Vladimir I. Monin

X-Ray diffraction technique applied to study of residual stresses after welding of duplex stainless steel plates

Duplex stainless steel is an example of composite material with approximately equal amounts of austenite and ferrite phases. Difference of physical and mechanical properties of component is additional factor that contributes appearance of residual stresses after welding of duplex steel plates. Measurements of stress distributions in weld region were made by X-ray diffraction method both in ferrite and austenite phases. Duplex Steel plates were joined by GTAW (Gas Tungsten Arc Welding) technology. There were studied longitudinal and transverse stress components in welded butt joint, in heat affected zone (HAZ) and in points of base metal 10 mm from the weld. Residual stresses measured in duplex steel plates jointed by welding are caused by temperature gradients between weld zone and base metal and by difference of thermal expansion coefficients of ferrite and austenite phases. Proposed analytical model allows evaluating of residual stress distribution over the cross section in the weld region.

Portable x-ray apparatus for stress measurements

Portable apparatus presented in this paper is an x-ray equipment permitting to carry out traditional stress determination by x-ray diffraction method both in-laboratory and in-field conditions. The portability of apparatus is achieved by construction of compact and light high voltage source coupled with special x-ray tube and using of coordinate sensitive detector. Other distinctive characteristic of apparatus is an absence of a goniometer. Special collimator and simple meter of incidence angle permit to substitute the goniometer and to carry out the stress measurements of different industrial equipments such as pipelines, tanks. Software program executes a control of measurement procedure and carries out data processing experimental results.

Simulation of X-ray Diffraction Line Broadening Caused by Stress Gradients and Determination of Stress Distribution by Fourier Analysis

Different physical, mechanical and chemical processes, such as: ion implantation, oxidation, nitridation and others create on the surface of materials residual stress state, characterized by high level and strong gradient. X-ray diffraction method widely used for stress measurements has some difficulties in interpretation of experimental data, when the depth of X-ray penetration is compared with thickness of surface layer where inhomogeneous stress distribution is localized. Early it has been shown by authors that diffraction line broadening occurs when analyzed surface is characterized by strong gradient. The interest to study the diffraction line broadening is connected to the possibility of obtaining information about parameters of surface stress distribution. In the present paper the convolution and deconvolution concepts of Fourier analysis were applied to study X ray diffraction line broadening caused by surface stress gradients. Developed methodology allows determining of stress distribution in superficial layers of materials.

Study of superficial stress gradients by computer simulation and x-ray diffraction experiment

Study of stress gradients is one of the important problems of the X-ray tensometry, especially, in the case of analysis of residual stress state arising after different modern treatments like material modifications by ion beam technologies or surface treatments by laser. These problems related directly with incompleteness of theoretical and experimental measurement techniques with using of X-ray diffraction for study of stress gradients and they are connected with nonlinear character of dependency of diffraction angle θφ,ψ versus sin2ψ and with broadening of diffraction line caused by surface stress gradient. Computer simulation gives possibility to resolve the problem of determination of stress state characterized by strong gradient. The objective of presented paper is to develop a methodology of determination of stress gradient parameters. The methodology is based on computer simulation of diffraction line and permits to make corrections of stress measurements made by diffraction sin2ψ-method.

X-ray tensometry for study stress distribution and mechanical behavior of components of silumin fabricated by powder metallurgy

Aluminium-silicon alloy or silurnin fabricated by powder metallurgy is a material widely used in aircraft and precision mechanics industries because of homogeneous composition and high mechanical properties. Residual stresses arising in this kind of composite material caused by the difference of thermal expansion coefficients of components have negative influence on the working of Al-Si parts and equipments. X-ray diffraction method of stress measurements is unique method allowing study the individual stresses acting in each component of composite material. In the present paper the stress distribution and mechanical behavior of aluminum matrix and silicon particles have been studied by X-ray diffraction method. Interpretation of experiment stress measurements was made on position of mechanics of composite materials.

X-ray analysis of stress distribution in ferrite and austenite of duplex steel during tensile loading

One of characteristic feature of stress determination by X-ray diffraction technique is the possibility to analyze stress state in individual phases of a multiphase material. Duplex steel widely used in chemistry and oil refinery equipments is an example of this kind multiphase material consisting of approximately equal quantities of ferrite and austenite. These phases have different mechanical properties that cause a different stress distribution under loading. In the present paper mechanical behavior of a duplex steel and their ferrite and austenite phases have been studied by X-ray diffraction technique. Stress distribution has been analyzed both in elastic and plastic region.

Study of stress gradients using computer simulation of diffraction data

Difficulties of determination of surface stress gradients using X-ray diffraction technique are connected with interpretation of non-linearity of θφ,ψ versus sin2ψ experimental curves. The problem is that the scattering of experimental data conceals a non-linear character of sin2ψ dependency and does not allow to determine correctly the parameters of stress gradient. The solution of this problem can be resolved experimentally by stress analysis of a sample with known parameters of stress gradients or by computer simulation of a diffraction profile created by surface layers with stress gradient. The first is not successful because of the difficulty to make the samples with the known parameters of stress gradient. The second is more productive because it allows to simulate an experimental θφ,ψ versus sin2ψ dependency and to obtain the relationships between stress gradient parameters and non-linearity of sin2ψ plots. Computer simulation of diffraction data presented in this paper permits also to analyze directly the broadening of diffraction line caused by stress gradient.

Computer simulation of line profile and data processing in diffraction experiments

Data processing of a line profile is one of the most important procedures in a diffraction experiment. The main problem is connected with the presence of K(alpha 1) and K(alpha 2) wave components in X-ray radiation that produces the principal errors while determining the angular position or width of a diffraction line. By using computer methods in data processing, it is possible to realize effectively the Rachinger method of separation of K(alpha 1) and K(alpha 2) components. In this paper, computer simulation of diffraction profiles was used to analyze the possibilities of the Rachinger method. A separation criterion based on searching true principal parameters, namely the distance and intensity interrelation between K(alpha 1) and K(alpha 2) components, was proposed. The separation method is incorporated into the data processing for a portable diffractometer developed by authors from Polytechnical Institute (UERJ).The data processing includes control of an experimental procedure for the case of macro and microstress measurements.