Mechanical properties and thermal stability of tungsten boride films deposited by radio frequency magnetron sputtering

Tungsten and boron compounds belong to the group of superhard materials since their hardness could exceed 40?GPa. In this study, the properties of the tungsten boride WB_x coatings deposited by radio frequency magnetron sputtering were investigated. The sputtering was performed from specially prepared targets that were composed of boron and tungsten mixed in a molar ratio of 2.5 and sintered in Spark Plasma Sintering (SPS) process. WB films were deposited on silicon (100) and stainless steel 304 substrates at temperatures of 23 ÷ 770?°C. Microstructure, chemical and phase composition were investigated by using Scanning Electron Microscope (SEM), X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD), respectively. The mechanical properties like Vickers hardness and Young's modulus were obtained by using nanoindentation test at a load of 5 ÷ 100 mN. The friction coefficient and wear resistance of αWB coatings were investigated in scratch test and reciprocal sliding wear instrumentation. Moreover, in order to investigate thermal properties, the αWB films were annealed at 1000?°C in argon/air for 1?h and at 250?°C for 2?h in air atmosphere. Results of our research confirm that αWB coatings can be considered as an alternative to superhard materials in the production of wear resistant, long-lasting tools.     

Transition between free-space Helmholtz equation solutions with plane sources and parabolic wave equation solutions

The slowly varying envelope approximation is applied to the radiation problems of the Helmholtz equation with a planar single-layer and dipolar sources. The analyses of such problems provide procedures to recover solutions of the Helmholtz equation based on the evaluation of solutions of the parabolic wave equation at a given plane. Furthermore, the conditions that must be fulfilled to apply each procedure are also discussed. The relations to previous work are given as well.     

The effects of power characteristics on the heat transfer process in various types of motionless mixing devices

The main objective of this paper is to present the measurement results of the pressure drop and the heat transfer coefficient in the various types of static mixers. The experimental investigations are provided for the explanation of the influence of hydrodynamic conditions on the heat transfer enhancement for different static mixers. Based on the analysis of the experimental database and theoretical considerations, original formulas are proposed for the determination of the power consumption and the heat transfer in various types of motionless mixing devices. In this paper a new criterion is also defined which takes into consideration both the heat transfer process and hydrodynamic conditions. This criterion may be successfully applied to the selection of a static mixer for the heat transfer problems.     

Mechanical Behavior of a Continuous-SiC-Fiber-Reinforced RBSN-Matrix Composite

The results of a detailed study are presented on the toughening of reaction-bonded silicon nitride reinforced with large-diameter SiC monofilaments at ambient and elevated temperatures. Composite stiffness, strength, toughness, and R -curve behavior were investigated at ambient temperature, with strengths measured up to 1400°C. At elevated temperature, toughening mechanisms were explored by investigating crack initiation and growth under creep conditions. The results show that, at ambient temperature, the composite exhibited noncatastrophic failure with substantial toughening associated with contributions of both fiber pullout and elastic bridging of fibers in the crack wake, consistent with predictions using available models. Limited R -curve measurements suggest that large-scale bridging effects may be present. At elevated temperature, crack initiation occurred in the matrix at about 1000°C, but in the fiber at higher temperatures. Growth of cracks is governed by time-dependent bridging of unbroken fibers in the crack wake, consistent with a model based on fiber pullout by viscous sliding of fibers out of the matrix along amorphous interfacial layers.     

Creep crack growth in fiber reinforced composites with rate-dependent bridging - Role of a viscous fiber matrix interface

A model is developed for creep crack growth in continuous fiber reinforced composites wherein a growing matrix crack is subjected to rate-dependent bridging by unbroken fibers. The rate-dependence in this model arises as a result of the presence of a viscous fiber/matrix interfacial layer. Under load this layer undergoes shear flow causing time-dependent pull-out of bridging fibers from the crack surfaces. The mechanics of time-dependent bridging is combined with a failure criterion based on secondary failure in a crack-tip creep process zone. The dependence of the matrix creep crack growth rates on flaw size and crack wake parameters as well as on composite microstructure is derived. It is shown that the crack wake plays a predominant role in influencing not only the magnitude of creep crack growth rates but also the relationship of growth rates to the crack sizes. A closed form expression is derived for the dependence of crack growth rates on loading, creep and bridging parameters in the regime wherein crack growth rates are independent of crack size.     

A recursive method for the investigation of the linear separability of two sets

A recursive method for finding a hyperplane separating two given finite sets X₁ and X₂ in Euclidean space Eⁿ is presented. It is unknown a priori if these two sets are linearly separable. According to the proposed method, a certain sequence (a_{i)i = 1^m} of nonzero vectors in E^{n + 1} is generated, where m denotes the number of elements in the set X = X₁ ∪ X₂. If the sets X₁ and X₂ are linearly separable, then each of the members a_i determines a hyperplane H_i ? Eⁿ separating the subsets X_jⁱ = X?X_j:X?X_{qq = 1}ⁱ, j = 1, 2, of the set X = x_{ii = 1}^m, where (X_i)_{i = 1}^m denotes a sequence obtained by arbitrary ordering of X. Thus, to get the information as to whether the considered sets are linearly separable, it is sufficient to check if each of the hyperplanes H_i separates the sets X₁ⁱ and X₂ⁱ. If this is the case, then H_m separates X₁ and X₂. In the opposite case, the procedure of generation of the sequence (a_i)_{i = 1}^m is stopped when any hyperplane H_i does not separate the sets X₁ⁱ and X₂ⁱ. Index i of the recently generated vector a_i informs us as to how far the realization of the method is advanced.     

STM induced modification of gold surface in the presence of TMP amine

In this paper we present scanning tunneling microscopy (STM) investigations of gold with 2,2,6,6-Tetramethylpiperidine (TMP) overlayer. During the STM experiments the creation of holes and hills or no changes of the surface were observed depending on the applied bias voltage and polarity. No modifications were observed in the bias range from −0.5 to +0.5 V. The holes were created for the bias voltages greater than +0.5 V and hills for the bias voltages lower than −0.5 V. The observed changes of the surface morphology suggest the presence of electrochemical reaction between the tip and the surface. Additionally, our results suggest that TMP lowers the electrochemical activation energy of gold to +0.5 eV.     

Knowledge verification for fuzzy expert systems

Abstract

The introduction and use of fuzzy logic has strengthened knowledge representation and reasoning capability in expert systems; nevertheless, it also increases the complexity and difficulty of knowledge verification, which is known to be an important issue for building reliable and high performance expert systems. In the past decade, knowledge verification problems, e.g., redundancy, conflict, circularity and incompleteness of knowledge, have been widely discussed from the viewpoint of using binary logic; nevertheless, the issue of verifying fuzzy knowledge is seldom discussed. In this paper, we attempt to detect potential structural errors among fuzzy rules by proposing a fuzzy verification algorithm. Moreover, a system for verifying fuzzy knowledge base has been developed based on the novel approach.     

Surface probing simulator for the evaluation of CMM probe radius correction software

Scanning coordinate metrology is largely based on recording the position of a spherical tip which is maintained in contact with the surface to be measured. The coordinate measuring machine (CMM) software converts these tip coordinates into coordinates of points on the measured surface, a process called probe radius correction. In order to investigate the probe radius correction accuracy of specific CMM software in scanning measurements, a surface probing simulator is developed. It calculates the coordinates of probe tip center points (virtual indicated measured points) as raw measurement data by numerically probing a known virtual surface. An iterative solution based on geometric criteria is used to achieve the necessary tangential contact conditions. Various sculptured surface profiles, probe radii, and scanning increments can then be simulated. These raw data are then fed to the CMM software where the probe radius correction is performed. The CMM results are then compared with the known surface to evaluate the probe radius correction accuracy of the CMM built-in algorithm. The simulator allows a rapid CMM software capability check for a variety of situations and may pinpoint shortfalls that may be avoided through alternative measurement procedures. It may also be used to motivate the development of new probe radius correction techniques and assist in their evaluation. Tests were conducted on a Zeiss and a Mitutoyo CMM to demonstrate the usefulness of the simulator.     

Impact of enzyme on quality of blackcurrant and plum juices

The aim of work was optimization of technology of cloudy blackcurrant and plum juices production. The major concern was the increase of product cloudiness and its stability. Red fruit were processed with commercial pectinolytic preparations (Pectinex BE Colour, Pectinex BE XXL, and mixture of Rohapect PTE with Rohament PL). The effect of enzyme dose, maceration time and addition of ascorbic acid (in case of plum) on juices quality was investigated. Using single enzyme, either polygalacturonase or pectin lyase did not allow obtaining juices with high enough turbidity, however appropriate enzyme mixture allowed to obtain cloudy juice with the turbidity of at least 230 NTU for blackcurrant and above 500 NTU for plum juice. The best pressing-yield for blackcurrant was achieved with polygalacturonase and pectin lyase, 65 g/100 g after 1 h and 74 g/100 g after 4 h of pectinolysis. The macerating mixture gave about 58÷59 g/100 g yield, irrespectively of enzymation time. Pressing-yield of plum juices was in the range of 94÷97 g/100 g due to the fact that practically only skins were retained on pressing cloth. Addition of ascorbic acid (AA) during plum juice processing in quantity of 500 mg/kg had protective effect on anthocyanins. In control plum juices range of anthocyanins contents were 12.1÷16.5 mg/100 ml while in juice with AA addition even 21.4÷24.5 mg/100 ml.