Jacopo Tirillò

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.

Effect of different lignocellulosic fibres on poly(ε-caprolactone)-based composites for potential applications in orthotics

This work compares the mechanical and thermal behaviour of fully biodegradable biocomposites based on polycaprolactone reinforced with three different natural fibres, namely hemp, sisal and coir, for potential applications in the field of orthoses. The same properties were further compared to those of two commercially available materials commonly used in the same prospective field. The results confirmed that the addition of natural fibres, irrespective of the origin of the fibres (leaf, bast or fruit) to a biodegradable matrix allows for significant improvement of the mechanical behaviour of the ensuing composites compared to traditional thermoplastic materials used in orthotics.

Mechanical characterization of hydroxiapatite micro/macro-porous ceramics obtained by means of innovative gel-casting process

An innovative gel-casting process was developed in order to obtain macro porous ceramics scaffolds of hydroxyapatite to be used in regenerative medicine for bone tissue reconstruction. Mechanical investigation was carried out on different formulations of dense hydroxyapatite samples in order to evaluate the effect of the gel casting process parameters on the density, the elastic modulus, the tensile and the compressive strength. The fracture critical stress intensity factor (KIC) was also evaluated by means of microhardness measurements. The correlations between KIC and tensile and compressive strength were examined taking into account the average and maximum size of porosity. The mechanical properties of macro and micro-porous HA are in agreement with the model of Gibson and Ashby.

Synthesis and Characterization of Magnetic Nanocomposites for Environmental Remediation

In the present study, the effect of nano-magnetite (Fe3O4) content on mechanical and magnetic properties of polypropylene matrix is investigated. Magnetite nanoparticles were successfully synthesized by co- precipitation while the composites were prepared by an ex situ processing method involving solvent casting followed by compression molding. The nanoparticles and resulting nanocomposites were characterized by X- ray diffraction, thermogravimetric analysis, scanning electron microscopy, tensile testing and vibrating sample magnetometry. It was found that composites have tailorable mechanical and magnetic properties dependent on the content of magnetic filler. Increase of concentration of magnetite particles provides a significant increase of Young’s modulus without affecting the yield strength and the ductility. As regards the magnetic properties, nanocomposites having 10 wt% of nanoparticles exhibited a superparamagnetic behaviour that can be exploited in environmental applications.

Dense and cellular zirconia produced by gel casting with agar: preparation and high temperature characterization

A modified gel-casting process was developed to produce both dense and highly porous (40% volume) yttria tetragonal zirconia polycrystal (Y-TZP) using agar, a natural polysaccharide, as gelling agent. A fugitive phase, made of commercial polyethylene spheres, was added to the ceramic suspension before gelling to produce cellular ceramic structures. The characterization of the microstructural features of both dense and cellular ceramics was carried out by FEG SEM analysis of cross-sections produced by focused ion beam. The mechanical properties of the components were characterized at room temperature by nanoindentation tests in continuous stiffness measurement mode, by investigating the direct effect of the presence of residual microporosity. The presence of a diffuse residual microporosity from incomplete gel deaeration resulted in a decay of the bending strength and of the elastic modulus. The mechanical behavior of both dense and cellular zirconia (in terms of elastic modulus, flexural strength, and deformation at rupture) was investigated by performing four-point bending tests at the temperature of 1500°C.

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.

Effect of glycerol on the physical and mechanical properties of thin gellan gum films for oral drug delivery

Graphical abstract Figure. No caption available. ABSTRACT In this work, deacylated gellan gum and the plasticizer glycerol were used as primary components for the preparation of thin films intended for the oral delivery of therapeutic molecules. The samples were prepared by a solvent casting method and characterized for their thickness, tensile properties, swelling ability, mucoadhesion capacity and uniform drug distribution. The amount of glycerol was varied from 20% to 75% w/w in order to obtain films with tunable mechanical properties and high drug loading efficiency. The addition of glycerol was able to positively influence the mechanical characteristics of gellan gum thin film overcoming the brittleness caused by the rigid interconnection among the polymeric chains. Plasticized gellan gum films containing 50% w/w of glycerol showed optimal mechanical resistance and mucoadhesion capacity, which were adversely affected by the inclusion of higher concentrations of glycerol. On the contrary, only high amounts of the plasticizer (≥70% w/w) enabled a homogeneous distribution of the model drug fluconazole within the polymeric matrix. Overall, these results indicate that gellan gum‐based thin films can be potentially used for buccal drug delivery upon precise selection of the appropriate concentration of glycerol used as a plasticizer.

Evaluation of Stress Equilibrium in Dynamic Tests on Agglomerated Cork

In this work, experimental compression tests have been performed on rectangular specimens cut from a cork slab. The tests have been performed both using a quasi-static testing machine and a Split Hopkinson Bar. The dynamic tests revealed a high sensitivity of the material to the strain rate, with stress strain curves significantly higher than in quasi-static condition. Given the low density of the cork, the specimen material may suffer from non-equilibrium; for this reason, a high speed camera was used to frame acquire pictures of the sample during the deformation, which have been used to perform DIC analyses. Indeed, inhomogeneous strain distributions were found, especially due to the low density of samples tested at the higher speed. Moreover, the low impedance of the tested material also determines difficulties in signal synchronization and, hence, in the correct calculation of the stress in the sample. Data from DIC analyses were then used to calculate the true strain in different portions of the specimen and to evaluate the stress due to inertia effect.

Dual morphology (fibres and particles) cellulosic filler for WPC materials

Wood-plastic composites (WPC) were fabricated by using a polyethylene (PE) matrix and filling it with wood flour in the amount of 30 wt.%, and compared with the same composites with further amount of 10 wt.% of cellulosic recycled fibres added. The materials were produced by turbomixing and subsequent moulding under pressure. Mechanical properties of both WPC and WPC with cellulosic recycled fibres were evaluated through mechanical and physical-chemical tests. Tensile tests clarified that a moderate reduction is strength is observed with the bare introduction of wood flour with respect to the neat PE matrix, whilst some recovery is offered by the addition of recycled cellulose fibres. Even more promisingly, the elastic modulus of PE matrix is substantially improved by the addition of wood flour (around 8% on average) and much more so with the further addition of recycled cellulose (around 20% on average). The fracture surfaces from the tensile test were analysed by scanning electron microscope (SEM) indicating a reduction in microporosity as an effect of added cellulose. The water absorption test and the hardness measure (Shore D) were also performed. SEM analysis underlined the weak interface between both wood particle and cellulosic recycled fibres and matrix. The water absorption test showed a higher mass variation for pure WPC than WPC with cellulosic recycled fibres. The hardness measurement showed that the presence of cellulosic recycled fibres improves both superficial hardness of the composite and temperature resistance.Wood-plastic composites (WPC) were fabricated by using a polyethylene (PE) matrix and filling it with wood flour in the amount of 30 wt.%, and compared with the same composites with further amount of 10 wt.% of cellulosic recycled fibres added. The materials were produced by turbomixing and subsequent moulding under pressure. Mechanical properties of both WPC and WPC with cellulosic recycled fibres were evaluated through mechanical and physical-chemical tests. Tensile tests clarified that a moderate reduction is strength is observed with the bare introduction of wood flour with respect to the neat PE matrix, whilst some recovery is offered by the addition of recycled cellulose fibres. Even more promisingly, the elastic modulus of PE matrix is substantially improved by the addition of wood flour (around 8% on average) and much more so with the further addition of recycled cellulose (around 20% on average). The fracture surfaces from the tensile test were analysed by scanning electron microscope (SEM) indic...