Digital tribology and the industry 4.0: a note

Industry 4.0 or the Fourth Industrial Revolution is driven by innovative technologies that have profound effects on production systems. Recent research results and industrial experiments show paradigm shifts in problem solving, which affect many areas, including tribology. Quantitative information obtained through the digital approach of the tribological study in the interface regions of the contact pairs, exhibit a strong potential for the optimization of the productive processes as a whole. In this sense, the concepts of Digital Tribology, presented here, are perfectly aligned with the new technologies in this era of digitalisation and emergence of intelligent, efficient and autonomous solution required by industry 4.0.in publicatio

Estudo de condutores iónicos à base de pirocloros Yb2Ti2O7

Doutoramento em Engenharia dos MateriaisO presente trabalho é uma contribuição para o entendimento dos efeitos exercidos pela história térmica e condições de preparação na estrutura, microestrutura e propriedades de transporte nos materiais à base de Yb2Ti2O7. Foram preparados pós por reacção no estado sólido, e amostras cerâmicas mediante sinterização a altas temperaturas e arrefecimento a taxa controlada. As amostras foram caracterizadas estruturalmente por difracção de Raios-X, incluindo refinamento estrutural, e espectroscopia Raman. Foi usada microscopia quantitativa para obter uma caracterização microestrutural detalhada. Foram preparadas três séries de composições: Série A - materiais Yb2±xTi2±xO7±d com substituição parcial de Ti por Yb ou vice-versa; Série B - materiais Yb2+xTi2-x-zNbzO7-d com substituição parcial de Ti por Nb e Série C -. materiais Yb2+xTi2−-x-yFeyO7−d com substituição parcial de Ti por Fe A condutividade iónica dos materiais Yb2±xTi2±xO7±d pode ser melhorada por variação de composição, combinada com optimização das condições de processamento, incluindo o ciclo térmico da sinterização e a preparação de pós. A influência do método de preparação de pós foi confirmada por comparação entre a condutividade de amostras da Série A preparadas por métodos alternativos, i.e., síntese química ou reacção no estado sólido Verificou-se, por refinamento estrutural, que ocorre troca catiónica entre as posições A e B nos casos de amostras com excesso de Yb ou excesso de Ti e também uma ligeira permuta em materiais com composição nominalmente estequiométrica, isto é, (Yb2−δTiδ)(Ti2−δYbδ)O7. Os resultados mostram que um pequeno excesso de Yb faz baixar a condutividade iónica e que ligeiro excesso de Ti tem efeito oposto. Estes efeitos podem ser explicados pelas diferenças estruturais significativas exercidas pela inserção parcial de Tin+ na posição A e inserção parcial de Yb3+ na posição B do pirocloro. As maiores diferenças na condutividade foram observadas nas amostras com composição nominal Yb2Ti2O7, em concordância com efeitos estruturais e/ou microestruturais induzidos pela história térmica das amostras. A utilização de diferentes métodos de preparação de pós poderá sobrepor-se aos efeitos da história térmica, possivelmente devido a alterações na homogeneidade da distribuição catiónica das amostras. O comportamento eléctrico das fronteiras de grão também é influenciado por esses factores. A substituição parcial de Ti por em amostras Yb2+xTi2-x-zNbzO7-d produz os efeitos previstos para a adição de um dador. A adição do Nb fez baixar a condutividade total em ar e aumenta a condutividade tipo-n. Para teores de Nb suficientemente elevados observou-se um patamar na variação de condutividade total com a pressão pressão de oxigénio, correspondente a concentração electrónica constante e fixada pelo teor de Nb. O decréscimo de condutividade em condições oxidantes pode ser interpretado por alterações na química de defeitos, traduzindo-se numa evolução gradual das condições de neutralidade de n≈[D•], em condições redutoras, para [Oi ”]≈[D•]/2, em condições suficientemente oxidantes.. Efeitos combinados do excesso de Yb com a adição de Nb nas composições do tipo Yb2+xTi2-x-zNbzO7+d mostra que o efeito aceitador da troca de Yb3+ por Ti4 não reverte totalmente o efeito do Nb, sugerindo que a adição de Nb também afecta a mobilidade iónica.The present work is a contribution to understand the effects of thermal history and precursor powder synthesis on structure, microstructure and transport properties for Yb2Ti2O7-based materials. Most samples were prepared by solid state reaction, and sintered by different firing schedules, including changes in cooling rate. X-Ray diffraction, including structural refinement, and Raman spectroscopy were used for structural characterizations. Quantitative microscopy was used for detailed microstructural characterization. One prepared three series of compositions: Series A -:Yb2±xTi2±xO7±d materials with partial substitution of Yb fore Ti or viceversa, Yb2+xTi2-x-zNbzO7-d materials with partial substitution of Ti by Nb, and Series C - Yb2+xTi2−x-yFeyO7−d with partial substitution of Ti by Fe. The ionic conductivity of Yb2±xTi2±xO7±d materials can be improved by compositional changes, combined with optimized processing, including thermal history and powder preparation. Effects of powder preparation were confirmed on comparing conductivity data for Series A samples prepared by different methods, i.e., chemical synthesis and solid state reaction. Structural characterization showed that cationic exchange between A and B-site positions compensates for the excess of Yb or excess of Ti. In addition, one also found anti-site cationic exchange for materials with nominal stoichiometry, i.e. (Yb2−δTiδ)(Ti2−δYbδ)O7. Results show that a small Yb-excess actually suppresses the ionic conductivity. On the contrary, the highest conductivity in air was found for samples with slight excess of Ti. These effects can be explained by significant structural differences between off-stoichiometric and stoichiometric compositions. The results also suggest that samples with nominal composition Yb2Ti2O7 are more likely to undergo significant structural changes on cooling from sintering temperatures, and thus dependence of transport properties on thermal history. The effects of powder preparation might be superimposed on those ascribed to thermal history, possibly due to differences in homogeneity of chemical composition of precursor powders. The electrical behaviour of grain boundaries is also affected by those factors. Partial substitution of Nb for Ti in Yb2+xTi2-x-zNbzO7-d exerts effects expected for donor-type additives; this includes increase in n-type conductivity and decrease of total conductivity in air. For sufficient contents of Nb, the dependence on oxygen partial pressure shows a conductivity plateau, corresponding to constant concentration of electrons and constant conductivity. The conductivity decrease for oxidizing conditions, which can be interpreted by changes in defect chemistry, with gradual evolution in charge neutrality from electronic compensation n≈[D•], under reducing conditions, to ionic compensation [Oi ”]≈[D•]/2, for sufficiently oxidising conditions. Combined effects of excess Yb and addition of Nb in Yb2+xTi2-x-zNbzO7-d show that acceptor-type substitution of Yb3+ for Ti4+ does not completely reverse the effects of Nb, and indicate that additions of Nb suppress the mobility of ionic species in addition to its donor effect

Material model assessment in Ti6Al4V machining simulations with FEM

Ti6Al4V alloy is a well-known difficult-to-cut material used in different industrial applications, to achieve the expected component quality, proper definition and control of the machining process parameters must be accomplished. To address this problem, simulations with finite element method (FEM) seem to be an interesting engineering tool to model and optimize machining processes. Nevertheless, the model capability in capturing the behaviour observed in real machining processes is associated with the definition of the model and parameters that describe the workpiece flow stress. This contribution aimed to study the performance of built-in AdvantEdge-2DTMmaterial laws applied in Ti6Al4V orthogonal cutting simulations under dry conditions. The numerical models were created under three levels of cutting speed, a constant feed rate and depth-of-cut, a variable tool rake angle (of 20° and -6°/0 °), but also using four Ti6Al4V constitutive laws, namely, one suggested in AdvantEdgeTM library, a Johnson- Cook (JC) model, a Power law (PL) and a PL coupled with ductile damage model. Experimental results were used to assess the numerical models’ accuracy in predicting the machining forces and metal chips. Satisfactory results regarding the machining forces prediction were achieved with all material laws, yet when the damage criterion was coupled with the constitutive laws (PLD and AE standard material law), the simulations were also were able to achieve the expected chip morphology (serrated metal chips). Keywords: Ti6Al4V, AdvantEdge, orthogonal cutting, power law, Johnson-Cook material model, machining forces, saw-tooth chips.publishe

Correlative microscopy analysis of surface topography in machining Ti-6Al-7Nb

Titanium alloys, namely Ti-6Al-7Nb, are used in the biomedical industry. The study of surface topography is crucial for the development of medical components. The objective of this work is to propose the correlative microscopy technique developed for the analysis of surfaces machined by the turning process of Ti-6Al-7Nb alloy. This technique was based on the association of the 3D reconstruction by extended depth- of-field method from Optical Microscopy (OM) with the Scanning Electron Microscopy (SEM) and microanalysis modes. The correlative microscopy allows a correspondence between the cutting conditions and the material properties, through the analysis of the machined surface.in publicatio

Comparison of surface topography in machining Ti alloys for biomedical applications: correlative microscopy approach for qualitative and quantitative analysis

In the last decades, the demand for biocompatible materials has increased because they are widely selected to manufacture medical devices such as dental and surgical implants. The improvement of these materials used to fabricate biocomponents is a constant objective in research focused on reducing negative impacts on patients. Currently, the most commonly used metal alloy in the biomedical industry is Ti-6Al-4V. Although it has interesting properties, this material may present a risk to the patient due to the presence of vanadium. Alternatively, the Ti-6Al-7Nb alloy may be a candidate to replace traditional alloys, however more studies are required for understanding the machining techniques of biomedical components. The study of surface topography, through modern microscopy techniques, presents great potential to optimize the machining process of this material. The objective of this work was to propose a correlative microscopy technique for a comparative analysis of surfaces machined by the turning process of the Ti-6Al-4V and Ti-6Al-7Nb alloys. This technique was based on the association of the extended field-depth method from Optical Microscopy (OM) with Scanning Electron Microscopy (SEM) and microanalysis modes.publishe

Intelligent machining methods for Ti6Al4V: a review

Digital manufacturing is a necessity to establishing a roadmap for the future manufacturing systems projected for the fourth industrial revolution. Intelligent features such as behavior prediction, decision- making abilities, and failure detection can be integrated into machining systems with computational methods and intelligent algorithms. This review reports on techniques for Ti6Al4V machining process modeling, among them numerical modeling with finite element method (FEM) and artificial intelligence- based models using artificial neural networks (ANN) and fuzzy logic (FL). These methods are intrinsically intelligent due to their ability to predict machining response variables. In the context of this review, digital image processing (DIP) emerges as a technique to analyze and quantify the machining response (digitization) in the real machining process, often used to validate and (or) introduce data in the modeling techniques enumerated above. The widespread use of these techniques in the future will be crucial for the development of the forthcoming machining systems as they provide data about the machining process, allow its interpretation and quantification in terms of useful information for process modelling and optimization, which will create machining systems less dependent on direct human intervention.publishe

3-D reconstruction by extended depth-of-field in tribological analysis: Fractal approach of sliding surface in Polyamide66 with glass fiber reinforcement

The objective of this work was to inspect the fractal behavior of sliding surfaces in Polyamide66 with 30% glass fiber reinforcement. Tribological tests were performed under different conditions and the fractal values were correlated to tribological parameters and evolution of morphological aspects along the surface. Elevation maps of the sliding surfaces were built from images obtained from a conventional optical microscope. Extended depth- of-field method allowed the ordering of stacks of images to quantitative investigation of behavior of surfaces. A robust method to establish the threshold between micro-scale and macro-scales for multi-fractal behavior was proposed, allowing to compare mono-fractal behavior with the ‘‘structural’’ (micro scale) and ‘‘textural’’ (macro- scale) mixed fractal components. It was found that fractal dimension data were depended on tribological con- ditions and positions along sliding surfaces.publishe

Otimização multiobjectivo usando o método dos elementos finitos na maquinagem sustentável da liga TI6AL4V

Sem resumo disponível.publishe

Surface topography in machining Ti alloys for biomedical applications: correlative microscopy approach for qualitative and quantitative analysis

V-Free Ti-6Al-7Nb alloy may be an interesting candidate as a substitute to the traditional Ti-6Al-4V alloy on development of biomedical components. The inspection of surface integrity through digital microscopy techniques shows strong potential for comparative analysis and optimization of manufacturing processes. This work deals with the comparative analysis of turned surfaces of dual-phase (α+β) titanium alloys: Ti-6Al-4V and Ti-6Al-7Nb, under different cutting conditions. Digital image processing and analysis technique has been used to evaluate the volume fraction of phases and their distribution. An innovative methodology for digitizing the surface topography was applied, based on the association of modern microscopy techniques with digital image processing-Correlative Microscopy. The global outcomes show that Ti-6Al-4V samples presented better homogeneity, with a mean β volume fraction of about 17%, compared to 11% of Ti-6Al-7Nb samples. Combination of higher feed rate and lower velocity produce rougher topography for both alloys, while the topographic formation obtained by the combination of lower feed rate and higher velocity seems smoother. In addition, Ti-6Al-4V alloy presents rougher topography in comparison topography of Ti-6Al-7Nb, under all conditions, probably due to the different phase distribution. The correlative microscopy allowed a correspondence between the cutting conditions and the microstructural properties of the both Ti-6Al-4V and Ti-6Al-7Nb alloys, through the analysis of the machined surface.in publicatio

Morphological characterization of surfaces manufactured by High-speed machining: fractal approach of surface topography of tibial insert in UHMWPE

The complex surface geometry in tibial insert of the knee prosthesis, developed by High-speed machining, demands strict surface topography quality requirements, mainly to prevent osteolysis [1]. The fractal analysis is an effective tool in monitoring the milling of these components, since it is a technique sensitive to the self-affinity characteristics of these surfaces [2]. The objective of this work was to propose a method based on the fractal approach for the inspection of surface topography of the tibial insert manufactured by High-speed machining. Test pieces of tibial insert were prepared by varying the machining strategy. The material used was a UHMWPE. The evolution of fractal values were correlated to cutting tool trajectories and compared to average roughness, Ra. Extended depth-of-field method allowed the ordering of stacks of images obtained from optical microscopy, to quantitative investigation of behavior of surfaces. A method to establish the threshold between different scales for multi-fractal behavior of the machining surfaces was proposed, allowing comparing mono-fractal behavior with mixed fractal. The fractal analysis machined surfaces of the tibial insert can be successfully conducted from elevation maps resulting by combining conventional optical microscopy and 3-D reconstruction by extended depth-of-field.publishe