The fracture strength properties of porous ceramics were examined by 3-points bending tests and rotary bending fatigue tests. The 3-points bending strengths of porous ceramics depended on effective volumes of specimen and the fracture was similar to that of Al_2O_3. Also, the rotary bending fatigue strengths of the porous ceramics didn't decrease at (10)^3∿(10)^7 cycles.

抄録全体を表示

The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviors, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strength of these singular points using two stress singularity parameters H and λ. The difficulty with this method was in obtaining the critical value of the intensity of the stress singularity parameter Hc for each order of stress singularity λ. We therefore present in this paper methods of formularizing Hc by λ based on typical strength parameters such as the fatigue limit σ_<w0> and the threshold stress intensity factor range ΔK_<th>. These critical value Hc (λ) agreed well with the experimental results. Using these easily obtained formularized critical value Hc (λ), we can estimate the fretting fatigue crack initiation criteria for each contact edge angle, and thus optimize the contact edge geometry. Finally, we discuss the development of these strength criteria in terms of stress singularity fields for general stress concentration fields.

抄録全体を表示

Fatigue tests under 0-compression strain were conducted at room temperature for stainless steel which is used for brake discs. The experimental results revealed that cracks occurred due to cyclic 0-compressive strain. The crack initiation mechanism is as follows. At the first loading cycle, the material compressively yields when the applied compressive strain is great. Resultantly, the tensile stress was induced when the strain becomes zero. Then, material is cyclically subjected to compression - tension alternative lads. Such fatigue loads cause cracks in the material even at low cycle fatigue.

抄録全体を表示

Rotating bending fatigue tests were carried out for an aluminum oxide dispersion strengthening copper alloy at room temperature and 350℃, in order to investigate the effect of elevated temperature on the fatigue strength. A crack propagation morphology was ductile at room temperature and brittle at elevated temperature. Both of crack initiation and propagation were suppresed by oxidation at elevated temperature.

抄録全体を表示

This paper describes failure assessment curves of a pressure vessel of boiling water reactor containing a longitudinal surface crack at an inner surface. The failure assessment curves are derived from the J-integral based on the deformation theory of plasticity using the stress-strain curves of low alloy steel A508cl.3. The authors have made clear the dependence of failure assessment curve on crack geometry and compared with the curve for ferritic steel pipes given in the ASME Code Case N-494. Detail discussions are shown in the following.

抄録全体を表示

Fatigue crack growth behavior of A533B steel was studied in 288℃ water environment using CT specimens machined from four different orientations of the material with 150mm thick. Fatigue crack growth rate in water at ambient air and in hydrogen gas was also examined. The effects of anisotropy, test frequency, water temperature and hydrogen gas on the crack growth behavior of A533B steel were evaluated. The results show that anisotropy did not have a significant effect on the fatigue crack growth rate in 288℃ water at frequency of 0.5 to 0.05Hz. The fatigue crack growth rate in ambient water was slightly higher than that in 288℃ water and in ambient air. At ΔK above 40 MPa m, the fatigue crack growth rate in hydrogen gas was markedly accelerated compared to that in 288℃ water.

抄録全体を表示

To increase the fatigue limit of the Carburized gears, the following five techniques need to be developed : a)Reduce abnormal surface structure. b)Obtain a fine grain size. c)Decrease the retained Austenite. d)Increase hardness under the surface. e)Improve the residual stress distribution under the surface. For this purpose, the authors conducted a study by using DSG1 steel gears on the new compound surface refining method consisting of Vacuum Carburizing, Contour Induction Hardening and Double Shot Peening. The results showed that the fatigue limit of the gears processed by the new compound surface refining method achieved 150% better than that of the conventional Vacuum Carburized gears.

抄録全体を表示

The most widely used material for aluminum cylinder head is 356 alloy, because of the excellent elongation. However, according to the higher performance required in diesel engine, the surface of combustion chamber on cylinder head, which is up to 573k in maximum ascent temperature as estimated. In this high temperature, heat cracks are often occurred in the weakened matrix of casting. This paper is aimed at improving the mechanical properties of aluminum cylinder head casting with laser re-melting and cladding.

抄録全体を表示

Water jet peening (WJP) treatment is one of the surface improvement technique. It is mainly used preventing the stress corrosion crack (SCC) damage. In this study, in order to investigate the effect of WJP treatment on the fatigue properies of SUS304 austenite stainless steel, rotating bending fatigue tests were carried out on the WJP treated SUS304 steel. In consequence, the fatigue strength of the WJP treated SUS304 was improved. And the X-ray measurement and the hardness tests were also carried out on the WJP treated SUS304,it shows that there exists the hardening layer and the compressive residual stress layer on the surface. It was successful that the WJP treatment improves the fatigue properties of SUS304.

抄録全体を表示

The Water Jet Peening (WJP) is a well-known method to reduce residual stress. While direct injection water jet is usually used for the WJP, it was found that reflected water jet is also effective for reducing stress. By using this Reflected Water Jet Peening (RWJP), it can be easier and simpler to conduct the WJP onto secluded surfaces or components with a complicated shape. The RWJP was applied to a shroud weld line behind a core spray sparger in a pressure vessel of a domestic BWR.

抄録全体を表示

Recently, automobile companies re directing their efforts toward lowering mileage, making compact and etc. of automobile engines for the economical and environmental reasons. Therefor, weight reduction of engine parts, such as forged connecting rods is most important item. To increase fatigue limit of the connecting rods, the following four characteristics to be developed : a)Decarburized depth b)Hardness c)Residual stress d)Notch (surface flaw, surface roughness). So, the authors investigated influence of residual stress and surface flaw upon fatigue limit of forged connecting rods. The main result shows as follows : Fatigue limit of the connecting rods in proportional to the surface residual stress.

抄録全体を表示

Rotational bending fatigue tests for KSFA80,KSFA110 were carried out to clarify the property of fatigue strength of high tensile forged materials. Fatigue fracture occurred even though the repeated stress exceeded (10)^8 cycles, which started at interior non-metallic inclusion. Fatigue strength of the forged material shows anisotropy depending on the relative direction of specimen to forged grain flow, and it is shown that this anisotropy of fatigue strength is due to the projective size/shape of non-metallic inclusions at crack origin to a plain perpendicular to the maximum stress direction. Fatigue tests of shot peened specimens for KSFA110 were also carried out. The effect of shot peening process on improvement of fatigue strength are clarified.

抄録全体を表示

For increase in the bending and torsion fatigue limit of Crank shaft, it is important to produce high hardness and introduce large compressive residual stress under the surface of Crank shaft pin fillet-R and Oil holes. For this purpose, surface treatment methods, such as Nitrocaburizing (NH), Induction hardening (IH) and etc. are useful techniques. Therefore, the authors conducted an experiment using the following five types of surface treated Crank shaft for heavy duty diesel engine : a)NH b)IH c)IH+Shot peening (SP) d)NH+IH e)NH+IH+SP. And evaluated their surface characteristics and fatigue limits. The main results are as follows : 1) Extremely high bending fatigue limit of IH+SP Crank shaft, i.e. 31% higher limit than the NH Crank shaft. 2) Considerably increased torsion fatigue limit of NH and NH+IH+SP Crank shaft, i.e. 90% and 107% higher than the IH Crank shaft, respectively.

抄録全体を表示

A steel member would have cracks during manufacturing process and long-term service. The cracked member could failure when an earthquake happened. This paper describes a new experimental equipment enables us to evaluate a load history effect on plastics collapse loads in a single edge cracked member subjected combined tension and bending. The experimental result shows the load history effect on the plastics collapse loads in the members.

抄録全体を表示

It is known that higher steel strength, lower its fracture stress in hydrogen environment. In this paper, it is found that the shape of crack tip and metallurgraphical characteristics have an effect on strength of grain boundary and these characteristics are associated with the sensibility of delayed fracture in hydrogen environment.

抄録全体を表示

Changes of fracture modes and of the critical stress intensity factor (K_<IH>) for hydrogen assisted-cracking (HAC) were studied using wedge opening-load (WOL) specimens (made of AISI 4340) as a function of tempering temperature. The test result showed that with the rise of tempering temperature, fracture modes and the K_<IH> markedly changed beyond the critical tempering temperature about 500℃.

抄録全体を表示