Stress corrosion cracking (SCC) of austenitic stainless steel type 304 has been investigated as functions of chromate concentration and test temperature in 0.82kmol/m3 H2SO4-NaCl solution under a constant applied load by using a constant load method. The linear relationship between the logarithms of time to failure and steady state elongation rate was obtained under a constant applied stress of 388MPa (or 392MPa) irrespective of NaCl concentration, chromate concentration and test temperatures as follows: loglss=-logtf+C. Under the present experimental conditions, the steady state elongation rate was was found to be a useful parameter both for predicting time to failure and for the assessment of SCC susceptibility. The critical chromate concentration (CcriNa2CrO4) and critical test temperature (Tcri) were estimated under a constant nominal stress of 388MPa and were obtained below, respectively; logCcriNa2CrO4=0.70·logCNaCl-0.73 103/Tcri=-0.64logCNa2CrO4+2.11 The results obtained were discussed in terms of ion selectivity of film formed, corrosion current density at crack tips and the length of crack propagation.
From research concerning to atmospheric corrosion, it is understood a little that rust differs with anions in water films, pH, wet-dry conditions, etc. But, there are many unknown parts in the growing process of rust. In order to study the relationship between corrosive factors and corrosion products, wet-dry cycle tests using several kinds of solutions were carried out. Weathering steel was used as a specimen material. Corrosion products were investigated under parameters of the kind of solutions, water film thickness, solution concentration, etc. As a result, it was observed for the easier generation of α-FeOOH than γ-FeOOH in the Na2SO4 solution, which depended on the solution concentration and water film thickness, etc. 1) α-FeOOH was mainly produced under water film which contained the 0.1mol/m3 Na2SO4 or more. 2) γ-FeOOH was produced under water film of less than 0.1mol/m3 Na2SO4 in a solution and in the drying process of water film.
The effect of ultra-violet (UV) light irradiation on corrosion behavior of carbon steel in acid rain was investigated by immersion tests and electrochemical measurement. From the result it was found that (1) corrosion loss of the steel in artificial acid rain increased with decrease of solution pH, (2) corrosion loss and anodic current density of the steel under UV irradiation was larger than those without UV irradiation, and (3) the effect of UV irradiation on corrosion of the steel increased with immersion time. It is considered that the rust on the carbon steel acts as a photocatalyst and to enhance the corrosion in acid rain. From a semiconductive property of the rust, we proposed an enhancement mechanism of the corrosion by UV light irradiation.
It was verified by two experiments that the potential in soil satisfied the Laplace equation, which is usually assumed in numerical analysis methods for the catholic protection of buried steel structures. In the first experiment, where the current distribution was uniform, it was found that the relationship between the potential and the distance was linear. In the second experiment, where the current distribution was complicated, it was found that the experimental results agreed well with the calculated results based on the Laplace equation. The polarization curve for steel in soil was also measured and its characteristics were discussed from the viewpoint of use in the numerical analysis.
The corrosion rates of thermal sprayed WC cermet coatings in 0.05mol/dm3 sodium sulfate solutions at pH 1.0, 6.5 and 12.0 have been measured using AC impedance method and quantitative analysis of the solutions. The cermet coating films were made of WC-Co, WC-Co-Cr and WC-Cr-Ni powder matrials by the high velocity oxygen-fuel spraying method. The WC-Co coating film has shown the lowest corrosion rate in the acidic solution. The WC-Co-Cr and WC-Cr-Ni coating films have shown better corrosion resistance in the neutral and the basic solutions. It was found that corrosion current measured by AC impedance corresponds to that calculated by the quantitative yield of dissolved metal ions.
Microcrack generation and propagation play an essential role to predict the long-term behavior of crystalline rock. We developed a new relaxation testing equipment that enables us to observe a granite specimen under the state of relaxation. Series of relaxation tests have been performed under constant temperature. In this paper, we show a few patterns of microcrack propagation and the relationship between pre-existed crack and crack development under the state of relaxation.
Autogenous shrinkage and drying shrinkage tests were carried out to make clear the shrinkage characteristics of high-strength concrete. Three levels of water-to-cementitious materials ratio (W/(C+SF)) of 20, 30 and 50%, and three levels of silica fume replacement ratio of 0, 7.5 and 15%, were chosen. The shrinkage test with specimens of 10×10×40cm under the condition of 20±1°C and 60±5%RH started at the age of 7 days or 28 days after the measurement of autogenous shrinkage. The autogenous shrinkage strain was also measured in another specimen until the age of about one year. The autogenous shrinkage strain increased both in its amount and its percentage in the total shrinkage strain with the decrease of W/(C+SF) ratio. Almost the same total shrinkage strain after about one year was observed in the specimens under the drying condition. The difference of the total shrinkage strain by the mix proportion of concrete, and the curing method and period was small.
This paper deals with an interaction problem of two rectangular inclusions under longitudinal tension. The body force method is used to formulate the problem as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where the unknown functions are the densities of body forces distributed in infinite plates having the same elastic constants as those of the matrix and inclusions. In order to analyze the problem accurately, the unknown functions are expressed as piecewize smooth functions using two types of fundamental densities and power series, where the fundamental densities are chosen to represent the symmetric stress singularity of 1/r1-λ1 and the skew-symmetric stress singularity of 1/r1-λ2 Then, generalized stress intensity factors at the end of inclusions are systematically calculated for various locations, spacings and elastic modulus of two rectangular inclusions in a plate subjected to longitudinal tension. The present method is found to be useful for accurate and efficient analysis of rectangular inclusions.
The strength of gas-pressure welded joint is evaluated as strong as the strength of the using reinforcement. But, many gas-pressure welded joints were damaged in RC and SRC structural buildings at the 1995 Hyogoken Nanbu Earthquake. After earthquake, we picked up 365 test pieces of gas-pressure welded joints from the damaged RC and SRC structural buildings, and those pieces were tested by the tension test. The 12.6% pieces in all test specimens were fractured. Therefore, the strength of gas-pressure welded joints in the existing concrete structural buildings are not able to apply the present evaluation. This paper is a study on the revaluation of strength of gas-pressure welded joints. The strength of gas-pressure welded joints were revaluated by the research data of Hyogoken Nanbu Earthguake and another test data of 23 public experiment institution in Japan. From the research of this study, we took mainly the following conclusions. (1) The strength of gas-pressure welded joint used in the existing concrete structural buildings were not evaluated as strong as the strength of the using reinforcement. (2) We proposed the method of revaluation of the strength for gas-pressure welded joints used in the existing concrete structural buildings.
Low cycle fatigue tests using smooth specimens of Mar-M247 are conducted at room temperature to simulate the fracture under out-of-phase thermal fatigue and the behavior of initiation and growth of small cracks is identified. Three kinds of specimen are cut from a cast plate such that their axes possess angles of 0°, 45° and 90° with respect to the ‹001› orientation that is parallel to the solidification direction; these specimens being denoted the specimen 0°, the specimen 45° and the specimen 90°, respectively. The results are discussed in connection with the anisotropic and composite microstructures. They are summarized as follows. (1) Transgranular cracks are initiated in all specimens. The first crack in Specimen 0° nucleates at 8000 cycles and those in other two specimens at about 1000 cycles. Cracks of Specimen 0° are initiated from casting defects at surface of the specimen, whereas cracks of Specimens 45° and 90° originate mostly in slip bands and the number of cracks per unit area is 200 times as large as that of Specimen 0°. (2) Cracks in Specimen 0° grow each other independently. On the other hand, cracks in Specimens 45° or 90° coalesce frequently. Grain boundaries, dendrite arms and γ-phase precipitates do not work as barriers to the crack growth unlike the creep fatigue crack. However, the direction of crack growth has a strong dependence on the crystallographic orientation of the γ-matrix. (3) The crack growth rate tends to be the lowest in Specimen 0° for the same half crack length. This is caused by the smallest Young's modulus, the largest resistance for slip band formation, and the lowest crack density and hence the crack growth without coalescence.
Room and high temperature four point bend tests for Si3N4/SUS304 joints were carried out at various crosshead speeds. Ceramics/metal interface region and brazing zone were analyzed using a vickers hardness tester, SEM and EPMA to discuss the relation between strength of joints and microstructure. Furthermore, the fracture strength and the nature of its scatter were estimated based on the proposed model. Failure of brazed Si3N4/metal joints occurred at a flaw in ceramics near bonding interface. Therefore, the bending strength of the joints was dominated by a magnitude and distribution of stress concentration induced in ceramic region. The magnitude of stress concentration induced in ceramic region was dependent on deformation resistance of interlayer. This buffer effect of interlayer depended on exposed time of the specimen at test temperature, which inversely corresponds to loading rate. The dispersion of strengths of the joints was well described according to the weibull distribution using unified estimation method. The estimation equation was proposed to evaluate the bending strength and its nature of scatter.
Generally, air bubbles are easily formed on the surface of concrete products made of self-compacting concrete due to its high viscosity. These bubbles affect unfavorably the appearance and durability. In order to reduce the surface air bubbles, the authors used low frequency vibration. However, vibration applied to the concrete products during compaction, even with a low frequency, causes a segregation of coarse aggregate in the self-compacting concrete. In this research, the effect of the low frequency vibration on the formation of surface air babbles and the segregation of coarse aggregate were investigated by comparing with cases under the following conditions. In Case1, compaction was performed without vibration. In Case2, the concrete was filled up while vibration was applied. In Case3, the concrete was vibrated after being filled up. The conclusions are summarized as follows. (1) The surface air bubbles decreased as the vibration time after filling up of concrete increased. (2) In the concrete filled up with vibration, the amount of surface air bubbles and the segregation rate of concrete increased as the filling time increased. (3) Those amounts were less than those in the other cases. (4) From these results, an effective casting method of self-compacting concrete, by which the surface air bubbles can be decreased without causing segregation is considered to be filling up with vibration for an adequately short time, and then applying for an appropriate period of time.
From author's previous study, it was considered that fine particles of “Shirasu” which is one of pyrociastic flow deposits would cause the pozzolanic reaction. Purposes of this study are clarification of the pozzolanic reaction on Shirasu and determination of manufacturing condition as concrete admixture. In this study, the mortars are made by several types of Shirasu blended cement. And the following results are obtained; (1) Using the Shirasu particles having 90% or more of glass contents and crushed at the fineness condition of 5000cm2/g or more, same workability as on normal cement mortar and same strength as on fly-ash cement mortar could be secured on this Shirasu blended cement mortar. (2) The pozzolanic reaction having the Shirasu particles in the mortar could be clarified by using the chemical analysis methods, such as differential thermal analysis, scanning electron microscope and X-ray analysis.
Recently, many kinds of superabsorbent polymers were developed. In this research, three special applications of the polymers, that is 1) application for simplifying curing of concrete at early age, 2) application for preventing cracking of concrete caused by initial drying shrinkage, and 3) application for preventing leakage of water through cracks, were proposed. The superabsorbent polymer used for this study can hardly absorb alkaline water in fresh/hardened concrete, but can absorb much neutral/acid water and makes gel. Thus when the neutral water is poured on concrete only once after setting, face of the concrete can be coated with the gels, and the concrete can be kept without drying, so that the 1) effect can be achieved. The water confined in the superabsorbent polymer and gels may delay the immediate drying of concrete, and the 2) effect may be obtained. The some of polymers around cracks can catch much neutral or acid water passing through the cracks and the gels fill up the cracks, so that the 3) effect can be achieved.
Application of the fast multipole boundary element method (FMBEM) to corrosion problems is studied. It is found that this method can be successfully applied to corrosion analysis by employing the previous research results on the potential problems together with the following procedures; (1) use of M00 of the root cell (which is obtained in the process of multipole expansion) for the infinite region problems, and (2) modification of the residual calculation formula in the Bi-CGSTAB iterative method to cope with the nonlinearity caused by polarization curves. A pipe element which is suitable to the FMBEM is also developed to increase the efficiency of calculation for pipelines. A few examples are shown to demonstrate the applicability of the FMBEM to corrosion problems.
Firstly, the service life of the 28-year-old plastic covering material of cables for the long bridge was evaluated. Mechanical degradation such as crack generation and remarkable bending strength reduction on the plastic covering material was not found because of the past adequate maintenance for coating film layer covered on the plastic covering material. However, by means of chemical evaluation method such as FT-IR, the slight chemical degradation was confirmed and shown as follows. (1) Main molecular chains of the coating film (polyester) and side chains of base resin (PMMA) were detached by hydrolysis. (2) The glass transition temperature of the base resin was raised by polymerization. Secondly, to examine effective degradation detection methods, the degradation experiment was conducted on PMMA test samples without containing anti-oxidants and pigments in the autoclave at 70°C with saturated water and pure O2. Effective degradation detection methods were as follows: inspection with optical microscope, measurement for bending strength, dynamic hardness, dynamic viscoelasticity, FT-IR, DSC, and solid 13CNMR.