Papers by Author: Jorge Cruz Fernandes

Abstract: The objective of this work is to present a new laboratory testing methodology suitable for estimate the forces generated during multiple blade gangsawing employed on marble and limestone. This methodology allows analysing the tool behaviour aiming to contribute for developing new products and/or optimize the working conditions for processing different classes of stones. In the present research, 3 different diamond linear blades were tested against 2 types of stones (limestone and marble), studying the effect of two working parameters. The linear blades differ in the characteristics of the segments: size of diamond grit and type of metallic binders used to embed the diamond. The classification equipment used in this work consists in a special bridge cutting machine incorporating a tailored instrumentation / sensing system to control the working conditions while all the necessary cutting outputs are monitored and stored by special software. Taking into account the output parameters measured to evaluate the tool behaviour (vertical and horizontal forces, electric energy consumption, vibrations measured by accelerometers and tool wear); it is possible to classify and select tools with relation to the efficacy of the cut.

Abstract: A test methodology is employed to investigate the cutting behaviour of five different diamond impregnated tools for cutting hard materials, such as rocks. A set of parameters, which characterise the tool wear (specific wear loss in the tool), and its relationship with the cutting force of the examined tools, are established to evaluate the tool wear performance. The procedure established in this work describes the specifications of the equipment used to carry out the tests, the different cutting conditions, the format of the output parameters and the characterisation of the different materials used (binders and rocks), hence allowing to discuss the overall cutting wear behaviour of the tools. The methodology presented indicates a universally applicable procedure for measuring the wear performance of the diamond tools as, at the same time, it establishes a relationship between wear and the mechanical parameters of the different metallic binder materials used to manufacture the correspondent tools. The procedure is proven to be an indispensable instrument for correctly carrying out wear performance tests and for reliably interpreting the wear mechanisms of the tool.

Abstract: The present study investigates the effect of rock aggregate size on the fracture toughness of a petreous macrocomposite material (concrete). The effect of aggregate size on the fracture properties of concrete was studied by analysing the fracture toughness KIC results obtained using single edge notched beam (SENB) specimens submitted to 4-point bending test. The results were obtained according to the methodology proposed by Srawley and Gross for monolithic ceramic materials. Additionally, the effect of aggregate size has been analysed by performing fractographic examination of unnotched beam specimens also submitted to 4-point bending test. KIc values obtained via linear elastic fracture mechanics (LEFM) theory applied to the fractographic data were comparable to those obtained by SENB method. The obtained results show that the fracture toughness of concrete depends on the aggregate particle size, although KIC is not linearly related with the particle size. Fracture behaviour depends on the interaction between the used mortar (a mixture of portland cement with sand and water) and the different rock (aggregate) particle sizes. This kind of studies allows further extending the knowledge on the failure mechanisms of concrete, which permits to improve the characteristics of these macrocomposite materials by understanding the effects related to the modification of their structure.

Abstract: This paper presents a comparative study between 3- and 4-point bending tests applied to five Portuguese limestones. The study has been conducted on sawed limestone specimens, all showing the same surface finishing. The materials were compared for two distinct situations: i) using a 3-point flexure loading configuration in batches of materials with larger cross sectional specimen dimension (50 × 30 mm2); and ii) using a 4-point flexure loading configuration in the same batch of materials but with smaller cross sectional dimensions (30 × 25 mm2). In all situations, the materials have broken due to intrinsic volume defects. Formulae for the effective volumes and effective surfaces for rectangular beam specimens loaded in flexure were reviewed in order to analyse the strength scaling effect. The results show the applicability of the Weibull statistics to explain the differences in the results of the 3-point and 4-point bending tests, even when different cross sectional sizes are employed. Among other important remarks, in all the different limestone specimens used it was possible to confirm that the strength values determined experimentally via 3-point bending are of the same order as those estimated for the same loading configuration but via experimental data of 4-point bending tests using the Weibull strength scaling approach, even if employing a different cross-sectional dimension.

Abstract: Synthesis of single-phase tungsten sub-carbide W2C was attempted by heating pellets made out of a source of carbon (graphite-G) and W powders with G/W atom ratio between 0.35 and 0.50 to two target temperatures, namely 1600°C and 1900°C in an argon atmosphere using a solar furnace at PROMES-CNRS in Odeillo (France). The results showed that synthesis of single-phase W2C phase was difficult at either target temperature yielding the W2C co-existed with free metallic W. It was noted that the thin top surface layer of the solar-synthesised tungsten carbide pellets heated to 1900°C was distinguishable from the rest of the bulk specimen showing localised growth of nano-meter scale WC whiskers over W2C grains. Detailed XRD (X-ray diffraction) results on the effect of both G/W ratio and temperature on W2C lattice parameters are discussed.

Abstract: In the present work a new testing method for assessing the wear resistance of matrix materials employed in the manufacture of diamond tools is presented and discussed. The method allows assessing the wear behaviour of different metallic matrices by simulating a circular cutting action of a tool where, instead of a normal abrasive element (matrix impregnated with diamond) only the matrix material is tested. This method has originated a preliminary model of continuum abrasive contact layer between a rotating circular element made of a metal matrix and a glass material. The model allows the determination of the matrix wear rate at different applied forces. To validate the methodology used, different matrix materials (with different mechanical properties) have been analysed in relation to the experimental wear rate.

Abstract: Hydroxyapatite (HA) is widely used as a bone repair material. The use of microwave radiation as energy source for powders densification opens new opportunities for sintering HA at lower temperatures than by conventional sintering (electric furnace). The aim of this work was to compare the densification behaviour of a commercial hydroxyapatite powder under microwave and conventional heating conditions through evaluation of the elastic properties of the resulting sintered materials. The effect of green density, sintering temperature and dwell time on the Young’s modulus E (measured by the impulse excitation of vibration method) of microwave sintered HA was evaluated by using the Taguchi method. Under the set of controlled parameters investigated, green density was the most significant factor affecting E. It was verified that the highest E values obtained with each sintering process are similar (104 and 105 GPa for microwave and conventional sintering, respectively). These values were obtained at 1250°C for 2 h in conventional sintering and at 1200°C for 10 min with microwave sintering. This illustrates the advantage of microwave processing on energy and time savings over conventional sintering.

Abstract: Petrography and X-ray diffraction techniques are used in this work to determine the mineralogical composition of a granite, a gabbro and a quartzite. The experimental difficulties and the results obtained by both methods are described and discussed. The semi-quantitative procedure of XRD analysis used in this work allows an estimate of the relative mineral phase composition of each type of rock. Petrography was found to be crucial in terms of textural analysis.

Abstract: Additions of γ-Al2O3 and Al(OH)3 powders produced at INETI from spent baths resulting from the aluminium transformation industry were made to a commercial cordierite batch formulation (without Al2O3 addition), known as DC4, developed by Rauschert Portuguesa Lda., in order to evaluate the possibility of replacing with benefits the conventional α-Al2O3 source used. The resulting samples were found to be denser than the commercial ones. This is related to the higher reactivity of these particular sources of alumina as compared to that added to the commercial product. Consequently, higher Young’s modulus (100-114 GPa) and flexural strength (80-98 MPa) were achieved for the developed materials in comparison to those obtained for commercial cordierite (96±2 GPa and 67±5 MPa, respectively). In addition, slightly lower thermal expansion coefficients were observed (3.6x10-6 K-1) and the thermal shock resistance was found to increase from 325 K to 350 K. The developed technology can be regarded as suitable for reducing the environmental impact of deposition of wastes from the aluminium transformation industry.

Abstract: When applied to product engineering, the Taguchi method allows the identification of the conditions that lead to the development of similar products with a small variation around a particular target value. In the present work, the Taguchi method was used to evaluate the effect of four processing parameters on the mechanical properties of a commercial dense cordierite in order to maximize the flexural strength of the resulting bodies. Using a L9 orthogonal array, four control factors (named A, B, C and D) at three levels, namely type (AS1, AS2 and AS3) and content (18, 20 and 22 wt%) of alumina added, cooling rate (1, 3 and 5 °C⋅min-1) and average particle size of each batch (5, 6 and 7 μm) were set. Hence, with a reduced number of experiments, it was possible to identify the factors and their levels, which have most contributed to an increase in flexural strength of the resulting cordierite bodies. The optimum conditions to obtain bodies having a flexural strength higher than 100 MPa were the addition of 22 wt% of AS2 alumina, an average mixture particle size of 5 μm and a cooling rate of 1 °C⋅min-1. The type of alumina had a negligible effect on flexural strength whereas the other factors affect considerably the strength.