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Univerzitet u Zenici
  Doctoral theses defended at the University in Zenica

Date and place of thesis defense:
06.10.2011, Zenica
Candidate:
Mr. Fuad Hadžikadunić, grad. eng. of mechanical engineering
Mentor:
Prof. dr. Dušan Vukojević

Thesis title:

AN APPENDIX TO THE DEVELOPMENT OF VSR METHOD ON THE SPACE MODEL OF WELDED STEEL BEAM

Summary:
The dissertation presents an analytical, numerical and experimental approach to the study of VSR method on the model of welded steel beam. Based on the principle of the planned experiment, the scope of technical and technological parameters for making of samples are defined, as well as for monitoring process of VSR treatment, as a basis for further scientific analysis of the entire process.. To implement the above analysis of dynamic behavior of the observed system and assess the effect of the applied method for stress relieving on test samples, there is a logical necessity of experimental determination of characteristic parameters, such as the amount of heat introduced, frequency, size and character of residual stresses, acceleration, displacement, etc. In the experimental part of study by using regression and dispersion analysis the extent and level of parameter influence on size and nature of residual stress relief is determined, and also the effectiveness of VSR process. The aim of this study was to make better scientifical knowledge in field of VSR after welding, using the methodology of two-axial tretment for test examples in form of I-beams. This approach allows the determination of the actual behavior of structures, reliable prediction of structural response in service, determining the parameters of choice and decision, determining the causes of bad behavior, pointing the methodology and parameters that will increase the level of structure relief, and enhance its stability.
Two basic hypotheses are proved: 1) by applying the methodology of two-axial bending vibration, an affection to the relaxation of residual stresses over entire cross sections of welds can be achieved, 2) it is possible to establish a methodology and provide mathematical interpretations which is based on statement that according the flexion of construction before and after VSR treatment an information about the real relief, i.e. residual stress relaxation could be achieved.
The presented method is applicable to various types of structures, but with appreciation of its geometric, technological, dynamical and all other specifics. This means that different types of constructions require in a certain domain the general approach of treatment applying, but there is also a domain specific to each type of structure that must be taken into account in terms of overall effectiveness of treatment. Therefore, through the dissertation, the importance and specifics of frequency analysis of the dynamic response of the system are emphasized.
There are many influential parameters on the final effect of treatment, and one of the most important are dimensions of treated objects, material and applied welding technology.
Softwares applied for acquisition and data processing, numerical and statistical analysis were: Meta-Lax 2700-CC 2.0, RSM, EVAL, Catman 5.0 i AP, Origin 5.0, Matlab 7.0 and KOMIPS.

Key words :
residual stresses, VSR method, space beam


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