Small fatigue crack initiation and growth behavior at elevated temperatures were investigated using ultra-fine grained P/M (Powder Metallurgy) aluminum alloy of which grain size was from 200 to 500nm. Reversed plane bending fatigue tests were conducted at three different temperatures of room temperature (R.T.), 200°C (473K) and 250°C (523K), and crack initiation and small crack growth were studied in detail by means of replication technique. The fatigue strength decreased as test temperature increased. The cracks initiated at the boundary between powders regardless of test temperatures, and total fatigue life was dominated by crack initiation life. The fatigue crack initiation and growth behavior was almost irrelevant to the test temperatures. Fatigue crack growth rates, da/dn, were slightly accelerated at a fixed Kmax with increasing test temperature, while da/dn evaluated in terms of Kmax/E (E : Elastic modulus) agreed well. The dependence of fatigue strength and crack growth rate on test temperature was much smaller than that of conventional aluminum alloys, indicating the high heat resistance of ultra-fine grained P/M aluminum alloy.
In order to obtain a data to streamline the system including a method of flaw detection and its interval for normalized axles equipped with rolling stock running on existing narrow gauge lines, fatigue tests were conducted on normalized axles with artificial flaws of various depths and crack propagation property from artificial flaws was evaluated. The axles with semi-elliptical artificial flaws of depths from 0.5mm to 3mm at the wheelseat fractured at the inner end of press-fitted gear-side wheelseat adjacent to the stress relief groove of 1mm depth under cyclic nominal stress of 80MPa. Although some cracks initiated from the bottom of each artificial flaw, fretting fatigue cracks progressed to main cracks and led to the failure. On the other hand, as a test result on axle with same sizes of artificial flaws under cyclic nominal stress of 60MPa after 5.4×107cycles, neither a prominent progressive crack from the artificial flaw nor the initiation of a fretting fatigue crack was observed. To discuss the above fatigue test results, the stress generated at the wheelseat during the fatigue test was analyzed by FEM, and then the stress intensity factor range was calculated with the analysis result. The evaluation results of crack propagation property by the calculated stress intensity factor range in view of fracture mechanics corresponded with the above test results.
A new process for producing 0.5%Ti-0.07%Zr-Mo alloy with low-oxygen content and high strength at elevated temperature was successfully developed, where the mixed TiC, ZrC and Mo powders were liquid-sintered without addition of C or Mo2C as aids for degassing of oxygen. The developed new TiZrC alloy indicated high strength at elevated temperature even under low forging rate compared to the conventional TiZrO alloy and commercial TZM alloy. Ti and Zr carbides with high melting points were precipitated along Mo grain boundaries in TiZrC alloy, while Ti and Zr combined oxide particles with low melting points were precipitated in Mo grain boundaries in TiZrO alloy. The high strength at elevated temperature in TiZrC alloy will result from the grain boundary precipitation of the carbides, which suppressed grain growth and were stable at elevated temperature. The amount of CO gas emission from the TiZrC alloy were almost equivalent to that from the conventional TiZrO alloy during heating in X ray tube.
This paper describes flexural strength characteristics of concrete with high volume fly ash. Coal-fired power plants have produce about 9,200,000tons coal ashes per year in Japan. The number of coal-fired power plants has been increasing, and amount of coal ash will increase gradually in future. About 90 percent of coal ashes is fly ash and the other bottom ash. Concrete with high volume fly ash may decrease the workability and strength. Short-term strength becomes low due to late reaction of fly ash. Slump as the pavement concrete with high volume is less than the half of the slump of the normal concrete. This results in a suitable pavement concrete. This study aims to investigate the feasibility of pavement concrete with high volume fly ash. Pavement concrete is designed based on the flexural strength. Flexural strength is determined by the failure at the weakest location in the tensile side of the specimen, and is determined by the amount of defects in the mortar and transition zone around aggregates. This may be verified by the distance of two loads over the flexural test specimen. Resultantly, high volume fly ash concrete is affected by the defect based on fly ash. In order to investigate variation of concrete strength, several tests have herein conducted. The strength variation is also analyzed by the Monte Carlo Simulation, which is based on the weakest-link-model. The numerical analysis agrees well with experimental results.
Failure of various types of wood-based panels was observed under in-plane shear. The notched specimens were loaded for a shear test in a manner similar to that for a two-rail shear test. The shear behavior was recorded using a digital camera and analyzed by digital image correlation. During the shear test, initial cracks were formed on the notch in almost all of the specimens. As the load increased, the cracks propagated in an inclined direction. The propagation appears to be due to tension fracture under principal stress. Only in conifer plywood, the initial crack resulted from a split of the surface veneer, and the fibers therein peeled with an increase in the load. Since various fracture shapes were observed in the different types of wood-based panels, the formation process of the final fracture would depend on the mechanical properties of the constituting element (fiber, strand, or veneer). Strain distribution between the notches was measured by digital image correlation, and the “true curve of stress-strain” under in-plane shear was derived. Even if the specimen exhibited a stress concentration area, its shear modulus could be calculated from the curve. Moreover, it was observed that stress decreased with an increase in the shear strain in nonlinear region of the true curve of stress-strain. The initial fracture could not develop immediately into the final fracture, and it probably remained in the form of a small crack.
In the present study, to clarify the relationship between stress-wave velocity of standing trees and their wood quality, stress-wave velocity of 122 standing trees in 27-year-old Hinoki (Chamaecyparis obtusa Endle.) plantation were measured by using a commercial hand held stress-wave timer (FAKOPP). Ten trees were cut down for examining the anatomical properties, static bending properties of small-clear specimen, and quality of square timber (1700 by 55 by 55mm). Stress-wave velocity of standing trees appeared to be affected by wood quality, especially by basic density and Young's modulus in juvenile wood. Significant relationships between stress-wave velocity of standing trees and dynamic Young's modulus or modulus of elasticity in static bending of square timber were found. However, it was very difficult to evaluate the modulus of rupture in static bending of square timber by stress-wave velocity of standing trees, because square timber had some defects such as knots. These results suggested that modulus of elasticity in static bending of square timber can be predicted by the stress-wave velocity.
In recent years, the noise, one of environment problems, has been paid more attention. And the utilization of the high performance sound-proof materials is an effective method to solve the problem. However, traditional sound insulation materials, mostly made from concrete and plumbum, are of high hardness, heavy and difficult for design. In this paper, flexible sound-proof materials made from glass fabric reinforced polyurethane (PU) resin were developed. To maintain the soft features and effectiveness of particulate fillers, we used the PU resin filled with silica particles only in its hard segments. Both the sound-proof performance and flexural ability for the developed materials were evaluated. As a result, the influence of the silica content on material properties and the transmission loss were clarified. Although the increment of silica content may decrease the flexural ability and increase the loop hardness even up to 50%, the loop hardness was about 1N, which still indicated the excellent flexibility. The effectiveness of the PU hybrid with hard segments of silica particles on the sound-proof behavior was confirmed and this resulted in the developed materials with high performance of sound-proof even for very thin and low area density one. The influence of the silica content and area density on both flexible ability and sound performance are also made clear. Furthermore, the prediction of transmission loss is conducted and a good agreement with the experimental results was obtained.