Gruppo Italiano Frattura (IGF)
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Investigation via morphological analysis of aluminium foams produced by replication casting
No full textFoams and porous materials with cellular structure have many interesting combinations of physicaland mechanical properties coupled with low specific weight. By means of replication casting it is possible tomanufacture foams from molten metal without direct foaming. A soluble salt is used as space holder, which isremoved by leaching in water. This can be done successfully if the content of space holding fillers is so high thatall the granules are interconnected. One of the main advantages of using the replication casting is a close controlof pore sizes which is given by the distribution of particle sizes of the filler material. This contrasts with thepore size distribution of the materials foamed by other processes where a wider statistical distribution of poresis found. On the other hand, the maximum porosities that can be achieved using space holders are limited tovalues below 60%, whereas the other methods allow for porosities up to 98%. Temperature of the mould andinfiltration pressure are critical process parameters: a typical problem encountered is the premature solidificationof the melt, especially due to the high heat capacity of the salt.In this work foam properties such as cell shape, distribution and anisotropy and defect presence are investigatedby using digital image processing technique. For this purpose replicated AlSi7Mg0.3 alloy foams are producedby infiltrating preforms of NaCl particles, varying the metal infiltration pressure and the mould preheatingtemperature.An original procedure based on image analysis has been set up to determine size, morphology and distributionof cells. The paper demonstrates that this methodology, coupled with microstructural analysis, is a useful toolfor investigating the effects of process parameters on foam properties
Un approccio innovativo per l'analisi quantitativa delle superfici di frattura a fatica nelle ghise sferoidali mediante elaborazione di immagini.
No full textLe osservazioni al microscopio elettronico a scansione (SEM) delle superfici di fratturaottenute a seguito di rotture per fatica consentono di evidenziare alcuni meccanismi di avanzamento che dipendono dal materiale e dalla modalità di applicazione delle sollecitazioni. L'introduzione di moderne tecniche di analisi di immagine assistite al calcolatore permette di elaborare un numero di informazioni elevato che consente di porre in relazione le caratteristiche morfologiche locali con il comportamento meccanico macroscopico del materiale. In questo lavoro è stata implementata una tecnica innovativa di analisi di immagine basata sull'analisi della tessitura, valutando l'influenza delle condizioni di applicazione della sollecitazione (LlK applicato) sulla evoluzione del clivaggio rilevato sulle superfici di frattura a fatica di una ghisa sferoidale ferritoperlitica
Bearing capacity of mixed soil model
No full textThe main objective of this research is the improvement of red soil by the addition of construction materials. This method could provide a scientific way to create a soil foundation with sufficient stability against geo-technical problems or instabilities. Laboratory tests have been conducted to characterize the behavior of red soil when amended with different types of gravels, soils and sand under compacted conditions with Optimum Moisture Content (OMC). Safe bearing capacity of all models have been calculated to identify the best and worst soil mixed model
Sulla storia degli studi di frattura in Italia
No full textHistory of studies of fracture is inherently intermingled with the history of technology developments.
In the beginning very little was written about. We must credit Leonardo and Galileo as the first
ones that wrote about the problem and on how to measure and foresee rupture loads. Later, nineteenth century
italian scientists distinguished themselves in attempting to establish material laws and multiple stresses
rupture criteria. A review of the works of past centuries italian scientists is presented, along with a critical
comparison with the work of other past european scientists
Effect of Carbon and Nitrogen content on deformation and fracture of AISI 304 austenitic stainless steel
No full textIn questo lavoro è stato studiato l'effetto di modeste differenze nel contenuto di carbonio e di azoto sulla deformazione e il comportamento a frattura a temperatura ambiente di un acciaio inossidabile austenitico AISI 304. Nell'acciaio contenente il più basso contenuto degli elementi interstiziali si forma una maggiore quantità di martensite indotta dalla deformazione plastica dell'austenite; ne risulta un aumento dell'incrudimento, della deformazione uniforme e della deformazione totale. La presenza di aree martensitiche di dimensioni significative nella sezione resistente causa però localizzazione della deformazione all'interfaccia austenite/martensite, e questo promuove la nucleazione di cricche e la loro propagazione all'interfaccia stesso. Questo fenomeno determina una diminuzione di UTS. La trasformazione martensitica indotta dalla deformazione causa inoltre una diminuzione della "strain rate sensitivity"
Proposta di utilizzo di metodologie termografiche per il controllo di qualità di componenti meccanici
No full textIn base all’esperienza maturata in anni di sperimentazione sull’analisi delle caratteristichemeccaniche dei materiali mediante indagine termografica, nel presente lavoro è proposta una procedura per ilcontrollo di qualità di componenti meccanici in linea di produzione, che è già stata argomento di brevetto.Lo sviluppo di questo lavoro si colloca nell’ambito del progetto FIRB “Sistemi di produzione intelligenti,flessibili e riconfigurabili”. L’attività svolta dal DIIM riguarda il controllo avanzato dell’affidabilità dicomponenti meccanici per l’industria automobilistica. Viene proposta, quindi, la realizzazione di una cella dicontrollo in linea di produzione capace di valutare la presenza di eventuali componenti difettosi attraversol’analisi termica degli stessi, sollecitati secondo un modello predefinito.L’attività, svolta in questa prima fase in laboratorio, è facilmente trasferibile in linea di produzione,considerando la possibilità di realizzare celle di prova in ambiente controllato, con condizioni praticamenteidentiche a quelle di laboratorio, eliminando gli effetti di disturbo che possono influenzare la rispostadell’indagine termografica in ambiente non strutturato
On the influence of T-Stress on photoelastic analysis under pure mode II loading
No full textAccording to the classical definition for in-plane modes of crack deformation, the constant stress term T exists only in the presence of mode I. However, recent studies show that this term can exist in mode II conditions as well, and significantly affect the elastic stress field around the crack tip. These effects can be visualized using the experimental method of photoelasticity. Based on the analytical studies, presence of the T-stress in mode II cracks transforms the isochromatic fringe patterns from symmetric closed loops to asymmetric and discontinuous shapes. In this paper, presence of the T-stress in mode II cracks and its effects on the fringe patterns is experimentally investigated. The test specimens are Brazilian disks containing very sharp central cracks: experimental results indicate that these specimens contain negative values of T-stress. Experimental values are then compared to numerical results. To better understand the differences between experimental and numerical values, a thee dimensional analysis is performed with the finite element method: results show the influence of the real geometry of the crack front on the stress intensity factors
Fatigue characterization of mechanical components in service
No full textThe quickly identify of fatigue limit of a mechanical component with good approximation iscurrently a significant practical problem not yet resolved in a satisfactory way. Generally, for a mechanicalcomponent, the fatigue strength reduction factor ( ?i) is difficult to evaluate especially when it is in service.In this paper, the procedures for crack paths individuation and consequently damage evaluation (adopted inlaboratory for stressed specimens with planned load histories) are applied to mechanical components, alreadyfailed during service. The energy parameters, proposed by the authors for the evaluation of the fatigue behaviorof the materials [1-5], are defined on specimens derived from a flange bolts. The flange connecting pipes at hightemperature and pressure. Due to the loss of the seal, the bolts have been subjected to a hot flow steamaddition to the normal stress.The numerical analysis coupled experimental analysis (measurement of surface temperature during static anddynamic tests of specimens taken from damaged tie rods), has helped to determine the causes of failure of thetie rods.The determination of an energy parameter for the evaluation of the damage showed that factors related to theheat release of the material (loaded) may also help to understand the causes of failure of mechanicalcomponents
Notiziario n. 18 - Luglio 2007
No full textIN QUESTO NUMERO1) Editoriale del Presidente IGF;2) Cariche sociali biennio 2005-2007;3) Verbale dell’Assemblea Annuale dei Soci 2006;4) Verbali dei Consigli di Presidenza;5) Resoconti delle attività del 2006;6) XIX Convegno Nazionale IGF – Milano 2007;7) Convocazione Assemblea Annuale dei Soci 2007;8) Calendario congressi internazionali ;9) Modulo di iscrizione IGF-ESIS
Influence of dipping time on cracking during bending of hot dip galvanized coatings with Sn and Ti contents
No full textIn the last years, the attention to environmental topics led a new approach solution in classical protection techniques, introducing innovative way oriented to optimize different coating properties. Hot-dip galvanizing is a classical process aimed to generate coatings on iron-based surfaces, used unchanged since 200 years: some chemical elements are added in the bath with different aims (e.g., Pb is really important for its fluidizing properties, sometimes replaced by Sn) but sometimes these elements are dangerous for human health (e.g. … Pb!).In this work, the influence of dipping time and coatings chemical compositions on damaging micromechanisms was investigated considering different Sn and Ti contents. Main damaging micromechanisms in hot dip zinc coated ipersandelin steel specimens were investigated by means of bending tests. Longitudinal sections of bended specimens were observed by means of a LOM (Light Optical Microscope): main damage micromechanisms were identified as longitudinal and radial cracks