In this study, a quantitative analysis for shape irregularity of ceramic particles was performed by applying the concept of fractal proposed by B.B. Mandelbrot. Two types of ceramic particles processed by different methods were employed as the samples. Silhouette of the particle was repeatedly observed along three dimensional Cartesian axes, after which Richardson effects of the configurations of the respective silhouettes were normalized. In this normalized Richardson effect, characteristic aspect concerning the microscopic and macroscopic irregularities of the particle shapes was found. The microscopic irregularity was successfully represented by fractal dimension, while the macroscopic one was evaluated by a parameter of macroscopic shape index.
Fractal concepts have recently been introduced to the field of fractography in order to characterize the fractured surface quantitatively. This paper puts great emphasis on the self-similarity of inhomogeneous deformation which results from the finite geometric changes of microstructure with strain. Fractal dimensions are obtained by using the familiar Richardson's structured walk method. Correspondence of the fractal property to the formation of crystallographic microstructure is discussed. We also perform fractal analyses for the pseudo-roughening profiles generated by computer simulations to interpret qualitatively the results obtained from the profiles of roughening in aluminum foils subjected to biaxial tension. Two kinds of roughening profiles are given by pure aluminum and aluminum alloy foils subjected to biaxial tension. The paper submitted formerly reported that the inhomogeneous deformation formed by the superposition of two kinds of microstructural changes was observed on pure aluminum. Fractal analyses to such profiles gave the following conclusions. The fractal dimension for pure aluminum increases a little with strain. On the other hand, as for the aluminum alloy it holds almost constant. The difference between them may be dependent on the mechanism of the formation of these roughening. This tendency also has good qualitative agreement with the results from the computer simulations by using the Gaussian distribution. Roughening formed by two kinds of the microstructural changes gives two different fractal dimensions, corresponding to the characteristic length of them.
The fundamental deformation behaviour of rubber composites, especially the nonuniform distributions of stress and strain in the material was studied. A plane model of rubber composites with elliptic heterogeneous rubber was employed. Namely, elliptic regions having different elastic constants were assumed to be present regularly in the matrix. Tensile deformation of the composites was analyzed numerically under the condition of the plane stress with the Mooney-Rivlin type strain energy function. The finite element method was used for the numerical simulation. It was shown that the deformation mode of the model was similar to that of constant strain as the shape of the elliptic region became slender in the tensile direction. The distributions of stress and strain in the elliptic region were nearly constant. The deformation mode of the composites was quantitatively described by introducing a scalar parameter called constraint ratio.
Deformation characteristics of a superplastic Al-5.5Mg-2.4Si prepared by a simple processing consisting of continuous casting, homogenization and cold rolling were examined. Strain rate sensitivity showed a maximum of 0.52 at 863K at a strain rate of 1×10-2S-1. The strain rate was 1 or 2 order higher than that of superplastic I/M 7475 or 5083 aluminum alloys. It is clear that the higher strain rate was obtained by a fine grain structure including a lot of sub-grains. The fine microstructure is due to retardation of recrystallization and grain growth at higher temperatures than 823K by secondary phase particles composed of Al, Si and Mn, which sometimes include Cr too. A maximum elongation of 900% was obtained at a lower strain rate of 1×10-4S-1 at 863K while elongation was only 270% at the higher strain rate of 1×10-2S-1. This decrease of elongation may be due to the increase in volume fraction of cavities which increases with increasing strain rate. Cavities are sometimes observed near the secondary phase particles of Mg2Si.
Effect of a small amount of hydrogen on the deformation of martensite phase in a Ti-50.0 at. %Ni shape memory alloy was investigated. Mechanical properties such as tensile strength, total elongation and reduction of area decreased even with a small amount of hydrogen. On the one hand, the stress for the self-accommodation process of martensite variants and the elongation corresponding to this process were not influenced by hydrogen. These results indicated that the influence of hydrogen on mechanical properties arose in the later stage of deformation where slip deformation was introduced. In the case of cyclic deformation, cyclic stress decreased because of interaction between hydrogen and dislocations which were introduced during deformation cycles. From the results of hydrogen discharge tests and low electric current density of cathodic charging, hydrogen which interacts with dislolations is considered to be in solid sulution state. Hydrogen which is released from the trap sites of a weak binding energy can also be taken into consideration.
A crack sometimes occurs at the underhead fillet of a bolt in the hot dip galvanizing process. In the preceeding paper, the effect of pretreatment in this process on crack nucleation was investigated experimentally. In this study, to investigate the crack nucleation time in hot-dip galvanizing and the effect of cooling condition on crack nucleation at the hot dip galvanizing process, some experiments and thermal stress analysis by FEM were performed. The main results are as follows. (1) The crack occurred at the underhead fillet of a bolt which had been dipped in a zinc bath over 10 seconds. (2) The crack occurred at the underhead fillet of a bolt when the bolt had been cooled by water, but it did not occur when the bolt had been cooled by air. (3) It was found by numerical calculation of FEM that high tensile thermal stress occurred during the cooling process after the hot dip galvanizing process.
The crack propagation behavior of welded material SM50A under a negative stress ratio condition was evaluated with the maximum stress intensity factor Kmax and the effective stress intensity factor range ΔKeff. The crack opening stress σop was measured by means of the strain interference method. The crack opening stress σop in the welded metal was lower than that in the base metal due to the tensile residual stress. Also, the negative value of the crack opening stress σop was measured in the case of the welded metal. Therefore, the relation between Kmax and the crack propagation rate da/dN was found to be different between the welded metal and the base metal. However, the relationship between ΔKeff and da/dN could be evaluated with the same equation in all the present experimental cases. Thus, it is confirmed that ΔKeff is one of the reasonable parameters for the evaluation of fatigue crack propagation and the strain interference method is useful for the measurement of crack opening point.
Effect of water flow rate on fatigue crack growth behavior in high temperature water simulating BWR environments was examined by using a flow rate change test method. Materials used in this work were two types of low alloy pressure vessel steels A533B cl 1; one was medium sulfur material (S=0.014 wt%) and the other low sulfur material (S=0.004 wt%). Corrosion potentials during the tests were successfully measured in the relevant conditions. As a result, the fatigue crack growth rate in high temperature water was more accelerated with decreasing flow rate, and this trend was more striking for the medium sulfur material compared to the low sulfur material. Change of corrosion potential during the tests showed a good correlation with the change of water flow rate.
The scatter in creep-rupture data and the accuracy of prediction by TTP (Time-temperature parameter) method for long-term creep rupture strength have been examined for 16 types of ferritic heatresisting steels. The logarithm of long-term creep rupture time was observed to be normally distributed. The TTP of Larson-Miller (LMP) and Manson-Haferd (MHP) was used for prediction of long-term creep rupture strength. The constants of TTP (C=20 for LMP, Ta=450 and Ya=14.55 for MHP), which are the average values of the optimized constants for each heat, were applied. An excellent prediction of long-term creep rupture strength whose RMS (root mean square) value is less than 0.3 was achieved for 95% of 87 heats of a wide variety of low alloy steels from 0.5Mo steel to 5Cr-0.5Mo steel.
The use of adhesive and adhesive/rivet or spot combined bonding methds to join steel plates has been increasing recently because of the high joint efficiency thus obtained. In this study, the tensile shear strengths of adhesive and adhesive/rivet combined joints were statistically evaluated. The probability of failure was calculated for the two kinds of joints, rivet and adhesive/rivet combined joints. Each data set was then plotted using normal, Weibull and doubly exponential functions. In addition, the effects of the combination of adhesive with rivet on mean tensile shear strength and coefficient of variation were investigated. The main results obatined are summarized as follows; (1) The strength distribution of adhesive joint was well approximated by Weibull or doubly exponential distribution function. However, in the case that the tensile shear strength is considerably improved by combination with rivet, the strength values of the combined joints do not form a straight line on any of the normal, Weibull and doubly exponential distribution graph paper. (2) With increasing ratio of strength of rivet joint to that of adhesive joint, the mean strength of the combined joints increased and the coefficient of variation decreased.
Fracture strength of amorphous insulating aluminum oxide ceramic thin film coated on a Fe-42%Ni base metal was investigated under static loadings by using a four point bending apparatus. It was found that the static fracture strength of thin film decreased with increasing coating thickness. Observations in detail by optical and scanning electron microscopes revealed that splash particles deposited in the coating process became crack initiation origins. It was also found that a large number of big splash particles in the thick films reduced the fracture strength with increasing thickness of film. An evaluation method of fracture strength of thin film was discussed based on the fracture mechanics approach and the critical value of strain intensity factors for fracture was found to be almost constant regardless of the film thickness and processing lot of materials.
Three kinds of unsaturated polyester resins having different toughness were used as the matrix of GFRP and their influences on the fracture toughness of GFRP were investigated. The crack propagation behaviour in a mat-GFRP could be classified into three categories: Region I with a linear relationship between load and crack opening displacement, without any crack propagation and damage initiation in the vicinity of crack tip; Region II with stable crack propagation, accompanied by fiber pull out or breakeage near the crack; Region III with rapid unstable crack propagation and load dropping after reaching its maximum load. The fracture toughness values, Ki and Kmax, which are related to the stable and unstable crack propagation respectively, did not depend on the ratio of initial crack size to the width of specimens, a0/W. Therefore, it is reasonable to consider them as material properties. The Ki value, different from the Kmax value, was dependent on the fracture toughness of the matrix resins. This suggests that the fracture toughness, related closely to the stable crack propagation or the initiation of damage in the GFRP, is mainly affected by the fracture toughness of the matrix resins, while the final fracture related to the Kmax value of GFRP is deternined by the glass fiber.
Three kinds of unsaturated polyester resins having different toughness were used as the matrix of GFRP and their influences on the interlaminar fracture toughness, behaviour of penetrating impact and stress corrosion cracking of GFRP were studied. The results obtained were as follows: (1) The fracture toughness of matrix resin influenced the interlaminar fracture toughness of GFRP. (2) In the penetrating impact test, the energy absorbed from the beginning to the maximum load was strongly dependent on the fracture toughness of matrix resin, while the total penetrating energy absorbed was related little to the properties of resin. This is considered as a result of widening of the damage area which compensated the insufficiency of the fracture toughness of matrix resin. (3) From the stress corrosion cracking test, a linear relation was found between the stress intensity factor KI and the crack growth rate or the time to failure. This indicates that these parameters have close relation to the fracture toughness of matrix resin.
This paper is concerned with the loading rate and temperature dependences on flexural fatigue behavior for CFRP laminates consisting of satin woven carbon cloth and epoxy rasin. The flexural fatigue tests for CFRP were conducted at two levels of loading rate and three levels of temperature. The fatigue strength of CFRP changed considerably with loading rate and temperature as well as the number of cycles to failure. Therefore, the estimation method using the master curve of time and temperature dependent flexural static strength and the slope of S-N curves is proposed based on the concept that the fatigue life is determined by loading rate, temperature and the number of cycles to failure.
FRP honeycomb sandwich constructions are light and high rigidity members which have a good corrosion resistance. These constructions have been by many different molding methods and used for many appliances. So in this paper, we have examined the practical properties of FRP honeycomb sandwich constructions which are used for underground laid application. The practical properties examined were alkali (pH 12) resistance, the dependence of heat circumstance and freezing-hot water (60°C) heat cycle resistance. Especially fracture pattern and mechanism were considered in testing of alkali resistance. The results obtained confirmed that FRP honeycomb sandwich can be applied for the structural members of underground laid uses. From the flexural test after dipping test of high alkali solution, it was clarified that there are different fracture patterns (one or both side fracture of facing, shearing fracture of core and combination fracture of facing and core) of FRP honeycomb sandwich constructions.
Recently, it has become important to develop new building materials which have various performances to create safe and comfortable space to live in. In the present study, the authors found the procedure to obtain light-weight powders (Surface Modified Slag; SMS), which can be used as a raw material of high performance building material, from blast furnace slag which is known as a recycle oriented material. SMS is prepared from water-granulated fine blast furnace slag through hydraulic reactions by treating with NaOH aq. solution. The slag powder surface can be drastically modified to increase its specific surface area by the treatment. By using SMS, the authors developed a light-weight body which has various desirable properties such as high strength, incombustibility and machinability. To obtain these properties, the following items were studied; (1) processing condition of SMS, (2) improvement of polymer emulsion as a binder of this body to increase strength and machinability, (3) surface modification of glass fiber as a reinforcement to improve strength performance of this body, and (4) forming condition of this body. The results proves that this body is useful as a building material because of having various performances to create safer and more comfortable space. Such performances can be accomplished by means of suitable combination of raw materials such as SMS, polymer emulsion and fibers, mixing compositions of these raw materials and processing condition. Moreover, this body has a hygroscopic performance and is easily colored and embossed because of large specific surface area and finess of SMS powder.