Lashko Y. Decreasing the defectiveness of the surface layer of carbon-carbon composites in abrasive water jet cutting

Dissertation is devoted to solving actual scientific and technical problem of decreasing the defectiveness of the surface layer of carbon-carbon composites in abrasive water jet cutting. It has been established that the hollow structure and the differences in the strength characteristics, as well as the properties of the jet stream selectively flow around the obstacles, leads to the formation of a significant number of surface defects, and even to the complete destruction of the workpiece. It is shown that the location of the point of application of the hydrodynamic effect in relation to the reinforcing fiber tows plays an important role in the formation of blurring and development of the initial macrocavities in material. The scientific provisions of the interaction of a two-phase abrasive water jet stream with a loose anisotropic half-space have been formulated, the basic regularities of the formation of surface defects have been revealed. A test for cutting workpieces was carried out and a series of slices were obtained, which allowed identifying the proposed mathematical model of the development of the breakage whirl, which can be used to estimate the defect of the formed surface layer. Microelectronic studies of microcracks origination have been carried out; influence of processing modes on cracking phenomena has been estimated. The application of the chemographic method for studying surfaces for fixation of formed microcracks is proved. The water content of the surface formed during cutting and the evaporation of moisture in the process of drying have also been evaluated. It has been shown that the process of abrasive water jet cutting of carbon-carbon materials of the 3-D structure requires a mandatory start from the jet entry element, which can be like a separate mask, and a cavity between two tows of reinforcing fibers. On the basis of comparison of the energy of the high speed stream with the operation of the destruction using the reference sample, the method for determining the consumption of the abrasive has been improved and the direct amount of abrasive grains participating in the destruction has been established. The engineering methodology for forecasting defects of the surface layer and recommendations for assignment of processing modes are given. It is shown that the use of the recommendations formulated in the process of work on the dissertation allows obtaining the maximum accuracy of the shape of samples, minimizing surface defects and proving that the use of abrasive water jet cutting in the manufacture of samples practically does not affect the accuracy of the taken characteristics of the material.