Tribological and vibro-acoustic behaviour of a lubricated contact subjected to the stick-slip phenomenon: the case of the spring-brake system

The main objective of the PhD thesis is the analysis of stick-slip phenomena in lubricated contacts, by merging the physical, experimental and numerical points of view and proposing a novel methodological approach, applied here to an industrial case. Nowadays, in the field of applied mechanics and tribology, one of the most important challenges is the ability to predict and reduce surface damages, failure of machine components and undesirable frictional and dynamic characteristics. In particular, the appearance of friction-induced vibrations at the contact is hardly controllable and can result in high local contact pressure, elevated stresses, system oscillations, discontinuous motion and premature failure]. Understanding the conditions for which the system is more predisposed to the stick-slip phenomenon may allow preventing the appearance of such instabilities, and the related vibrations and noise emission. Friction-Induced Vibrations are a phenomenon that engages multiple scientific challenges, due to the complexity of their physics. Focusing the attention on stick-slip phenomena, these are generally characterized by a saw-tooth displacement-time evolution. Each change in the contact parameters influences directly the dynamic and frictional response of the system, due to the mutual influence of the local scale (contact) and the system scale (macroscopic frictional and vibrational response). Moreover, the presence of a lubricant, and in particular of grease, at the contact interface, increases the complexity of the phenomenon, from both a tribological and dynamic point of view. Lubricated systems are supposed to reduce the frictional losses and wear, but they can also collaborate in the appearance of dynamic contact instabilities, due to the friction-velocity characteristics when passing from boundary to mixed contact regimes. The complex rheology of a grease, function of both the matrix, additive and oil responses, becomes then a key point for the occurrence and evolution of stick-slip. Despite the great importance of this phenomenon, from both scientific and industrial points of view, a lack emerges into the literature about stick-slip of lubricated interfaces. The few works are manly focused on molecular dynamics simulations and numerical modelling of the dynamical response of the system. The different role of the grease components, during the sliding, is nowadays still not clear. Nevertheless, the complex rheology of a grease, function of both the thickener, the base oil and the additives, is a key point for understanding and controlling the occurrence and evolution of stick-slip. Moreover, a general approach is needed to account for the coupling between the local phenomena (e.g. lubricated contact response) and the system dynamic response. Aiming to improve the understanding of stick-slip in lubricated contacts, the present Ph.D. work proposes a novel methodological approach to the stick-slip problem of a lubricated contact, referring to a real industrial case, in order to deploy the obtained results in a more realistic and detailed manner. The subject of the investigation is a mechanical brake used in tubular electric actuators, which can present frictional instabilities originated at the lubricated contact between the two main brake components. The methodology used is twofold: i) on one hand, experimental tests are carried out to understand the local frictional response of the lubricated contact; ii) on the other hand, a lumped model is created in order to simulate and analyse the system dynamic response. Introducing the information about the local lubricated contact behaviour (friction law), achieved experimentally, into the numerical model, it is possible to investigate the parameters for which the system is more predisposed to the stick-slip phenomenon and recreate a representative scenario of its appearance. Particular attention has been placed on the analysis of the lubricant rheology, dealing with different types of lubricants and regimes of lubrication, with both oils and greases. The frictional response has been thus related to the different contributions of the grease components (i.e. thickener, base oil and additives) on the rheology at the interface. The obtained local information has been then integrated in the lumped model to evaluate the unstable dynamic response of the entire system (i.e. the stick-slip phenomena) and identify the lubrication parameters that most influence its appearance. The numerical analysis had the dual objective of understanding the role of the local contact response in the system instability and investigating the stick-slip occurrence as a function of the key system parameters. The obtained results allowed to identify the lubrication components, and the respective friction-velocity curves, more favourable for the stick-slip occurrence. Combining the grease rheology evolutions with the stick-slip dynamic response represents a further challenge in both the domains of research. The Ph.D. thesis has been developed in collaboration between the Sapienza University of Rome, Department of Mechanical and Aerospace Engineering (Rome, Italy), the Institut National des Sciences Appliquées (INSA) of Lyon, laboratory LaMCoS (Lyon, France), and the company SOMFY S.A. (Cluses, France)

Auxiliary selection in Italian intransitive verbs: a computational investigation based on annotated corpora

The purpose of this paper is the analysis of the auxiliary selection in intransitive verbs in Italian. The applied methodology consists in comparing the linguistic theory with the data extracted from two different annotated corpora: UD-IT and PoSTWITA-UD. The analyzed verbs have been classified in different semantic categories depending on the linguistic theory. The results confirm the theoretical assumptions and they could be considered as a starting point for many applicative tasks as Natural Language Generation.Obiettivo di questo lavoro è l’analisi della selezione dell’ausiliare dei verbi intransitivi in italiano. La metodologia applicata consiste nel confrontare la teoria linguistica con dati estratti da due corpora annotati: UD-IT e PoSTWITAUD. I verbi analizzati sono stati classificati nelle categorie semantiche individuate partendo dalla letteratura teorica. I risultati confermano con buona approssimazione gli assunti teorici e possono quindi essere il punto di partenza per l’implementazione di strumenti come sistemi di Natural Language Generation

Interactions between inorganic pigments and rabbit skin glue in reference paint reconstructions

The thermal degradation of rabbit skin glue, a collagen-based proteinaceous material used as a paint binder in paintings, was investigated in this paper. Paint reconstructions of the glue on its own or mixed with azurite (Cu3(CO3)2(OH)2), calcium carbonate (CaCO3), hematite (Fe2O3nH2O) and red lead (Pb3O4) were analysed using a thermoanalytical approach. This method enabled us to investigate the interactions between the glue and pigments before and after artificial indoor light ageing. The study was carried out using differential scanning calorimetry, thermogravimetry and thermogravimetry/FTIR analysis already successfully employed to characterize the paint binders. The results highlighted that all the inorganic pigments interact with rabbit skin glue, thus decreasing the thermal stability of the binder. Light ageing further decreased the thermal stability of pigmented paint replicas, suggesting a moderate increase in the rate of the degradation

Endogenous erythropoietin as part of the cytokine network in the pathogenesis of experimental autoimmune encephalomyelitis

Erythropoietin (EPO) is of great interest as a therapy for many of the central nervous system (CNS) diseases and its administration is protective in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Endogenous EPO is induced by hypoxic/ischemic injury, but little is known about its expression in other CNS diseases. We report here that EPO expression in the spinal cord is induced in mouse models of chronic or relapsing-remitting EAE, and is prominently localized to motoneurons. We found a parallel increase of hypoxia-inducible transcription factor (HIF)-1 alpha, but not HIF-2 alpha, at the mRNA level, suggesting a possible role of non-hypoxic factors in EPO induction. EPO mRNA in the spinal cord was co-expressed with interferon (IFN)-gamma and tumor necrosis factor (TNF), and these cytokines inhibited EPO production in vitro in both neuronal and glial cells. Given the known inhibitory effect of EPO on neuroinflammation, our study indicates that EPO should be viewed as part of the inflammatory/anti-inflammatory network in MS

Fourier transform infrared spectroscopic study of rabbit glue/inorganic pigments mixtures in fresh and aged reference paint reconstructions

We studied the interactions of rabbit glue, a collagen-based proteinaceous binder, with azurite (Cu3(CO3)2(OH)2), calcium carbonate (CaCO3), hematite (Fe2O3·nH2O), red lead (Pb3O4) and cinnabar (HgS) by Fourier transform infrared spectroscopy (FT-IR). The research was carried out on a set of paint reconstructions, which were analysed before and after artificial light ageing. A deconvolution of the amide I FT-IR absorption peak was performed with a written-in-house LabVIEW program to study the secondary structure of the glue.The changes in the glue conformation highlighted that all the inorganic pigments interact with the proteinaceous binder. The conformational changes were correlated with a loss of stability of the collagen structure, especially after ageing, likely due to the interlayer coordination of metals salts and oxide with protein functional groups. These results were correlated with the lower thermal stability of the glue/pigment mixtures with respect to the pure glue, evidenced by thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses performed in a previous step of this work

SerpinA1 levels in amyotrophic lateral sclerosis patients: An exploratory study

Background: SerpinA1, a serine protease inhibitor, is involved in the modulation of microglial-mediated inflammation in neurodegenerative diseases. We explored SerpinA1 levels in cerebrospinal fluid (CSF) and serum of amyotrophic lateral sclerosis (ALS) patients to understand its potential role in the pathogenesis of the disease. Methods: SerpinA1, neurofilament light (NfL) and heavy (NfH) chain, and chitinase-3-like protein-1 (CHI3L1) were determined in CSF and serum of ALS patients (n = 110) and healthy controls (n = 10) (automated next-generation ELISA), and correlated with clinical parameters, after identifying three classes of progressors (fast, intermediate, slow). Biomarker levels were analyzed for diagnostic power and association with progression and survival. Results: SerpinA1serum was significantly decreased in ALS (median: 1032 μg/mL) compared with controls (1343 μg/mL) (p = 0.02). SerpinA1CSF was elevated only in fast progressors (8.6 μg/mL) compared with slow (4.43 μg/mL, p = 0.01) and intermediate (4.42 μg/mL, p = 0.03) progressors. Moreover, SerpinA1CSF correlated with neurofilament and CHI3L1 levels in CSF. Contrarily to SerpinA1CSF , neurofilament and CHI3L1 concentrations in CSF correlated with measures of disease progression in ALS, while SerpinA1serum mildly related with time to generalization (rho = 0.20, p = 0.04). In multivariate analysis, the ratio between serum and CSF SerpinA1 (SerpinA1 ratio) and NfHCSF were independently associated with survival. Conclusions: Higher SerpinA1CSF levels are found in fast progressors, suggesting SerpinA1 is a component of the neuroinflammatory mechanisms acting upon fast-progressing forms of ALS. Both neurofilaments or CHI3L1CSF levels outperformed SerpinA1 at predicting disease progression rate in our cohort, and so the prognostic value of SerpinA1 alone as a measure remains inconclusive

Erythropoietin (EPO) increases myelin gene expression in CG4 oligodendrocyte cells through the classical EPO receptor

Erythropoietin (EPO) has protective effects in neurodegenerative and neuroinflammatory diseases, including in animal models of multiple sclerosis, where EPO decreases disease severity. EPO also promotes neurogenesis and is protective in models of toxic demyelination. In this study, we asked whether EPO could promote neurorepair by also inducing remyelination. In addition, we investigated whether the effect of EPO could be mediated by the classical erythropoietic EPO receptor (EPOR), since it is still questioned if EPOR is functional in non-hematopoietic cells. Using CG4 cells, a line of rat oligodendrocyte precursor cells, we found that EPO increases the expression of myelin genes (myelin oligodendrocyte glycoprotein (MOG) and myelin basic protein (MBP)). EPO had no effect in wild-type CG4 cells, which do not express EPOR, whereas it increased MOG and MBP expression in cells engineered to overexpress EPOR (CG4-EPOR). This was reflected in a marked increase in MOG protein levels, as detected by western blot. In these cells, EPO induced by 10-fold the early growth response gene 2 (Egr2), which is required for peripheral myelination. However, Egr2 silencing with a siRNA did not reverse the effect of EPO, indicating that EPO acts through other pathways. In conclusion, EPO induces the expression of myelin genes in oligodendrocytes and this effect requires the presence of EPOR. This study demonstrates that EPOR can mediate neuroreparative effects

Different MRI patterns in MS worsening after stopping fingolimod

Objective To analyze MRI images in patients with MS who experienced worsening of neurologic status (WNS) after stopping fingolimod (FTY).MethodsIn this retrospective study, demographic, clinical, and radiologic data of patients with MS who experienced WNS after stopping FTY were retrospectively collected. We introduced the "\u3b4Expanded Disability Status Scale (EDSS)-ratio" to identify patients who, after FTY withdrawal, showed an inflammatory flare-up exceeding the highest lifetime disease activity level. Patients with \u3b4EDSS-ratio > 1 were enrolled in the study.ResultsEight patients were identified. The mean (SD) age of the 8 (7 female) patients was 35.3 (4.9) years. The mean FTY treatment duration was 3.1 (0.8) years. The mean FTY discontinuation-WNS interval was 4 (0.9) months. The 4 patients with \u3b4EDSS-ratio 65 2 developed severe monophasic WNS (EDSS score above 8.5), characterized by clinical features and MRI findings not typical of MS, which we classified as "tumefactive demyelination pattern" (TDL) and "Punctuated pattern" (PL). Conversely, patients whose \u3b4EDSS-ratio was between 1 and 2 had clinical features and brain MRI compatible with a more typical, even if aggressive, MS relapse. In patients with TDL and PL, the flare-up of inflammatory activity led to severe tissue damage resulting in T2 but also T1 lesion volume increase at 6-month follow-up.ConclusionsPeculiar MRI features (TDL and PL), different from a typical MS flare-up, might occur in some patients who experienced WNS after stopping FTY. Further studies, also involving immunologic biomarkers, are necessary to investigate TDL or PL pathophysiology