Iurzhenko M. Scientific basis and technologies of welding of engineering and high-performance plastics.

The thesis is devoted to the establishment of general patterns of influence of parameters and welding modes on structure and properties of the welded joints of plastic, the study of the features of thermomechanical processes implemented in the welding zone of plastic using methods of mathematical modeling and comparative experimental investigations, development of effective technologies and equipment on the basis of a new generalized knowledge. Structure and properties of the welded joints of model polymeric materials, namely technical types of polyethylene have been investigated, and relationship between them as well as with parameters and conditions of welding has been dedicated. It has been found that during welding of plastics more ordered structure with specific properties and improved operational characteristics, which differ from structure, properties and characteristics of a basic polymeric material that is welded, is formed in a welded joint due to melting of its crystalline phase, orientation of its macromolecules with change of their conformation that is accompanied by their interaction and formation of a mixed structure of their segments and nucleuses of joint crystallites, and further its partial crystallization under the impact of thermal and force fields. The possibility of directional regulation of structure and properties of the welded joints by varying of parameters of welding processes as well as directional impact of external factors, for example, constant magnetic field, has been found. Basing on generalized results of theoretical and experimental studies, including mathematical modeling, technologies and correspondent equipment for welding of pipes and sheets made with engineering and high-performance plastics have been developed, their approbation and implementation have been carried out.