the non-dimensional intensity of stress singularity was calculated based on applied force and characteristic length, i.e., width and thickness of adhesive layer, and the relationship between the interfacial average stress in delamination and the non-dimensional intensity of stress singularity was finally derived.
Fatigue tests were conducted on 90°V-shape bending-worked cold rolled steel sheet specimens under fully-reversed out-of-plane bending to investigate the fatigue strength of bending-worked plates. The tests were also performed on low-temperature annealed specimens with no work-hardened layer formed by the bending-work. For annealed specimens, the fatigue strength decreased with reduction in radius of curvature of bending. The fatigue life can be estimated with sufficient accuracy taking account of the influence of elastic-plastic stress concentration at critical location. For bending-worked specimens without annealing, the fatigue strength was relatively higher than those of annealed bent specimens in relation to the existence of work-hardened layer. The increase of fatigue strength due to work-hardening was estimated based on the difference in S-N diagrams of both specimens. Consequently, the fatigue life of bending-worked specimens without annealing can be evaluated taking the effects of stress concentration and work-hardening into consideration.
We focus on the carbon powder as a conductive material which provides new feature and added value to concrete. In this study, the electromagnetic wave shielding property of mortar with carbon powder was examined by transmission test and reflection test.Also, complex specific permittivity that indicates the electrical property of material was calculated from experimental result of transmission test. Accordingly, in the transmission test, transmission amount turned out to be decreasing along with increase of carbon powder additive rate, and electromagnetic wave shielding property was improved. It was found that presumed complex specific permittivity tends to be largeboth on real part and imaginary part, along with increase of carbon powder additive rate.
Bacterial cellulose (BC) is one of the eco-friendly materials, and is synthesized by several species of bacterium. In this paper, the fabrication method of Carbon/Carbon composites made from BC and Phenol resin, and its tribological properties were investigated. In order to clarify the effect of temperature in fabricating process on tribological properties, the testing specimens were carbonized at various carbonizing temperatures and heating rates. The tribology test for nano-C/C composites was conducted under dry sliding condition. The mean friction coefficient took the low values of 0.12 ~ 0.20 for 10°C°・h-1, the specific factors of wear element loss varied at 2.71×10-10 ~ 8.33×10-10 mm2/N. It was revealed from the experimental results that with an increase in the carbonizing temperature, nano-C/C composites exhibited better wear resistance, higher hardness and bending strength.