Shear Lag And Beam Theories For Structures

Dynamic problems are solved using beam theory and shear lag approximations, and also FEM. For a laminated plate incorporating through-thickness fibers, highlights are: 1) Inertia complicates the fiber pullout problem considerably. 2) Disturbances propagate along frictionally coupled fibers at less than the bar wave speed. 3) Unstable regimes appear in interfacial friction. 4) Large scale bridging creates oscillatory, predominately mode II crack profiles and 5) strongly modifies fracture at low to intermediate velocities. These results imply that dynamic delamination damage evolution will be dominated by distributed (not localized) bridging and friction effects. Solutions for single cracks with small process zones are less relevant than those for multiple cracks with large scale bridging, for which some initial solutions are discussed

Development of a dual-wavelength thermo-optical transmittance analyser: characterization and first results

Carbonaceous aerosol (CA) plays an important role in many different issues ranging from human health to global climate change. It mainly consists of organic carbon (OC) and elemental carbon (EC) although a minor fraction of carbonate carbon could be also present. Thermal-optical methods (TOT/TOR) are presently the most widespread approach to OC/EC speciation. Despite their popularity, there is still a disagreement among the results, especially for what concerns EC as different thermal protocols can be used. In fact, the pyrolysis occurring during the analysis can heavily affect OC/EC separation, depending on PM composition in addition to the used protocol. The main hypothesis at the basis of the technique relies on the optical properties of EC and OC: while EC is strongly light absorbing, OC is generally transparent in the visible range. However, a fraction of light-absorbing OC exists: the Brown Carbon (BrC) (Andreae and Gelencs\ue9r, 2006). The presence in the sample of BrC can shift the split point since it is slightly absorbing also @ 635nm, the typical laser wavelength used in this technique (Chen et al., 2015). At the Physics Department of the University of Genoa, a Sunset EC/OC analyser unit has been modified in order to monitor the optical transmittance during the thermo-optical analysis at two different wavelengths: 635 nm (the original wavelength of the instrument) and 405 nm (Fig.1). The additional use of the 405 nm transmittance measurement provides valuable information about the composition of the sample as well as on the pyrolytic carbon formation, both able to affect the instrumental \u201csplit point\u201d (i.e. the moment of the analysis in which the laser transmittance is back to its starting value, thus defining EC/OC separation). We present here the new instrument set-up, providing its full characterization with \u201csynthetic\u201d samples (i.e. mixtures of sucrose, graphitic carbon, and pure scattering particles). Moreover, we show also the results obtained analysing at 2-\uf06c - with both NIOSH and EUSAAR_2 protocols - real PM samples collected in very different conditions (i.e. summer-winter) and sites (ranging from urban to rural/mountain). Furthermore, we have recently introduced a new possibility, based on the apportionment of the absorption coefficient (babs) of particle-loaded filters, for correcting the thermo-optical analysis of PM samples (Massab\uf2 et al, 2016), an example in Fig.2. The apportionment is based on the optical analysis performed by the Multi-Wavelength Absorbance Analyser (MWAA), an instrument developed at the Physics Department of the University of Genoa (Massab\uf2 et al., 2015). The apportionment method uses the information gathered at five different wavelengths in a renewed and upgraded version of the approach usually referred to as Aethalometer model (Sandradewi et al., 2008). We present here also the results of the thermo-optical analysis correction (Massab\uf2 et al., 2016) applied to the dual-\uf06c analysis, which lead to a better homogeneity between the results obtained with different thermal protocols

Light extinction estimates using the IMPROVE algorithm: The relevance of site-specific coefficients

Atmospheric aerosol and gases affect visibility by scattering and absorbing the incoming radiation (Watson, 2002; Pitchford et al, 2007). While the role of gases is relatively well understood, the effect of particulate matter (PM) is more complicated to be assessed since it depends on several factors such as particles size distribution and chemical composition as well as meteorological parameters (e.g. relative humidity \u2013 RH). The U.S. Interagency Monitoring of Protected Visual Environments (IMPROVE) network proposed a method to retrieve atmospheric light extinction coefficient (bext, Mm-1) in national parks from compositional and meteorological data (Malm et al, 1994; Watson, 2002). The result of this approach (often called chemical light extinction) allows the evaluation of visibility indicators such as visual range (VR) via the Koschmieder equation VR=3.912/bext. In this study we tailored the IMPROVE equation using site-specific dry mass extinction efficiencies and hygroscopic growth functions in order to obtain bext estimates which better reflect the typical atmospheric characteristics of the sampling site and period. The revised formulation was tested for the first time in the urban area of Milan, for two weeks during the winter season in 2015. Moreover, it was applied to a large and fully characterized dataset referred to PM1 samples collected in winter 2012. Following the IMPROVE algorithm (Malm et al, 1994; Watson, 2002; Pitchford et al, 2007) the chemical light extinction equation used in this work was: bext = k1 x f1(RH) x [AMSUL] + k2 x f2(RH) x [AMNIT] + k3 x f3(RH) [OM] + k4 x [fine soil] + bap + 0.60 x [coarse mass] + 0.33 x [NO2] (ppb) + Rayleigh scattering, where inputs are the concentrations of the five major PM components (ammonium sulphate - AMSUL, ammonium nitrate AMNIT, organic matter - OM, fine soil, coarse mass) in \u3bcg m-3, NO2 concentration (in ppb), Rayleigh scattering by gases (Mm-1) and aerosol light absorption coefficient (bap, Mm-1) measured with a home-made polar photometer on PTFE filters. Dry mass extinction efficiencies (k1-k4, m2 g-1) for every chemical component of interest were calculated considering size distributions measured in Milan (Vecchi et al, 2012), particles densities and complex refractive indices (Watson, 2002). Furthermore, hygroscopic growth functions fi(RH), defined as the ratios between ambient and dry aerosol scattering coefficients bsp), were also calculated (using hygroscopic growth factors taken from the literature) and were applied to those PM components (AMSUL, AMNIT and OM), whose bsp are enhanced by their water uptake at medium-high RH values. It is worthy to note that in the original IMPROVE algorithm (Malm et al, 1994; Watson, 2002) the hygroscopic growth function f(RH) is calculated referring only to AMSUL ygroscopic properties and it is applied also to AMNIT, whereas OM is considered as non-hygroscopic. Non-negligible discrepancies were found between tailored dry mass extinction efficiencies and the original IMPROVE ones. Furthermore, differences between calculated fi(RH) and IMPROVE hygroscopic growth function were found. The methodology here described was applied to a PM1 dataset thus retrieving the extinction contribution given by the different PM1 components as well as by the major aerosol sources. Both methodological and experimental results will be shown in the presentation. This work shows that \u2013 due to the large variability in size distributions and aerosol composition at sites with different characteristics (e.g. urban, industrial, rural) \u2013 it is advisable to calculate site-specific k1-k4 and fi(RH) coefficients instead of using the original IMPROVE ones, which refer to aerosol properties measured at U.S. national parks

Characterizing mode II delamination cracks in stitched composites

This paper deals with characterizing the bridging mechanisms developed across delamination cracks by through-thickness reinforcement, using stitched carbon/epoxy laminates under mode II loading as a prime example. End Notched Flexure (ENF) tests are performed which show that stitching can provide stable crack growth. The bridging law, which characterizes the bridging action of the stitches, is deduced from both crack profile measurements and load vs. deflection curves. Consistent results are obtained from the two methods. The inferred laws imply that delamination cracks will commonly grow in conditions that are neither accurately nor properly described by linear elastic fracture mechanics. Large scale bridging calculations are required, in which the essential material property is the bridging traction law. The level of detail in which the law must be determined can be inferred from the sensitivity of predicted crack growth to variations in the law. It is recommended that the required parametric traction law be deduced in engineering practice from load vs, deflection data from the standard ENF (or similar) test, with due regard to selecting the notch size and other specimen dimensions to ensure that crack growth is stable in the test

A new instrument prototype for aerosol light absorption measurements

The prototype for an innovative instrument has been built and validated at the Department of Physics, University of Genoa. The purpose of the instrument is to measure the light absorption properties of atmospheric aerosol sampled on a filtering support, over a wide spectral range with a high wavelength resolution. The preliminary tests of the prototype have been carried out on aerosol produced in an atmospheric simulation chamber. The performance of the prototype has been validated against the previously assessed Multi Wavelength Absorbance Analyzer (MWAA), with a scatter plot slope of A = 0.95 ± 0.03, and a coefficient of determination of R2 = 0.97. Preliminary results show the data analysis possibilities that an instrument with a high spectral resolution can offer

Un modo alternativo per misurare la distribuzione dimensionale dei componenti del particolato atmosferico

In un precedente lavoro [1] era stata introdotta una metodologia per l\u2019apporzionamento del numero di particelle separate in diverse classi dimensionali a partire da serie di dati di concentrazione elementale ad alta risoluzione temporale. Qui lo stesso approccio viene esteso e verificato con campioni giornalieri di PM10 raccolti nell\u2019area portuale della citt\ue0 di Genova per circa cinque mesi. Le concentrazioni elementali dal Na al Pb sono state ottenute con l\u2019analisi dei campioni di PM10 tramite ED-XRF (Energy Dispersive X-Ray Fluorescence) e, successivamente, il contributo delle diverse sorgenti al PM10 \ue8 stato determinato analizzando le serie temporali di concentrazione con il modello a recettore denominato Positive Matrix Factorization (PMF, [2]). Durante il campionamento del PM10, l\u2019utilizzo di un contatore ottico di particelle, OPC (Grimm 1.108), ha permesso di misurare la distribuzione in numero delle particelle in diverse classi dimensionali. Questo strumento rileva le particelle con diametro compreso tra 0.25 Pm e 32 Pm suddividendole in 31 classi dimensionali. A partire dall\u2019andamento temporale, risolto mediante l\u2019analisi PMF, delle sorgenti che contribuiscono al PM10, una regressione lineare multipla permette di ottenere l\u2019apporzionamento del numero di particelle in ciascuna classe dimensionale [1]. Assumendo che tutte le particelle abbiano la stessa densit\ue0 e sommando su tutte le classi dimensionali \ue8 possibile calcolare un nuovo ed indipendente apporzionamento del PM10 che pu\uf2 essere confrontato con i risultati standard forniti dall\u2019analisi PMF dei campioni di PM10. I risultati ottenuti con i due metodi sono risultati in accordo. Combinando la conoscenza del contributo di ciascuna sorgente in ciascuna classe dimensionale con i profili delle sorgenti forniti dall\u2019analisi PMF, \ue8 possibile ottenere, per ciascun elemento, la frazione di massa in ogni intervallo dimensionale risolto dall\u2019OPC. Le distribuzioni dimensionali cos\uec ottenute sono state confrontate con quelle misurate direttamente con un impattore inerziale a cascata (SDI-Dekati\uae) in alcuni giorni della campagna PM10. Le pi\uf9 importanti caratteristiche delle distribuzioni dimensionali, quali, ad esempio, le concentrazioni dei singoli elementi nelle frazioni PM10, PM2.5 e PM1, sono ben riprodotte. In conclusione, questo studio mostra che l\u2019uso contemporaneo di campioni di PM10 giornalieri e di un OPC permette di ottenere sia l\u2019apporzionamento del PM10 che del numero di particelle in diverse classi dimensionali. Lo stesso approccio fornisce anche la distribuzione dimensionale dei singoli elementi e, da questo punto di vista, \ue8 complementare all\u2019uso degli impattori inerziali a cascata che, per la complessit\ue0 del loro utilizzo, vengono solitamente utilizzati per periodi limitati. Con questo nuovo metodo invece si ottengono informazioni che sono mediate e rappresentative di periodi pi\uf9 estesi. Dal punto di vista metodologico la scelta dell\u2019ED-XRF per le analisi di laboratorio \ue8 assolutamente non essenziale e l\u2019approccio qui descritto pu\uf2 essere utilizzato con serie di dati composizionali ottenuti con qualunque tecnica analitica. [1] Mazzei, F.; Lucarelli, F.; Nava, S.; Prati, P.; Valli, G.; Vecchi, R.. A New methodological approach: The combined use of two-stage streaker samplers and optical particle counters for the characterization of airbone particulate matter. Atmospheric Environment 41, 2007, 26, 5525-5535. [2] Paatero, P. Least square formulation of robust nonnegative factor analysis. Chemometrics and Intelligent Laboratory Systems, 1997,223-224