Stefan Fabbro


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Fabbro

First Name

Stefan

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0000-0003-1663-3163

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Publications1 - 4 of 4
  • The wear behaviour of different metallic bond alloys tested in a modified B611-13 test in an acidic, neutral and alkaline media
    Item type: Journal Article
    Fabbro, Stefan; Kondratiuk, Jens; Tomandl, Alexander; et al. (2023)
    Wear
    The abrasive and adhesive wear behaviour of metallic bonds can be significantly affected by varying pH values of the attacking medium. However, the knowledge about the pH value influence on diamond impregnated bits used in core drilling industry is still limited. One recent publication shows the advantage of modifying a standard ASTM B611-13 test to investigate the abrasive and adhesive wear behaviour of a diamond segment bond material in a neutral regime (pH7). This study mainly focuses on the effects of a varying surrounding media on the tribological behaviour using an acidic, neutral and alkaline slurry. This emulates more aggressive conditions for the diamond segments used in mining as well as construction industry. The pH value at which such diamond segments operate can differ from pH2 up to a value of pH13. The present work studies the wear behaviour of two metallic bonds in a modified B611-13 arrangement at 4 m/s sliding speed and different pH values. The tested specimens are investigated with regard to their change in mass and microstructure at the sliding interface zone. The results reveal a significant influence of the pH value on the wear behaviour of the bond system.
  • Geometric-kinematic model for reinforced concrete core drilling
    Item type: Journal Article
    Marra, Lucas; Fabbro, Stefan; Kuffa, Michal; et al. (2023)
    The International Journal of Advanced Manufacturing Technology
    Since diamond-impregnated tools have a big share on tools for construction, the development of more efficient ones is necessary in the near future. The drilling speed performance is one of the concerns during the development of new diamond-impregnated segments in concrete core drilling. However, observations only based on experiments can be very costly, considering a quite demanding amount of material and workforce. One of the solutions to overcome these issues is the development of a geometric-kinematic model (containing a kinematic process model, material model, and drilling force model) to simulate the tangential and normal forces of diamond-impregnated segments in core drilling process. Such model is regularly used in the literature for the simulation of a bonded-abrasives process. The main purpose of the geometric-kinematic model is to generate simulations for the concrete core drilling for the tool performance estimation. This allows an evaluation of the geometric characteristics' (diamond morphology, orientation, size, and positioning) impact of diamond-impregnated segments and of drilling parameters on the drilling force. The geometric-kinematic model will use detailed segment descriptions with stochastic and deterministic variables. The drilling simulation delivers a consistent drilling forces prediction in Utliberg concrete and ASTM A615 steel at the frequently used core drilling feed window. Besides, the model shows the competence to evaluate the impact of a diamond layer characteristics (diamond size and number of rows), allowing the comparison of distinct diamond arrangements designs between each other.
  • Geometric-kinematic model for wear simulation of diamond-impregnated segments in concrete core drilling
    Item type: Conference Paper
    Marra Araujo, Lucas; Borges Esteves, Paulo; Fabbro, Stefan; et al. (2023)
    Procedia CIRP ~ 19th CIRP Conference on Modeling of Machining Operations
    The main concerns during the development of new diamond-impregnated segments in concrete core drilling are the tool lifetime and its capacity to self-sharpen, since tool sharpening is, most of the time, not acceptable under the conditions on the construction site. However, development only based on experiments can be very costly, considering that the amount of material and workforce are quite demanding. One of the solutions to overcome these issues is the development of a geometric-kinematic model to simulate the wear of diamonds in the segments due to the core drilling process. The main purpose of the model is to simulate the reinforced concrete core drilling, providing an estimation of the diamond wear states proportion for the segment diamond layer. This can allow an evaluation of the geometric characteristics impact of diamond-impregnated segments (diamond size, geometry, pattern, etc.) and of drilling parameters on the tool self-sharpening capacity. A specialized kinematic model, process force model and diamond wear model are the main ingredients. For the model validation, diamond wear states characterization after core drilling tests are carried out. The wear simulation delivers a tendency of a diamond layer design in specific process conditions, providing orthogonal worn/fractured profile, number of active diamonds and number of diamond pull-outs.
  • Diamond impregnated segments and their wear behaviour used in reinforced concrete core drilling
    Item type: Doctoral Thesis
    Fabbro, Stefan (2023)
    The presented work describes an experimental analysis of the wear behaviour of two metallic materials and, subsequently, the material removal behaviour of monocrystalline synthetic diamonds as used in diamond impregnated segments. A specially developed experimental set-up is used to simulate a realistic application environment and to investigate the different wear characteristics under laboratory conditions. In order to be able to investigate the bond wear, a standardized B611-13 test rig is modified so it is possible to simulate the two dominant wear patterns, such as abrasive and adhesive wear. For this purpose, a sintered silicon carbide wheel is introduced as a counter body in addition to the steel wheel. The silicon carbide wheel makes it possible to imitate drilling in pure concrete, whereas the steel wheel represents rebar core drilling. The two tested diamond segment alloys, the copper-rich Segment A and the iron-rich Segment B, are standard alloys as used in the construction industry. As a first step, parameter investigations are carried out. Here, the wear behaviour is compared at a set upper and lower parameter limit. The upper limit of 200 N and 4 m/s describes the force and speed acting on the segment during core drilling, whereas the lower limit of 59 N and 2 m/s is intended to simulate moderate application parameters in the experiment. While the iron-rich segment B wears similarly to what is observed in core drilling experiments, the wear of the copperbased segment decreases with increasing force and test speed. It is subsequently shown that a hardened layer forms on the copper-based segment, which protects it from further wear. It is possible to detect this layer not only by metallographic methods but also as a result of an increase in hardness measured by nanoindentation methods. In addition to the parameter studies, special attention is paid to the influence of different pH values on segment wear. Wear tests are carried out on the modified B611-13 test rig with two different pH values. For this purpose, a dilute sulphuric acid or sodium hydroxide solution is used to adjust the water-slurry mixture to pH2 and pH13, showing a significantly reduced wear when changing to pH13 solutions instead of pH7. The wear is again reduced in experiments performed at pH2. At pH13, this can be explained by the formation of oxide/hydroxide layers in the interface between the wheel and the segment. Whereas the formation of low friction sulphide films at pH2 explain the low wear, it is shown that by modifying the B611-13 test the same binder material wear values can be measured as observed under real core drilling conditions and that this test is a valuable tool for the development of new binder systems. In addition to the investigation of the binder system, the cutting behaviour of individual diamond grains is investigated. Here, the focus is on conditions close to the application. For this reason, a 5-axis milling machine is modified to examine single grain scratch tests. Diamond particles with a defined orientation are subsequently brazed onto a steel pin and connected to a force measurement platform. The crystallographic orientation is taken into account and the diamonds are applied in (111) or (100) orientation. In order to compare the measured process forces with the wear tests or with real application conditions, a cutting speed of 4 m/s is set. Since the focus is mainly on concrete core drilling, both concrete and steel are selected as the base material. An important factor for determining the material removal behaviour is the process temperature. For this purpose, the measuring tip of a 2-colour pyrometer is positioned directly in front of the cutting edge and the average temperature for both steel and concrete is displayed. To reduce the effort for future investigations regarding cutting behaviour of single grain diamonds in different orientations or geometries, a Smoothed Particle Hydrodynamics (SPH) simulation approach is presented in this work. The SPH model describes process forces and temperatures of diamonds of different orientations, which remove the steel material at increasing penetration depths. The simulated values show very good agreement with the experimentally determined data for both the predicted process forces and temperatures. This work thus shows that it is possible to carry out both an application-oriented and laboratory based development of metallic binder systems and to analyse the influence of different diamond orientations on the removal behaviour by means of SPH simulation. These two approaches subsequently lead to a resource-saving and cost-effective alternative compared to costly prototype tests in the field of diamond segment development.
Publications1 - 4 of 4