Advanced Methods for the Mechanical and Topographical Characterization of Technological Surfaces

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An uncertainty-based quality evaluation tool for nanoindentation systems

Instrumented Indentation Test (IIT) is a nonconventional mechanical tests allowing multi-scale mechanical characterisation. It is employed for research and quality control in strategic manufacturing fields for developing edge technologies. The state-of-the-art lacks a robust methodology to assess quality of indentations and benchmark indentation devices. This is limiting the application of IIT for specifying and verifying tolerances. This work proposes an uncertainty-based quality evaluation tool for IIT. A non-parametric uncertainty evaluation of calibration contribution is proposed. The method shows the statistical significance of indentation sets modelled by the bootstrap samples. The uncertainty is then propagated according to the law of uncertainty propagation for the evaluation of mechanical characteristics. The methodology is applied to five case studies. Results show that the uncertainty evaluation model can achieve robust and sensitive quantification of the indentation results and system quality, thus providing a useful practical tool for industrial and academic practitioners within a metrological framework

Inference on errors in industrial parts: Kriging and variogram versus geometrical product specifications standard

This article focuses on the inference on the errors in manufactured parts controlled by using measurements devices. The characterization of the part surface topographies is core in several applications. A broad set of properties (tribological, optical, biological, mechanical, etc.) depends on the micro- and macrogeometry of the parts. Moreover, parts usually show typical deterministic geometric deviation pattern, referred to as manufacturing signatures, due to the specific manufacturing processes and process setup parameters adopted for their production. In several situations, the measurements may also be affected by systematic errors due to the measurement process, that might be caused, for example, by a poor part alignment during the measurement process. Measurement techniques and characterization methods have been standardized in the International Standard ISO 25178, defining parameters characterizing the surface topography and supplying methods and formula adapt to deal with this issue computationally. In the present article, we consider a type of spatial dependence between measured values at different points that suggest the use of the variogram to identify patterns in the parts. We offer a comparison, based on a real set of measures, between the latter approach and the conventional as a test of the efficient performance of our findings

Improvement of instrumented indentation test accuracy by data augmentation with electrical contact resistance

Instrumented Indentation Test allows thorough surface multi-scale mechanical characterisation by depth-sensing the indenter penetration and correlating it with the indenter-sample contact area and the applied force. Localised plastic phenomena at the indentation edge, i.e. pile-up and sink-in, may bias the characterisation results. Current approaches attempt correcting related systematic errors by numerical simulation and AFM-based techniques. However, they require careful tuning and complex and expensive experimental procedures. This work proposes a methodology based on in-situ Electric Contact Resistance which augments information on the contact area and allows edge effect correction. The methodology is demonstrated and validated on industrially relevant metallic materials

Optimisation of laser welding of deep drawing steel for automotive applications by Machine Learning: A comparison of different techniques

Laser welding is particularly relevant in the industry thanks to its simplicity, flexibility and final quality. The industry 4.0 and sustainable manufacturing framework gives massive attention to in situ and non-destructive inspection methods to predict laser weld final quality. Literature often resorts to supervised Machine Learning approaches. However, selecting the ApTest method is non-trivial and often decision making relies on diverse and unclearly defined criteria. This work addresses this task by proposing a statistical comparison method based on nonparametric tests. The method is applied to the most relevant supervised Machine Learning approaches exploited in literature to predict laser weld quality, specifically, considering the optimisation of a new production line, hence focussing on supervised Machine Learning methods that do not require massive data set, that is, Generalized Linear Model (GLM), Gaussian Process Regression, Support Vector Machine, Classification and Regression Tree, and Genetic Algorithms. The statistical comparison is carried out to select the best-performing model, which is then exploited to optimise the production process. Additionally, an automatic process to optimise Machine Learning models and process parameters is resorted to, basing on Bayesian approaches, to reduce operator effect. This work provides quality and process engineers with a simple framework to compare Machine Learning approaches performances and select the most suitable process modelling technique

Il ritratto dell’adolescente ne «Gli anni impossibili» di Romano Bilenchi

Il saggio propone un profilo critico incentrato sulla figura del personaggio adolescente protagonista del romanzo Gli anni impossibili di Romano Bilenchi. Il discorso prende avvio da una discussione preliminare sul significato del tema dell’infanzia e dell’adolescenza nell’opera dell’autore. In merito agli Anni impossibili, poi, verrà sottolineato in modo particolare il motivo del confronto tra mondo dell’infanzia e mondo adulto in merito a due opposte visioni della vita. Riguardo al personaggio protagonista, infine, si rileveranno le forme di una strategia rappresentativa funzionale a un ritratto del puer caratterizzato da una profonda ambivalenza.The essay proposes a critical profile focused on the figure of the adolescent character who is the protagonist of Romano Bilenchi’s novel Gli anni impossibili. The speech begins with a preliminary discussion about the meaning of the theme of childhood and adolescence in the author’s works. Concerning Gli anni impossibili, then, it will be particularly highlighted the motif of a contrast between the child’s world and the adult’s world, in regards to different visions about life. As for the boy protagonist, finally, the essay will notice the forms of a representative strategy that is functional to convey a deeply ambivalent portrait of the puer

Pulsioni e dinamiche dell’eros infantile negli «Anni ciechi» di Pier Antonio Quarantotti Gambini

Uno dei maggiori motivi di interesse dell’ambizioso e incompiuto ciclo degli Anni ciechi, in cui Quarantotti Gambini cercò di conciliare le memorie autobiografiche della propria infanzia e le risorse dell’invenzione letteraria, è il trattamento complesso, dinamico e spregiudicato che l’autore riservò al tema della scoperta dell’eros e al racconto del progressivo evolversi delle pulsioni di Paolo, il bambino protagonista delle vicende narrate. Scopo di questo saggio è dimostrare come la resa letteraria di tale ambito della Bildung non si esaurisce nella descrizione di contenuti manifesti della coscienza di Paolo e nella narrazione di eventi esplicitamente connessi a un discorso sull’erotismo infantile e sul confronto con il mondo della sessualità adulta, ma è orientata a una densa rappresentazione di istanze pulsionali profonde, ibride e ambivalenti, nella quale convergono i moti della sfera affettiva del bambino, i tratti psicologici fondamentali del suo carattere, gli apporti di ricordi sintomatici, fantasie, rielaborazioni immaginative e alcune tracce riconducibili al dominio dell’inconscio.One of the major matters of interest concerning the ambitious and unfinished cycle of Gli anni ciechi (The blind years), in which Quarantotti Gambini tried to reconcile the autobiographical memories of his childhood and the resources of literary invention, is the complex, dynamic and unprejudiced treatment that the author reserved for the theme of the discovery of erotic desire and the progressive evolution of the impulses of Paolo, the child protagonist. The purpose of this essay is to demonstrate how the literary rendering of this field of Bildung does not exhaust itself in the description of the manifest contents of Paolo’s conscious mind, nor in the narrative of events explicitly linked to a discourse on infantile eroticism and the confrontation with the world of adult sexuality, but is geared to a dense representation of deep, hybrid and ambivalent instinctive instances in which converge the motions of the child’s affective sphere, the fundamental psychological traits of his character, the provision of symptomatic memories, fantasies, imaginative re-elaborations and some traces pertaining to the domain of the unconscious

Defect Probability Estimation for Hardness-Optimised Parts by Selective Laser Melting

The development of reliable additive manufacturing (AM) technologies to process metallic materials, e.g. selective laser melting (SLM), has allowed their adoption for manufacturing fnal components. To date, ensuring part quality and process control for low-volume AM productions is still critical because traditional statistical techniques are often not suitable. To this aim, extensive research has been carried out on the optimisation of material properties of SLM parts to prevent defects and guarantee part quality. Amongst all material properties, defects in surface hardness are of particular concern as they may result in an inadequate tribological and wear resistance behaviour. Despite this general interest, a major void still concerns the quantifcation of their extent in terms of probability of defects occurring during the process, although it is optimised. Considering these issues, this paper proposes a novel approach to quantify the probability of occurrence of defects in hardness-optimised parts by SLM. First, three process variables, i.e. laser power, scan speed and hatching distance, are studied considering their efect on hardness. Design of Experiments and Response Surface Methodology are exploited to achieve hardness optimisation by controlling process variables. Then, hardness defect probability is estimated by composing the uncertainty afecting both process variables and their relationship with the hardness. The overall procedure is applied to AlSi10Mg alloy, which is relevant for both aerospace and automotive applications. The approach this study proposes may be of assistance to inspection designers to efectively and efciently set up quality inspections in early design phases of inspection planning

Measurement noise evaluation, noise bandwidth specification and temperature effects in 3D point autofocusing microscopy

In this work, we evaluate the measurement noise of a commercial point autofocus surface topography measuring instrument. This metrological characteristic was determined using a calibrated optical flat following methodologies described in good practice guidelines and draft ISO specification standards, using the averaging and subtraction methods. The static noise of the instrument was investigated by examining the repeatability of the vertical Z-axis. The autofocus sensor repeatability was assessed by measuring its vertical positioning deviation, whilst focused on an optical flat, but without scanning laterally. During the investigation, the instrument proved to be sensitive to environmental temperature disturbance, which introduced a significant distortion in the measured topography and resulted in relatively high measurement noise. The spatial frequency of the distortion in the topography was found to be consistent with the frequency of temperature fluctuation in the measurement chamber. Similarly, static noise and autofocus sensor repeatability were affected by temperature fluctuation. However, after applying the built-in drift correction routine in the instrument software during measurement, the effect of temperature fluctuation was significantly reduced from a measurement noise of 20 nm to 2 nm, with a sampling frequency of 30.6 Hz. In this paper, we specify measurement noise along with the corresponding measurement bandwidth

Direct calibration of indenter tip geometry by optical surface topography measuring instruments

Instrumented indentation test (IIT) is a depth-sensing hardness test allowing nano- to macro-mechanical characterisation of surface mechanical properties. Indenter tip geometry calibration allows nano-scale characterisation, overcoming the limits of conventional hardness tests. Calibration is critical to ensure IIT traceability and applicability for quality verification in manufacturing processes. The accuracy and precision of IIT are mainly affected by the indenter tip geometry calibration. State-of-the-art indenter tip geometry calibration reports either direct calibration by AFM, which is highly expensive and unpractical for industry, or indirect calibration methods, which are less accurate, precise and robust. This work proposes a practical, direct calibration method for IIT indenter tip geometry by optical surface topography measuring instruments. The methodology is complemented by uncertainty evaluation. The proposed approach is applied to Berkovich and Vickers indenters and its advantages are proven in terms of accuracy and precision of mechanical characterisation on metallic and ceramic material