Slow Growth Region Research Articles

Short fatigue crack growth mechanism in Ni-Co based superalloy at elevated temperatures and in oxidative atmospheres

In this study, to elucidate the oxidation effect on the short fatigue crack growth (SFCG) characteristics of Ni-Co based TMW-4M3 superalloy, fatigue tests were conducted at room/elevated temperature in air/vacuum and three-dimensional microscopic observation of the SFCs using a plasma focused ion beam – scanning electron microscope (PFIB – SEM) system. Fatigue lives tested under vacuum at elevated temperature were comparable to those at room temperature while those tested at elevated temperatures in air showed shorter fatigue life in higher stress regions and longer fatigue life in lower stress regions than the others. In situ observation of SFCs at elevated temperatures in air revealed SFCG deceleration in the small ΔK regions and acceleration in large ΔK regions. SFCs opening/closing behaviours at elevated temperatures measured by digital image correlation (DIC) showed the crack opening stress to be higher at elevated temperature in air, possibly due to oxide-induced crack closure. However, the crack closure effect did not fully explain the difference in FCG rate between room and elevated temperatures in air. Three-dimensional investigations revealed SFCs to form at elevated temperatures in air, showing straight transgranular FCG to be insensitive to microstructure in slow growth regions, and intergranular FCG to precede that in the surrounding material in fast growth regions, in contrast to microstructural SFCs features at room temperature. It appears that slow and straight unique SFCG at elevated temperatures might occur due to intermittent brittle fracture of oxides formed at the crack tip. This suggests a possible role of the oxide layer at the crack tip in broadening the plastic deformation distribution, thus contributing to FCGR deceleration.

Effect of Nonparallel End Face on Energy Dissipation Analyses of Rocklike Materials Based on SHPB Tests

To evaluate the effect of nonparallel end face of rocklike specimens in SHPB tests, the characteristics of energy dissipation are analyzed based on numerical simulations for end‐face nonparallelism from 0% to 0.40% and Young’s modulus from 14 GPa to 42 GPa. With the increment of end‐face nonparallelism, both energy consumption density and dissipated energy density show a slight increase trend, while releasable elastic strain energy density presents a slight decrease trend. Existence of elastic unloading in the damaged rocklike specimen leads to a reduction of energy consumption density and a constant dissipated energy density during total strain shrinkage. At peak dynamic stress, dissipated energy density presents a linear upward trend with the increment of end‐face nonparallelism and Young’s modulus, while releasable elastic strain energy density shows an inverse trend. A binary linear regression equation is deduced to estimate the energy dissipation ratio. Mechanical damage evolution of the rocklike specimen is divided into two regions in line with the two regions in dynamic stress‐strain curves, and the transition between the slow‐growth region and rapid‐growth region is shifted to the right with the increment of end‐face nonparallelism. Due to the presence of nonparallel end face, fluctuation presents in energy density evolution and mechanical damage evolution. The fluctuation is enhanced with the increment of end‐face nonparallelism and weakened with the increase of Young’s modulus. Based on energy density evolution and mechanical damage evolution analyses, the maximum end‐face nonparallelism should be controlled within 0.20%, twice the value in ISRM suggested methods, which reduces the cost and time for processing rocklike specimens.

Coverage and rate analysis in the uplink of millimeter wave cellular networks with fractional power control

In this paper, using the concept of stochastic geometry, we present an analytical framework to evaluate the signal-to-interference-and-noise-ratio (SINR) coverage in the uplink of millimeter wave cellular networks. By using a distance-dependent line-of-sight (LOS) probability function, the location of LOS and non-LOS users are modeled as two independent non-homogeneous Poisson point processes, with each having a different pathloss exponent. The analysis takes account of per-user fractional power control (FPC), which couples the transmission of users based on location-dependent channel inversion. We consider the following scenarios in our analysis: (1) pathloss-based FPC (PL-FPC) which is performed using the measured pathloss and (2) distance-based FPC (D-FPC) which is performed using the measured distance. Using the developed framework, we derive expressions for the area spectral efficiency. Results suggest that in terms of SINR coverage, D-FPC outperforms PL-FPC scheme at high SINR where the future networks are expected to operate. It achieves equal or better area spectral efficiency compared with the PL-FPC scheme. Contrary to the conventional ultra-high frequency cellular networks, in both FPC schemes, the SINR coverage decreases as the cell density becomes greater than a threshold, while the area spectral efficiency experiences a slow growth region.

Coverage, Capacity, and Energy Efficiency Analysis in the Uplink of mmWave Cellular Networks

In this paper, using the concept of stochastic geometry, we present an analytical framework to evaluate the signal-to-interference-and-noise-ratio (SINR) coverage in the uplink of millimeter wave cellular networks. By using a distance-dependent line-of-sight (LOS) probability function, the location of LOS and nonLOS users are modeled as two independent nonhomogeneous Poisson point processes, with each having a different pathloss exponent. The analysis takes account of per-user fractional power control (FPC), which couples the transmission of users based on location-dependent channel inversion. We consider the following scenarios in our analysis:1) pathloss-based FPC (PL-FPC) which is performed using the measured pathloss and 2) distance-based FPC (D-FPC) which is performed using the measured distance. Using the developed framework, we derive expressions for the area spectral efficiency and energy efficiency. Results suggest that in terms of SINR coverage, D-FPC outperforms PL-FPC scheme at high SINR where the future networks are expected to operate. It achieves equal or better area spectral efficiency and energy efficiency compared with the PL-FPC scheme. Contrary to the conventional ultra-high frequency cellular networks, in both FPC schemes, the SINR coverage decreases as the cell density becomes greater than a threshold, while the area spectral efficiency experiences a slow growth region.

The Rotation of Complex Plasmas in a Stratified Glow Discharge in the Strong Magnetic Field

The dusty plasma was created in a glow discharge in a magnetic field with induction up to 10 000 G. The setup and dc discharge conditions for this unique experiment are described. Dusty plasma exists in the form of volumetric dust structures or dust clusters rotating in the magnetic field. Quantitative results are presented in the form of dependence of an angular velocity of rotation on the magnetic induction. The rotational dynamics of a dusty plasma found experimentally is complex. It has a rotation inversion, a sharp change in the growth rate, and an instability region in which a partial loss of the dust component occurs. In the case where it is possible, the quality interpretation for the obtained dependence is given. The regions of the magnetic field are found in which the ion drag force dominates, the region where the dust structure is entrained by the moving gas of the discharge, and the region of slow growth of the rotation speed, which has not yet been uniquely interpreted.

Reliable and Repeatable Evaluation of Kinetic Hydrate Inhibitors Using a Method Based on Crystal Growth Inhibition

Low dosage hydrate inhibitors (LDHIs)—antiagglomerants (AAs) and kinetic hydrate inhibitors (KHIs)—are increasingly used as an alternative to the traditional thermodynamic hydrate inhibitors for controlling gas hydrate problems in the petroleum industry. As nucleation inhibitors, KHIs induce an extended induction time (ti) at particular subcoolings before nucleation of hydrate can proceed to growth. However, due to the stochastic nature of nucleation, gaining repeatable and transferrable induction time results can be very challenging and time-consuming. To overcome this problem, study on KHI crystal growth inhibition (CGI) has yielded a KHI evaluation technique which is considerably simpler than induction time measurements. Moreover, this study shows that KHIs create a number of well-defined hydrate CGI regions as a function of subcooling which are completely repeatable and transferrable between different setups. These regions range from complete inhibition (CIR), to slow growth region (SGR), and ultimate...

A study of fatigue and fracture response of cantilevered luminaire structures made from aluminum alloy 6063

In the experimental results elegantly and exhaustively elaborated upon in this paper the local stresses, obtained from finite element analysis, was used to develop estimates of the stress intensity factor (SIF). In combination with crack growth data, the fatigue lives of both the through-plate and an integrally stiffened socket connection were estimated using software developed by the U.S. Air Force (and referred to as AFGROW). The fatigue life estimates correlated well with the test results provided the crack growth rate data was obtained under conditions of minimal closure at higher stress ratios (of the order R=0.7). In an attempt to establish the fatigue lives in the high cycle regime, the measured residual stresses had to be included in the analysis. For identical stress ranges, the 25mm thick through-plate socket connection exhibited noticeably lower fatigue lives when compared to the integrally stiffened shoe-base structure. Scanning electron microscopy observations revealed pockets of well-defined striations consistent with stable growth of the crack through the microstructure prior to the onset of unstable crack growth culminating in catastrophic fracture. In the slow growth region, the fracture surface revealed pockets of shallow, well-defined striations that were uniformly spaced indicative of the occurrence of localized microplastic deformation.

Influence of magnetic field on ferrite transformation in a Fe–C–Mn alloy

The kinetics of ferrite transformation in a Fe–0.10mass%C–2.94mass%Mn alloy in a strong magnetic field of 8 T were studied with regard to alloying element-partitioned and partitionless growth. According to the theory of diffusion-controlled growth, the slow Mn diffusion dictates partitioned growth that occurs at a low undercooling, whereas partitionless growth at a larger undercooling is rate-controlled by fast carbon diffusion. The alloy was austenitized and isothermally reacted at temperatures that encompass the two growth modes. The nucleation and growth rates of ferrite increased at all temperatures in the magnetic field, whereas the amount of increase was somewhat greater at lower temperatures. In the region of slow growth, besides its sluggish diffusion Mn possibly destabilizes the ferrite phase due to the influence on the magnetic moment and the Curie temperature of bcc Fe solid solution, and partially offsets the accelerating effect of transformation. The temperature of transition from the slow to the fast growth is predicted to increase, due to the shift in the ferrite/austenite phase boundaries in the presence of magnetic field.

Producing regionalism: regional movements, ecosystems and equity in a fast and slow growth region

Urban development pressures, preservation of environmentally sensitive areas and regional planning are the focus of current debates on regionalism in both fast and slow growth regions. Based on two cases—a campaign to preserve ecological integrity and reduce sprawl on the Oak Ridges Moraine in the Greater Toronto Area and Rochester’s anti-sprawl campaign for regional equity—the paper examines how two anti-sprawl campaigns brought to the fore alternative constructions of regionalism. In the fast growing Toronto region, citizen mobilization and upper tier intervention resulted in a legislative base for regionalism. In the slow growth Rochester region, the city had limited success in gaining regional redistribution. Such divergent outcomes relate to differences in intergovernmental relations, the city’s influence on the region, receptivity of suburbs to smart growth, and the potential for values of nature preservation and justice to mobilize regional coalitions.

Privatizing the fringe: patterns of private streets in a slow growth region

Recent studies of private streets have focussed on urban and suburban areas experiencing rapid growth; however, private road networks are also proliferating in some exurban and rural regions in areas of modest or slow growth. This study examines development on private roads in the commuter-shed of Halifax, Nova Scotia. On the basis of a detailed investigation of private roads conducted in 2006, we document how developers use private streets, describe the design features that result, and consider the socio-spatial implications private streets generate. The analysis reveals different ‘classes’ of private landscapes: from low end rural tracks with mobile homes or cars under repair in front yards, to high-end lakefront homes with expensive cars parked in the driveways. While private streets in the urban context facilitate sustainability goals like intensification and walkability, in the rural and exurban context private streets may reveal a second-class landscape where the affluent have good streets, the poor have potholes, and everyone has to drive everywhere.

THE PARADOX OF SLOW-GROWTH HIGH-INCOME REGIONS

We attempt to provide an economic theory and the empirical evidence to explain why slow-growth regions, like Quebec in Canada, enjoy as high living standards as rapidly growing regions. In the long term quantities not prices adjust (except for the price of land, a resource in fixed supply). Despite variations in regional growth rates, real per capita income adjusted for housing costs converge in all regions. The analysis offers important insights into regional development and has far-reaching implications for federalism.

Anomalous two-stage spherulite growth in poly(aryl ether ketones) during isothermal crystallization

Anomalous two-stage spherulite growth has been observed in poly(aryl ether ketones) during isothermal crystallization. The first stage consists of a conventional growth with Maltesecross pattern at a lower growth rate. The morphology shows a smooth interface, dense structure and negative birefringence. The second stage grows in the form of “aggregate” at a higher rate. The morphology shows an open dendrite structure without preferred optical orientation. The second morphology is also termed the “overgrowth.” The occurrence of overgrowth is favored only near the maximum growth rate region and diminishes in the slow growth region. The transition of the two-stage growth is attributed to the change of growth direction of the constituent lamellae. We have confirmed this by microbeam small-angle light-scattering measurements. The lamellar structures in both growth stages were followed by time-resolved small-angle synchrotron x-ray scattering. It was found that the lamellar structures of the crystals formed at both stages are the same. A possible explanation for the two-stage growth is the interface breakdown caused by large perturbations of local composition and/or stress fields. © 1996 John Wiley & Sons, Inc.

Fracture study of a polyacetal resin

Fracture experiments have been carried out with unnotched and notched tensile specimens of a polyacetal resin at room temperature at various rates of extension. An increase of approximately 13% in yield stress was observed in the unnotched tests with increased deformation rates from 1–1000 mm min−1, whilst strain to failure was reduced from about 85% to approximately 0.05%. In all specimens, failure appeared to have taken place by initiation of a microscopic flaw upon yielding, and this flaw then slowly grew into a critical size when catastrophic fracture set in. In the slow-growth region, the mechanism of failure was by void growth whereby the lamellar texture was transformed into a fibrillar one. However, on the rapid fracture surface, there was evidence of lamellar texture being retained, but with small voids in the stacks of lamellae, In notched fracture specimens containing sharp razor cut, a fracture toughness, Klc, of approximately 5 MPa m1/2 was obtained between crosshead speeds of 0.5 and 50 mm min−1. At speeds of 500 and 1000 mm min−1, the Klc was reduced to 4 MPa m1/2. In the absence of a starter crack, blunt notch fracture toughness of about 6.3 MPa m1/2 was observed at all test speeds. In specimens with a razor cut, the slow-growth region decreased as test speed increased; this can be used to construct an R-curve.

Study of the inhomogeneity and domain structure of polar ATGSP crystals

Abstract ATGSP crystal is a typical polar material. The crystal growth rate, domain structure and some properties in the polar direction (±b, are quite different. The distribution of domain in the crystal has been investigated by decoration method. The parameters such as internal bias field in the different regions of the crystal were measured by hysteresis loop method. It is found that in the fast growth region (along +b axis), the bias field is low, the doping is inhomogeneous and some reverse domains exist in the crystal, while in the slow growth region (along - b, axis), the case is quite the opposite. Taking advantage of these growth characteristics and using directional growth technique, homogeneous doped and single domain crystals have been grown.

Fracture and fatigue in M-50 and 18-4-1 high speed steels

The plane strain fracture toughness values,K Ic , the fatigue crack growth rates and the tensile properties of M-50 and 18-4-1 high speed steels have been measured as a function of tempering temperature. The M-50 was a vacuum arc remelted grade (VIM-VAR) and the 18-4-1 an electroslag grade, and both are used in mainshaft gas turbine bearings. At the usual hardness for bearings, Rockwell C 62, 18-4-1 exhibited a slightly higher fracture toughness (21 MPa·m1/2) than M-50 (18 MPa·m1/2). The fatigue crack growth rates were very similar, and in the slow growth region followed the usual power law,dC/dN=(ΔK) m withm=3 to 4. The crack propagation rates were still significant at values as low as ΔK=5 MPa·m1/2. SEM studies of the fracture surfaces showed complex transgranular fracture paths for both steels. The tensile strengths and the elongations of M-50 were somewhat higher than the corresponding values for 18-4-1 but the yield strengths of the two steels were similar. The microstructures of these steels were markedly different, with M-50 exhibiting 2.6 vol pct undissolved carbides and the 18-4-1 showing 15.2 vol pct carbides, but the fatigue and fracture behaviors were similar.

Growth studies on the lactic streptococci. 3. Observations on continuous growth behaviour in reconstituted skim-milk.

SummaryThe behaviour ofStreptococcus cremorisAM1and AM2, andStreptococcus lactisML8in continuous growth in reconstituted skim-milk medium under controlled conditions of pH has been investigated.At 20°C under aerobic conditions small quantities of oxygen were found to stimulate the growth rate ofStr. lactisML8between pH 5·05 and 5·45. Growth between pH 5·45 and 6·35 became erratic due to the accumulation of hydrogen peroxide. Above pH 6·35 hydrogen peroxide could not be detected in the continuously growing culture and below pH 5·05 the growth rate of the culture was not affected by small quantities of oxygen. An effect of direct oxygen toxicity on growth, distinct from that of hydrogen peroxide accumulation, was observed over the limited pH range investigated. After 48 h growth in the presence of small concentrations of oxygen the effect disappeared.At 30°C under anaerobic conditions a region in the dilution rate curves was observed withStr. cremorisAM1and AM2andStr. lactisML8which suggested the occurrence of a growth-limiting component. This region of slow growth could be correlated with diminished soluble nitrogen values, and was eliminated by enrichment of the medium with soluble nitrogen.An unusual feature of the investigation was the dilution rates, indicative of extremely fast specific growth rates, experienced forStr. lactisML8. It was thought unlikely that wall growth contributed appreciably to the dilution rate as a similar phenomenon was not observed withStr. cremorisAM1or AM2.