Journal of the Society of Materials Science, Japan

Carbon Fiber and its Related Materials

Sugio OTANI

1975 Volume 24 Issue 265 Pages 927-932
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.927

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The Effect of High Tensile Pre-load on Rotating Bending Fatigue Strength of Carbon Steel

Keiro TOKAJI, Zenji ANDO, Norihiko NAKANO

1975 Volume 24 Issue 265 Pages 933-939
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.933

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High load levels are sometimes observed in randomly varying loads applied to some structures or machine parts, owing to sudden accidents or some other causes. Recently, furthermore, materials are being used under severe loading conditions and often subjected to stresses comparable to the range. In case of designing, it is dangerous to neglect such high load levels.
The purpose of the present study is to investigate the effect of high tensile loads (in plastic range) on rotating bending fatigue strength of carbon steel. In this paper, as the first step, in order to obtain the fundamental data, the fatigue tests were carried out on smooth specimens of 0.33%C carbon steel subjected to a static high tensile load prior to stress cycling. The results were discussed on the basis of hardness change, residual stress change, surface observation during the fatigue tests and the effect of heat treatments.
The conclusions obtained are summarized as follows:
(1) In many cases, the tensile pre-load lowers the rotating bending fatigue strength. Especially, in the case of the lower yield point pre-load, the decrease of fatigue strength is more pronounced and in the case of the highest pre-load just under the tensile strength, the fatigue strength increases slightly above that of a virgin specimen.
(2) As the reasons of change in fatigue strength by the tensile pre-load, it is necessary to consider the stress concentration due to non-uniformity of work hardening as well as the residual stress and work hardening.
(3) By the heat treatments after pre-load, the fatigue strength of pre-loaded specimens increases, because the annealing effect by the heat treatment reduces the stress concentration due to non-uniformity of work hardening.

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On the Shape Factor of Particles by ‘Circular Arc Method’

Sanji NAKANO, Sotoo ENDO

1975 Volume 24 Issue 265 Pages 940-943
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.940

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An attempt to obtain a three-dimensional shape factor of a particle, Ψ_R, was made by determining the two-dimensional shape factors of projected particle figure, φ_R and φ_R', and by considering the wave and roughness of the surface of projection.
In‘Circular arc method’, the ratio of similarity to circle, φ_R is defined as A_m/A₀, where A₀ is the area of minimum circle circumscribing the projection of particle.
The circumcribed circle is appropriately divided into equal parts by the lines passing through the circumcenter. Each divided part of the projection is again circumscribed by the maximum and the minimum circular arcs which contact with the contour line of the projection at more than one point. A_m is defined as an area of the circle with the mean radius of the above circles for each part of projections. Thus A_m represents an approximate area of the projection.
By taking into consideration the characteristics of plane and side figures, an equation Ψ_R=φ_R √φ_R' is more appropriate than Ψ_R'={(√φ_R+√φ_R')/2}³.
Comparison was carried out with various kinds of model particles and degrees of ratio to sphere.
The results clearly demonstrated that Ψ_R determined by the‘Curve-fitting method’was nearly equal to the degree of ratio to sphere for the model particles calculated from the ratio between the true area and the area of its circumscribed circle of the projection.

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Fatigue Strength of Polycrystalline Aluminum

Toshiji KUROBE

1975 Volume 24 Issue 265 Pages 944-949
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.944

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The fatigue test has been carried out on polycrystalline aluminum under plane bending in order to investigate the effect of atmosphere on the fatigue strength of aluminum. The experiments were conducted in the pressure range from ambient pressure to 6×10^-5 Torr to know the pressure dependence of the fatigue life of aluminum, and the fatigue failure process of a specimen was examined by stress cycling using the surface profilometer and the micro-Vickers hardness tester to understand its failure mechanism more. Furthermore, the effect of test temperature on the fatigue fracture of aluminum was investigated and discussed from the chemomechanical view points.
The main results obtained were as follows:
(1) The fatigue strength of aluminum in vacuum was higher than that in air. The fatigue resistance of a specimen decreased with increasing temperature both in vacuum and in air.
(2) The increase of fatigue life of aluminum depends upon the degree of vacuum. The transition exists in the pressure range of 10^-2∼10^-3 Torr, independently of either the applied strain or the test temperature.
(3) The effect of a two-stage environmental fatigue test on the fatigue life of aluminum was notable in the experiments performed at the low stress level but it was not so at the high stress level.
(4) The surface roughness and Vickers hardness of a specimen subjected to fatigue stressing in vacuum were higher than those in air. This tendency became more pronounced at the high stress level.

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On the Fatigue Crack Propagation Behavior in Cast Iron under Rotating Bending

Sachio UEDA

1975 Volume 24 Issue 265 Pages 950-955
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.950

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Low cycle fatigue tests of circumferentially notched flake graphite- and spheroidal graphite-cast irons were performed in rotating bending.
The primary results obtained are summarized as follows:
(1) The fatigue crack propagation curves of cast irons almost coincide with their deflection curves during the fatigue test.
(2) The fatigue striations were observed only in the ferrite regions on the fracture surface of spheroidal graphite cast iron.
(3) The rate of fatigue crack propagation (dl/dN) was closely related to the stress intensity factor K and could be expressed by
dl/dN=CK^6.1 for flake graphite cast iron
dl/dN=CK⁵ for spheroidal graphite cast iron.
(4) Under the low cycle rotating bending tests, the relation between N and σ_a/σ_Bn for both notched specimens of the flake graphite- and spheroidal graphite-cast irons can be given by almost the same straight line on logarithmic scale coordinates. (N: number of cycle to failure, σ_a: stress amplitude, σ_Bn: notched tensile strength.)

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A Fractographic Study of Fatigue Crack Propagation under Variable Stresses with Special Reference to Crack Closure Phenomenon (Part 2)

Ryoichi KOTERAZAWA

1975 Volume 24 Issue 265 Pages 956-960
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.956

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Effects of stress change on the fatigue crack propagation of aluminum alloys (7075-T6, 5052-0 and 2017-T4) were studied in detail by means of striation analysis of the fracture surfaces and the results were interpreted on the basis of the crack closure concept. In the same way as the case of 2017-T4 alloy reported previously, a single increase or decrease of the maximum stress caused an acceleration or a retardation, respectively, of crack propagation of the 7075-T5 and 5052-0 alloys and these could be interpreted fairly well on the basis of the effective stress range above the crack closure level. Effects of repeated change of stress conditions were investigated with 2017-T4 alloy and the results were essentially the same as the case of a single change of stress. Two opposing effects of stress change, the acceleration by the maximum stress increase and the retardation by the maximum stress decrease, made the total effect small, so that the cummulative cycle ratio was close to unity (between 1-2).

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Environmental Stress Crazing of Rigid Polyvinylchloride

Satoshi OKUDA, Takayuki IGUCHI

1975 Volume 24 Issue 265 Pages 961-965
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.961

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The crazing which is induced in various environmental liquids has a very important influence on the long time strength of polymer.
Here, the craze initiating time and the craze propagation rate of rigid polyvinylchloride were measured in various liquids. And the following results were obtained.
(1) The Gibbs' free energy change which was introduced previously by the authors as a parameter to predict the possibility of the environmental stress cracking of polypropylene, could be adapted to the crazing time of rigid polyvinylchloride also.
(2) In the transient region of craze propagation, the relation between the craze length l and time t was expressed by the equation of l=P(t-t₀)^Q, where P and Q were constants. The craze induction period, t₀, was introduced conveniently, which was determinable experimentally.
(3) Under a relatively low stress, the craze propagation rate was very small, and actually no propagation seemed to take place. The actual allowable stress was different depending upon the kinds of environments.

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Electron Microscopic Observation of Environmental Stress Cracking of Polypropylene

Satoshi OKUDA, Takayuki IGUCHI

1975 Volume 24 Issue 265 Pages 966-973
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.966

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It is important to study the craze propagation process in connection with the environmental stress cracking. In various chemical environments, the crazes were induced on the polypropylene specimens. And the propagation of these crazes was observed electron microscopically by using the surface replica method. The shape of crazes was influenced by the kind of the environmental agents, and it was observed that the shape in polypropylene was strongly affected by the environments in the order of the concentrated sulfuric acid, isopropanol, castor oil, Noigen, ethyleneglycol, water and air. Under the environments giving a slight influence on polypropylene, the initial small crazes had usually curved shape but later they became to show branching. And the propagation of crazes became to slow or stop. On the other hand, the crazes under the environments giving severe influence such as isopropanol and castor oil were straight and sharp initially. These crazes propagated rapidly, and caused the specimens to crack. The typical craze propagation process in various environments was indicated schematically in Fig. 21.

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Acoustic Emission during High-Cycle Fatigue Testing

Hajime HATANO

1975 Volume 24 Issue 265 Pages 974-979
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.974

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Acoustic emission (or stress wave emission) is measured during high-cycle fatigue testing of pure aluminium specimens. Experimental results obtained are as follows:
(1) Burst-type acoustic emission begins to radiate intermittently in the early stage of fatigue testing before the macroscopic crack growth is observed.
(2) Smoothed specimen radiates acoustic emission of several mV peak. Notched specimen radiates much larger acoustic emission of scores of mV peak under the same cyclic load.
(3) Most of the acoustic emission signals are detected around the instance that the cyclic load attains a maximum.
(4) It is clear that the acoustic emission measurement using a peak voltmeter is useful for the study of fatigue, particularly that of microscopic fatigue crack growth.

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Strength Development of Cold Setting Epoxy Resin Mortars and Properties of Binders before Gelation (Part 2)

Sadahiro INOUE

1975 Volume 24 Issue 265 Pages 980-986
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.980

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One kind of hardener, four kinds of polyepoxide diluents, and nine kinds of liquid resins were used in the present study. As the result of experiments on the temperature dependence of viscosity using liquid epoxy resins in the temperature range of +19°to -16°C, it was found that all materials should be modified when used under conditions below freezing point.
The viscosity of 144 kinds of liquid resins prepared by adding diluents to liquid epoxy resins at the ratio of 12 to 48phr was measured at -6°C. Using 65 kinds of liquid resins with viscosity under 50000cps, the bond strength by tension was measured according to JIS K 6849 at -6°C.
The bond strength of 51 kinds of liquid resins showed values higher than 150kg/cm². Eight kinds of liquid resins were selected from these and used in the subsequent experiments.
The viscosity and gel time of equivalent mixtures of liquid resins and hardeners were measured. All mixtures showed viscosity under 50000cps.
Strength tests of epoxy resin mortars subjected to 8 days or 6 months curing, and 6 months cured jointing of successive pours to cement mortar were conducted. The strength of test specimens of 6 months curing generally was low in the case when the binders gave negative or negligible heat generation during gelation.
The best results can be obtained in the case of epoxy resin mortars using liquid resins which contained diglycidyl ether of resorcinol as the main ingredient.

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Electrochemical Behavior of Ferritic Stainless Steels in Sulfuric Acid

Fumio HINE, Masaki YASUDA, Masatoshi HIGUCHI, Tomoji YOSHIDA, Motonobu ...

1975 Volume 24 Issue 265 Pages 987-992
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.987

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The anodic polarization curves of ferritic stainless steels, Type 405, 430, 446, and E-Brite 26-1, under various conditions of H₂SO₄ concentration and temperature were obtained by means of the potential sweep method. The Flade potential, E_F, with potential scan to the noble direction is more noble than the potential with scan to the backward direction. The critical current density, i_F, at E_F is large compared to the current density, i_F' at the Flade potential, E_F', with the backward scan. The Flade potential tends to noble with the solution temperature, and the critical current also increases. In a relatively dilute solution less than 30% H₂SO₄, the critical current density decreases with increase in Cr content of the alloy, whereas the current increases with the Cr content in 50% and/or 70% H₂SO₄. The critical current is also a function of the H₂SO₄ concentration. That is, a maximum current was observed in 30% H₂SO₄. The critical current decreased in concentrated solutions such as 50% H₂SO₄, probably due to oxidation of steel surface by sulfuric acid. The passivation current density, i_P, is a function of the solution temperature and the set potential, but is almost independent of the H₂SO₄ concentration. The Type 405 steel showed the largest current.

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Reliability Analysis of Fatigue Lives of Machines and Structures under Service Loads

Part VII. Reliability-based Design under Joint Consideration of Distributions Both of Load and of Strength (1)

H. Ishikawa

1975 Volume 24 Issue 265 Pages 993-1000
Published: October 15, 1975
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.24.993

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