Development of vibratory stress release equipment on the basis of investigation of the relationship between residual stresses and vibration characteristics of mechanical structures

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Supervisor:
Dr. Augusztinovicz Gusztáv Fülöp
Department of Networked Systems and Services

Today’s world relies heavily on the use of different metal components – their production and machining acts as a driving force for a variety of fields in contemporary science and engineering. One of the key technological challenges regarding the quality of the produced metal parts, is to effectively reduce the residual stresses introduced to the material during production. As an alternative to the traditional and very costly methods, the use of mechanical vibrations - relying on the component’s resonant behaviour to achieve residual stress relief - is gaining popularity. Academic professionals constantly debate and have not come to an agreement regarding the application and physical backgroud of the process, while at the same time it is widely applied in industry and frequently researched – both with mixed success. An especially disputed field of vibratory stress relief is its applicability to cast iron parts, which will be the central topic of this thesis, with the aim of designing the necessary equipment and process needed for successful application.

The present thesis approaches the problem from the viewpoint of vibrational acoustics. Based upon the theoretical background of the underlying phenomena found in today’s literature, we implement mechanical finite element simulations, and back up the result with corresponding measurements. By modelling the vibrational behaviour and the frequency-dependent displacement, acceleration and mechanical stresses induced in the selected part by application of specified external forces, and comparing the data to those gained from measurements, we attain valuable experience to rely upon in the design of the necessary equipment and operating algorithm.

We demonstrate for castings the phenomenon of decreasing resonance frequencies seen in the force-acceleration transmission function during treatment, which according to the relevant literature is associated with the reduction of residual stresses. For the already machined parts subject to measurement, both the mentioned changes regarding the transmission functions and the reduction of deformations introduced during heat treatment were found to be of significant magnitude. According to the FEM simulations performed, the induced mechanical stresses corresponding to the applied force were at level with those suggested by sources mentioning „local plasticity” as an underlying physical process.

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