When a compressive load is applied to a Fiber Reinforced Plastics (FRP) tube, a continuous fracture phenomenon called “progressive crushing” which shows highly effective energy absorption appears. The purpose of the study is to clarify the relationship between fracture toughness value and crack propagation characteristic changes and fracture mode. The authors have constructed a flat plate FEM model that can reproduce the process up to progressive crushing. In the study, the difference in fracture form due to fracture toughness values, and crack propagation characteristics under the condition with the same energy release rate was considered by using the model. Furthermore, a designing guideline to increase the energy absorption of the FRP tube was derived.
In a Robinson type steel-concrete composite deck, headed studs and rib plates are usually welded on its bottom steel plate. The authors have investigated a welding ferrule to realize improved headed studs with higher durability. In contrast, the weight of bottom steel plate generally occupies about 55% in a whole weight of the Robinson type steel-concrete composite deck. On the bottom steel plate welded with rib plates, the thickness of bottom steel plate such as 8mm or 9mm is usually used, because there is concern about its thermal deformation in welding. A cold tandem welding method, which is recently used, can reduce heat input and suppress the thermal deformation of the bottom steel plate. Then, it has been possible to adopt a thinner steel plate such as 6mm to the bottom steel plate. To achieve a rational fatigue design, the tensile fatigue strength of such a thin steel plate welded with headed studs or rib plates has to be evaluated. The aim of this study is to compare the tensile fatigue strengths of a steel plate welded with each conventional and improved headed stud or a rib plate with the fatigue design recommendations of JSSC. From the fatigue test results, it was confirmed that the fatigue strengths of the steel plate welded with each conventional and improved headed stud satisfied E-grade of JSSC. Furthermore, the steel plate welded with a rib plate also satisfied E-grade of JSSC.
Calcined dolomite shows excellent adsorption ability for heavy metals, metalloids and halogens (hereafter collectively referred to as “heavy metals”) in soil, compared with raw dolomite. It is well known that dolomite is thermally decomposed into MgO and CaO in two stages. To study the relation between the heavy metal adsorption ability and crystal structure of calcined dolomite, 1) adsorption test using a solution containing heavy metals 2) specific surface area measurement 3) quantitative determination of the crystal phase by Rietveld analysis, and 4) K-edge XANES (X-ray Absorption Near-Edge Structure) analysis of Mg and Ca, were performed. The results of measurement of specific surface area after calcination and Rietveld analysis showed that there is a relation between the dolomite phase reduced by thermal decomposition and the specific surface area value and adsorption ability for heavy metals. The measured XANES spectra revealed that the local structure around Ca atoms did not change during calcination but that the local structure of Mg atoms changed gradually during calcination. Furthermore, the Mg K-XANES spectra measured in Partial Fluorescence Yield (PFY) mode and in Total Electron Yield (TEY) mode showed different spectra variations. These results suggest that MgO derived from calcined dolomite has structural differences between the outermost layer and the inside.
Pure titanium has been widely used as one of the primary metals in aerospace and biomedical fields for the last few decades, since the strong demands for the light weighted and strong materials have been increasing in the fields. Despite the great enhancements, pure titanium is still one of the difficult materials to predict the deformation behaviors. To study the effects of complicated microscopic non-uniform deformations on the surface roughness, a uniaxial tensile deformation of poly-crystalline pure titanium sheet by finite element analysis based on the crystal plasticity theory was conducted in the present work. It was found that the microscopic deformations around 0.2% strain range decided the surface roughness and the approximate surface’s shapes of the present material. In other words, the surface roughness of the pure titanium was determined by the deformation at the small macroscopic strain around 0.2%, rather than, that at the macroscopic larger strain. The subsequent deformation after 0.2% strain could only rescale the size of the surface roughness without any further changes in the shape of surface roughness.
To examine the effect of pre-plastic deformation of austenite phase on pearlitic transformation plasticity, three point bending tests, wherein the specimens fixed at one end and simply supported at the other were performed. First, specimens were heated to austenitization temperature, then the austenitization temperature of the specimens were kept constant for several minutes and finally cooling and loading processes were performed. During the cooling process, the specimens were subjected to the tensile stress in plastic range on the austenite phase and then, just before transformation start point, the bending stress in elastic range (less than the yield stress) was applied to the specimens during the phase transformation. The maximum bending deflections due to the austenite-pearlite transformation were measured under multiple loading condition and transformation plasticity coefficients were determined. It was shown from the tests that the transformation plastic deflection due to the pearlitic transformation decreases with increasing pre-plastic deformation. The equivalent strain-dependent transformation plastic constitutive equation was constructed on the basis of the test results. Then finite element analysis was performed using this equation. The calculated transformation plastic deflections quantitatively agreed well with the measured ones, suggesting the validity of the proposed equation.
In this study, the strength and characteristics of cement paste exposed to 200 °C was examined focusing on the cement paste for SAGD (Steam Assisted gravity Drainage) well where vapor steam with about 200 °C is injected to extract heavy oil. The commercial oil-well cement (OWC) and geothermal-well cement (GWC) and the GWC with fly ash were used for the cement paste. When the hardened paste was exposed to drying at 200 °C, the compressive strength was slightly increased in all cement cases comparing to that with sealed curing at 20 °C. It can be attributed to the increase of solid surface energy due to evaporation of adsorbed water. The compressive strength of OWC cement paste exposed to saturated steam at 200 °C was greatly reduced because the pore structure became very coarse. On the other hand, the strengths of GWC and GWC with fly ash cement pastes subjected to 200 °C steam were increased. The hydration products of GWC and GWC with fly ash were mainly Xonotrite and Tobermorite, respectively and leading to finer pore structure and larger strength. It is concluded that the appropriate replacement of fly ash with GWC can be effective to make pore structure dense and to improve the strength of cement paste if the moisture can be supplied to SAGD well from surrounding soil.
Organotin compounds used as catalysts for the production of chemically adsorbed monomolecular films suffer from adversely affects on the environment and toxicity. In this study, we attempted to form a chemically adsorbed monomolecular film using a terminal alkoxysilane adsorbents and a chlorosilane compound as a novel catalyst replacing the organotin compound. Since the chlorosilane compound has high activity, it is possible to form a monomolecular film in a short time. Also, since it does not remain in the adsorbed base material, it can be expected to be applied to a wide range of applications. Therefore, we tried to form a chemically adsorbed monomolecular film from the terminal alkoxysilane adsorbent by comparing the conventional organosuccinic system with the chlorosilane-based catalyst as the catalysts. At that time, the activities were compaired under the equivalent amount of active groups and the equal weight of the catalysts. On the water drop contact angle measurement results, the contact angle of 90 ° was obtained by using the chlorosilane type catalyst in a shorter time, indicating that the activity of the chlorosilane type catalysts was higher than that of the conventional catalysts. Also on FT-IR RAS spectra measurement, since the similar peak intensities were exhibited by 180 minute adsorption with the conventional catalyst and 60 minute adsorption with the chlorosilane type catalyst. This indicate that the activity of the chlorosilane type catalysts were higher than that of the conventional organotin catalyst. If the concentration was further reduced in order to reduce the generation amount of the hydrochloric acid which was a severe problem, the reaction promoting effect was weakened, and an effect comparable to the conventional organotin catalyst was not obtained. However, it was confirmed that tetrachlorosilane (TCS), which is a representative of a chlorosilane compound, is useful for prepareing a chemically adsorbed monomolecular film using the terminal alkoxysilane adsorbents as a reaction accelerator in terms of shortening the preparationtime and reducing residual tin on the substrate.