Various types of lightweight soils have been developed as fill materials over soft grounds and/or behind retaining walls in order to achieve the stability and less deformability. In this study, wasted rigid polyurethane foam (PUF) was used as the lightweight plastic material for a new type of lightweight soil. Since a large amount of the rigid PUF was disposed of every year, if the rigid PUF can be effectively used, the resulting lightweight soil will greatly contribute to the improvement of our environmental problems. The effect of the rigid PUF on the strength and deformation properties of lightweight stabilized soil was investigated based on unconfined compression tests. The main results obtained from this study were: 1) Peak and yielding strengths of the new lightweight soil mixed with PUF depend on the cement content, but not the type of PUF. 2) The stress-strain curves obtained from the compression tests for lightweight soil specimens with the rigid PUF showed a clear yielding phenomenon, and 3) the yielding stress and strain depend on the type of rigid PUF.
It is necessary to utilize coal fly ash in geotechnical engineering field. Coal fly ash is a useful material. In case of using as reclamation material, cement is mixed into coal fly ash to stabilize the ground before reclaiming coal fly ash. Effects of cementation on mechanical properties of coal fly ash should be investigated. Authors focus to utilize coal fly ash as reclamation material in the coastal area. In order to investigate effects of cementation on mechanical properties of sedimented coal fly ash, triaxial compression tests were carried out. From a series of triaxial test results and considerations, the following conclusions were obtained: (1) Coal fly ash sedimented in looser condition with increasing amount of cement. (2) The increase of shear resistance caused by cementation effects appeared in small strain and low confining stress level. (3) Dilatancy property of sedimented coal fly ash-cement mixture depended on confining stress and cementation.
A new triple liner system for waste disposal sites was proposed and some laboratory test results on the materials used in this system were introduced. This system consists of double geomembrane sheets with an intermediate protective material made of cast in place polybutadiene urethane elastomer. It is applicable to the waste disposal sites in the land and at the sea. Laboratory test results on polyurethane elastomer are as follows: (1) It has enough viscosity and hardness which are possible to grout on the site. (2) It has high waterproofing capabilities (hydraulic conductivity, less than 10-12cm/s). The construction joint also has same level of waterproofing capabilities. (3) It has high flexibility as same as outside double geomembranes. (4) The tensile strength of construction joint is above 80% of the intact tensile strength. Consequently, this triple liner system has enough to apply safe to waste disposal sites.
Hydraulic conductivity and unconfined compressive strength on soil-cement mixtures that are applied to the waste containment cutoff wall are investigated to examine the effect of mixing proportion. Under several different sand/clay ratios, the fresh mixture is set to have the same Table Flow Value (20-23cm). Processed Kaolinite clay is used for the clay portion. Cement is added at 15% of dry soil. Hydraulic conductivity tests were conducted using flexible-wall permeameters. The test results show that the hydraulic conductivity of soil-cement specimens ranges from 1×10-8-5×10-7cm/s. The lowest hydraulic conductivity and the highest compressive strength are obtained when the sand portion is 80%. For the mixtures having the sand portion of 0-80%, the hydraulic conductivity and compressive strength is significantly correlated to the density and porosity of the specimen. Certain amount of sand portion contributes to the reduction of water/cement ratio to achieve the target Table Flow Value, consequently results in the denser mixture, and decrease the hydraulic conductivity.
The well resistance and consolidation delay by smear zone are reviewed and a new theory is proposed. Based upon the proposed theory, a required discharge capacity is defined as neglecting well resistance. Almost of PBDs recently supplied in Japan are proved by the experiment to have discharge capacity over the required value. Since there is the characteristics of structure affect the discharge capacity, two models for confining conditions are examined to predict the difference in the capacity.
Recently, the generation of unreusable surplus soils from various construction sites has been increasing. The hedoro, one of them, is difficult to reuse as construction materials owing to high water content and low strength, and the disposal sites of the hedoro have been decreasing. Therefore, it is very important to develop the significant improvement of the hedoro from the viewpoint of natural resource preservation and environmental impact mitigation. The purpose of this study is to clarify the possibility of reuse of coal fly ashes as effective hardening additives which affect the cement treated hedoro. The three kinds of coal fly ashes are used as hardening additives with cement stabilizer to increase the hedoro strength. As a result, it has been found that the strength of the cement treated hedoro mixed with coal fly ashes have been increasing during aging period, therefore, the coal fly ashes can be applied as hardening additives. In comparison with pulverized coal fly ashes, the fluidized bed combustion coal fly ashes including much SO3 and CaO give larger strength. So the fluidized bed combustion coal fly ashes are effective on the hedoro as hardening additives. On the other hand, pulverized coal fly ashes containing much SiO2 and Al2O3 have continued the strength development for long term. Furthermore, the main reaction products which contribute to strength are ettringite and calcium silicate hydrate compound.
Suitability of the compacted bentonite-soil mixtures as the landfill bottom liner was evaluated, mainly in the aspect of landfill stability, with the focus being on the shear strength properties of bentonite-soil mixtures affected by the increase in water contents. In the laboratory experiments, the hydraulic conductivity and soil-water characteristics curves for two types of bentonite-soil mixtures were determined to estimate the behavior of the water migration to the clay liner, using the unsaturated infiltration numerical analysis. The results showed the bentonite mixture liner constructed in the area where the ground water level is high, such as the canyon area, could easily reach the saturated condition. This increase in the water content had the adverse effect on the internal/interface shear strength parameters for bentonite-soil mixtures, mainly determined in the consolidated constant pressure direct shear tests. Two dimensional stability analyses were also performed on the cross section of a typical canyon solid waste landfills, considering the shear strength reduction due to the increase in the water content and the ground water level. Solid waste landfill stability was confirmed in the application of bentonite-soil mixtures as bottom liner materials, expect in the case that a significantly high level of leachate water existed in the landfill.
Application of pump & treat is one of the typical washing technologies for remediation of contaminated soils. However, it is very difficult to perfectly wash out contaminated substances existing in soils microstructures. We believe that such problems come from existence of numerous water paths in the soil structures which ease flow of air or water without carrying contaminating substances. In order to develop an alternative method to overcome such a problem, we focus on ice segregation phenomena in a freezing soil. This paper introduces an experiment to demonstrate the applicability of the idea. NaCl was used as a pollutant material. The freezing and thawing method was compared with an existing method which is application of pressure. The experimental results showed that approximately 80% of NaCl was removed after five cycles of proposed freezing and thawing. It was demonstrated that freezing and thawing can be used as a powerful remediation method for contaminated soils.
The transformation temperatures of shape memory alloy vary with the composition, processing and manufacturing conditions of the alloy. The purpose of the present paper is to clarify the influence of cold working ratio and heat treatment temperature on transformation temperatures, and to propose the formula to estimate the transformation temperatures from modeling. The shape memory alloy used for investigation is Ti-41.7Ni-8.5Cu(at%). As a result, the transformation temperatures depend on the cold working ratio and become lower with increasing cold working ratio. Transformation temperatures also depend on the heat treatment temperature and rise with elevating the heat treatment temperature. Therefore, the transformation temperatures could be formula-modeled considering the effect of the cold working ratio and the heat treatment temperature. The probabilistically estimated formulas were proposed considering the scatter of characteristic value and confidence interval.
It is very important for the reliability fatigue design of mechanical structures to draw the best fitted curve of an S-N data set. This paper describes a new non-linear regression method for adopting some S-N models for fatigue data regarding metallic materials. The proposed method has an advantage of the best curve fitting for the various types of the S-N data in the fatigue strength database, which was established by the JSMS Committee on Fatigue. This new method is based essentially on the conventional Gauss-Newton method. Furthermore, an additional parameter is introduced in order to achieve high iterative stability for various types of data. Accurate results regarding the curve fitting were obtained using the proposed regression method.
To use effectively various strength data of ceramic/metal joints for materials development, structural design, and strength reliability analysis in the future, fracture strength database was constructed by using commercial software of easy operativeness. The database has been collected the strength data of about 1800 or more obtained by bending, fatigue, creep, and heat cycle test, etc. It is equipped with the function of addition/edit and retrieval/extraction of data. Furthermore, as one of utilities of this database, a basic strength properties and strength reliability of joints were mentioned in this paper, and the unified strength estimation method was applied to the joints. As the results, an evaluation equations that were derived by considering scatter of joint strength, can estimate the strength that corresponds to various test situations from basic strength such as bending strength.
Recent fitness-for-service standards for pressure vessels and pipes tend to adopt the two-parameter approach to evaluate structural integrity of components with crack-like flaws. Some probabilistic methods have also been developed to make quantitative assessments of structural reliability based on the two-parameter approach because there exist a large amount of uncertainties in the assessment parameters. However, most of them employ restricted numerical integration or tedious Monte Carlo simulation methods to calculate failure probabilities, and sufficient sensitivity studies have not yet been carried out. In this paper, making use of the first-order reliability method (FORM) is suggested to efficiently and generally compute failure probabilities based on the two-parameter approach. To confirm adequacy of employing FORM, the failure probabilities of a plate with a center through-wall crack subject to uniform tension are computed by FORM and Monte Carlo simulation methods considering uncertainties in crack size, tensional stress, yield stress and fracture toughness. The results show that FORM provides satisfactory estimates for the wide range of fracture mechanics parameters. Furthermore, the effect of a correlation of yield stress and fracture toughness on the failure probability is also investigated. It is revealed that a positive correlation between yield stress and fracture toughness results in the increase of the failure probability as long as the limit-state surface may be approximated by a hyper-plane near the design point in the standard normal space.
In this study, the tunneling method is applied to the reliability analysis of a laminated composite plate subject to in-plane loads. In the first order reliability method (FORM), the structural reliability is evaluated as the minimum distance from the origin to the limit state surface in the standard normal distribution space. It is formulated as a nonlinear optimization problem. However, it is difficult to find the design point, when the limit state surface has several local minimum points such as a case of the laminated composite plate subject to the first ply failure. In order to find the global design point, the tunneling method is applied as one of global optimization methods. A new tunneling function suitable for the FORM is proposed to find the other design point which has a lower objective function value and satisfies the equality constraint. Through numerical calculations, the efficiency of the tunneling method is demonstrated.
Many highway bridges were damaged by a great earthquake that hit west part of Japan on Jan. 17, 1995. Especially, steel as well as RC pier structures designed according to the old versions of design codes were injured. It was pointed out that the reliability level was different depending on each version of design code as well as types of structures. In this study, in order to know the reliability level of pier structures designed according to each version of design codes that have been used before 1995, reliability analyses were performed at first yield limit state for typical types of steel rigid-frame piers selected out of existing bridge piers. It was verified that the reliability level of pier structures designed according to 1964 version was lowest. Further, several shortcomings inherent in the current design codes based on the allowable stress design method were pointed out.
Diaphragms made of a stainless steel plates are widely used as switching parts in electronic devices. Due to the cyclic loading applied to these diaphragms, the estimation of the lives of diaphragms is important to decide that of the electronic devices. The fatigue characteristic of the diaphragm must be discussed with considering the large scatter of material properties induced by the anisotropy. In this study, the tensile and the fatigue tests have been carried out some specimens with a direction to cold rolling direction. A pulley driving system was adopted as a fatigue testing apparatus because the load can be easily applied even when the thickness of the specimen is less than 0.1mm. From the experimental results, we have decided the S-N curve by applying large scatter of fatigue lives to the probability distribution based on reliability, and drew the Goodman diagram to avoid the effect of the mean stress. The obtained results can be used for fatigue design considering the anisotropy in the case of high cycle fatigue for diaphragms.
Thermal barrier coating (TBC) was applied on the Co based superalloy specimens, where CoNiCrAlY bond coat was deposited by high velocity oxygen fuel (HVOF) spraying and 8mass% yttria stabilized zirconia (YSZ) top coat by atmospheric plasma spraying. The isothermal oxidation behavior of TBC at high temperature was characterized by scanning electron microscopy, EPMA mapping analysis, energy dispersive spectroscopy and X-ray diffraction. The Alumina and complex oxide layers were formed along the interface between the top coat and the bond coat, and the thickness of the oxide layers increased with increasing heating temperature and holding time. When the delamination of the top coat occurred during the holding of the specimen at 1473K for 1732ks and on cooling after holding at 1273K for 3960ks, half-sphere-shaped cracks grew along the interface between unmelted bond coat particles and Al2O3 layer, and propagated in the complex oxide or the top coat. In tensile test and edge-indent test, the delamination of top coat started near the top of particles and extended in the top coat under shear stress.
Thermal barrier coating (TBC) was applied to Co based superalloy specimens, where bond coat was CoNiCrAlY deposited by high velocity oxygen fuel (HVOF) spraying and top coat was 8mass% yttria stabilized zirconia (YSZ) by atmospheric plasma spraying. After the specimens were heated and held at high temperature, tensile tests and edge indent tests of the specimens were carried out to measure interfacial fracture toughness and delamination energy of the coating, respectively. The results showed that Al2O3 oxide was formed along the interface between the top coat and the bond coat, and the thickness of Al2O3, BAl, increased with increasing heating temperature T and holding time t. The growth behavior of Al2O3 layer was expressed by the equation: BAl=A·exp(-Q/RT)·tn, where Q is apparent activation energy, R is gas constant, and A and n are constants. The interfacial fracture toughness and the delamination energy increased with increasing BAl when it was less than about 2μm, while when BAl exceeded 8-10μm, both of them decreased drastically. By using a critical oxide layer thickness where the delamination strength was still maintained, a combination of operation temperature and time during which the delamination of coating would not occur was determinated.
Titanium nitride (TiN) films for a wide range of applications were prepared by nitrogen ion irradiation with 2keV during titanium vapor deposition, i.e., ion mixing and vapor deposition technique. The TiN films deposited onto stainless steels exhibited the columnar structure with the preferential crystal growth of (111) or (200) plane, and they contained more or less pinhole defects. Pinhole defects of TiN films were evaluated potentiodynamically in a deaerated 0.5kmol/m3H2SO4+0.05kmol/m3KSCN solution at 298K. The critical passivation current density icrit of TiN film decreased successfully with increasing film thickness and substrate temperature. Here, the area ratio of pinhole defects was evaluated by the ratio of icrit of coated and non-coated specimens. Based on such electrochemical evaluation, the optimum preparation conditions for the corrosion-resistive dry coating films were discussed.
Matrix hybrid laminates can produce the more extensive mechanical properties rather than the conventional laminated composites, because the matrix hybrid laminate has various parameters, resin ratio, stacking sequence, fiber orientation and so on. However experimental approach needs long period and high cost in the practical designing. In other words, the application of finite element method to the designing is very effective. In case that the mechanical behaviors of the composite materials are predicted, the modeling method of the heterogeneity for the composite materials is important. In this paper, we proposed the new numerical model that considered the heterogeneity in matrix hybrid laminates. In the proposed model, the heterogeneity is expressed by the combination of two different elements. Using the proposed model, the damage propagation analyses under three-point bending load are carried out. The validity of the proposed model is checked by comparison with experimental results. It is confirmed that the proposed model is effective for the prediction of both the bending properties and damage propagation process. Furthermore, the damage propagation mechanisms of matrix hybrid laminates with different fiber orientation and antisymmetric laminates can be also predicted.