Aluminium titanate (Al2TiO5:AT) is known as one of the low expansion ceramics for high temperature uses. However, its low fracture strength makes the ceramics less useful in industry applications. Recently, the present authors reported that the feldspar-doped AT ceramics exhibit better mechanical strength and maintain a low expansion coefficient. It is expected that silica, as one of the main constituents of the feldspar, plays a crucial role for the improved thermal and mechanical properties. In the present study, effects of silica doping on the thermal and mechanical properties of AT ceramics are examined. The silica-doped AT ceramics exhibit improved mechanical property in addition to the low thermal expansion coefficient. It was found that the Si doping into AT lattice and the residual glassy phase at the grain boundaries improved the properties.
In order to investigate the interior-induced fatigue crack propagation behavior of spring steel (SUP7), fatigue tests in axial loading were performed for 4 kinds of specimen with different hardness (tempered at 450℃ or 386℃) or residual stress (finished by grinding, electrochemical polishing or shot peening). Harder specimen has indicated longer fatigue life resulting from its mechanical properties of matrix. Ground specimen and shot-peened specimen also provided longer fatigue life than electrochemical-polished specimen, and the fatigue life of shot-peened specimen was almost same as one of ground specimen. After fatigue tests, fracture surfaces were observed using a scanning electron microscope (SEM). In some cases, non-metallic inclusion was not observed at interior fracture origin, but granular microstructure was observed. Profile analysis and crack-path analysis with FRASTA (Fracture surface topography analysis) method were performed to investigate the fatigue fracture mechanism induced by the granular microstructure. As results of these analyses, it was clarified that a facet of the granular microstructure was inclined from 33 to 42 degrees to the fracture surface. It was another finding that small countless cracks emanated discretely inside the granular microstructure during fatigue process.
The effects of fine particle peening on the fatigue properties of transformation-induced plasticity (TRIP)-aided bainitic ferrite steel were investigated for applications to precision gears. Fine particle peening increased the fatigue limit and lowered the notch-sensitivity in the TRIP-aided bainitic ferrite (TBF) steel, compared with SNCM420 steel. In the stress intensity range of less than 25 MPa m1/2, TBF steel subjected to fine particle peening exhibited a larger threshold value of the stress intensity range and higher crack propagation rate than SNCM420 steel. The increased fatigue properties are principally associated with (1) higher Vickers hardness, (2) higher compressive residual stress and (3) plastic relaxation resulting from the strain-induced transformation of metastable retained austenite in a surface hardening layer, which may suppress fatigue crack initiation and propagation.
This study investigates characteristics of drying shrinkage and creep of “Steel Chip Reinforced Cementitious Composite (SCRCC)”. Firstly, four restrained wall specimens made of normal mortar and the SCRCC with varied amount of steel reinforcing bars (4 or 10) are prepared to compare the drying shrinkage characteristics. The specimens are restrained on rigid laboratory floor so that shrinkage cracks are induced. The drying shrinkage strains are measured by contact gauge method and compared with unrestrained small specimens. Number of cracks are simultaneously observed. Secondly, creep test is carried out to improve accuracy of analysis of the drying shrinkage behaviors. Twelve block specimens are made and constant flexural load is applied for 7, 14, and 28 days. The shrinkage strains and creep strains of SCRCC are modeled by modifying CEB-FIP Model Code 1990. These models are incorporated with bond computation between SCRCC and steel bar to predict the number of drying shrinkage cracks.
The discharge amount of coal ash was around 10 million tons every year from all coal-fired power plants, so there is a need to obtain new efficient usage of fly ash. Recently, aluminosilicate material processed by alkali activation attracts attention as structural material. In this study, authors reported that the paste mixing fly ash with alkali hydroxide solution and curing under hydrothermal condition has high strength and high content of zeolites. Zeolites usually have cation exchange ability, so this hardened material was expected to have an ability to remove hazardous trace elements. This study discusses the mechanical property, microstructure and cation exchange ability of this proposal material that cured under hydrothermal condition at 140℃ and 180℃. The crystalline and glassy products in the hardened material were identified by XRD, the pore size distribution was measured by mercury intrusion porosimetry. The fracture surface and polished surface were observed by SEM and EPMA respectively. The adsorption properties for cesium cadmium, and lead were measured, and the CEC was measured by Wada and Harada’s method. The compressive strength and bending strength of hardened body cured at 180℃ were 48.6 N/mm2 and 8.42 N/mm2 respectively. Main product was Gmelinite, and its plate shaped crystalline were precipitated among fly ash particles. The CEC of proposed material was 128cmol/kg, and it has good adsorption property against cesium, cadmium and lead ions. In addition, this material has much better moldability than conventional zeolite used materials.
The discharge amount of coal ash was around 10 million tons every year from pulverized coal-fired power plants in Japan, so some efficient usage of fly ash is needed. Alkali activated aluminosilicate material, i.e. fly ash, attracts attention as a new usage of fly ash. Authors reported that the hardened material made of fly ash and sodium hydroxide with curing under hydrothermal condition at 180℃ obtained high strength and high cation exchange ability against cesium. This paper discusses the influence of mixing ratio among fly ash, sodium hydroxide and water on physicochemical properties of hardened material. We mainly focused on optimal mixing ratio between fly ash and sodium hydroxide to obtain high cation exchange capacity, CEC, with high adsorption performance against cesium ion. Through the parametric experiments, it was found that there are optimal mixing ratio between fly ash and sodium hydroxide to obtain high strength with enough amount of composed zeolite, and characteristic tendency between CEC and adsorption performance against cesium. With the increase in dosage of sodium hydroxide, CEC increased with reduction of adsorption performance against cesium. When NaOH/FA and water/FA was 8.2mass% and 33.8mass% respectively (molarity of NaOH was 5.9mol/L), hardened zeolite had high strength (σc=52.1N/mm2, σb=10.3N/mm2), cation exchange capacity (CEC, 152cmol/kg) and adsorption ability of cecium (Kd=35.4L/g).
The discharge amount of coal ash was around 10 million tons every year from pulverized coal-fired steam plants in japan. Alkali activated aluminosilicate material, i.e. fly ash, attracts attention as a new usage for building material. Authors produced zeolite composed hardened material by mixing fly ash with sodium hydroxide solution and curing under hydrothermal condition at 180℃. This material has high strength and cation exchange ability against cesium. This paper discusses the influence of variation in physicochemical property of fly ash on mechanical property and mineralogical aspects of hardened materials. There are suitable range of Si/Al ratio of glassy phase and preferable grain fineness of fly ash to obtain enough strength and production amount of zeolite under constant mixing ratio of fly ash and sodium hydroxide. Gmelinite was the main products in any cases. On the hand, production amount of Zeolite NaP1, Hydroxysodalite and unidentified product with 9-10° broad peak in XRD depended upon the properties of fly ash. Strength showed good correlation with pore size distributing property of hardened materials. The low strength specimen had much porosity at diameter of 1-10μm. On the other hand, high strength specimen showed less porosity in 1-10μm and much porosity in 0.01-0.1μm. Cation exchange capacities of powderized hardened materials were 80-150 cmol/kg, the higher reaction rate of fly ash, the higher cation exchange capacity. The partition coefficients for cecium were 33-71L/g.
Stress corrosion cracking (SCC) of extruded magnesium alloy AZ80 in 0.004wt% sodium chloride (NaCl) solution at 298K was studied by slow strain rate tensile technique. The alloy was treated with naturally or artificially aging heat treatment. The eutectoid phase was precipitated by artificially aging. The specimen was machined from different orientations. One is loaded in the transverse direction with crack propagation in the longitudinal direction (i.e., T specimen). The other is loaded in the longitudinal direction with crack propagation in the radial direction (i.e., L specimen). The strain rate was changed from 8.33×10-6 to 8.33×10-3 s-1. The susceptibility to SCC was evaluated by fracture energy obtained by slow strain rate tensile tests. The SCC susceptibility of magnesium alloy increased with a decrease in strain rate irrespective of heat treatment and specimen orientation. The SCC susceptibility of L specimen was higher than that of T specimen. This was related with the anisotropy in corrosion resistance. In the case of L specimen, the SCC susceptibility was not affected by heat treatment condition. On the other hand, the SCC susceptibility of artificially aged T specimen is surely higher than that of naturally aged one though the artificially aging improved the corrosion resistance. It was suggested that SCC susceptibility of magnesium alloy is related with texture orientation and distribution of eutectoid phase.
In this study, we investigated the effects of the cross-head speed during tensile testing on the fracture strength of notched plates of glass-fiber-reinforced syndiotactic polystyrene (GF/SPS). GF/SPS is well suited for the manufacture of electronic components for hybrid electric vehicles because of its high heat resistances, electrical properties, and low specific gravity. GF/SPS plates containing 30% e-glass fiber by weight were prepared by injection molding. The notch-root radii were 0.5, 1, and 2 mm, while the notch depth ranged from 2 to 5 mm. The tensile tests were performed at cross-head speeds of 104, 103, 102, 1, 8.33×10-3 and 8.33×10-5 mm/s at a temperature of 23℃. It was found that all the notched specimens failed in a brittle manner at the maximum load. The maximum elastic stress at fracture was determined from the notch-root radius and the time to fracture but was independent of notch depth. The obtained results could be explained of the basis of the severity of the stress fields near the notch roots of the specimens. Furthermore, it was verified that a fracture criterion based on the severity of the stress fields near the notch roots is applicable in the case of GF/SPS.
The evaluation of fatigue limit is important in designing products. The fatigue limit estimation based on dissipated energy has been getting considerable attentions. In this method, the temperature change due to irreversible energy dissipation is measured by infrared thermography for various levels of stress amplitude. It is known that the dissipated energy increases with increasing stress levels, and a certain stress level, where the change in dissipated energy shows the sharp increase, coincides with the fatigue limit of the material. In this study, the dissipated energy measurement was applied to the estimation of the crack initiation location. The fatigue limit estimation was carried out for the specimen that had multiple notches. The estimated fatigue limit showed similar value at each notch and that gave close agreement with the fatigue limit obtained from conventional fatigue tests. On the other hand, the magnitude and change of dissipated energy at each notch were different. In experiments of fatigue limit estimation, the notch, where the maximum value of dissipated energy was measured, was different from the notch where the maximum sum of principal stress was measured. To investigate the location of the crack initiation, the same specimen was carried out in the constant stress amplitude fatigue test. It was found that the notch where the largest dissipated energy was observed coincided with the crack initiated notch. Therefore, it was considered that the location of crack initiation could be estimated at the early period of fatigue by using the dissipated energy measurement.