The effect of surface plastic hardening technology, residual stresses and boundary conditions on the buckling of a beam

The complex influence of the surface plastic hardening technology, residual stresses, and boundary conditions on the bending of a hardened beam of EP742 alloy was performed. A phenomenological method of restoring the fields of residual stress and plastic deformations performed by its experimental verification in the particular case of ultrasonic hardening is given. The correspondence of the calculated and experimental data for the residual stresses is observed. For assess the influence of the formed residual stresses on convex cylinders, the calculation methods are used for initial strains based on using analogies between the initial (residual) plastic strains and temperature strains in an inhomogeneous temperature field. This allowed us to reduce the consideration of the problem to the problem of thermoelasticity, which was further solved by numerical methods. The effect of four types of boundary conditions for fixing the ends of the beams (rigid fastening and articulation of the ends and ribs in various combinations, cantilever) on the shape and size of the bending of the beam 10×10×100 mm after ultrasonic hardening is studied in detail. It was found that the minimum deflection is observed with a hard seal of both ends of the beam. The effect of the thickness of the beam, which varied from 2 to 10 mm, on their buckling under the same distribution of residual stresses in the hardened layer was studied, and the nonlinear nature of the increase in the deflection boom with decreasing thickness for all types of boundary conditions was established. It is shown that under all boundary conditions, the curvature along the length of the beam practically does not change, therefore it can be considered constant. The consequence of this is the preservation of the hypothesis of flat sections after the hardening procedure, which is confirmed by the calculated profile of the beam section in plane symmetry, close to a straight line. The influence of the anisotropy of surface plastic hardening on the buckling of the beam was found to be significant, which can serve as the basis for choosing the optimal hardening procedure. The performed parametric analysis of the task is presented in the form of graphical and tabular information on the results of the calculations.

Determination of metallization degree of pre-reduced chromite with image and rietveld analysis

Metallization degree of pre-reduced chromite samples was determined using two methods. The chromite samples were reduced in the solid state by the use of methane-hydrogen gas mixtures. First method was image analysis of micrographs obtained by scanning electron microscope where heavier metallic phases appear as bright white areas which are relatively easy to segment using a thresholding algorithm. The second technique was Rietveld analysis of X-ray powder diffraction pattern which fits a calculated profile onto a measured X-ray diffraction pattern to gain information about phase quantities. Rietveld refinement and phase composition analysis was performed with PANalytical?s X?Pert HighScore Plus program from the XRPD (X-ray powder diffraction) data. The results from both techniques were in good agreement. Metallization degrees for the investigated samples ranged from 15 to 65 percent depending on the extent of reduction which was a function of time, reduction temperature and methane content of the gas mixture. These results are promising and show that either image analysis or X-ray Rietveld analysis can be used as a relatively fast method to determine the degree of metallization of pre-reduced samples in comparison to the slow and tedious chemical analysis.

Theoretical Studies for Si and C Emission into SiC Layer during Oxidation

To understand the structure of SiC–oxide interface more in detail, we propose a profiling theory of Si and C emission into SiC layer during oxidation. Simulations of the depth profiles of Si and C interstitials results in the structures analogous with those observed from a spectroscopic ellipsometry. To determine the diffusivities of Si and C interstitials, we performed capacitance–voltage measurements for examining the re-distribution profiles of nitrogen after oxidation and compared between observed and calculated profile. The calculated nitrogen profiles showed good fits to the observed ones in the case of self-diffusivity of C interstitials magnified by several 10 times for literature value. Finally, we discuss the validity of the proposed theory.

An Improved Fourier Eight-Sensor (F8S) Method for Separating Straightness, Yawing and Rolling Errors of a Linear Slide

This paper proposes an improved Fourier eight-sensor (F8S) measurement method for separating the straightness, yawing and rolling motion errors as well as determining the profile of a linear slide. The previous F8S method [1] used the constant parameters C2 and C4 to estimate the profile function f1(θ) in different angle ranges and f2(θ) is also computed with the same fused sensor data. By constant parameters, the profile estimation and error separation are implemented via iterative method which is a time-consuming procedure and can not maintain the acceptable accuracy. Here, the improved F8S method applies the matrix technique instead of the iterative method to estimate the profile functions by three distinct sets of C2 and C4 parameters and different fused sensor data according to the linear slide motion within different angle ranges. Furthermore various errors can be separated through simple equations based on the calculated profile functions. In the second part of this paper the uncertainty induced by the sensor reading error is analyzed in both frequency and spatial domains, and the uncertainty for the profile function can also be obtained. The simulation results confirm that the improved F8S method provides better performance and effectiveness, and is more feasible than the previous F8S method [1].

Mathematical Modeling of Interface Movement during Diffusional Bonding of Surfaces

The concentration profile of Cu is modelled using semi-infinite geometry for diffusion couples of α and β phases in Cu-Al system. The dimensionless interface movement parameter γ is calculated, for various combinations of time and temperature, by root bracketing, bisection and inverse quadratic interpolation. A computational procedure is presented to calculate the concentration profile where the interface velocity (dε/dt) is high and/or with steep concentration gradient of the specie in the shrinking phase. In all cases the interface compositions are set at the equilibrium values given in the phase diagram with fixed composition of end members. The calculated profile match well with the experimental concentration profile as reported by Romig [3].

Full-profile refinement by derivative difference minimization

A new method of full-profile refinement is developed on the basis of the minimization of the derivatives of the profile difference curve. The use of the derivatives instead of the absolute difference between the observed and calculated profile intensities allows refinement independently of the background. The procedure is tested on various powder diffraction data sets and is shown to be fully functional. Besides having the capability of powder diffraction structure analysis without modelling the background curve, the method is shown to allow the derivation of structure parameters of even higher quality than those obtained by Rietveld refinement in the presence of systematic errors in the model background function. The derivative difference minimization principles may be used in many different areas of powder diffraction and beyond.

Kinetic analysis of nitrifying biofilm growing on the rotating membrane disk

The authors have proposed a novel water treatment process in which nitrifying bacteria are fixed on the surface of rotating membrane disks. This biofilm-membrane process can perform strict solid-liquid separation and oxidation of ammonia nitrogen simultaneously. In this research, applicability of the conventional biofilm model (assuming the biofilm structure to be flat, homogeneous and continuous) to analysis of the biofilm developing in the proposed process was examined. A long-term operation for culturing the active nitrifying biofilm was carried out prior to kinetic investigation. By cryosectioning of the biofilm and image analysis, the thickness of the biofilm was determined to be 87 μm. From this biofilm thickness and the result of the batch ammonia consumption test, the intrinsic zero-order ammonia consumption rate of the biofilm was estimated precisely to be 930 g/m3/h. Using these parameters, the ammonia concentration profile in the biofilm was calculated by the conventional model, and the applicability of the model was examined by comparing the calculated profile with the ones measured with a microelectrode. The calculated profile was very close to the measured ones, which indicated feasibility of the conventional model to the analysis of the biofilm grown in the proposed process. The studied biofilm actually had a simple, i.e. flat, homogeneous and continuous, structure due to membrane filtration. This was the reason why the conventional model could still be employed. In the analysis of the data dealing with low concentrations of ammonia, however, first-order kinetics should be used. The first-order ammonia consumption rate constant of the studied biofilm was estimated to be 808 h-1.

Radial Mixing in an Axial Turbine

The objective of this work was to examine radial mixing in an axial turbine from a number of different perspectives. These include: (1) its impact on the spanwise distributions of the force on the airfoils and the change in the fluid momentum as it passed between them, (2) the mixing coefficient distribution based on measured secondary flow velocities, and (3) comparisons of measured and calculated profile redistribution for an axisymmetric inlet profile and for profiles generated by introducing hot and cold streaks upstream of the turbine. It was seen that a simple diffusive transport model could give a good prediction of most of the measured results.

Radial Mixing in an Axial Turbine

The objective of this work was to examine radial mixing in an axial turbine from a number of different perspectives. These include: (1) its impact on the spanwise distributions of the force on the airfoils and the change in the fluid momentum as it passed between them, (2) the mixing coefficient distribution based on measured secondary flow velocities, and (3) comparisons of measured and calculated profile redistribution for an axisymmetric inlet profile and for profiles generated by introducing hot and cold streaks upstream of the turbine. It was seen that a simple diffusive transport model could give a good prediction of most of the measured results.

Application of Bodner Viscoplastic Theory to Pressure-Shear Plate Impact Experiment

An application of the unified elastic-viscoplastic constitutive theory of Bodner [5] is presented. The material parameters in the theory, which includes directional hardening, are determined from results of uniaxial stress tests at constant strain rates. The constitutive equations are then used in numerical modeling of pressure-shear plate impact experiment. The results show that the measured normal component of the wave agrees well with the calculated profile. A small discrepancy, which can be accounted for by the presence of a Bauschinger effect, exists between the theoretical and the experimental shear component of the wave profiles.