Half-value Breadth Research Articles

The X-Ray Investigation of Internal Stress in Electrodeposited Chromium

It is well known that the internal stress in electrodeposited metals is varied by the electrolytic conditions and the internal stress effects on some properties of the electrodeposited metals.Therefore, it is important to measure the internal stress in electrodeposited metals. Hitherto, many workers have developed the methods to measure the internal stress in electrodeposited metals. The principles of those methods are based on the measurement of deflection of a thin strip or a spiral helix which is electrodeposited on the one side. These methods do not give a direct information on the lattice deformation in electrodeposited metals.The X-ray diffraction methods are expected to give more exact information on the lattice distortion in electrodeposited metals. Recently, a number of X-ray diffraction methods for stress measurements have been developed in the field of the testings for metallic materials. The authors applied these X-ray diffraction methods to measure the internal stresses in electrodeposited chromium. In order to measure the internal stress of the first type (macro stress) in electrodeposited chromium by Sin2ψ method, the authors modified an ordinary diffractometer to be fulfilled the following conditions: (1) the specimen axis can be fixed at an arbitrary angle, the receiving slit and the GM tube being made to scan. (2) the receiving slit and the GM tube can be slided precisely to the focusing point in the radial direction of the goniometer which corresponds to the value of ψ0. The errors in this stress measurement which is apt to be caused by the sliding of the receiving slit and the GM tube were determined at 2θ=0°, and the influence of deviation in the position of the receiving slit from the focusing point on the measured value of stress was discussed by measuring the stress free iron powder. In measuring the internal stress of the second and third type (micro strains) in the electrodeposited chromium, the half-value breadth of several diffraction lines were measured by using Cu-Kα radiation and Hall's equation was applied to determine the micro strains.The chromium was plated on annealed copper plate from a bath containing CrO3:250g/l, H2SO4:2.5g/l and current density was 60A/dm2. The range of thickness of the deposits was from 10 to 30μ.From the experimental results, the following conclusions were derived.(1) It was confirmed to be possible to measure accurately the internal stress of the first type by using the modified diffractometer.(2) It was found that the internal stress of the first type in electrodeposited chromium measured by Sin2ψ methed on (211) diffraction line with Cr-Kα radiation was tensile stress at bath temperature range of 40-65°C, and the stress decreased with increasing bath temperature, and above 70°C the stress was compressive stress.(3) The half-value breadth of (211) diffraction line with Cr-Kα1 radiation decreased with increasing bath temperature from 40°C to 75°C.(4) It was found that the internal stress of the second and third type was a maximum at bath temperatures of 40-50°C. This tendency corresponded to the results of deflection obtained by a thin strip contractometer which showed a maximum value at bath temperatures of 40-50°C.

Variation of Residual Stress in the Fatigue Process of the Induction Hardened Steel

As part of the program of the cooperative researches sponsored by the Society of Materials Science, Japan, we have carried out the test in our laboratories in which the different heat treatments were performed for carbon steel and chrome-molybdenum steel, and the variation of residual stress and half-value breadth in the fatigue process was estimated. Among them, the test results on induction quenched materials are mentioned in this report. As for the variation of residual stress and half-value breadth, various test results had hitherto been reported from several laboratories. The final object of those researches as production makers is to grasp the fatigue process of real production parts, that is to say, to predict the break-down. Therefore we have continued for several years the basic tests for putting the X-ray residual stress measurement to practical use. As a result, it was found that it was difficult to predict the break-down of real production parts. Accordingly the other test method (Sonic test) was utilized jointly with the above mentioned method. Consequently we have attained to the following conclusions.(1) Residual stress, when repeated stress is over the fatigue limit, varies rapidly at an early stage of fatigue, and, after that, does not vary remarkably until break-down. When the repeated stress is under the fatigue limit, nothing but variation of tolerance is observed.(2) In the diffraction pattern photographed at the measurement of residual stress, obvious change of repeated stress, when it is over the fatigue limit, is observed before and after the fatigue test.(3) The result of sonic test does not vary so remarkably at the early stage of fatigue, when the repeated stress is over the fatigue limit, that is different from the above mentioned residual stress. But when it approaches the fracture point, it varies suddenly. Also, when the repeated stress is under the fatigue limit, little variation is observed.(4) The expected object of the present tests was achieved by the above mentioned results; As for the early stage of fatigue, the variation of residual stress and half-value breadth are measured by X-ray method. As for the final stage of fatigue, it will be concluded that it is possible to grasp the fatigue process and predict the fracture.(5) Although the real production parts were not utilized for the basic test this time, it is expected that X-ray method and sonic test will be jointly used to observe the fatigue process of real production parts for the future plan.

X-Ray Investigation on Fatigue Damage of Metals under Mean Stress : 2nd Report, Torsional Fatigue

Following the previous studies under cyclic bending stresses, the changes in half-value breadth, residual stress, hardness and microstructure have been investigated under completely reversed torsional stress amplitude and under alternating torsional stress with mean stress. It is found that the mean stress has little effect on the aforesaid changes. So it is deduced that, in the case of torsional stresses, the fatigue mechanism is not influenced essentially with mean stress, and consequently mean stress has little effect on fatigue life. It is also found that in torsional fatigue, tensile residual stress appears on the specimen surface at the initial stage of fatigue, and then it decreases with the number of stress cycles. It seems that the tensile residual stress is due to the absorption of excess vacancies, which are produced with stress cycles, by specimen surface.

X-Ray Investigation on Fatigue of Polycrystalline Metals : On the Relation between Crystal Orientation and Deformation in fcc Crystal

When polycrystalline metals deform plastically, the behaviour of every grain would be affected by its orientation in regard to the direction of applied stress. The values of resolved shear stress that causes a slip would be different from grain to grain according to its orientation. Observing the diffraction plane dependence of the change in half-value breadth of X-ray diffraction line as has been reported previously by the authors, the influence of crystal orientation of grains during fatigue as well as after plastic deformation is investigated on copper. And the difference of behaviour of crystals between fatigue and plastic deformation is studied. It is found that the slip occurred in the most favourably oriented crystals in the case of fatigue, while in plastic deformation a slip was produced almost equally in all grains. These results support the fact that the Tresca's law is appropriate as the criterion of the fatigue failure under combined bending and torsional stresses. Further discussions are made on this point.

X-Ray Investigation on Fatigue Fracture of Notched Steel Specimen : Observation of Fatigue Phenomena of Annealed Low-Carbon Steel by X-Ray Microbeam Technique

It was successful to apply the X-ray microbeam technique for observing fatigue phenomena of annealed low-carbon steel. The following conclusions were obtained : (1) Misorientation and lattice strain increase quickly in the early period of fatigue process, and subsequently they continue to increase till initiation of a crack. Formation of subgrains proceeds relatively slowly in the early period, and it becomes thereafter a main process of fatigue. Formation of subgrains is not observed for fatigue below fatigue limit. (2) Density of excess dislocation of one sign in subboundaries for fatigue is much smaller than those for uniaxial tension and rolling. (3) It is considered that the reason why the half-value breadth increases during fatigue is not the formation of subgrains but is mainly the increase of lattice strain. (4) Schematic diagram of deformation in a grain for fatigue is suggested. The formation of subgrains is closely related to fatigue fracture.

X-Ray Investigation on Fatigue of Polycrystalline Metals

In their previous paper, the authors have reported the study on the relation between the change in half-value breadth of X-ray diffraction line and the orientation factor μ of the reflecting crystals under cyclic or static stress of relatively low magnitude (σ_??_10kg/mm2). (Whereτs=μσ; σ is applied stress and τs is resolved shear stress). It was found that, under cyclic stress the half-value breadth showed great change in proportion to the values of μ of the grains, that is, slip occurred preferentially in the favourably oriented crystals. Under static stress, however, it was found that the change in half-value breadth was almost the same irrespective of the μ-values of the crystals. This may be understood from the mutual restriction of grains during the static straining.In the present paper, then, the changes in half-value breadth are investigated under cyclic and static stresses of relatively high magnitude (σ_??_10mg/mm2). It was found that, in contrast to the previous paper, the changes in half-value breadth could be interpreted more properly in terms of the orientation dependence of the work hardening rate g of corresponding single crystal, than orientation factor μ. This suggests that the orientation dependence of the work hardening rate of crystals in polycrystalline aggregates is similar to that of single crystals. It can be concluded that; (1) the fatigue mechanism of Cu is different depending of applied stress levels, (2) the orientation dependence of the work hardening rate of the crystals must be taken into account in order to get a relevant model of polycrystalline aggregates of Cu.

X-Ray Investigation on the Mechanism of Fatigue Deformation and Fracture in Metals

In their previous papers, the authors made some studies of annealed 6-4 brass, and particularly investigated its changes in residual stress, in half-value breadth and in micro-structure, during its fatigue process under constant and varying stress amplitudes, and found that its second phase showed some peculiar phenomena.One of these results showed the dependency of the changes in diffraction line widths on its crystal lattice plane in its α-phase. The authors tentatively interpreted this phenomenon as resulting from the heterogeneity of fatigue deformation as in the case of plastic deformation.Considering the character of fatigue fracture, however, it is questionable to ascrible the variation in the change of half-value breadth on diffraction crystal lattice planes only to the heterogeneity of plastic deformation.The authors examined therefore, during his X-ray investigations of fatigue deformation and fracture mechanism, first, the relationship between the tensile and the fatigue deformation, and secondly, fracture as dependent on the presence of a second phase.Heterogeneity in the tensile deformation had been commonly indicated as anisotropy of crystal, that is, orientation factor μ Accordingly, the authors attempted to make it clear whether this conception was applicable to a case of fatigue deformation or not. In case the application failed what sort of factors would be required?Heterogeneity as due to external forces had been investigated by Laue's reflection methods in single crystals, and the presence of asterism in the Laue spots on an individual crystal lattice plane showed anisotropy in tensile deformation. The reports, of which there had been a few, that no asterism was found in fatigue deformation process, requires reinvestigation, being a merely qualitative matter. The authors made inquiries, therefore, as to in what kind of changes in Laue spots the heterogeneity in the fatigue deformation appeared, and whether the dependency on the crystal lattice plane should have anything to do with asterism.The synopsis in this paper are as follows:(1) The changes in half-value breadth of 6-4 brass during the stretching process showed a variance in feature. The crystal plane dependency was seen in the β-phase but not in the α-phase on (420) and (331) planes. The changes in the half-value breadth of 7-3 brass and pure copper (α-phase only) were quite similar in general feature to the α-phase of 6-4 brass. From these experimental results it is evident that the crystal lattice plane dependency of the changes in diffraction line widths of the α-phase crystals was not affected by that of the β-phase crystals.(2) The interpretations of the dependency of the changes in the diffraction line widths on the crystal plane are based on the idea that each crystal in the polycrystalline aggregates is fit for the slip due to its orientation. Therefore, the authors adopted this idea to explain the changes in the half-value breadth. It is thought that the diffraction planes lying in parallel with the specimen surface occasioned by the experimental condition of X-rays considerably inclined up ward by some external force, and by reason of the crystals getting slips diverged broadly, while those planes of which the crystals are free from slips remained sharp.As for the plastic deformation of crystal, what is component of the shear stress τ in the slip plane along the slip line is all that is important. This shear stress is the result of the relation τ=μ×σN, where σN represents the normal stress and μ is the orientation factor. The latter is also indicated as μ=cosφ·cosα, where φ=the angle that the slip plane normal makes with the direction of the stress, and α=the angle that the slip direction makes with the direction of the stress.

X-Ray Investigation on Fatigue Damage of Metals under Mean Stress : (1st Report, Plane Bending Fatigue)

In the previous papers, the authors have investigated the behaviour of half-value breadth of X-ray diffraction line, residual stress and micro-structure under completely reversed stress amplitude, and have discussed on the changes in half-value breadth in relation to the basic mechanism of fatigue. In the present paper, as a continuation of the previous studies, the authors carried out some investigations on the changes in half-value breadth, residual stress and micro-structure in a case of fatigue under bending stress amplitude combined with mean stress, for the purpose of studying the mechanism of fatigue failure of metallic materials under mean stress. It has been found that, in the early stage of fatigue which corresponds to the period of fatigue hardening, there is little difference between the changes caused by stress alternation with positive mean stress and those with negative mean stress. However, in the second stage of fatigue which corresponds to the period of the growth of micro-crack, the changes in half-value breadth and residual stress become rapid, while they become slow with compressive mean stress. On the other hand, from microscopic observation, it has been confirmed that tensile mean stress promotes the growth of macro-crack and compressive one suppresses it. Then, it is suggested that the mean stress affects the growth rate of micro-crack just the same as macro-crack, and consequently influences the fatigue life.

The Study of Strength of Metals by X-Ray Diffractions

There are several ways of approach in the study of problems concerning the strength of metallic materials. The strength of materials is discussed for its basis in the scope of atoms composing the materials with respect to their order. In order to eliminate the factors affecting the complex character of the strength, single crystals or specimens of extremely coarse grains of pure metals or metals of simple chemical composition have been used as the test materials in this line of works. We are amply equipped with knowledges of the strength of materials.A great number of studies, on the other hand, have been made in application of engineering science. In this line of work, the materials to be subjected to experiments are mainly engineering metals of rather complex composition, and the strength of materials is observed or interpreted from macroscopic or submacroscopic viewpoint. This side of approach is, of course, of immense importance to machine designers and metallurgists.Various criterions in the strength of materials have been proposed. These criterions have in general been derived from probable models of the strength of materials that have been introduced from the findings in the fundamental study in atomic order. Although some of the criterions are useful for the prediction of strength of materials, we are seldom convinced of the mechanism because of lack of vivid proof of the strength of materials on engineering materials. In this sense, the authors believs that there still remains a gap to be fulfilled between the study of strength in engineering field and those in physical aspects. It is desirable therefore to make efforts in search of practical experimental means to find the change in microstructure of engineering materials, to enable us to recognize the property of the strength of materials.The application of X-ray diffraction is no new technique as means of experimental study. It has often been adopted for direct and non-destructive observation of changes in the micro-structure of crystalline materials in fundamental researches. It has been the plan of the authors to adopt this technique of applying X-ray diffraction to the experiment to elucidate the minute variation of micro-structure that has occuried in engineering materials.The authors have hitherto adopted the technique of applying a series of X-ray diffraction in the study of the strength of engineering materials where X-ray stress measurement and its half-value breadth have been adopted as the measure of changes in the structure. The X-ray measurement has been applied to various kinds of stresses. Especially its application marks one of our most successful work in measuring the residual stress of cold worked metals under the conditions of various kinds of cold work by using sin2φ method. The relation of half-value breadth and number of cycles of fatigue stresses has been studied in detail for various sorts of engineering metallic materials. As the results of a number of experiments, it has been found that the variation in half-value breadth shows very regular relation with number of cycles.The technique of X-ray diffraction that used to be employed in studies of earlier days was, however, of usual back-reflection, being a merely conventional means in industry for practical estimate of the strength of the materials, and so the findings obtained thereby were not sufficient for microscopic interpretation of the strength of the materials. In place of the ordinary back-reflection technique that is commonly used for the study of strength of engineering metallic materials, as being of insufficient resolving power, the X-ray microbeam technique has recently been introduced, whereby it is expected that engineering metallic materials will reveal more clearly the feature of variation in micro-structure, and the understanding of the findings in the early studies will be supported by the observation of the micro-structure.

A Contribution to Improving the Accuracy of X-Ray Stress Measurement

The authors have pointed out in their previous papers that both the accuracy and reliability of X-ray residual stress value on the samples with narrow breadth of X-ray diffraction profile were sufficiently good. However, no results on the sample whose X-ray diffraction profile is very broad have yet been obtained. As the measurement of peak position of X-ray diffraction profile, although the half-value breadth method can be employed and good results were obtained in the case of sharp diffraction profile, this method cannot be applied to the case of broad diffraction profiles, because the back ground line of the profile cannot be clearly determined. Consequently, it is considered that the accuracy of the stress value obtained is not sufficiently good. Therefore, it is necessary to develop a new method for the measurement of the peak position of diffraction profiles.In addition to this problem, the effect of Kα2 component on the measuring stress ought to be considered. Furthermore, the effect of the Lorentz polarization factor and the absorption factor should be taken into account when the measuring sample has a large amount of residual stress with a broad diffraction profile.In the present study, the authors attempted to separate the Kα1 component from Kα doublet by using Fourier analysis so that this procedure may be applied to any shape of profile, and so they discussed the effects of the Lorentz polarization factor on the stress value.For the determination of the peak position, first, two assumptions were made as follows:-1) The intensity distribution curve actually observed Φ(x) is given by the sum of the intensity distribution curves φ1(x)and φ2(x) diffracted from Kα1 and Kα2 radiations, respectively. 2) The following relation holds between φ1(x) and φ2(x), φ2(x)=kφ1(x-Δx)where k is a constant and Δx is the distance between the peak positions of the intensity curves diffracted from Kα1 and Kα2 radiations. Next, the intensity distribution curves Φ(x) and φ1(x) were represented by the Fourier series respectively, and φ1(x) was separated from Φ(x), and the Lorentz polarization factor was inducted into φ1(x). Lastly, the peak position of intensity distribution curve obtained by the above manner was determined by the parabola fitting method. These calculations were carried out by the digital computer.By using this method, the residual stresses on the some samples were measured, and on the basis of the experimental results, the following conclusions were derived.(1) It is considered that the effect of Kα doublet can be ignored from the view point of the accuracy of stress value even if the value of residual stress is large.(2) It is supposed on the other hand that the effect of the Lorentz polarization factor on the measured stress is remarkable especially for the specimen which has a broad profile. However, when the half-value breadth of the profile given by Kα doublet is less than 3°, it may be considered that this effect can be neglected.(3) By separating the Kα doublet and then correcting the Lorentz polarization factor, the X-ray residual stress on the shot peened carbon steel specimen agrees fairly well with the mechanical one, compared with the X-ray residual stress obtained by the raw data.(4) Although the effect of Kα doublet can be neglected, it is considered that this method has the characteristic of being suitable to the measurement of the peak position of diffraction profiles with whatever shapes including broad ones.

Variation of Residual Stress and Half-Value Breadth of X-Ray Diffraction Line of Structural Steel Sheet during Fatigue Process of Reversed Bending

In the first place, several statical tension and bending tests were carried out ranging from the elastic to the plastic with annealed specimens, and the surface stress and the half-value breadth were measured by X-rays at several steps of strain during and after the loading.Then, completely reversed bending fatigue tests ranging from high to low load were performed with annealed, pre-pulled and shot peened specimens. The residual stress and the half-value breadth were measured by X-rays at intervals during the fatigue process together with hardness measurement.The results obtained are as follows.1. In the statical tension tests, the residual stress was observed immediately after the nominal stress exceeded the tensile yield point, and the increase of half-value breadth or hardness started at the same time. In the case of bending tests, although the residual stress began to increase at the stress level near the tensile yield point, the increase of half-value breadth or hardness was not observed till the yield in bending took place.2. During the reversed bending tests under high loads, the initial residual stresses varied intensely in the first few cycles, and faded away prior to fracture in the case of pre-pulled as well as shot peened specimens.3. By the action of reversed bending under low loads, the initial residual stresses of pre-pulled specimens diminished with ease and faded away, but those of shot peened specimens decreased gradually according to the stress levels, and remained almost constant under the stress level of the endurance limit.4. The half-value breadth and hardness measured at intervals during fatigue process were found to keep a fairly good linear relation.

X-Ray Investigation on the Prediction of Fatigue Life : On the Changes in Half-Value Breadth of Carbon Steel under Varying Stress Amplitudes

It has been reported by the authors that the estimation of fatigue life of the materials under constant stress amplitude can be made using the liner relation of b/B-logn/N (where B and b are the initial and the current half-value breadth of diffraction line in fatigue and n/N is the cycle ratio). In the present paper, the following experiments were performed ; the first, the experiments were made on the case of varying stress amplitude of two stress levels above fatigue limit and investigated the change of half-value breadth due to varying stress amplitude. The second, the half-value breadth was measured by using satisfactory method in physical meaning and compared with the conventional method which has been adopted in these series of investigations. Finally, discussed on a change of half-value breadth under varying stress amplitude and postulated a certain method for nondestructive estimation of fatigue life.

X-Ray Investigation on the Prediction of Fatigue Life : On the Changes in Half-Value Breadth of Age Hardenable Alloy under Constant and Varying Stress Amplitude

As a continuation of previous investigation concern with prediction of fatigue life of steels under constant or varying stress amplitude, the fatigue process in age-hardenable Al-Cu alloy is studied by observing the half-value breadth of intensitity distribution curves taken from X-ray diffraction lines. It is found that the fatigue process of Al-Cu alloy is similar to that of annealed carbon steel from the stand point of the change of half-value breadth, namely, the relation between b/B and log n/N or log Σ n/N, where b and B are the current and the initial value of half-value breadth and n/N and Σ n/N are the cycle ratio or summation of cycle ratio respectively, is represented by a liner relation of magnitude or history of alternate stress amplitude. This relation offers a certain method of the prediction of fatigue life.

Joint Mechanism of Ultrasonic Welding

Much has not hitherto been known about the joint mechanism of ultrasonic welding. In the present work this mechanism has been studied by means of microscopic observation, X-ray diffraction, temperature measurement of joined parts, X-ray microanalysis, etc. The results obtained may be summarized as follows: (1) In the section of an ultrasonic bond, the temperature rise of the bond beyond the recrystallization temperature of material was revealed according to the microscopic observation. Neither intermetallic compounds nor other phases were observed in the interface by electron microscopy. (2) The recrystallization texture was observed by X-ray diffraction in the interface of the ultrasonic bond between two different foils, and neither intermetallic compounds nor other phases were observed in the X-ray diffraction pattern. (3) The variation in the half value breadth of X-ray diffraction lines obtained from the ultrasonic bond shows that the temperature rise in the interface of joined materials is by far larger than that in the place being in contact with the sonotrode tip. (4) The temperature of joined parts was measured with an alumel-chromel thermocouple and an oscillograph, and the temperature rise was found to be most affected by ultrasonic power. (5) X-ray microanalysis showed that the interatomic diffusion occurs in the ultrasonic bond between copper and titanium. (6) The joint strength between copper-beryllium alloys heat treated at 350°C for 15∼30 min and silver-copper alloys was about twice as much as that obtained from unaged ones. The joint strength of the bond was markedly influenced by the aging condition for the age-hardenable alloy.

X-Ray Investigation on Fatigue Damage of Metals : On the Changes in Half-Value Breadth of X-Ray Diffraction Line, Residual Stress, Micro-Structure and Micro-Hardness for Cold Worked Carbon Steel and Al-Cu Alloy in Fatigue Process

X-Ray Investigation on Fatigue Damage of Metals : On the Changes in Half-Value Breadth of X-Ray Diffraction Line, Residual Stress, Micro-Structure and Micro-Hardness for Cold Worked Carbon Steel and Al-Cu Alloy in Fatigue Process

X線による金属材料疲労破壊に関する研究

In the previous papers, the authors investigated the change in residual stress and microstructure in relation to the change in half-value breadth of annealed carbon steel in fatigue process, adopting (310) diffraction line. Based on the results of the experiments, the following conclusions were derived. Slip traces appear as regularly arranged line in the special slip planes of certain crystal grains in the early stage of alternating stressing, and they grow longer and wider with the increase of the number of cycles. In this period, both half-value breadth and compressive residual stress increase rapidly. It was considered that the broadening of half-value breadth comes from the accumlation of dislocations that occurs predominantly on the slip plane {110} by cross slip mechanism. In other words, it may be assumed that the extrusion and intrusion phenomena occur and the fatigue damage proceeds mainly by Cottrell and Hulls mechanism, and this also causes compressive residual stress to generate. In the second stage of fatigue, the half-value breadth increases gradually, while compressive residual stress decreases steeply and thereafter no change cccurs till fracture. Micro-structure shows distinctly that slip bands spread in the limited zone in certain grains. We may assume that micro-cracks initiate in these active slip bands and they promote the development of the visible cracks.However, there are two sorts of ploblems regarding the above investigation made by the authors. The first is that; in order to obtain an experimental proof to support the previous discussion, direct observations of the micro crack, extrusion, intrusion and cross slip phenomena are to be made in fatigue processs for present material. The second is that; according to the extrusion and intrusion mechanism, it is expected that the X-ray diffraction plane dependency of the change in half-value breadth and that of the changes in residual stress are present. In these connections, the authors attempted to investigate the relation between changes in half-value breadth diffracted from several atomic planes (310), (211), (220), (200) and (110), and changes in residual stress obtained from different lines of (310), (211) and (220) atomic planes. Specimens used in these series of experiments are annealed and electro-polished 0.07% carbon steel plate. A reversed bending fatigue testing machine was used for the fatigue test, and the speed of repetitions was 1700 cycles per minute. Residual stress was measured from (310), (211) and (220) diffraction lines, using CoKα1 and CrKα1 radiations, adopting the well known two exposure method at vorious numbers of stress cycles. The CoKα radiation was used to measure the change in half-value breadth of (310), (220), (211), (200) and (110) diffraction lines due to stress repetitions by normal X-ray diffractometer arrangement.Obtained conclusions are as follows;(1) Cross slip traces, extrusion and intrusion phenomena appeared extinctly in the first stage of fatigue stressing in the certain grains, and intensified gradually with increasing number of stress repetitions.(2) Micro cracks initiate in active bands zone, namely, it is observed obviously by electronmicroscope at the bottom of the intrusion slip at the stage of transition point from first stage to second. This micro cracks developed into visible cracks which lead to fracture during the second stage of fatigue.(3) The changes in half-value breadth of (220) and (211) diffraction lines during stress repetitions are quite similar to that of the (310) diffraction line which has been pointed out in previous papers. However, (200) diffraction line width changes greatly and that of (110) is a little in fatigue process.

X-Ray Investigation of Fatigue Damage of Metals : On the Changes in Half-Value Breadth of X-Ray Diffraction Line, Residual Stress, Micro-Structrue, and Micro-Hardness Due to Stress Repetitions

In the previous papers, the authors reported that the half-value breadths of metals read from X-ray diffraction lines changed with the application of alternating stresses at constant or varying stress amplitude, and it was found that the change of half-value breadth b/B (B and b are the initial and the current value of half-value breadth respectively)-logn/N (n/N is the cycle ratio) or b/B-logΣn/N (Σn/N is the summation of cycle rations under a varying stress amplitude) relations were expressed by a straight line irrespective of the magnitude of applied stress or stress history. Namly, the authors offered a certain method of nondestructive prediction of fatigue life. The studies carried out by the authors previously, however, did not treat the interpretation of the change in half-value breadth from the viewpoint of the mechanism of fatigue. In this connection, in order to reach a better understanding of the change in half-value breadth, they investigated the changes in half-value breadth of X-ray diffraction line, residual stress, microstructure, and micro-hardness due to stress cycles, and discussed on a change of half-value breadth.

X線による切欠材の疲労破壊に関する研究

In the present paper, the results of the X-ray study on fatigue fracture of notched specimen that has been performed as a preliminary examination on the mechanism of the fatigue fracture are described.The specimen used was 0.07%C carbon steel plate, having 60-deg. V notch, and was loaded under full reversed bending stress by the Nishihara's type fatigue testing machine. The change in micro-structure at the notch root of specimen was observed by optical micro-scope and the dimension of plastic region appeared in the vicinity of the notch root, that meant the region enveloping the slip band which came in sight until the macro-scopic crack appeared, was measured, by optical micro-scope as for cases with various stress concentration factors and various nominal stress magnitudes.On the other hand, the change of half-value breadth of X-ray diffraction line taken at the notch root in fatigue process was measured with notched specimen having a stress concentration factor of 2.0. The obtained results are summerized as follows:(1) At the very early stage of fatigue process, the slip lines appears in quite localized region close to the notch root, and as the number of stress repetitions increases this plastic region develops wider and longer progressively until macro-scopic crack is initiated.(2) When stress concentration factor is constant, the plastic region that comes in sight until the crack initiation occurs depends upon the magnitude of nominal stress applied. On the contrary, the plastic region decreases as stress concentration factor increases, when the maximum stress at the notch root is constant.(3) The plastic region at the tip of crack is much smaller than that of the notch root, and is nearly constant in the course of propagation of fatigue crack. The plastic region at the tip of crack depends on the magnitude of nominal stress, and the plastic region measured in the direction of crack propagation is likely to converge into about 0.02mm when nominal stress is small.(4) The half-value breadth of X-ray diffraction line at the notch root of specimen increases with the number of stress repetitions, corresponding to the structural change, that is, the halfvalue breadth increases rapidly at the very early stage of fatigue process and at the next stage it increases gradually, and nearing the point of crack initiation it increases rapidly again. After the crack initiation has occurred, the half-value breadth increases very slowly with the increase of the number of stress cycles.

X-Ray Investigation on the Prediction of Fatigue Life

It has been reported by the authors that the estimation of fatigue life of the materials under constant stress amplitude can be made using the liner relation of b/B-log n/N (where B and b are the initial and the current half-value breadth of diffraction line in fatigue and n/N is the cycle ratio). In the present paper, the following experiments were performed; the first, the experiments were made on the case of varying stress amplitude of two stress levels above fatigue limit and investigated the change of half-value breadth due to varying stress amplitude. The second, the half-value breadth was measured by using satisfactory method in physical meaning and compared with the conventional method which has been adopted in these series of investigations. Finally, discussed on a change of half-value breadth under varying stress amplitude and postulated a certain method for nondestructive estimation of fatigue life.

Studies on the Surface Layer of Machined Steel : 2nd Report, On Some Aspects of the Surface Layer of Steels Which Were Finished by the Surface Milling and Surface Grinding

Some experimental studies on the aspects of surface layer of various steel specimens were carried out. The chief conclusions obtained are as follows : (1) The depth of the machined surface layer (on this expression, the author mentioned in the previous report(1)) decreases as the hardness of the base-metal increases. (2) The depth of the machined surface layer of austenitic steels is more deeper than that of ferritic steel. (3) Two types of the distribution of the half value breadth of the X-ray diffraction pattern and the micro hardness in the surface layer existed. (4) Many forms of the distribution of the residual stress in the machined surface layer were observed. These distributions are explained qualitatively by a superimpose of the effects caused by four origins. (5) The half value breadth of the X-ray diffraction pattern is correlative to the hardness value.