Effect of Underload Cycles on Oxide-Induced Crack Closure Development in Cr-Mo Low-Alloy Steel

Underload cycles with small load amplitudes below the fatigue crack growth threshold are dominantly considered as insignificant cycles without any influence on fatigue lifespan of engineering structural components. However, this paper shows that in some cases these underload cycles can retard the consequent crack propagation quite significantly. This phenomenon is a consequence of oxide-induced crack closure development during cyclic loading below the threshold. The experimentally described effect of fatigue crack growth retardation was supported by measurement of the width and the thickness of the oxide debris layer using the EDS technique and localized FIB cuts, respectively. Both the retardation effect and the amount of oxide debris were larger for higher number and larger amplitudes of the applied underload cycles. Crack closure measurement revealed a gradual increase of the closure level during underload cycling. Specimens tested in low air humidity, as well as specimens left with the crack open for the same time as that needed for application of the underload cycles, revealed no retardation effect. The results can improve our understanding of environmental effects on fatigue crack propagation and understanding the differences between the results of laboratory testing and the fatigue lives of components in service.

Low-Cycle-Fatigue Crack Closure Effect of Ship Cracked Plate Considering the Accumulative Plastic Damage

In this paper, the relationship between crack closure level and the crack length is studied with experiment and numerical simulation under different low cycle fatigue (LCF) loads. The evolution mechanism of crack closure behavior is explored through the variations of the accumulative plastic strain and compressive stress near the crack-tip. The compressive residual stress is separated into two parts for comparative analysis, namely: the stress field ahead of the crack tip and the stress field of the wake region. The magnitude of the compressive stress field is obtained by the integration along the crack propagation direction of the normal stress. The results show that there is an excellent correlation between LCF crack closure level and the magnitude of the compressive stress in the plastic wake, which provides a new way to further study the complex mechanism of crack closure under LCF loads.

EFFECTS OF INLET CLOSURE LEVEL ON VIBRATION CHARACTERISTICS OF A MODIFIED CENTRIFUGAL FAN

Inlet is one of the key parameters that plays an important role in a centrifugal fan. The change of parameters in an inlet can cause static and dynamic pressures in the fan housing. As a consequence, high turbulence can produce vibration. The aim of this research is to study the inlet closure level effects on the vibration characteristics of a modified centrifugal fan. The Inlet closure levels consist of 0; 25; 50; 75; 85; 100% that were tested to examine the vibration characteristic value (x, m, k, Ck, C). The test used a randomized complete design with full factorial experiment. Data analysis employed variance and regression analysis. The results show that the inlet closure effect is significant to the value of the vibration characteristics. The increase of the inlet closure level can cause the quadratic decrease of the values of the vibration characteristics. In addition, the increase of the inlet closure level had no impact on the applied resonance frequency levels. These experimental results obtained the highest values of the vibration characteristic at the inlet closure level of 25%.

Skull morphometry and vault sutures of Myrmecophaga tridactyla and Tamandua tetradactyla

ABSTRACT This study aimed to examine the relationship between skull size and the level of cranial vault suture closure. A total of 50 Myrmecophaga tridactyla Linnaeus, 1758 and 178 Tamandua tetradactyla Linnaeus, 1758 skulls were analyzed in relation to 18 skull dimensions. The skulls were grouped into three levels of suture closure: no sutures closed (level 0), one or all the fallowing sutures closed: interfrontalis, sagitalis and coronalis (level 1) and all sutures closed (level 2). The results indicated that among the 18 variables measured, 17 showed significant differences (p ≤ 0.01) between level 0 and level 1 skulls of T. tetradactyla; as well as between level 0 and level 1, and level 0 and level 2 skulls of M. tridactyla. M. tridactyla level 1 and level 2 had no significant difference among any of the 18 dimensions. The foramen magnum height in both species showed no significant difference (p > 0.05) among any suture categories. In principle, suture closure level and cranial dimensions are related. The specimens with larger cranial dimensions showed greater number of cranial vault sutures closed for both species of anteaters. Tamandua tetradactyla and M. tridactyla specimens with none of the cranial vault suture closed have a foramen magnum height similar to those with cranial vault suture closed.

Coordination of Velopharyngeal Muscle Activity during Positioning of the Soft Palate

The relative contributions of the levator veli palatini, palatoglossus, and palatopharyngeus muscles were assessed relative to a range of positions of the velopharynx during production of the vowels [a] and [I] by four normal adult speakers. The results indicate that velopharyngeal positioning is determined by the relative contributions of the levator veli palatini, palatoglossus, and palatopharyngeus muscles. There was an increase In coefficients of determination (i.e., amount of closure level variability explained) when activity levels of all three muscles are included in the statistical model compared to activity in any one muscle analyzed independently. Both consistent and inconsistent relations among activity levels in the three velopharyngeal muscles studied were observed across speaker and vowel produced.

Risk Assessment Methods for Establishing Clean Closure Levels

Establishment of clean closure concentrations for low levels of hazardous constituents in soils, ground water, and other environmental media by assessing risks to human health and the environment is a tool that is being used with increasing frequency. The four-step process sanctioned by the U.S. Environmental Protection Agency (EPA) includes: 1) hazard identification, 2) exposure assessment, 3) toxicity assessment, and 4) risk characterization. This paper describes the methodology and applies it to the closure of a hazardous waste surface impoundment in Florida. To date, the closure process has taken nearly five years and, pending the EPA's and Florida Department of Environmental Regulation's (FDER's) final approval, will result in clean closure of a small facility that has spent in excess of $450,000 U.S. during this period for removal of 516 cubic metres of sludge and other solids. If clean closure is approved, as is concluded to be protective of human health herein, the facility owner stands to save $275,000 U.S. that is estimated would be required to monitor ground water and to maintain an impermeable cap for the 30-year post closure period currently required under U.S. and Florida regulations. The risk assessment discussed in this paper began when soil samples collected after excavation of 516 cubic metres of sludges, soils, and other solids showed that the preliminary soil closure levels sanctioned by the FDER for chromium and nickel had not been achieved. Continued excavation would have cost a minimum of $50,000 to $100,000 U.S. (in 1988 dollars) and still may not have reached closure levels for these two metals. It is concluded in this paper that the maximum levels of chromium and nickel remaining onsite after remedial excavation (2.1 and 3.7 mg/kg, respectively) do not pose a risk to human health, and that the agency could raise the allowable closure level for these two metals from the current values of 1.1 and 0.70 mg/kg to these maximum values.

Analysis of Turbulent Gas-Solid Suspension Flow in a Pipe

The mixing length theory is extended to close the relevant momentum equations for two-phase turbulent flow at a first-order closure level. It is assumed that the mass fraction of the particles is on the order of unity, that the particle size is so small that the particles are fully suspended in the primary fluid, and that the relaxation time scale of the particles is sufficiently small compared with the time scale of the energy containing eddies so that the suspended particles are fully responsive to the fluctuating turbulent field. Bulk motion of the particles is treated as a secondary fluid flow with its own virtual viscosity. The proposed closure is applied to a fully developed gas-solid pipe flow in which the particles are assumed to be uniformly distributed across the pipe section. Predicted velocity profiles and the friction factors are in good agreement with available experimental data.