The corrosion fatigue tests in city water were carried out on precipitation hardening stainless steel, SUS630, variously heat treated (H1075, H1025, and H900), which was manufactured by three different melting processes (air, double and triple melting process). The results obtained are as follows. The corrosion fatigue strength of all H1075 specimens manufactured by three melting processes decreased compared with fatigue strength in air. The triple melted H1075 specimen showed the highest value of corrosion fatigue strength, followed by the double melted and air melted specimens in the descending order. This result seemed to be connected with the maximum size of inclusions in the specimens. As for the triple melted specimens subjected to different heat treatments, the H1025 specimen showed the highest value of corrosion fatigue strength and the H900 and H1075 specimens were about the same.
An innovative hydrogen measuring method applicable to high temperature systems such as oil refinery plants is presented. The electrochemical measurements of permeability., diffusivity and content of hydrogen permeated through a plain carbon steel at 823K were made by using a proton conductive solid electrolyte (5mol% Yb2O3-SrCeO3). A space was introduced between steel and filler metal in order to improve the accuracy of measurements. As a result, it was substantiated that molecular hydrogen produced during diffusion in steel can be measured with high accuracy for a longer period in comparison with the previous method.
A new measurement method (M-EPR) for evaluating a degree of sensitization (DOS) of stainless steels was proposed, which is the combination of EPR (electrochemical potentiokinetic reactivation) method (JIS G 0580) and random potential pulse one. The applicability to the DOS was examined by comparing the results of the EPR with that of the new method. The following results were obtained; (1) The reactivation ratio obtained by the M-EPR method was proportional to that by the EPR one, and the coefficient of correlation between the two methods was 0.986. (2) The coefficient of variation of the M-EPR was 0.18, indicating the same degree of reproducibility as that of the EPR. (3) The shapes of voltammogram obtained by the M-EPR changed with dissolution behavior and corrosion forms of steels. It was indicated that the M-EPR method could be used for identification of corrosion forms by pattern recognition. These results show that this new technique is applicable to the rapid evaluation of the DOS of stainless steels.
The corrosion behavior of carbides has been studied by an electrochemical method in sodium chloride solution at 50°C. The anodic dissolution current of tungsten carbide and vanadium carbide readily increased with a little polarization from immersion potential. Tungsten carbide formed a thick corrosion product (WO3·2H2O). The corrosion product of vanadium carbide was slight by reason that the rate of its dissolution probably exceeded the rate of formation of oxide. Rapid anodic dissolution of titanium carbide and chromium carbide begun at about 0.5V (vs. Ag/AgCl), in the trans-passive region. Niobuim carbide was stable in sodium chloride solution.
The immersion test of carbon cement containing furan or phenol resin was conducted for 20 hours in 40% H2SO4-2% HCl solutions with different amounts of HNO3 at 120°C. The corrosion behavior was evaluated by the ratio of dark area to the total area of a replica film obtained from the corroded surface of carbon cement which was polished before immersion test. The replica was observed by using an image analyser. It was found that carbon cement was attacked by the test solution when the content of HNO3 was higher than 0.1%. Then the ratio of dark area of the replica became about 50% from the initial value 14% for phenol cement. It is concluded that the image analysis method of measuring the ratio of dark area of the replica is feasible to evaluate the corrosion rate of carbon cement in corrosive solutions.
This paper describes the effect of stacking fault energy (SFE) on cyclic constitutive relation under nonproportional loading. Proportional and nonproportional tension/torsion step-up tests were carried out at room temperature on five materials which have different SFE; they are SUS 304 stainless steel, pure copper, pure nickel, pure aluminum and 6061 aluminum alloy. The material which has small SFE exhibited large additional hardening in nonproportional tests, while the material with large SFE showed no additional hardening due to nonproportional loading. The difference in additional hardening due to SFE was discussed in relation to slip band and cell size. For SUS 304 stainless steel and pure copper, which have small SFE, the interaction between planer slip bands in nonproportional loading was the cause of large additional hardening. On the other hand, for pure nickel, pure aluminum and 6061 aluminum alloy which have large SFE, wavy slips occurred in proportional and nonproportional loadings. Dislocations in large SFE materials can easily change their slip planes so that small or no additional hardening was found in large SFE materials. As SFE decreases, the cell size becomes smaller in nonproportional loading.
Plastic strain distributions in large deformation were obtained at the net section of the central notch of cylindrical specimens with three identical circumferential U-notches spaced longitudinally with an equal spacing. These strain distributions were numerically calculated from the distributions of the hardness number at the net section. Each specimen was loaded up to Pmax (maximum tensile load) and beyond Pmax. In the central notch of the notched specimens subjected to strong effect of notch interference, the axial strain at the center of the net section was greater than that at the notch root and was maximum in the net section. The shape of plastic region in the longitudinal section was an X-shape, which is formed by connecting diagonally two notch roots situated on both sides of the central notch. This shape of plastic deformation remained as the principal plastic deformation up to Pmax, although it became weak with increasing deformation. Beyond Pmax, plastic deformation occurred mainly in the vicinity of the net section of the central notch, causing unstable deformation.
The effect of LiNO2 on the suppression of expansion due to alkali-aggregate reactions was investigated by preparing mortars with a reactive andesite sand and measuring the expansion at the prescribed times of the mortars cured up to 7 months. The test results showed that the addition of LiNO2 giving a Li/Na mole ratio of 0.4 conspicuously suppressed expansion of mortars stored in a fog box and immersed in 1N NaCl solution at 40°C. Furthermore, none of the mortar specimens containing the amount of LiNO2 which exceeded a Li/Na mole ratio of 0.8 expanded even under the severe condition of 6 months immersion in 1N NaOH solution at 20°C. Expansion tests of mortars using reactive sand particles impregnated with LiNO2 solution were conducted as well. The use of the impregnated sand particles was found to suppress expansive alkali-aggregate reactions promoted by the intrusion of Na+, Cl-, and OH- ions. it was also confirmed that the compressive and tensile strengths of mortars changed little by the application of LiNO2. The results obtained show that LiNO2 may be able to use as a chemical admixture for preventing alkali-aggregate expansion of concrete.
It is desirable to examine the validity of a proposed method, if possible, from a different standpoint. In the present study, the strength of RC-member in a short column supported laterally at both ends was calculated under an axial load at a given eccentricity by a simple method of neglecting an effect of lateral deformation of the member, and the result was compared with that by a usual method of considering its effect. Consequently, it is proposed that the reduction factor of the strength by a simple method, in which the variations in strength of both reinforcing bars and concrete were taken into account, is adequete for compressive failure but should be reduced for tensile failure. Also, the upper limit of slender ratio of the member should be reduced to 21 instead of 35 which is provided in the JSCE-Code, if the reduction foctor of 1/1.15 provided in the Code is applied in the whole range of eccentricity.
Free edge stress singularities on and near the interface of dissimilar materials were investigated using a characteristic equation deduced in terms of Airy's stress function and the boundary element method. The values of the order of stress singularities determined by boundary element analyses under uniform tension agreed well with the values calculated by using the characteristic equation. The stress singularities disappear for certain combinations of wedge angles of the pair of materials. The stress distribution calculated by the boundary element method in the vicinity of the intersection of the surfaces and the interface agreed well with that obtained by using the stress function.
When a projectile with high velocity impacts onto a target, several fracture modes (such as spall fracture, plug fracture, penetration fracture and so forth) appear in the target. Therefore, in order to identify an impact fracture strength of materials, a particular type of impact experiments should be undertaken. For example, an impact experiment for flying plate is suitable to determine the spall fracture strength. Different impact conditions, however, may bring in different fracture strength even for the same target material. For the purpose of clarifying perforation dynamics (mechanism) by means of computer code, it is necessary to provide a unified fracture condition which enables to explain all modes of spall fracture, plug fracture and penetration fracture. Under this fracture condition, fracture takes place when the strain has attained its critical value, which may be affected by pressure and temperature. In the present study, the unified fracture condition was examined through comparison between the back surface velocity of flying plate impact experiment and the velocity calculated from computer code by using Ni-Cr-Mo steel (SNCM-630 steel). The computer code used here was that of one-dimensional large deformation stress wave propagation by finite-difference-method. The experimental results and computer code results were well in accord with each other, confirming the applicability of the unified fracture condition to perforation dynamics.
Fracture toughness tests of P/M high speed steels with different carbide sizes were carried out by using three point bend specimens with fatigue precrack. Tensile and bending strength tests were also carried out. The heat treatment to control the size of carbide particle also resulted in the change of volume fraction of carbide particles: the volume fraction of carbide particles decreased with an increase in the size of carbide particle. These two competitive factors, the size and volume fraction of carbide particles, simultaneously influenced the fracture toughness of the product in such a way that smaller size and higher volume fraction result in lower fracture toughness. Tensile and bending strengths increased with reducing the size of carbide particle. In the tensile and bending tests, fracture occurred from the site where some carbide particles or inclusions were segregated. Since the size of the initiation site was in proportion to the size of carbide particle, it is apparent that the both strengths increased with reducing the carbide particle size.
The effect of solution treatment temperature on the rolling contact fatigue strength of mild steel with carbon 0.17%, was studied by using specimens which were annealed, age-hardened at room temperature (20°C) after keeping for 20 minutes at solution temperatures of 700°C, 650°C, 600°C and 500°C, and tempered at 670°C to have almost the same hardness as the specimen solution treated at 700°C. Rolling contact fatigue tests were carried out with each pair of the same specimens by a Nishihara-type wear testing machine under pure rolling contact with lubricant. The results obtained are as follows; (1) The rolling contact fatigue strength of rolled steel for general structure (SS34) is increased markedly by the age-hardening treatment. (2) In order to produce the maximum rolling contact fatigue endurance limit of rolled steel for general structure (SS34), a solution treatment temperature of 600°C is necessary. (3) The propagation depth of crack formed in rolled steel for general structure by repeated contact stress tends to be in the vicinity of the region (Z0) where the maximum shear stress value becomes maximum.
Hydrogen embrittlement has been investigated on metastable and stable austenitic stainless steels cold-rolled by 0% to about 60%. The specimens were made of Fe-18% Cr-8% Ni (18-8), Fe-25% Cr-19% Ni (25-19) and Fe-24% Cr-13% Ni with 0.3% N (24-13/N); N was added to save the Ni content. The bend test was used to evaluate the hydrogen embrittlement, and the number of bending before failure was measured for H-free and H-charged specimens (N: H-free, NH: H-charged). The main results are as follows: (1) The number of bending before failure decreased with increasing H-charging. For specimens with the same Vickers hardness, NH was in the order of 24-13/N>18-8>25-19. (2) The ratio of hydrogen embrittlement [RH=(N-NH)/N] was in the order of 18-8>24-13/N>25-19. For 18-8, RH increased with increasing Vickers hardness. For 25-19 and 24-13/N, however, RH decreased with increasing Vickers hardness and RH for 25-19 was smaller than that for 24-13/N. (3) The thickness of the hydrogen embrittlement layer in 18-8 increased with increasing cold-reduction but those of 25-19 and 24-13N did not change. (4) H-charging produced surface cracks on solution-treated specimens and less cracks on cold-rolled specimens: blisters were most noticeable on cold-rolled 18-8. The surface change due to H-charging was more marked on 25-19 than on 24-13/N. (5) For 25-19 and 24-13/N, hydrogen-induced ε-martensite content decreased with increasing cold-reduction. The ε-martensite content of 25-19 was larger than that of 24-13/N.
The holding-load and fractographic (HLF) method proposed by the present authers was applied to hydrogen assisted cracking (HAC) test for five different heat-treated 2-1/4Cr-1Mo steels with different strength, and the effects of material strength and test condition on the threshold stress intensity factor KIH and fracture toughness KCH of hydrogen charged materials were discussed. The KIH decreased with an increase in accumulated hydrogen density in a specimen and showed just a little dependence on the tensile strength. The KCH was shown to be independent of the hydrogen density and the amount of crack extension during the HAC test, and it approximately coincided with the fracture toughness KIC before hydrogen absorption. These results indicate the applicability of the HLF method to HAC test with high accuracy.
Fatigue tests of 0° unidirectional and ±45° cross-ply composites of epoxy resin reinforced by two types of an aramid fiber (HM50, Teijin and Kevlar 49, Dupont) were carried out in air and in water at a low test frequency of 1Hz, in order to investigate the influence of water absorption on the fatigue mechanism at such a low test frequency. The following was found. In the case of ±45° cross-ply composites in air, the fatigue strength increased at 1Hz from that of 16.7Hz due to the scarce generation of heat. More fibers were pulled out in water than in air because of the weakening of the resin and fiber/resin interface due to the long exposure in water. A large splitting of Kevlar 49 fibers was found in the fatigue test in water, which had a meaningful effect on the fatigue strength. In the case of 0° unidirectional composites in water, the fatigue strength at 1Hz increased from that of 30Hz because the plasticization of resin and local re-alignment of fibers were promoted more at 1Hz. Though both unidirectional HM50 and Kevlar 49 fibers always broke with a certain amount of splitting in water, the fiber splitting did not appear to have a significant effect on the fatigue strength.
The failure assessment method based on non-linear fracture mechanics has been developed to show the integrity of high temperature components. J-integral is the feasible parameter to represent creep-fatigue crack growth, but there are many difficulties to calculate accurate J-integral in the component. Though finite element analysis and/or boundary element analysis are currently the most powerful tool to evaluate J-integral in complex structure, they require much man-power, cost and know-how. This paper shows various simplified methods to evaluate J-integral for creep-fatigue crack growth, and a comparison of the round-robin results with the experimental and detailed numerical results.
A personal computer program by using the intelligent finite-element method has been developed in order to analyze the construction and stacking sequence of laminate by which some design objectives can be satisfied. In this paper, the strength, weight and cost of laminate were selected as the design objectives. As the examples of its application, the kind of lamina and the stacking sequence were analyzed for a laminated plate under the conditions of bending load and combination of bending and tension loads. As there are many possible laminate constructions by which the design objectives could be satisfied, it is difficult to determine uniquely the construction of laminate. So, a method for selecting a suitable laminate construction was also proposed. As a result, it is recognized that the optimum laminate construction for each of these conditions can be determined by the proposed method.
The objective of this paper is to provide the tables in order to estimate the confidence limits for the parameters and percentile points of the extreme-value and two-parameter Weibull distributions. The confidence limits of percentile points are sometimes called the tolerance limits. Two different methods were selected as parameter estimators in this paper. They were: a combination of the median ranks and the method of least squares and the best linear unbiased estimators (BLUEs). Since these tables are not analytically obtainable, Monte-Carlo techniques were used. The Monte-Carlo simulation generated 100000 sets of complete samples for each sample size. By using these data and pivotal (parameter-free) quantities, the desired tables were derived. The sample sizes were 3(1)20, 25(5)50, and 60(10)100 for the combination of the median ranks and the method of least squares, and 3(1)25 for the BLUEs.
In general, plastic sheet displays vibration-damping by converting vibration energy into thermal energy. Laminated steel plates were prepared by putting a plastic sheet between two steel plates. The extent of vibration-damping of the laminated steel plate was evaluated for two types of plastics by measuring the loss factor. The resins investigated were acrylonitrile (A)-styrene (S)-butyl acrylate (B) terpolymer and methyl methacrylate (M)-butyl acrylate (B) copolymer. We prepared eight kinds of specimens having different butyl acrylate contents. A cantilever method was adopted for obtaining frequency response spectra, from which the loss factor was derived according to ASTM-E756. Laminated steel plates with AS-B terpolymer gave the maximum loss factor at temperatures above 100°C. The factor was as high as 0.5 at 40°C for the plate prepared from the M-B copolymer having butyl acrylate of 54mol%. The plates with M-B copolymer are expected to be very useful for vibration-damping near room temperature.