By using ψ0 oscillation method with CrKβ γ(311) diffraction, the X-ray stress measurement was made on five specimens, which were obtained by water toughening and various plastic working treatments (tensile pre-strain, hammered and explosive hardening) from Hadfield's high manganese austenitic steel, and their mechanical elastic constants, X-ray elastic constants and the accuracy of measurement were examined. The results obtained are as follows: (1) The mechanical elastic constant for 13% Mn austenitic steel after water toughening was 18900kg/mm2. This value gradually decreased with increasing tensile pre-strain. But it changed little when the specimen was treated by hammered or explosive hardening. (2) The K-value (KX=-37.26kg/mm2/deg) of austenitic steel adopted in the standard method of X-ray stress measurement is considered suitable for the X-ray stress measurement of 13% Mn austenitic steel which has not been subjected to severe plastic deformation. (3) The error in stress measurement Δσ in the X-ray stress measurement of high manganese austenitic steel becomes larger, depending more on the statistical fluctuation parameter, than that of ferritic steel.
This paper describes the structural dependence of ψ-splitting behavior observed in the X-ray stress measurement of worked surfaces. In order to investigate at first the effect of the cementite phase on the X-ray residual strain distribution, the lattice spacings at many orientations (φ, ψ) were measured for the ground or orthogonally planed surfaces of annealed S55C and pure iron. The variation of measured interplanar spacing against sin2ψ for S55C was closely approximated by the following fundamental triaxial stess-strain relation: εφψ=1/2s2[σ11cos2φ+σ12sin2φ+σ22sin2φ-σ33]sin2ψ+1/2s2σ33 +s1[σ11+σ22+σ33]+1/2s2[σ31cosφ+σ23sinφ]sin2ψ. However, the values for pure iron showed remarkable deviations from the elliptic distribution in sin2ψ diagram because of sharp preferred orientations produced by hard mechanical working. Secondly, the effect of morphology of the cementite phase on the sin2ψ diagram was investigated for SK 3 specimens which were prepared by four different heat treatments in order to include the spheroidized structure and the pearlite structure. The interplanar spacings showed the ψ-splitting behavior between positive and negative ψ angles along the grinding direction and distributed approximately in the form of ellipse. The extent of the ψ-splitting was the greatest for the pearlite structure and became smaller with increasing mean interparticle spacing for the spheroidized structure. This can be understood by a high impediment in dislocation motion within the lamellate or fine dispersed structure, which causes the large back stress due to dislocation pile-up at the cementite phase.
Boronizing is one of the chemical methods for case hardening of steels. The hardness of the boronized layer is above 1400 Vickers hardness and it has a high resistance, especially against wear. In the present study, plane and rotating bending fatigue tests of boronized steels with various thickness of boronized layers were conducted. The effects of thickness and compressive residual stress of boronized layer on fatigue strength were investigated. Furthermore, the X-ray method was successfully applied to measure the changes in residual stress and half-value breadth during plane bending fatigue. The results obtained are summarized as follows; (1) Fatigue crack initiation occured both in the boronized surface layer and at the boundary between the boronized layer and the matrix. (2) The surface compressive residual stress hardly changed during fatigue, but half-value breadth increased. (3) The compressive residual stress is effective to increase fatigue strength when crack initiation occured at the surface. The maximum fatigue strength was obtained when the boronized area was controlled to be about 1.5% of the total area.
The technique analysing the cause and mechanism of fracture from the information obtained by X-ray irradiation on the fractured surface is called“X-ray fractography”. As a basic study of X-ray fractography, the relation between the residual stress on the fatigue fractured surface and some parameters of the fracture mechanics were investigated. The materials used were Ni-Cr-Mo-steel, 0.5%C steel and high strength steel (U.T.S.>588MPa). The test pieces were CT-specimens with W=51mm and B=12mm. The fatigue tests were carried out under constant load and constant range of stress intensity factor. On the fatigue fractured surface the residual stress along the crack propagation direction was measured by a parallel beam X-ray stress measurement system, and the half value breadths of the diffraction profile were also measured. The main results obtained were as follows. (1) In the linear crack propagation stage of conventional constant load fatigue tests the residual stress on the fractured surface increased at first, and then decreased with increasing ΔK after about ΔK=30MPa√m. (2) For Ni-Cr-Mo-steel and 0.5%C steel, the residual stess could be expressed as a function of ΔK and affected only slightly by stress ratio. (3) For high tensile strength steel, the relation between the residual stress on the fractured surface and ΔK showed a dependence on stress ratio. (4) In constant ΔK fatigue tests of Ni-Cr-Mo-steel, the residual stress on the fractured surface was almost constant and agreed with the value corresponding to the same ΔK by the constant load fatigue test. (5) The half value breadth of the diffraction profile had a good correlation with Kmax and increased with increasing Kmax except for the normalized high tensile steel.
An X-ray fractographic study was made on the fatigue fracture surface of SM50A steel. The residual stress and breadth of the diffraction intensity curve were measured at and beneath the fracture surface. The analysis of residual stress on the fatigue fracture surface was also conducted by using the finite element method. An emphasis was made on finding the correlation between the residual stress or the plastic zone size determined from the X-ray measurements and the applied stress intensity factor. Both the distribution of residual stress and half-value breadth were found to be useful for the prediction of monotonic plastic zone size or Kmax, although it still remained in question for the possibility of estimating cyclic plastic zone size. The correlation between the surface values of residual stress and the applied stress intensity factor was not clear in the present study. The effect of fatigue crack closure on the residual stress of the fracture surface was found to be relatively small and limited in the very thin layer near the fracture surface.
Thermal stress behaviors of tungsten fiber-copper composites have been studied in situ by means of X-ray diffraction technique. The composites with 50vol.% and 100μm diam. tungsten wires were fabricated by a liquid infiltration technique followed by hot rolling. The results obtained are as follows: (1) X-ray diffraction technique was found to be an effective method to analyze the thermal stress of the composites, and both the matrix and the fiber stresses could be measured in situ which were generated due to thermal expansion mismatch of two components. (2) Both the matrix and the fibers deformed so as to accommodate thermal expansion mismatch when the composites experienced temperature change. The resulting thermal stress in each phase satisfied an equilibrium condition, that was, the matrix stress was equal to the negative of the fiber stress since the volume fractions of both phases were equal. (3) On thermal cycling of 282K-503K, the matrix deformed plastically and a steady state of the thermal stress-temperature hysteresis loop was achieved after only a few cycles.
The elastic constants of nickel base alloy at high temperatures were studied by the X-ray method with a new apparatus consisting of a horizontal type tensile testing machine and a vacuum furnace. Residual stresses due to precipitation hardening were also studied. In connection with the above experiments, the authors performed the observations of microstructure of the material at various temperatures. After the heat treatment for precipitation hardening, all the plate specimens of Inconel X were finished and then electropolished before being exposed to X-ray. The characteristic X-ray of CrKβ was irradiated on them through a thin beryllium foil, and the strain was determined by measuring the diffraction from (311) atomic plane by means of the conventional sin2ψ diagrams using counter technique. The conclusions obtained are as follows. (1) The elastic constants of Inconel X obtained by the X-ray technique are in good agreement with those measured mechanically within the experimental errors. The values obtained, however, decrease slightly more with temperature. (2) The lattice spacings or lattice constants changed about 5.2 degree in 2θ from room temperature to 923K. Consequently, it is necessary to take great care of slight change in temperature for stress measurement by X-ray. (3) For precipitation hardened Inconel X, the compressive residual stress is generated on the surface and remains from room temperature to about 700K.
The standard method of testing grindability of coal by a Hardgrove-machine is commonly used to determine the relative grindability of various coals in comparison with the standard coal having 100 grindability. This method has not come into general use for materials other than coal. In this paper, a general method for determining grindability of materials other than coal by a Hardgrovemachine is proposed. The sample is crushed by a jaw crusher, and is graded between 1190 micron and 590 micron sieves. The sample weights 36ρ (kg), where ρ (kg/cm3) is the true specific weight of the material, determined from the true volume experimentally measured by the Beckman air comparison pycnometer. The ground material after the single grinding cycle of 60 revolutions, is sieved on a set of sieves. The crushing extension index CEI is calculated by CEI=2.6(W/ρ)2 where W(kg)=weight of material passing the 74 micron sieve, determined from the weight of the original sample (36ρ) minus the weight of the material retained on the 74 micron sieve. W/ρ (cm3)=true volume of the material passing the 74 micron sieve. CEI (cm2/kgcm)=crushing extension index. It is independent of the crushing condition but characteristic of the material to be crushed. The specific surface increase ΔS and the residue R of the crushed product are expressed as follows: ΔS=CEIAr/W0 R=e-(0.006ρΔsx')0.8 1/x'=1/x-1/x0 where x is the particle size, x0 the initial particle size, x' the modified particle size and Ar the crushing extension energy.
With the CrKβγ(311) diffraction plane, the X-ray stress measurements on coarse grained 18Cr-8Ni austenitic stainless steel was carried out by the complex oscillation technique using the ψ0 oscillation and specimen oscillation at the same time, and the accuracy of the measurements and the X-ray elastic constant were examined. The results obtained are summarized as follows. (1) Using the complex oscillation technique, the stress of 18-8 stainless steel having the average grain size 155μm can be measured with the error less than ±1kg/mm2, if the limit of confidence is set at 95per cent. (2) The X-ray elastic constant for the material having the average grain size 93μm is almost the same as those for the fine grained specimens. But the value for the one with grain size 155μm is different from these values.
The buckling strength of a thin pipe under external pressure had been theoretically analyzed by von Mises. However, the strength of a thin pipe with locally thinned parts had not been studied. In the previous paper, the present authors showed that the buckling strength for such a pipe decreases in a great deal compared with that of a pipe having no thinned part. Also, it was suggested that the specimen having two thinned parts may show lower strength than the specimen with a single thinned part. This paper reports the experiments carried out in order to ascertain the above suggestion by using the specimens having no pipe end restriction to deformation. The experimental results did not show any dependence of strength on the number of thinned parts, and this was explained by the stress distribution in the pipe.
A study was made to determine the effects of specimen size, configuration and crack orientation to the weld axis on the fatigue crack growth rate of mild steel butt welded joints. Two types of welded specimens, the compact type (CT) specimens with three different sizes and the center-cracked-tension (CCT) specimens were used. Residual stress distributions in CT specimens were examined by means of the strain gauge method. In the case of welded specimens, the fatigue crack growth rates of CT specimens having widths of 100 and 260mm were roughly the same regardless of crack orientations to the weld axis, while the crack growth rates in specimens with width less than 100mm were faster than those of the larger width specimens. In the case of base metal specimens, the specimen size had no appreciable effect on crack growth rates. The crack growth rates of welded CT specimens were markedly reduced as compared with those of CCT specimens. This discrepancy may be attributed to the difference in residual stress distribution between CT and CCT specimens. Therefore, if the test results of welded CT specimens were used to evaluate the life of a welded structure, it is on the unsafe side. The crack growth rates of specimens with welding residual stress were found to be governed by the magnitude of residual stress near the crack tip in the interior of a specimen. And the fatigue crack growth rates of base metal specimens and weld metal specimens were well correlated with ΔKeff estimated based on the crack closure experiments.
The effect of partial unloading on the corrosion fatigue strength in water was investigated on the notched specimens of SNCM439 steel quenched and tempered at 473K. The corrosion fatigue strength was markedly increased by the partial unloading method. This fact may be explained by the decrease of tensile stress at the notch root surface which suppresses the destruction of protective film due to repeating slips in the material and prevent the corrosion reaction.
Since the delayed fracture of glass was first reported, a lot of studies have been conducted. In general, it has been understood that the true character of delayed fracture behavior exists in the stress corrosion cracking process in humid environment. The process of delayed fracture in glass, however, has not been made clear sufficiently. One of the reasons for this situation is that delayed fracture characteristics depend extremely upon the defect statistics. On the other hand, when the strength of brittle materials such as glass or ceramics is examined, it is necessary to eliminate the effect of distributed Griffith cracks on strength characteristics. For this purpose, many kinds of testing methods using abraded specimens have been proposed. One of these testing methods utilizes Vickers diamond indented specimens, which may also be employed for the evaluation of delayed fracture characteristics of glass. In this paper, four points bending delayed fracture tests in deionized water were conducted by using the soda-lime-silica glass plate specimens with the initial crack and indentation pit by Vickers diamond indentation. The results show that the lateral crack morphology is a governing factor for the delayed fracture characteristics of the specimens used in this experiment. This fact is brought about by the crack propagation behavior that the initiated crack (radial crack) propagates around the lateral crack.
The glass forming regions in the systems of Na2O-Fe2O3-(SiO2 or B2O3) and CaO-Fe2O3-(SiO2, B2O3 or GeO2) were determined. (Na2O or CaO)-Fe2O3-SiO2 glasses were found to be capable of containing up to 30mole % Fe2O3, while (Na2O or CaO)-Fe2O3-(B2O3 or GeO2) glasses up to 20mole % Fe2O3. The glass forming region in the system (Na2O or CaO)-Fe2O3-(SiO2 or B2O3) was narrower than that in the system (Na2O or CaO)-Al2O3-(SiO2 or B2O3). Although the density of the CaO-Fe2O3-SiO2 glasses increased linearly with Fe2O3 content when CaO/SiO2 ratio was kept constant, the molar volume increased with Fe2O3 content. On the other hand at constant Fe2O3 content, the molar volume decreased with increasing CaO/SiO2 ratio. This implies that Fe2O3 tends to loosen the glass structure and CaO to tighten the glass structure in the systems containing less than 40mole % SiO2. The dissolution ratio of Ca2+ ions in water was almost constant for all the glasses studied, while that of Fe3+ ions varied considerably. The dissolution ratio of Fe3+ ions decreased when SiO2 was replaced by CaO or Fe2O3, and it became 1/10 when Fe2O3 was partially replaced by CaO. Such changes were considered to be associated with the variation of the coordination number of Fe3+ ions in the glass. The electrical conductivity of the CaO-Fe2O3-SiO2 glasses changed from 10-6 to 10-11/ohm-cm, depending upon the Fe2O3 content. This variation may be explained by the change in interatomic distances of iron ions in the glass.
The application of PIC (Polymer-Impregnated Concrete) to the container for conditioning and disposal of low and intermediate level radioactive wastes have been investigated, because the PIC has excellent characteristics such as high mechanical strength, high water impermeability, good corrosion resistance, good durability and so on. It is necessary to evaluate the resistance to gammarays considering the PIC-container for radioactive wastes. The radiation-resistance of PIC with test piece was evaluated by irradiation of gamma-rays. All the test pieces had JIS mortar size of 4×4×16cm. JIS mortar and concrete were used as specimens. The maximum aggregate size of concrete was 10mm. The specimens impregnated by MMA (methylmethacrylate) monomer and solution of 10% of PSt (polystyrene) in MMA monomer (MMA·PSt) were polymerized by irradiating for 5hr at the dose rate of 1MR (1×106 Roentgen)/hr. PIC specimens were exposed up to maximum 1000MR to 60Co gamma-rays in air and under water which simulate shallow land disposal and deep sea dumping conditions, respectively. The lowering of strength of the PTC exposed to gamma-rays under water was larger than that of the PIC in air. The improving effect of the added PSt on the radiation-resistance was observed. It was observed that the 50MR-irradiated MMA·PSt-PIC under water, which had the residual compressive strength of 85%, was resistant to gamma-rays. When this residual strength was regardedas a limit of radiation-resistance in air, the limit of MMA and MMA·PSt-PIC were approximately 25MR and 150MR, respectively. The lowering of strength was mainly due to the deterioration of MMA polymer in PIC. The total exposure dose for PIC-container was estimated by assuming the conditions about the packaged radioactive wastes, dose rate, container and so on. The total exposure dose on PIC- container for 100 years became roughly 1.25MR. Therefore, it is estimated that the PIC-containers for conditioning and disposal of low and intermediate level radioactive wastes have a sufficient resistance to radiation arising from wastes.
Finite element procedures were used to discuss the practicality of the electrical potential technique for monitoring the surface crack of a plate. The analysis applied to solve the potential field problems involves the solution of Laplace equation. Analytical figures were modeled as three-dimensional bodies using eight-nodes isoparametric elements. A computer program ADINAT was employed in this study. From finite element analyses, the following method of determining surface crack configuration was proposed. The electrical potential ratio is determined first at several positions from a crack center and the relationship between electrical potential ratio and distance from a crack center is obtained. By assuming that a surface crack takes a half elliptical configuration, the crack length c at surface can be estimated from the relation between the crack area ratio and the distribution of electrical potential ratio from a crack center. Then the crack depth a can be decided from the distribution of normalized electrical potential ratio.