Fatigue characteristics of continuous welded rails and the effect of residual stress on fatigue-ratchetting interaction

ABSTRACT

The importance of ratchetting-fatigue interaction is garnering interest due to complex failure mechanism of rail welds under cyclic loading. The objective of this paper is to investigate the fatigue characteristics of continuous welded rails (CWRs) and the effect of residual stress on fatigue-ratchetting interaction. For this purpose, UIC60 rails have been modeled using a three-dimensional finite element model, including a combination of nonlinear kinematic and isotropic hardening. In addition, the interaction between cyclic loading and the effect of residual stress on fatigue is taken into consideration. Finite element model is validated against representative experimental findings. Smith–Watson–Topper (SWT) method is utilized in order to estimate the fatigue life of rail welds under static and cyclic loading. Lower fatigue life is predicted with increasing load due to the contact between rails and wheels. Simulation results also show that failure in the form of ratchetting occurs during the 10,236th cycle, while failure corresponds to the 15,290th cycle and the 145,161st cycle based on the SWT and Coffin-Manson fatigue models, respectively. These findings suggest that investigations on ratchetting and fatigue should be carried out simultaneously to estimate the failure of the CWRs.     

User behavior modeling of voice communications: an empirical study

In this study, analysis and modeling of arrival and service processes are presented in a comprehensive fashion in order to determine statistical properties of voice traffic from end‐user perspective in accordance with the queueing theory. For the first time in the literature, we introduce a user centric approach and examine these services considering both flow directions of voice traffic, the uplink and the downlink as opposed to existing studies with the network centric approach. In our study, we use experimental data composed of actual phone calls collected from 2G/3G networks. To achieve this, we designed and implemented a data collection system for mobile users and compared the results by using data from an operational cellular network. In order to determine the time correlation of voice calls, Hurst parameter estimation methods are used. On the basis of the outcomes, independency of call arrivals is shown. Additionally, it is shown that calls acquired from user and network centric approaches are both Poisson distributed. Next, looking at the problem from service process perspective, thorough analyses are performed to determine mathematical models that can best characterize call holding times. Maximum likelihood estimation and expectation maximization algorithm are used, and it is shown that the optimum mathematical model for the characterization of call holding times is the lognormal distribution family. Copyright © 2014 John Wiley & Sons, Ltd.     

Aqueous-Based Cellulose Acetate Butyrate Dispersion: Screening of Process and Formulation Variables to Obtain Verapamil HCl-Controlled Release Beads

The objectives of the present investigation were to evaluate the possibility of using a custom-designed cellulose acetate butyrate (CAB) pseudolatex dispersion on Verapamil HCl-loaded beads for sustained release of the drug. Excipient compatibility was studied by thermal analysis, X-ray diffraction, and content analysis. Inert beads (Nupareil) were loaded with verapamil HCl and subsequently coated with CAB pseudolatex dispersion. Process and formulation factors were screened by Plackett-Burman screening design in order to identify the most important factors affecting the amount of verapamil HCl released in 12 hours. X-ray diffraction pattern and content analysis showed no degradation of verapamil HCl and suggested absence of any interaction. However, thermal analysis indicated an interaction between verapamil HCl and excipient. A polynomial equation was developed to show the relationship between dependent and independent variables. The mathematical model fitted the data and explained 98.05 % of variability in the response. The difference between observed and predicated values of any given run did not exceed 6 % of maximum cumulative release at 12 hours. Plackett-Burman screening design identified coating weight gain, duration of curing, and amount of plasticizer as the most important factors determining cumulative percent released in 12 hours. Amount of Polydextrose/HPMC (Opadry II), spray rate, fluid bed coater outlet temperature, and atomizing pressure had no statistically significant (p < 0.05) influence on the response.     

Hydropower Plant Site Assessment by Integrated Hydrological Modeling,Gene Expression Programming and Visual Basic Programming

Water Resources Management - The integrated hydrological modeling techniques were used to create a conceptual rainfall-runoff model for Hurman River watershed. The HEC-HMS and water modeling system...     

Determining the effect of trace elements on biohydrogen production from fruit and vegetable wastes

Trace elements are one of the important parameters for dark fermentative H₂ production because they work as co-factors in H₂ formation biochemistry. Lack or excess of trace element and its concentrations could be an important reason for the low yield of H₂ production. In this study, the effects of 11 different trace elements (Fe, Ni, Zn, Co, Cu, Mn, Al, B, Se, Mo and W) were tested at two levels in terms of biohydrogen production from Fruit and Vegetable Wastes (FVW) with Biochemical Hydrogen Potential (BHP) Tests using Plackett-Burman statistical design. 1.1–2.8 times enhancement of biohydrogen production was determined with its addition. The most effective trace elements were found as Zn and Ni. In order to reveal the resident microbial flora, Denaturing Gradient Gel Electrophoresis (DGGE) analysis was carried out on all BHP effluent samples. Results of DGGE analysis, four microbial sequences evaluated as Clostridium sp., Clostridium baratii, Uncultured bacterium, Uncultured Streptococcus sp., and their similarity rates were 99%, 100%, 89%, 98%, respectively.     

Influence of starters on chemical, biochemical, and sensory changes in Turkish White-brined cheese during ripening

Turkish White-brined cheese was manufactured using Lactococcus strains (Lactococcus lactis ssp. lactis NCDO763 plus L. lactis ssp. cremoris SK11 and L. lactis ssp. lactis UC317 plus L. lactis ssp. cremoris HP) or without a starter culture, and ripened for 90 d. It was found that the use of starters significantly influenced the physical, chemical, biochemical, and sensory properties of the cheeses. Chemical composition, pH, and sensory properties of cheeses made with starter were not affected by the different starter bacteria. The levels of soluble nitrogen fractions and urea-PAGE of the pH 4.6-insoluble fractions were found to be significantly different at various stages of ripening. Urea-PAGE patterns of the pH 4.6-insoluble fractions of the cheeses showed that considerable degradation of α_s1-casein occurred and that β-casein was more resistant to hydrolysis. The use of a starter culture significantly influenced the levels of 12% trichloroacetic acid-soluble nitrogen, 5% phosphotungstic acid-soluble nitrogen, free amino acids, total free fatty acids, and the peptide profiles (reverse phase-HPLC) of 70% (vol/vol) ethanol-soluble and insoluble fractions of the pH 4.6-soluble fraction of the cheeses. The levels of peptides in the cheeses increased during the ripening period. Principal component and hierarchical cluster analyses of electrophoretic and chromatographic results indicated that the cheeses were significantly different in terms of their peptide profiles and they were grouped based on the use and type of starter and stage of ripening. Levels of free amino acid in the cheeses differed; Leu, Glu, Phe, Lys, and Val were the most abundant amino acids. Nitrogen fractions, total free amino acids, total free fatty acids, and the levels of peptides resolved by reverse phase-HPLC increased during ripening. No significant differences were found between the sensory properties of cheeses made using a starter, but the cheese made without starter received lower scores than the cheeses made using a starter. It was found that the cheese made with strains NCDO763 plus SK11 had the best quality during ripening. It was concluded that the use of different starter bacteria caused significant differences in the quality of the cheese, and that each starter culture contributed to proteolysis to a different degree.     

A mixed mode fracture specimen for mode II dominant deformation

Several theories have been proposed for the failure of metals, as well as for the angle of crack propagation in mixed mode loading. In order to demonstrate the validity of these theories, the majority of tests have been carried out with an oblique crack placed in a uniaxial stress field. Better testing conditions may be achieved by placing a crack in a uniform bidimensional stress field. A specimen which was recently developed for $\text{K}{}_{\mathrm{IIC}}$ measurement may be readily adapted to achieve a bidimensional stress field and be used for mixed mode testing for the case in which shear deformation is dominant. The main aims of this study are to examine both the cracked and uncracked specimen by means of photoelasticity and finite elements in order to analyze the capabilities and limitations of this specimen for mixed mode testing. It will be demonstrated that there exists a nearly uniform biaxial field in the uncracked specimen. Moreover, calibration formulas will be presented for $\text{K}{}_{\mathrm{I}}$ and $\text{K}{}_{\mathrm{II}}$.     

The radiative transfer solution of a rectangular enclosure using angular domain discrete wavelets

The wavelet expansion is used in order to evaluate the angular dependence of the radiative intensity in the solution of the radiative transfer equation. The radiative intensity is expanded in terms of orthogonal Daubechies’ wavelet basis in the angular domain. The method is applied to a two-dimensional rectangular enclosure with an absorbing, emitting and nonscattering medium in radiative equilibrium. One of the boundary surfaces is maintained at constant temperature T₁, while others are kept cold. This boundary conditions are chosen to demonstrate the effectiveness of the method in dealing with the geometries which are sensitive to ray effects. Centerline emissive power and surface heat flux distributions are compared well with the results given by the standard discrete ordinates method, the modified discrete ordinates method and also with the available exact solutions.