PSI - Issue 16

Leonid Lobanov et al. / Procedia Structural Integrity 16 (2019) 27–34 Leonid Lobanov, Nikolai Pashсhin / Structural Integrity Procedia 00 (2019) 000 – 000

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Keywords: Residual welding stresses; electrode system; current pulse; Maxwell’s equation ; method of integral equations; electrodynamic force.

1. Introduction

High requirements, specified to welded structures of the new engineering, cause the need in development of technologies for their postweld treatment. The tendency of widening the application of a vibration treatment, postweld treatment of welded joints by a surface plastic deforming, electric hydro-pulsed and explosion treatment is observed. The processes, based on effect of electrodynamic forces on conductive materials during passing of electric current pulses (ECP), realized in the new technological process, i.e. electrodynamic treatment (EDT), are challenging. By using the energy of ECP and electrodynamic forces, generated by it, acting on metal structure elements treated in EDT, it is possible to influence the stressed state of metallic materials. Effectiveness of EDT is determined by the interaction of two components: an electric pulsed one, realized in ECP passing over the work piece treated and a dynamic one, preset by an amplitude-frequency characteristic of waves of dynamic stresses. The increase in service characteristics of welded joints as a result of EDT is due to a complex effect of the following factors. Thus, in the zone of treatment under the action of electrodynamic forces the elastic waves of stresses are formed in weld metal, which by the interaction with residual welding stresses, initiate their reduction. As a result of EDT the zones with refined grains are formed in metal, the structure evolution of which is determined by plastic deforming under the conditions of realization of electric plastic effect (EPE), based on electron-dislocation interaction (Baranov et al. (2001)). Taking into account the specifics of EDT of welded joints, to which a large extension of welded joints and their different spatial position can be referred, the possibility of mobile positioning of hardware means, realizing the electrodynamic effects, was envisaged. The peculiar features of welded joints define the requirements to hardware, designed for EDT fulfilment, which include:  hardware means for EDT should consist of separate composite parts, such as source of ECP (SECP), executive electrode device (ED), designed for realization of electrodynamic effects on welded joint treated, as well as means of communication between SECP and ED  ergonomic characteristics of ED and means of its communication with SECP should provide the convenience of application in realization of electrodynamic effects with a preset duration, amplitude and periodicity in a manual mode and in the composition of automatic welding complexes. On the basis of analysis of units of pulse current generation it was found that the most acceptable for the ECP formation in SESP is the application of capacitor systems, which have a number advantages over the other units, such as the feasibility of storage of controllable level of energy of an electric charge, creation of different shapes and duration of ECP, as well as simplicity of recovery of electric parameters of the discharge mode. The most effective method of control of ECP discharge parameters is the voltage control of charge of the capacitive energy storage (CES) before the discharge pulse passing. Another controlling parameter of the unit is pulse duration. For this, it is necessary to provide the possibility of changing the electric parameters of the storage discharge circuit. The inductance coil (IC), included into ED, is a controlling unit, with the help of which the pulse duration is adjusted. The inductance of coil can be changed within the wide range. Coming from the requirements, specified to ED, it is recommended to apply IC in the form of a plane inductor. Thus, the controlling parameters of SECP are the charge voltage of CES, which can be changed within the wide range by the control system as well as the discharge circuit inductance L . In operation, ED touches the metal by the electrode end and is set normally to the surface treated. The ECP passing through the inductance coil in a disc excites a magnetic field, generating the eddy currents in a disc. The interaction of set currents 1 with a magnetic field, excited them, leads to occurrence of electromagnetic force P . Schematic diagram of EDT of welded joints by a single-channel scheme is given in Fig. 1. 2. Experimental 2.1. Equipment