International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The chromium-molybdenum steel pipe P91 is widely used in the power plants construction, because they can withstand higher temperatures and operating pressures, in order to increase operating efficiency and output. This material has a complex microstructure which is extremely vulnerable to convert into Austenite form near the temperature for heat treatment. During the welding procedure should be very carefully, because otherwise the residual stress installed post welding will reach high values. A series of experimental studies was carried out, which has shown the development in the magnitude of transverse and longitudinal residual stresses and the values in both directions were determined. For but welded joints the residual stresses in the three direction were measured and the results are reported here. For measuring was used the hole drilling method through “measuring balls” or electrical strain gauge. Except the experiments the finite element method was used to determinate the value and the distribution of the residual stresses. The experimental and FEM results were compared between them and no discrepancy was found.

In the present study a comprehensive numerical study has been conducted to simulate the resistance spot welding process. The phase- field method is employed to model the phase change during the melting and solidification of the material. By this way, the martensitic properties are assigned at the nugget and heat affected zone. As a result of this modelling the residual stress at the heat affected zone is attained and shows maximum value on the heat affected zone.

In this paper a review of progresses occurred along the years in measuring residual stresses by optical methods is presented. These methods allow to implement the hole drilling procedure for residual stress profile measuring, without applying the strain gage rosette. This approach presents several advantages such as easier and cheaper preparation of the test beside the possibility to avoid eccentricity issues and to increase the amount of available data in view of the fact that each pixel can be considered as a measure point. In particular the evolution of the Electronic Speckle Pattern Interferometry (ESPI) technique will be presented showing how set up, methodologies and calculation approaches have developed along the last three decades.

The paper provides a comprehensive description of theoretical and practical aspects of electronic speckle pattern interferometry for technological residual stress measurement in various machine elements. Any results obtained by investigation of residual stress in a welded joint are presented.