The research activities of the department are aimed in particular at the disintegration of rocks and geomaterials by a high speed water jet. Problems related to rock cutting by mechanical tools, the determination of workability and abrasiveness of rocks are also studied.
Research activities are directed at the study of the dynamic behaviour of a pulsating water flow, the definition of excitation and propagation processes of high-frequency, high pressure pulsations in the liquid and their utilization in generating pulsating, high-speed liquid jets. The objective of the research is to understand the fundamental processes of generation and transmission of pulsations in the high-pressure system along with the formation of the pulsating jet and its interaction with the material.
This topic covers research carried out in the area of new abrasive materials (both natural and artificial). The research is aimed at defining the crucial properties of abrasive materials from the point of view of both maximizing the cutting performance and minimizing the wear on the cutting head. The negative impacts of these materials on the working and living environment is also studied. The objective of the research is to develop a new generation of abrasive materials.
Compressible liquid flow in the nozzle used in high-speed water jet technology represents the main application of numerical simulation in the department. Mathematical models are created using ANSYS software. Models allow the study of liquid behaviour in the tube and downstream at the nozzle exit. Subsequently, the whole solved assembly is optimized to obtain the best efficiency from the simulated system. Modifications are verified by laboratory experiments. Knowledge and skills obtained while using ANSYS software are also utilized for solving problems of liquid flow and stress analysis in cooperation with industry.
This area studies the influence of technological parameters on the topography of a machined surface for different types of materials. It also finds links between force action, vibration, working pressure fluctuation, acoustic emission and topography of the machined surface. Analysis is carried out by applying new layers to on the machined surface.
This research is oriented primarily around using the abrasive water jet in different machining techniques (turning, milling, polishing, drilling, etc.) in difficult-to-machine and non-machinable materials, such as composites, ceramics, high-strength alloys, glass, rocks, etc. It also studies the the utilization of high-speed water jets for ultra-fine grinding and disintegration of materials (primarily geomaterials) to produce submicron particles.
The result concerns the use of high pressure water jets for cutting and generally disintegrating materials. The generation of sufficiently high pressure pulsations in water upstream of the nozzle exit enables the creation of a pulsating liquid jet that emerges from the nozzle as a continuous stream which forms pulses at certain standoff distances from the nozzle exit. The advantage of such a pulsating jet over a continuous one is based on the fact that the initial impact of pulses on the target surface generates cyclically and an impact pressure that is several times higher than the stagnation pressure generated by the action of continuous jet under the same working conditions. In addition, the action of a pulsating jet also induces both fatigue and shear stresses in the target material due to the cyclic loading of the target surface and the radial high speed flow across the surface. This further improves the efficiency of the pulsating liquid jet in comparison with the continuous flow. An original method of generating a pulsating liquid jet was recently developed and extensively tested. The method is based on the generation of acoustic waves by an acoustic actuator on the pressurised liquid and their transmission via a pressurised system to the nozzle. Research into the fundamentals of the excitation process and the propagation of acoustic waves (and/or high-frequency pressure pulsations) in liquid via a high-pressure system and their influence on the formation and properties of a pulsating liquid jet was crowned by the granting of a Czech patent and the completion of a license agreement for the manufacture of one piece of an acoustic generator of pressurised pulsations. At present, the cooperative agreement with an industrial partner which will lead to the signing of an exclusive licence agreement for the manufacture, use and sale of generators based on the above mentioned patent is being prepared.
The achievement was included in most important results of basic and targeted research of the Academy of Sciences in 2008 (see Annual Report of the Academy of Sciences of the Czech Republic in 2008 , in czech).
Laboratory experiments concerned with the removal of degraded surface layers of concrete by high-speed continuous and pulsating water jets, were prepared in cooperation with Brno University of Technology, Faculty of Civil Engineering and VSB - Technical University of Ostrava, Institute of Physics. Concrete blocks of precisely-defined properties were created; some of them were stored or tested by cyclic loading in different corrosive environments (freezing effect, the effect of chemical de-freezing agents, long-term effects of chlorides, sulphates and nitrates). Several testing samples were left as reference samples, i.e. not exposed to any corrosive environment. The pulsating jet achieved a higher efficiency in all cases compared to a continuous jet under the same working conditions. However, the ratio of volume removed from the concrete test sample by both pulsating and continuous jets varied considerably according to type and degree of sample degradation and the cutting parameters. While continuous jets removed only the upper part of the cement paste, pulsating jets penetrated deeper and removed cement paste to aggregates at given testing conditions. Thus, pulsating jets are able to remove selectively degraded concrete layer and preserve “healthy concrete“ following the application of repair coatings and mortars also at low water pressures. A higher roughness of the concrete substrate treated by pulsating jets leads to better adhesion of newly applied layers.
Numerical models of high pressure systems with an integrated acoustic actuator of high pressure pulsations were created. They allowed for the theoretical study of the processes of excitation and propagation of pressurised pulsations. Results of numerical simulation of pressurised pulsations demonstrate that relatively complicated geometries with one or two L-bows or relatively long liquid waveguide allow propagation of pressure pulsations from source to nozzle. The intensity of pulsations upstream from the nozzle exit can be substantially affected by defining the dimensions of separate parts of the high-pressure system and its tuning to resonance.
A special method of visualization of pulsating water jets based on the application of stroboscopic effect was elaborated. The frequency of stroboscope flashing is controlled by the frequency of the pressure pulsations in the high-pressure system which generates the pulsating jet. The visualization is used to study the influence of operating parameters and the geometric configuration of the acoustic generator of pressure pulsations on the formation and the morphology of the pulsating water jets.
Abrasive materials were evaluated from both mineralogical and petrological points of view. Their behaviour during the process of abrasive water jet generation and its action on the material to be cut was also looked at. Methodologies for the assessment of the initial properties of abrasive concentrates, their cutting efficiency in reference materials and the wearing effects on the focusing tube were developed. This was together with a methodology for description and morphological analysis of grains and cutting kerfs in macro- and micro-scales by image analysis. The determination of biological noxiousness of the respirable dust fraction, which results from the disintegration of natural and synthetic abrasives and minerals of the quartz group during application of abrasive water jet,represents another original result of the research. The work contributed to the formulation of both enduring problems and new themes for further research in the above mentioned area.