Drilling polymeric matrix composites

This chapter presents the basics of drilling of polymeric matrix composites (PMCs). PMCs are becoming widely used in the manufacturing of products where a high mechanical strength must be accompanied by a low weight. However, the machining of PMCs implies coping with problems that are not encountered when machining other materials. Drilling is a particularly critical operation for PMCs laminates because the large concentrated forces generated can lead to widespread damage. This damage causes aesthetic problems but, more importantly, may compromise the mechanical properties of the finished part

Number of spanning clusters at the high-dimensional percolation thresholds

A scaling theory is used to derive the dependence of the average number of spanning clusters at threshold on the lattice size L. This number should become independent of L for dimensions d<6, and vary as log L at d=6. The predictions for d>6 depend on the boundary conditions, and the results there may vary between L^{d-6} and L^0. While simulations in six dimensions are consistent with this prediction (after including corrections of order loglog L), in five dimensions the average number of spanning clusters still increases as log L even up to L = 201. However, the histogram P(k) of the spanning cluster multiplicity does scale as a function of kX(L), with X(L)=1+const/L, indicating that for sufficiently large L the average will approach a finite value: a fit of the 5D multiplicity data with a constant plus a simple linear correction to scaling reproduces the data very well. Numerical simulations for d>6 and for d=4 are also presented.Comment: 8 pages, 11 figures. Final version to appear on Physical Review

conventional orthogonal cutting machining on unidirectional fibre reinforced plastics

Abstract The results of orthogonal cutting tests on unidirectional carbon and glass fibre reinforced plastics are presented. The specimens were under shape of rectangular plates, circular disks and cylinders with different fibre architectures and a milling machine, a lathe machine and a five-axis high-speed vertical machining centre, were used for the experimental tests. The cutting speed was varied. During the tests, performed at low cutting speed, avoiding thermal effects, and high speed, to investigate about the effect of the cutting velocity on the cut quality, the fibre orientation respect to the cutting direction, the tool rake angle and the depth of cut were varied to investigate their influence on the phenomenon. A high speed steel tool in different geometries, was used. The mechanisms of chip formation and the cutting quality were investigated. A tentative to correlate the mechanisms of chip formation and cutting forces signals was done. Since the anisotropy, the mechanisms of chip formation consists of different failure modes occurring simultaneously and their identification, on the basis of the cutting force evolution, is very complex. Only in particular conditions, the features of cutting forces allow a precise identification of the chip development and detachment. The results indicated that the fibre orientation respect to the cutting direction determines the mechanisms of chip formation and influences the cutting quality. It was noted that for fibre orientation higher than 60°, the quality of the surface was revealed unacceptable. These conclusions were obtained independently of the particular shape of specimen tested and of the speed adopted

VIAGGIO NELLA CLASSE OPERAIA AL TEMPO DI INDUSTRY 4.0. ORGANIZZAZIONE E CONDIZIONI DI LAVORO IN UNA PROSPETTIVA COMPARATA

Il lavoro di tesi intende indagare l\u2019impatto delle tecnologie e dell\u2019innovazione sulle condizioni di lavoro degli operai in Fiat, multinazionale produttrice di auto, che a partire dalla fine degli anni duemila ha implementato il suo nuovo modello produttivo, il wcm (World Class Manufacturing). Data la dimensione aziendale si \ue8 scelto di condurre l\u2019indagine attraverso uno studio di caso comparato prendendo in esame 4 stabilimenti del gruppo (Grugliasco, Melfi, Mirafiori e Pomigliano) sulla base di tre fattori (numerosit\ue0 operaia, livello di antagonismo sindacale e posizione geografica). Un modello produttivo impatta sulla realt\ue0 aziendale in maniera trasversale ed ogni ricerca sociologica che tenta di investigarne principi cardini ed effetti concreti rischia di scadere in opacit\ue0 e contorni non nettamente delineati. Nello strutturare la ricerca si \ue8 cercato di delimitare quanto pi\uf9 possibile tali contorni: individuato lo scenario di indagine (il nuovo modello produttivo), l\u2019obiettivo \ue8 stato indagare la soddisfazione del lavoro per capire come (e in che modo) tale modello produttivo ha impattato su di essa (job satisfaction solo degli operai, solo nei quattro stabilimenti individuati e solo del reparto assemblaggio). L\u2019indagine condotta (questionari, focus group, interviste semi-strutturate ed aperte) ci ha permesso, a partire dai risultati empirici sulla soddisfazione del lavoro, di fotografare i risvolti e gli effetti del modello produttivo in termini di pratiche gestionali del personale, partecipazione e coinvolgimento operaio, ambiente e condizioni di lavoro, tendenze nelle relazioni industriali: chiaramente l\u2019oggetto di indagine \ue8 la soddisfazione del lavoro che rappresenta la base di analisi che ci ha permesso di indagare da diversi punti di vista gli effetti del nuovo modello produttivo. Il lavoro si articola in quattro sezioni differenti: nella prima (capitoli 1, 2 e 3) vengono sintetizzati i riferimenti teorici attinti dalla sociologia economica e i principi manageriali tratti dalle scienze dell\u2019organizzazione con particolare attenzione al post-fordismo, alla lean production, ai meccanismi di produzione nelle catene globali del valore e agli attuali scenari organizzativi al tempo di Industry 4.0. La seconda sezione (capitolo 4 e 5) ispeziona il percorso metodologico, fondato sul paradigma di ricerca misto, del quale si da ampia giustificazione: vengono elencate le molteplici tecniche di analisi adottate (focus group, interviste aperte, questionari con relativa analisi dei dati e interviste semistrutturate) e la logica sottostante che ha guidato tali scelte. La terza sezione, invece, sintetizza risultati ed evidenze empiriche raccolte sul campo: in particolare nel primo capitolo empirico (capitolo 6) vengono riportati i dati relativi al comportamento della soddisfazione rispetto alle caratteristiche individuali, di contesto familiare e di vicende lavorative e viene esposto il modello di analisi probit sulla probabilit\ue0 di essere soddisfatti relativo ad ulteriori 16 variabili caratterizzanti il concetto di soddisfazione; nei successivi quattro capitoli (capitolo 7, 8, 9 e 10) vengono analizzate quattro distinte macro-dimensioni del lavoro (ambiente di lavoro, relazioni di lavoro, partecipazione al lavoro e teamworking) e per ognuna di esse vengono presentati i risultati delle interviste semistrutturate agli operai e delle regressioni effettuate tra singole variabili e soddisfazione generale del lavoro. Nella quarta sezione, alla luce dei dati emersi dalla ricerca, si elaborano considerazioni conclusive sulla condizione operaia in relazione al nuovo contesto organizzativo: ogni capitolo empirico della terza sezione presenta specifiche conclusioni legate alle singole variabili in esso analizzate che, per\uf2, si \ue8 voluto declinare in maniera integrata dando una visione d\u2019insieme ai risultati esposti, precisando potenzialit\ue0 e fallacit\ue0 del modello produttivo rispetto alla soddisfazione operaia e delineando possibili linee future di ricerca

Complex Effects of Ecosystem Engineer Loss on Benthic Ecosystem Response to Detrital Macroalgae

Ecosystem engineers change abiotic conditions, community assembly and ecosystem functioning. Consequently, their loss may modify thresholds of ecosystem response to disturbance and undermine ecosystem stability. This study investigates how loss of the bioturbating lugworm Arenicola marina modifies the response to macroalgal detrital enrichment of sediment biogeochemical properties, microphytobenthos and macrofauna assemblages. A field manipulative experiment was done on an intertidal sandflat (Oosterschelde estuary, The Netherlands). Lugworms were deliberately excluded from 1x m sediment plots and different amounts of detrital Ulva (0, 200 or 600 g Wet Weight) were added twice. Sediment biogeochemistry changes were evaluated through benthic respiration, sediment organic carbon content and porewater inorganic carbon as well as detrital macroalgae remaining in the sediment one month after enrichment. Microalgal biomass and macrofauna composition were measured at the same time. Macroalgal carbon mineralization and transfer to the benthic consumers were also investigated during decomposition at low enrichment level (200 g WW). The interaction between lugworm exclusion and detrital enrichment did not modify sediment organic carbon or benthic respiration. Weak but significant changes were instead found for porewater inorganic carbon and microalgal biomass. Lugworm exclusion caused an increase of porewater carbon and a decrease of microalgal biomass, while detrital enrichment drove these values back to values typical of lugworm-dominated sediments. Lugworm exclusion also decreased the amount of macroalgae remaining into the sediment and accelerated detrital carbon mineralization and CO2 release to the water column. Eventually, the interaction between lugworm exclusion and detrital enrichment affected macrofauna abundance and diversity, which collapsed at high level of enrichment only when the lugworms were present. This study reveals that in nature the role of this ecosystem engineer may be variable and sometimes have no or even negative effects on stability, conversely to what it should be expected based on current research knowledge

Flood susceptibility assessment in a highly urbanized alluvial fan: the case study of Sala Consilina (southern Italy)

Abstract. This paper deals with the risk assessment to alluvial fan flooding at the piedmont zone of carbonate massifs of the southern Apennines chain (southern Italy). These areas are prime spots for urban development and are generally considered to be safer than the valley floors. As a result, villages and towns have been built on alluvial fans which, during intense storms, may be affected by flooding and/or debris flow processes. The study area is located at the foothills of the Maddalena mountains, an elongated NW-SE trending ridge which bounds to the east the wide intermontane basin of Vallo di Diano. The area comprises a wide detrital talus (bajada) made up by coalescent alluvial fans, ranging in age from the Middle Pleistocene to the Holocene. Historical analysis was carried out to ascertain the state of activity of the fans and to identify and map the zones most hit by past flooding. According to the information gathered, the Sala Consilina fans would appear prone to debris flows; in the past these processes have produced extensive damage and loss of life in the urban area. The watershed basins feeding the fans have very low response times and may produce debris flow events with high magnitudes. Taking into account the historical damage, the fan surface morphology, and the present urban development (street orientation and hydraulic network), the piedmont area was zoned and various susceptibility classes were detected. These results may represent a useful tool for studies aiming at territorial hazard mapping and civil protection interventions