Fracture behaviour and cleavage initiation in hypoeutectoid pearlitic steel

The paper reports on an investigation of the micromechanism of cleavage fracture in hypoeutectoid pearlitic R7T steel, commonly used for producing railway wheels. The steel possesses extensive Lüders deformation, which somewhat complicates finite element (FE) modelling and analyses of fracture behaviour. Standard Charpy V-notch specimens were used in order to analyse the fracture behaviour at quasistatic and impact loading. Finite element 3D calculations were performed and the elastic-plastic behaviour of notched bars up to the fracture was simulated. Detailed fractographic analysis was carried out on a number of Charpy V-notch specimens in order to investigate the origin site of cleavage fracture initiation and its distance from the notch root. The suitability of the three-criterion micromechanical model (Chen et al. Acta Materialia 51:1841–1855, 2003) for cleavage initiation was verified. The R7T steel under investigation exhibited a cleavage fracture stress of 1,837 MPa. Its independence on temperature evidenced the micromechanism of cleavage fracture to be microcrack propagation-controlled. For the investigated blunt-notched bend bars, an active volume exists ahead of the notch root in which pearlite colony-associated initiation sites are located. The cleavage fracture initiation of the steel is thus governed by the sites lying in the active volume. The active volume is determined by the values of three parameters. A plastic strain lying in interval from to (for the steel investigated from 0.033 to 0.108) is necessary to create a cleavage crack nucleus at any location within the active volume depending on the local pearlite properties. A stress triaxiality parameter ranging from h _min to h _max (from 0.93 to 1.39) is supposed to prevent the blunting process at the site of the cleavage nucleus. Once the main principal stress σ ₁ exceeds the local cleavage fracture stress σ _CFmin, an unstable global cleavage fracture occurs in a blunt-notched bar.     

Modified aluminosilicates as low-cost sorbents of As(III) from anoxic groundwater

The utilization of low-grade clay materials as selective sorbents represents one of the most effective possibilities of As removal from contaminated water reservoirs. The simple pre-treatment of these materials with Fe (Al, Mn) salts can significantly improve their sorption affinity to As oxyanions. The natural kaolin calcined at 550 degrees C (mostly metakaolin) and raw bentonite (mostly montmorillonite) pre-treated with Fe(II), Fe(III), Al(III) and Mn(II) salts were used to remove of As from the model anoxic groundwater with As(III) concentration about 0.5 and 10 mg L(-1). All the pre-treating methods were appropriate for bentonite; the efficiency of As(III) sorption varied from 92 to >99%, by the sorption capacity higher than 4.5 mg g(-1). In the case of metakaolin, Fe(II)- and Mn(II)-treatments proved the high sorption efficiency (>97%), while only <50% of As was removed after Fe(III) and Al(III) pre-treatment. The sorption capacities of treated metakaolin ranged from 0.1 to 2.0 mg g(-1).     

New Aspects of Impact Reactivity of Polynitro Compounds,Part III. Impact Sensitivity as a Function of the Imtermolecular Interactions

Published data of impact sensitivity of 33 polynitro compounds detected by sound were expressed as the drop energy, E_dr, required for 50 percent initiation probability. A logarithmic relationship has been found between the E_dr values and heats of fusion of the said compounds. The relationship has been found to be in accordance with the idea concerning the role of plastic deformations of crystal played in the initiation of energetic materials by impact and shock. An analogous application of heats of sublimation has not given convincing results.     

Role of crystallographic texture on the improvement of hydrogen-induced crack resistance in API 5L X70 pipeline steel

The purpose of this work was to improve the resistance of hydrogen-induced cracking in API 5L X70 steel by engineering the crystallographic texture and grain boundary distributions via different rolling temperatures. Hydrogen-induced cracking and electrochemical hydrogen charging tests were carried out in two different conditions: commercially produced and isothermally rolled at 850 °C in laboratory. The results showed that the development of dominant {011} grains parallel to the normal direction, and a small number of {001}//ND grains obtained by isothermal rolling at 850 °C, increased the hydrogen-induced crack resistance; while the hot rolled sample with sharp {001}//ND textures was highly susceptible to cracking.     

miR-497-5p Decreased Expression Associated with High-Risk Endometrial Cancer

The current guidelines for diagnosis, prognosis, and treatment of endometrial cancer (EC), based on clinicopathological factors, are insufficient for numerous reasons; therefore, we investigated the relevance of miRNA expression profiles for the discrimination of different EC subtypes. Among the miRNAs previously predicted to allow distinguishing of endometrioid ECs (EECs) according to different grades (G) and from serous subtypes (SECs), we verified the utility of miR-497-5p. In ECs, we observed downregulated miR-497-5p levels that were significantly decreased in SECs, clear cell carcinomas (CCCs), and carcinosarcomas (CaSas) compared to EECs, thereby distinguishing EEC from SEC and rare EC subtypes. Significantly reduced miR-497-5p expression was found in high-grade ECs (EEC G3, SEC, CaSa, and CCC) compared to low-grade carcinomas (EEC G1 and mucinous carcinoma) and ECs classified as being in advanced FIGO (International Federation of Gynecology and Obstetrics) stages, that is, with loco-regional and distant spread compared to cancers located only in the uterus. Based on immunohistochemical features, lower miR-497-5p levels were observed in hormone-receptor-negative, p53-positive, and highly Ki-67-expressing ECs. Using a machine learning method, we showed that consideration of miR-497-5p expression, in addition to the traditional clinical and histopathologic parameters, slightly improves the prediction accuracy of EC diagnosis. Our results demonstrate that changes in miR-497-5p expression influence endometrial tumorigenesis and its evaluation may contribute to more precise diagnoses.     

Delay in Statistical Control of Systems with Wear

The target of statistical process control is to identify changes in the behavior of controlled process as quickly as possible. Therefore, as a quality measure of control charts, we use characteristics which quantify the delay between the occurrence of change and its identification by the control chart. The average run length is a commonly used characteristic which does not reflect a real situation. A new characteristic is suggested which is computed in the case of progressive wearing out of the system. We assume several types of progression. The Markov chain approach is used for computation of average delay. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparison of the Two-dimensional Fraunhofer and the Two-dimensional Fresnel Approximations in the Analysis of Surface Roughness by Angle Speckle Correlation

Abstract

In this paper we discuss some new theoretical results which we reached in the analysis of a random surface roughness in the framework of the two-dimensional (2D) Fresnel approximation. A comparison with 2D Fraunhofer approximation results is made. It is shown for experimentally reasonable values of the geometrical arrangement parameters of the method that the surface roughness measurement can be interpreted in the 2D Fraunhofer approximation only for surfaces with high slopes of surface irregularities. Surfaces with small slopes of irregularities require interpretation of the surface roughness measurement in the 2D Fresnel approximation. In this case, not only the standard deviation of surface height fluctuations but also the correlation length of the surface can be determined.     

Optical characterisation of SiOxCyHz thin films non-uniform in thickness using spectroscopic ellipsometry, spectroscopic reflectometry and spectroscopic imaging reflectometry

The combined optical method enabling us to perform the complete optical characterisation of weakly absorbing non-uniform thin films is described. This method is based on the combination of standard variable angle spectroscopic ellipsometry, standard spectroscopic reflectometry at near normal incidence and spectroscopic imaging reflectometry applied at normal incidence. The spectral dependences of the optical constants are determined using the non-imaging methods by using the dispersion model based on parametrisation of the density of electronic states. The local thickness distribution is then determined by imaging reflectometry. The method is illustrated by means of the complete optical characterisation of SiO_xC_yH_z thin films.     

IMPEDIMENT TO INCIPIENT FLUIDIZATION IN WET BEDS OF POROUS NONSPHERICAL PARTICLES

Fluidized-bed units are efficiently and advantageously employed for drying various wet and sticky particulate materials provided that the bed of such materials can be kept under a fluidized condition. The effect was explored with the incremental addition of water to the bed of nonspherical, porous particles of ceramsite and lignite fluidized with wet air. The limiting fluidization-defluidization point was determined by experiments in a cold model fluidized bed contained in a transparent glass column using wet and dry particles. On the basis of the data amassed, an empirical correlation was developed. This relationship makes it possible to predict the dimensionless excess gas velocity that keeps the wet bed fluidized, as a function of the relative amount of moisture in the bed and the dimensionless particle size.     

Fabrication of composite microcapsules by drop-on-demand inkjet: Effect of precursor composition on the process limits

The feasibility of using drop-on-demand inkjet technology for the fabrication of calcium alginate hydrogel microcapsules containing dispersed sub-micron solid particles (TiO₂ photocatalyst) was demonstrated. The influence of the printed solution viscosity on the micro-droplet size has been investigated and a study of the effect of solids fraction in the suspension on its printability was carried out. It was found that solutions with viscosities of up to 28 mPa s and solids content of up to 7.8 vol% can be reproducibly printed, resulting in droplets ranging from 45 to 105 μm depending on the inkjet operating conditions. In order to ensure stable and reproducible droplet formation, a pressure difference ranging from −200 to −1800 Pa had to be maintained in the nozzle. A uniform distribution of dispersed solids in the resulting microcapsules was achieved by adjusting pH and viscosity. The relationship between the printhead operating pressure, the fluid viscosity, the solids loading and the final size of the obtained microcapsules was established, allowing rapid prototyping of artificial cell-like structures with internal solid inclusions by the inkjet method.