Internal Inclusions Research Articles

Boundary element modeling for defect characterization potential in a wave guide

Wave scattering analysis implemented by boundary element methods (BEM) and the normal mode expansion technique is used to study the sizing potential of two-dimensional shaped defects in a wave guide. Surface breaking half-elliptical shaped defects of three opening lengths (0.3, 6.35 and 12.7 mm) and through-wall depths of 10–90% on a 10 mm thick steel plate were considered. The reflection and transmission coefficients of both Lamb and shear horizontal (SH) waves over a frequency range 0.05–2 MHz were studied. A powerfully practical result was obtained whereby the numerical results for the S 0 mode Lamb wave and n 0 mode SH wave at low frequencies showed a monotonic increase in signal amplitude with an increase in the defect through-wall depth. At high frequency (usually above the cut-off frequency of the A 1 mode for Lamb waves and the n 1 mode for SH waves, respectively), the monotonic trend does not hold in general due to the energy redistribution to the higher order wave modes. Guided waves impinging onto an internal stringer-like an inclusion were also studied. Both the Lamb and SH waves were shown to be insensitive to the stringer internal inclusions at low frequency. Experiments with piezoelectric Lamb wave transducers and non-contact SH wave electro-magnetic acoustic transducers (EMAT) verified some of the theoretical results.

GSW0442 Evaluation of long life fatigue strength at ultrasonic frequency

A C-Cr bearing steel (JIS SUJ2) was fatigued with the ultrasonic fatigue-testing machine (20kHz) in laboratory air. In the very long-life regime, the decline of fatigue limit was seen. The origins of crack initiation were mostly internal inclusions. However, even when the specimen broke in a long life region, some cracks were initiated from specimen surface. Fracture surface were observed with a scanning electron microscope (SEM). The fish-eyes were observed in the specimens broken from the internal inclusions. The fracture surface could be divided into three regions. The first region surrounding inclusion was a facet area. The crack propagation in the facet region was Stage A and the crack propagation outside the facet region was Stage B. When the fatigue cracks reached the specimen surface, the fatigue cracks propagated as surface cracks.The crack propagation rate in each region was estimated to be a power function of the stress intensity range. Fatigue life was calculated by integrating with the crack propagation laws determined from the data obtained for the rotating bending. The predicted fatigue life agrees with the experimental result.

715 高強度鋼の長寿命領域における疲労強度評価

A bearing steel (JIS SUJ2) and nickel chromium molybden steel (SNCM439) were fatigued with the ultrasonic fatigue-testing machine (20kHz) in laboratory air. In the very long-life regime, the decline of fatigue limit was seen. The origins of crack initiation were mostly internal inclusions. However, even when the specimen broke in a long life region, some cracks were initiated from specimen surface. Fracture surface were observed with a scanning electron microscope (SEM). The fish-eyes were observed in the specimens broken from the internal inclusions. The fracture surface could be divided into three regions. The first region surrounding inclusion was a facet area. The crack propagation in the facet region was Stage A and the crack propagation outside the facet region was Stage B. When the fatigue cracks reached the specimen surface, the fatigue cracks propagated as surface cracks. The crack propagation rate in each region was estimated to be a power function of the stress intensity range. Fatigue life was calculated by integrating with the crack propagation laws determined from the data obtained for the rotating bending. The predicted fatigue life agrees with the experimental result.

Fatigue crack propagation behaviour derived from S–N data in very high cycle regime

ABSTRACT The crack propagation law was derived from the S–N data in the very high cycle fatigue of a bearing steel. The propagation rate, da/dN (m/cycle), of surface cracks was estimated to be a power function of the stress intensity range, ΔK (MPa√m) with the coefficient Cs = 5.87 × 10−13 and the exponent ms = 4.78. The threshold stress intensity range was 2.6 MPa√m. The crack propagation from internal inclusions was divided into Stages I and II. For Stage I, the coefficient of the power law was C0 = 3.44 × 10−21 and the exponent m0 = 14.2. The transition from Stage I to II took place at ΔK = 4.0 MPa√m. For Stage II, the coefficient was Ci = 2.08 × 10−14 and the exponent mi = 4.78. The specimen size and loading mode did not influence the surface fatigue life, while the internal fatigue life was shortened in larger specimens and under tension–compression loading. For ground specimens, the surface fatigue life was raised by the compressive residual stress, while reduced by the surface roughness introduced by grinding. For shot‐peened specimens, fatigue fracture did not take place from the surface because of a high surface compressive residual stress. The internal fatigue life was reduced by the tensile residual stress existing in the interior of the specimens.

EMAT-Based Inspection of Concrete-Filled Steel Pipes for Internal Voids and Inclusions

Concrete-filled steel pipes have been used as piles for supporting civil and marine structures. These piles provide good bending resistance, and can be easily spliced for long depth installation. However, these piles are usually exposed in hostile environments such as seawater and deicing materials. Thus, the outside corrosion of the steel pipe can reduce the wall thickness and the corrosion-induced delamination of internal concrete can increase internal volume or pressure. In addition, the void that can possibly exist in the pipe reduces the bending resistance. To avoid structural failure due to this type of deterioration, appropriate inspection and repair techniques are to be developed. The acoustic method is attractive for this inspection since it is relatively simple and versatile. Especially, guided wave techniques have strong potentials for this inspection because of long-distance inspection capability. There are different transducer-coupling mechanisms available for the guided wave inspection techniques. Electro-magnetic acoustic transducers (EMATs) give relatively consistent results in comparison to piezoelectric transducers since they do not need any couplant. EMATs are used for transmitting and receiving cylindrical guided waves through concrete-filled steel pipes. It is shown that EMAT-generated cylindrical guided wave techniques have good potential for the interface inspection of concrete-filled steel pipes.

Analysis of Stress/Strain Concentration at Nonmetallic Inclusion and S-N Curve of Ultra-long Fatigue Failure of High-strength Steels.

It has been reported that, according to some rotating bending fatigue tests, the S-N curve for high-strength steels consists of two straight lines. One corresponds to the line for short life at high stress level due to fracture from a surface origin, and another corresponds to the line for ultra-long fatigue life at low stress level due to fracture from internal nonmetallic inclusions. In this study, stress/strain concentration around inclusions is analyzed by FEM to seek a possible mechanism for this particular S-N curve behavior of ultra-long fatigue failure of high-strength steels for rotating bending fatigue test. A special focus is put on the growth of plastic zone around an internal inclusion and near surface with increasing applied nominal stress. Considering the different scale of plastic zone near surface and around an internal inclusion, it can be concluded that, in case of rotating bending fatigue test, fracture is likely to occur from a surface origin at high stress level and from an internal inclusion at low stress level. However, this characteristic depends on several factors such as specimen size, residual stress, cyclic yield stress, size and location of the crucial inclusion.

Critical Fields for Displacing Domain Walls in Low-Alloyed Tempered and Martensite-Aging Steels

By analyzing experimental curves of differential magnetic susceptibility of thermally processed samples of 38KhS, 75G, and N18K9M5T steels versus magnetizing field, we have derived characteristic curves χ180(H) and χ90(H) due to displacement of 180° and 90° domain walls and determined critical fields H180 and H90 for these types of domain walls. Fields due to induced magnetic anisotropy have been calculated, alongside their components caused by internal stress and nonferromagnetic inclusions.

Effect of Frequency on Giga-Cycle Fatigue Properties for Low-Temperature-Tempered SNCM439 Steel.

Fatigue tests were carried out at frequencies of 20 kHz, 600 Hz and 100 Hz for low-temperature-tempered SNCM439 steel. Ultrasonic, high-speed servohydraulic and electromagnetic fatigue test machines were used for 20 kHz, 600 kHz and 100 Hz tests, respectively. The fatigue tests showed that fatigue properties were independent of the frequencies, while fatigue lives were distributed in wide range on the S-N diagram. Almost all specimens were broken from internal Al2O3 inclusions of various sizes between 9 and 82 μm. Fatigue lives were found to depend on the inclusion sizes. ODA, i.e. optically dark area, was observed in all specimens broken over 107 cycles. ODA sizes were also independent of the frequencies. The scattered S-N diagram was found to be expressed by an unique curve by normalizing stress amplitudes σa with fatigue limits σ'w estimated by Murakamis equation. The modified S-N diagram showed a clear fatigue limit between 109 and 1010 cycles.

430℃と500℃で焼戻されたばね鋼SUP7の10<SUP>10</SUP>サイクル疲労特性

Giga-cycle fatigue properties were investigated for SUP7 spring steels tempered at 430 and 500°C. Tensile strength levels were 1423 and 1730MPa. Rotating bending, electromagnetic, high-speed servohydraulic and ultrasonic testing machines were used for 30 or 100Hz, 120 Hz, 600Hz and 20kHz tests, respectively. 1010-cycles fatigue properties were obtained in 3 years under 100Hz rotating bending and in 7days under 20kHz uniaxial loading, using 6-and 3-mm-diameter hourglass specimens. 108-cycles fatigue properties were also obtained under 120 and 600 Hz uniaxial loading, using 6- and 3-mm-diameter hourglass specimens. Almost all specimens fish-eye-fractured at internal inclusions of Al2O3. Optically dark areas (ODAs) were formed around inclusions even at 20kHz. The data obtained was analyzed according to the predicted fatigue limit and control volume of specimen for fish-eye fracture proposed by Murakami and others. S-N curves for 430°C tempered steel under 100Hz rotating bending, and 600Hz and 20kHz uniaxial loading were coincident each other, because the control volume was almost the same of 34 and 33mm3. S-N curves under 120Hz unixial loading with the large control volume of 227mm3 shifted to the lower strength level. The inclusion size was nearly proportional to the control volume. Modified S-N curves, that is σa/σw' versus Nf curves, were independent on the test speed, loading type, specimen configuration and strength level. Here, σw' is the fatigue limite for fish-eye fracture predicted by Murakami and others. These results give us two findings. One is that fish-eye fracture is not the simple hydrogen embrittlement process. Another is that 20kHz ultrasonic machine is effective for accelerated testing method of giga-cycle fatigue.

Gigacycle fatigue properties for high-strength low-alloy steel at 100 Hz, 600 Hz, and 20 kHz

Fatigue tests were carried out at frequencies of 100 Hz, 600 Hz, and 20 kHz for low-temperature-tempered JIS SNCM439 steel. Almost all specimens were broken from internal inclusions and frequency effects were not found on the gigacycle fatigue properties. The fatigue limit appeared at over 10 9 cycles.

Enigmatic origin of ferruginous “coprolites”: Evidence from the Miocene Wilkes Formation, southwestern Washington

Excrement-shaped masses of siderite and limonite have been reported from clay-rich sedimentary rocks that range in age from Late Permian to Holocene. These objects have been widely accepted as being coprolites, but the ferruginous composition, absence of internal inclusions, and scarcity of associated vertebrate remains suggest that they may instead be pseudofossils created by mechanical deformation of plastic sediment. Possible abiotic mechanisms include coseismic liquefaction, intrusion of sediment into hollow logs, or expulsion of sediment in response to gravity. Alternatively, carbon stable isotope ratios indicate that sediment extrusion may have been related to emission of biogenic methane during early stages of diagenesis.

Influence of carbide and inclusion contents on the fatigue properties of high speed steels and tool steels

In this study the influence of carbide distribution, inclusion contents and the surface machining process on the fatigue properties of tool steels and high speed steels were investigated. Four different steels intended for cold work applications were included, of which three were powder metallurgically processed and one was conventionally ingot cast. One of the powder metallurgy steels was studied in four surface conditions namely hard turned, ground, polished and shot peened. Fatigue testing was performed on hour glass shaped specimens with a load ratio of R=0.05. The staircase method was used to determine the fatigue strength corresponding to a life of two million cycles. The causes of fatigue failures were determined from fracture surfaces. For the polished specimens of all steel grades it was found that internal inclusions and carbides caused the failures. Crack initiating internal carbides were found more frequently for one highly alloyed powder metallurgy steel and for the conventionally cast steel. For the other polished series, internal inclusions were controlling the fatigue failures. Surface crack initiation was encountered on the ground specimens as well as on the specimens that were hard-turned and subsequently shot peened as a final machining process. Fracture mechanics was used to describe the relation between inclusion and carbide sizes observed on fracture surfaces and the fatigue strength. A model was developed to predict the fatigue strength of the specimens. It was shown that the model managed to determine the fatigue life limiting factors, i.e. internal inclusions in “PM23” and ASP2014 and internal inclusions and internal carbides in VANADIS10 and M2. However, the predicted fatigue limits overall were lower for all steels than what was observed in practical experiments, hence the model was conservative.

Surface and Internal Fatigue Fracture of High Strength Steel

Low- and high-cycle fatigue properties were investigated for spring steels SUP7, 9A and 12, and tool steels SKD61 and 11 whose tensile strength ranged from 1300 to 2130 MPa. Surface fracture, where cracks initiated at the specimen surface, occurred at the low cycle region below 105 cycles, whereas internal fracture, where cracks initiated at the internal inclusions, occurred at the high cycle region above 105 cycles. An unique curve of σa/σyc vs. Nf was obtained for the surface fracture regardless of steel and strength level. Where σa and σyc are stress amplitude and cyclic yield strength, respectively. Using a crack propagation parameter of σa3ai1/2, it was observed that fatigue life for Al-oxide, Ca-oxide and Cr-carbide inclusions in the descending order. Where ai is inclusion diameter. This suggests that the internal fatigue properties are affected by species of inclusion as well as its size.

Monte Carlo Simulations of Light Scattering by Composite Particles in a Planetary Surface

Composite particles containing internal scatterers have been proposed as an explanation for the fact that most photometric studies of planetary surfaces based on Hapke's bidirectional reflectance model have found the planetary particles to exhibit moderately backscattering phase functions. However, an implicit assumption made in this explanation is that the scattering by composite particles containing multiple internal inclusions in a planetary surface can still be adequately computed using standard radiative transfer theory assuming the composite particles to be the fundamental scattering unit even though the particles are necessarily in close proximity to each other. This assumption was explored by J. K. Hillier (1997, Icarus 130, 328–335) using a Monte Carlo routine. However, in this initial study several simplifying assumptions were made. The internal scatterers were assumed to be isotropic and scattering off of the surface and absorption within the composite particle were ignored. While these assumptions are not very realistic, it was believed that the study could still provide insight into the light scattering by such surfaces. Here we relax these assumptions in order to examine the light scattering by more realistic particles. Almost all of the conclusions reached in the earlier paper remain valid. As before, we find that classical radiative transfer (assuming a random distribution of scattering particles) coupled with the assumption that the composite particle is the fundamental scatterer provides a good approximation in the high porosity limit. However, even for porosities as high as 90% the effects of close packing are clearly seen with the radiative transfer calculation underestimating the scattering by ∼10% at high phase angles. In contrast to the earlier study we find that the radiative transfer calculation tends to overestimate, not underestimate, the scattering at high emission but moderate phase angles. As the porosity is lowered further, the discrepancy becomes more severe and can reach 100% or greater. In particular, our main conclusion remains intact: the parameters derived using the classical radiative transfer theory will yield results intermediate between those of the composite as a whole and those of the internal scatterers and thus one should exercise caution in interpreting the results of models based on classical radiative transfer theory in terms of the physical properties of the surface particles.

Recent Continuous Casting Technologies of Steel in Japan

Recent development in continuous casting technologies in Japan is reviewed mainly from the stand-point of high casting speeds. Heat flux to the mold increases inevitably with higher casting speed and is consistent in both near net shape castings and conventional ones. Heat transfer to the mold is discussed in detail. Especially the selection and control of mold fluxes are of great importance. Stirring and braking of molten steel in the mold by an applied electromagnetic field have been successfully performed to reduce internal inclusions, unsteady casting parts and also to prevent longitudinal cracks. An electromagnetic pressure can impose an early stage of solidification of continuously cast steels which results in enhancing the surface qualitics remarkably.

Simulation of material behaviour under dynamic loading

Experiments and FE-simulations are carried out in order to characterise the mechanical behaviour of metals at high strain rates between 10 3 s −1 and 10 4 s −1. The non-uniformity of strain distribution is studied for the cases of tensile impact and forging. The behaviour of fibre-reinforced metals is investigated under impact compressive loading regarding the buckling of the slim fibres within the softer matrix. Failure criteria are deduced considering the interaction between mechanical waves and internal inclusions or external notches.

Internal inclusions in brown eggs: relationships with fearfulness and stress

Tonic immobility reaction and heterophil: lymphocyte ratio (indices of fearfulness and stress, respectively) were studied in hens laying eggs with or without internal inclusions (blood and meat spots). Two brown egg Spanish breed of chickens were used. There were no significant differences between groups in terms of tonic immobility duration. Birds of the group with internal inclusions appeared to be less fearful when defined by the number of inductions to achieve tonic immobility (1.4+/-0.1 vs 1.1+/-0.1; P < 0.01). Tonic immobility duration was significantly shorter in the group of hens with internal inclusions, when only those laying the abnormal egg the day before measurement of tonic immobility were included in this group (264+/-33 vs 395+/-30 s; P < 0.01). There was a significant difference in the heterophil:lymphocyte ratio between the two groups of hens (P < 0.01), mean value being significantly higher in the group with internal inclusions (0.43+/-0.02) than in the control group (0.33+/-0.02). Hens that laid eggs with internal inclusions had significant heterophilia (P < 0.01). Differences were consistent across the breeds. The incidence of internal inclusions was significantly greater (P < 0.001) in eggs with pink shells (an abnormality associated with the effect of stress). The results suggest that the laying of eggs with internal inclusions involves changes in fearfulness and stressfulness of hens.

Analysis of diamond crystal growth stability from graphite through a film of the metal solvent

During the growth of a diamond crystals from graphite through a thin film of metal-solvent a loss of growth stability and smooth edges is observed, when the crystal reach a certain size. This process is characterized by the formation of internal inclusions in a body of growing crystal, and diverse growth defects on a surface. For the analysis of the described process, a model of crystallization based on a cellular automata was used. The model took into account the kinetic phenomena of dissolution and crystallization of carbon on the surface graphite-metal and metal-diamond solubility difference between of graphite and diamond in liquid metal, and the process of a diffusion of carbon through the metal film. Simulation has shown that instability of crystal growth with smooth edges increases, owing to the origin of the feedback between the form of a crystal surface and the form of a dissolving graphite surface. This feedback amplifies in accordance with magnification of the size of a diamond crystal, owing to magnification of volume of the metal-solvent film. On the base of simulation analysis, conditions of large, perfect diamond crystal growth by recrystallization from graphite through a film of metal solvent were defined.

Scattering of Light by Composite Particles in a Planetary Surface

It has been proposed that composite particles containing internal scatterers may provide the explanation for the fact that most photometric studies of planetary surfaces based on Hapke's model of bidirectional reflectance have found the planetary particles to exhibit moderately backscattering phase functions. However, an implicit assumption made in this explanation is that the scattering by composite particles containing multiple internal inclusions in a planetary surface can still be adequately computed using standard radiative transfer theory assuming the composite particles to be the fundamental individual scatterers even though such particles are necessarily in close proximity to each other. In this paper, this assumption is explored by examining the effects of close packing on the light scattering by spherical particles containing isotropic internal scatterers using a Monte Carlo routine. As expected, classical radiative transfer (assuming a random distribution of scattering particles) coupled with the assumption that the composite particle is the fundamental scatterer provides a good approximation in the high porosity limit. However, even for porosities as high as 90% the effects of close packing are clearly seen with the radiative transfer calculation underestimating the scattering by ∼10% at high incidence, emission, and phase angles. As the porosity is lowered further, the discrepancy becomes more severe and can reach 50% or more. In contrast, assuming the individual scatterer properties in the radiative transfer calculation leads to a substantial overestimate of the scattering even for porosities as low as 27.5%. This suggests that parameters derived using the classical radiative transfer theory will yield results intermediate between those of the composite as a whole and those of the internal scatterers. Thus, one should exercise caution in interpreting the results of models based on classical radiative transfer theory in terms of the physical properties of the surface particles and, where possible, the bidirectional reflectance of densely packed composite particles should be computed using more accurate methods such as the stochastic radiative transfer theory.

FTIR Studies of Annealing Processes in Low Temperature Pure and Mixed Amorphous Ice Samples

Thin ice films produced by vapor deposition upon a bare CsI window as well as upon predeposited rare-gas layers or by co-deposition with rare gases may bear similarities to ices in the stratosphere and interstellar space. It was found that infrared band peak positions, bandwidths, and integrated intensities, especially those of the coupled and decoupled OH stretching mode bands, are very sensitive to structural modifications in the solid ice layers. Abrupt changes in the temperature-dependent curves of these parameters signify processes such as annealing, morphological changes, phase transitions, release of internal gas inclusions and of externally adsorbed gases, and ice grain ejection. It was shown that (H2O)as annealing is a gradual process taking place even at very low temperatures. Spectroscopic similarities exist between the bulk porous ice formed by rare gas release and supercooled water solid and both differ significantly in their infrared spectra from the usual vapor-deposited amorphous ices.