Francesco Marra

Post-impact mechanical characterisation of glass and basalt woven fabric laminates

Two woven fabric laminates, one based on basalt fibres, the other on E-glass fibres, as a reinforcement for vinylester matrix, were compared in terms of their post-impact performance. With this aim, first the non-impacted specimens were subjected to interlaminar shear stress and flexural tests, then flexural tests were repeated on laminates impacted using a falling weight tower at three impact energies (7.5, 15 and 22.5J). Tests were monitored using acoustic emission analysis of signal distribution with load and with distance from the impact point. The results show that the materials have a similar damage tolerance to impact and also their post-impact residual properties after impact do not differ much, with a slight superiority for basalt fibre reinforced laminates. The principal difference is represented by the presence of a more extended delamination area on E-glass fibre reinforced laminates than on basalt fibre reinforced ones.

Enhanced Lipid Extraction from Unbroken Microalgal Cells Using Enzymes

The marine microalga Nannochloropsis sp. was chosen as a model organism to investigate the feasibility of using cell wall-degrading enzymes to enhance the recovery of intracellular lipids. An enzyme cocktail containing galactomannanase, 1,4-β-cellobiosidase and β-glucosidase as main components was prepared from commercial enzyme preparations. The effects of pretreatment time (P), enzyme dosage (D), pH and temperature (T) on the amount of extracted lipids were investigated using response surface methodology. Under the best conditions (P = 90 min, D = 1.3 mg g–1, pH = 5, T = 36 °C) over 70 % of the lipids present in the microalga were recovered. SEM and TEM characterization of enzyme-treated microalgae showed extensive cell damage with significant disruption of the cell wall and release of algal material. Overall, the results obtained strongly support the use of commercial enzyme preparations to improve lipid recovery from microalgae and provide useful information on the influence of process conditions on the treatment efficiency.

Production and characterization of manganese oxide-based electrodes for anodic oxidation of organic compounds

Production and Characterization of Manganese OxideBased Electrodes for Anodic Oxidation of Organic Compounds Giovanni Sotgiu, Matteo Foderà, Francesco Marra, Elisabetta Petrucci a Dipartimento di Ingegneria, Università di Roma Tre, Via Vito Volterra, 62 00146, Roma b Dipartimento di Ingegneria Chimica Materiali Ambiente, Università degli Studi di Roma “La Sapienza”,Via Eudossiana, 18 00184, Roma *elisabetta.petrucci@uniroma1.it

Al2O3/ZrO2/Y3Al5O12 composites: A high-temperature mechanical characterization

An Al2O3/5 vol%·ZrO2/5 vol%·Y3Al5O12 (YAG) tri-phase composite was manufactured by surface modification of an alumina powder with inorganic precursors of the second phases. The bulk materials were produced by die-pressing and pressureless sintering at 1500 °C, obtaining fully dense, homogenous samples, with ultra-fine ZrO2 and YAG grains dispersed in a sub-micronic alumina matrix. The high temperature mechanical properties were investigated by four-point bending tests up to 1500 °C, and the grain size stability was assessed by observing the microstructural evolution of the samples heat treated up to 1700 °C. Dynamic indentation measures were performed on as-sintered and heat-treated Al2O3/ZrO2/YAG samples in order to evaluate the micro-hardness and elastic modulus as a function of re-heating temperature. The high temperature bending tests highlighted a transition from brittle to plastic behavior comprised between 1350 and 1400 °C and a considerable flexural strength reduction at temperatures higher than 1400 °C; moreover, the microstructural investigations carried out on the re-heated samples showed a very limited grain growth up to 1650 °C.

Numerical strategies for the bifurcation analysis of perfectly stirred reactors with detailed combustion mechanisms

Abstract The paper introduces a numerical tool based on a predictor–corrector continuation algorithm to obtain the bifurcation analysis of a perfectly stirred reactor with detailed reaction mechanisms. Each step of the continuation algorithm is reviewed and adapted to handle reaction mechanisms with hundreds of species and thousands of reactions. Particularly, the adoption of a Broyden solver in the predictor–corrector algorithm and a new formulation of the test functions are proposed. The implementation in Matlab and the adoption of the CANTERA Toolbox, make the tool easily applicable to reaction mechanisms available in CHEMKIN format. To validate and demonstrate the capability of the tool, the full equilibrium curves have been obtained for three different cases, having increasing number of species and reactions: methane–air (GRIMech.1.2), simple surrogates of Jet-A in air (JetSurF2.0) and a ternary surrogate of Jet-A in air (CRECK). The tool gets performances that make affordable the computations even with desktop computers.

Numerical Simulation of Oxy-Acetylene Testing Procedure of Ablative Materials for Re-Entry Space Vehicles:

A testing apparatus for flame exposure of ablative, high thermal flux-resistant materials has been designed and manufactured according to the ASTM E 285-80 standard. The test is useful for the selection of thermal protection systems (TPS) working as ablators and for the evaluation of their shielding performance. In order to support the material/component design and to offer new and differentiated tools for the screening phase of TPS materials, a CFD (computational fluid-dynamics) model of the burning test was developed. The model simulates the combustion of an oxygen—acetylene mixture occurring in a conventional welding torch, and calculates the heat flux incident on the sample and the related temperature fields. The validation of the model was obtained performing suitable instrumented tests enabling direct measurements of both incident heat flux and temperatures of the front and back surfaces of an ablative sample. Good agreement was found between numerical results and experimental measurements, encouraging the use of simulations for the design of the test environmental conditions.

Non-Linear Response to Periodic Forcing of Methane-Air Global and Detailed Kinetics in Continuous Stirred Tank Reactors Close to Extinction Conditions

This paper focus on the behavior of a continuous stirred tank reactor (CSTR) subject to perturbations of finite amplitude and frequency. Two main objectives are pursued: to determine the extinction line in the equivalence ratio (φ) - residence time (τ) plane, fixed the thermodynamic state conditions; and to characterize the response of the chemical system to periodic forcing of the residence time. Transient simulations of combustion of methane with air, using both global single-step and detailed chemical kinetic mechanisms, have been conducted and the corresponding asymptotic solutions analyzed. Results indicate very different dynamical behaviors, posing the issue of a proper choice of the kinetic scheme for the numerical study of combustion oscillations.

Bifurcation Analysis of Perfectly Stirred Reactors with Large Reaction Mechanisms

An accurate characterization of new generation fuels gets through a definition of the ignition and extinction conditions. According to the terminology of non-linear analysis the ignition and extinction conditions (critical conditions) are defined as the turning-points on the S-curve and are uniquely identified by two saddle-node bifurcations. The exact location of the critical points that mark the ignition and extinction conditions, the onset of instabilities, as well as the dependence of the location on parameter values, cannot be obtained easily using temporal simulations tools. For a systematic and accurate analysis, the bifurcation analysis and the parametric continuation technique are the tools of choice. Even when the reactive mixture is described by a simple surrogate, but in conjunction with very complex and detailed chemical mechanism, the computation of the critical conditions become computationally very demanding. Usually, these difficulties are overcome by using reduced schemes and allowing simplifications in the model, like constant averaged thermodynamic properties. In this work we explore these issues. Particularly, we show that the adoption of a Broyden type corrector in the continuation algorithm leads to performances that made affordable the computations even with desktop computers. Consequently, we introduce a suitable algorithm to investigate ignition, extinction and linear stability of the air-fuel mixtures in a Perfectly Stirred Reactor (PSR). The algorithm is based on the well-known Keller pseudo-arclength continuation method in order to compute steady state solution curves. The solutions stability and then ignition and extinction states are identified by test functions based on the numerical eigenvalues of the Jacobian of the governing system of equations. The algorithm is implemented in the numerical computing environment Matlab coupled with the CANTERA Toolbox for managing of complex chemical kinetic mechanisms. The algorithm is thus easily applicable to chemical schemes available in the standard ChemKin format. To illustrate the capability of the resulting method, the characteristic S-Shaped curve, including non-stable branches, for several air-hydrocarbon mixtures have been computed.

Generalized entropy production analysis for mechanism reduction

The paper introduces a generalized formulation for the computation of the relative contribution of each elementary reaction to the total entropy production, which has been proposed as a measure of the importance of elementary reactions and used for the reduction of detailed chemical reaction mechanisms. The reduction method is extended for the cases where the principle of detailed balance does not hold or apply, namely in the case of irreversible reactions or when the reverse rate constants are not computed via the thermodynamic equilibrium constants. Using a mechanism for n-butane consisting exclusively of reversible reactions, the new formulation is compared to the original one, and then applied for the construction of a skeletal mechanism for n-dodecane starting from a detailed mechanism which includes predominantly irreversible reactions. The skeletal scheme is found to accurately capture the ignition delay times over an extended range of pressure, initial temperature and equivalence ratio, the steady-state temperature as function of the residence time in a non-isothermal adiabatic perfectly stirred reactor, and the laminar flame speed of atmospheric flames at different unburned mixture temperatures and equivalence ratios.

Structures and Properties of Laser-Assisted Cold-Sprayed Aluminum Coatings

In the cold spray process, solid particles impact on a surface with high kinetic energy, deform plastically and form a coating. This enables the formation of pure and dense coating structures. Even more, coating performance and deposition efficiency can be improved by assisting the process with a laser. Laser-assisted cold spraying (LACS) has shown its potential to improve coating properties compared with traditional cold spraying. In this study, coating quality improvement was obtained by using a co-axial laser spray (COLA) process which offers a new, cost-effective laser-assisted cold spray technique, for high-quality deposition and repair. In the COLA process, the sprayed surface is laser heated while particles hit the surface. This assists the better bonding between particles and substrate and leads to the formation of tight coating structures. This study focuses on the evaluation of the microstructural characteristics and mechanical properties (e.g., hardness and bond strength) of LACS metallic coatings.