New perspectives have arisen on basalt fibre applications due to the potential low cost of this material together with its good mechanical performance, in particular at high temperature. The idea to ...fill these fibres into a polymer matrix is relatively recent and could offer very interesting perspectives that have not yet been sufficiently investigated. In this work, with the principal aim of evaluating the possibility to replace glass fibres in most of their applications, mechanical tests were carried out on comparable E-glass and basalt fibre reinforced plastic laminates. The latter were cut by square plates fabricated through vacuum bag technology. The results obtained on the two laminates were compared showing a high performance of the basalt material in terms of young modulus, compressive and bending strength, impact force and energy. These good properties suggest possible applications of basalt fibres in fields where glass composites are nowadays largely applied. The short-beam strength tests confirmed what above said by denoting an interfacial adhesion similar to that between E-glass and epoxy matrix.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Microwave thermal ablation (MTA) is a minimally invasive therapeutic technique aimed at destroying pathologic tissues through a very high temperature increase induced by the absorption of an ...electromagnetic field at microwave (MW) frequencies. Open problems, which are delaying MTA applications in clinical practice, are mainly linked to the extremely high temperatures, up to 120 °C, reached by the tissue close to the antenna applicator, as well as to the ability of foreseeing and controlling the shape and dimension of the thermally ablated area. Recent research was devoted to the characterisation of dielectric, thermal and physical properties of tissue looking at their changes with the increasing temperature, looking for possible developments of reliable, automatic and personalised treatment planning. In this paper, a review of the recently obtained results as well as new unpublished data will be presented and discussed.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Thermal properties of ex vivo bovine liver were measured as a function of temperature, by heating tissue samples in a temperature-controlled oil bath over a temperature range from about 21 °C to ...about 113 °C. Results evidenced temperature-dependent non-linear changes of the thermal properties, with the temperature of 100 °C representing a break point: the thermal properties increased with temperature up to 99 °C and then decreased above 100 °C. The rate of increase appeared dramatic between 90 °C and 99 °C, owing to the onset of vaporisation of water contained in the tissue. In particular, at 99 °C, the thermal conductivity reported an increase of about four times with respect to the value measured at 90 °C, whilst about a two-fold increase was reported for both the volumetric heat capacity and the thermal diffusivity. Temperatures higher than 100 °C were reached only after complete vaporisation of water contained in the tissue, resulting in about 70% loss of weight from the tissue. An overall decrease of about 71% and 63% was reported for the thermal conductivity and volumetric heat capacity, respectively, in the temperature range 101 °C-113 °C. A decrease of about 25% was reported in the measured values of the thermal diffusivity in the temperature range 101 °C-108 °C, whilst a slight increase of measured values, not statistically significant, was observed in the temperature range 108 °C-113 °C. The temperature dependent changes of the thermal parameters were modelled with non-linear regression analysis to calculate the best-fit curves interpolating measured data. The proposed regression models could be used to numerically assess the changes in the thermal properties of biological tissues at supra-physiological temperatures relevant in thermal ablation procedures, as well as their effect on the prediction of the ablation zone dimensions in computational models for treatment planning.
The present manuscript aims to provide an overview of the phenomenon of the low-velocity impact behaviour of composite materials at room and in extreme temperature conditions, by comparing the ...results obtained on different fibre-matrix combinations and giving a comprehensive review of the impact behaviour and evolution of damage of marine and aerospace composites. The latter was chosen to reduce the environmental impact of plastic wastes. Experimental impact tests up to complete penetration and at different increasing impact energy levels, were carried out by a modular falling weight tower.
The ability of different Non Destructive Techniques NDT in detecting and evaluating barely-visible and invisible impact damage on composite laminates was tested. The aspect related to the damage is, in fact, crucial for these materials because of their inhomogeneity and anisotropy.
The conventional and largely used UltraSound technique, US, was adopted to investigate the delamination caused by low-velocity impact loads. The results were compared with Electronic Speckle Pattern Interferometry, ESPI, as well as with theoretical and semiempirical formulations for the delamination prediction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Microwave thermal ablation (MTA) therapies exploit the local absorption of an electromagnetic field at microwave (MW) frequencies to destroy unhealthy tissue, by way of a very high temperature ...increase (about 60 °C or higher). To develop reliable interventional protocols, numerical tools able to correctly foresee the temperature increase obtained in the tissue would be very useful. In this work, different numerical models of the dielectric and thermal property changes with temperature were investigated, looking at the simulated temperature increments and at the size of the achievable zone of ablation. To assess the numerical data, measurement of the temperature increases close to a MTA antenna were performed in correspondence with the antenna feed-point and the antenna cooling system, for increasing values of the radiated power. Results show that models not including the changes of the dielectric and thermal properties can be used only for very low values of the power radiated by the antenna, whereas a good agreement with the experimental values can be obtained up to 20 W if water vaporization is included in the numerical model. Finally, for higher power values, a simulation that dynamically includes the tissue's dielectric and thermal property changes with the temperature should be performed.
Natural fibre composite have a potential to be widely applied in the alternative to a fibreglass composites in sustainable energy impact absorption structures. In this study, the behaviour of hemp ...fibre epoxy composites subjected to a low-velocity impact loading, using an instrumented falling weight impact equipment, is presented. Two types of hemp reinforcements were used: unidirectional and bi-directional fabric and three balanced laminates (0 degree /90 degree ) different in thickness were studied: 4 plies, 8 plies, 12 plies. The results were compared. The laminates were fabricated by RIFT process using a common epoxy matrix. The reached volumetric fibre percentage Vf was not too high. It assumed a value of 34% for the unidirectional reinforcement and an average value of 30% for the bidirectional one. Some laminates were impregnated by PLA resin at the aim to obtain a completely natural system. The impact behaviour was analysed carrying out tests impacting square specimens, 100100mm, with a hemispherical tup geometry with a diameter of 19.8mm and a velocity of 4.0m/s. Both penetration and indentation tests were performed at the aim to investigate about the damage start and evolution. The impact induced damage, characterised by an optical microscope, includes matrix cracking, delamination, fibre breakage and fibre pullout. An interesting compressed central zone of the laminate under the impact point was noted.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•A new nonlinear ultrasonic technique “Narrowband SPC-I” is proposed.•It is able to monitor damage in composite plates as the impact energy increases.•Combining nonlinear and linear techniques is not ...needed when using narrowband SPC-I.
An improved technique for sensing damage initiation and progression in thermoplastic resin composite plate specimens is presented in this study. The composite plate specimens are investigated by using a nonlinear ultrasonic (NLU) technique called Sideband Peak Count Index or SPC-I. The technique presented in this paper is an improvement from the previous SPC-I technique. This improved technique provides more reliable and consistent results and can monitor the damage progression over a wide range. In this paper the narrow band SPC-I technique is introduced to replace the conventional wide band SPC-I technique. The method implemented here is improved in three ways. First and foremost the narrow band SPC-I technique is introduced. Secondly, the non-permanently adhered gel coupled Lead-Zirconate-Titanate (PZT) transducers are used to reduce inconsistency in transducer adhesion and manufacturing. Lastly, higher sampling rate equipment is used for better signal resolution and peak counting. The experiments are performed on 4 sets of composite plate specimens fabricated using two composite fiber materials (Glass and Basalt) that have increasing levels of damage. The composite plate specimens were damaged by a falling weight impact machine with increasing impact energy (0 J, 10 J, 20 J and 30 J). The composite plate specimens were examined by propagating a narrow band chirp signal through the specimens using gel coupled transducers in a transmission mode setup. The received signals were recorded and analyzed using the NLU SPC-I technique. The modified SPC-I technique proposed in this paper can reliably and consistently detect both initiation and progression of damage in the composite plate specimens.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This work investigated the effect of repeated low-velocity impacts at different energy levels on vinyl ester composite laminates. In particular, hybrid composite laminates made by carbon woven fabric ...and glass woven fabric impregnated by vinyl ester resin were subjected to 1, 5 and 10 impacts for three different energy levels (U=5 J, 10 J and 20 J). The multi-impact damage evolution was studied by combining several non-destructive techniques such as Pulsed Thermography, Electronic Speckle Pattern Interferometry and Ultrasonic C-scanning. Along with images of detected damaged areas, some impact parameters such as contact force, deflection and absorbed energy were provided.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
The purpose of hybridization is to obtain a new material preserving advantages from all of its constituents. Hybridization offers intermediate properties respect to the original materials, by ...creating a balance effect within the fibres incorporated in the composite materials and leading to a composite with more tailored behaviour The increasing need to mitigate the environmental impact of synthetic fibres and polymers is promoting the use and application of natural materials orienting the research toward the development of biodegradable systems.
In this framework, hybrid reinforced laminates with flax and basalt twill layers alternatively stacked, were manufactured by resin infusion fabrication technology and impacted at low velocity to investigate their dynamic behaviour, in an attempt to couple the impact resistance of basalt fibres with the environmentally friendly nature of flax fibres. For comparison purposes, the same experimental characterization has been performed on laminates reinforced with only basalt or flax fibres. The experimental results confirmed the positive role played by fibre hybridization in terms of damage.
The Electronic Speckle Pattern Interferometry technique was adopted to analyze the internal damage and to provide information on the shape and the extent of the delamination, that was found concentrated under the impactor-material contact point for the basalt and flax/basalt laminates.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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