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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Low velocity impact tests at different impact energies were performed on basalt fibre reinforced plastic laminates, varying laminate thickness, stacking sequence, support dimensions and indenter ...diameter. A previous modified analytical model for the prediction of the indentation as a function of the impact energy, valid for carbon and glass fibre reinforced plastic laminates, was applied: a different behaviour was observed denoting an other damage mechanisms of the basalt fibre laminates. About the prediction of the penetration energy, the previous model largely applied in the literature showing the importance of the total fibre content was adopted, and a good agreement between the theoretical predictions and the experimental results was found. In analysing previous experimental data, in comparison to those of carbon fibre reinforced plastics, higher impact energy was found to be necessary to penetrate the basalt laminates whereas the indentation depth at the same impact energy was lower. A larger number of tests were carried out to validate a preliminary work done by the authors.
Full text
Available for:
NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
This paper aims to investigate the ability of ultrasonic and electronic speckle pattern interferometry to analyse the low-velocity impact internal damage mechanisms on basalt composite laminates and ...to provide information on the shape and the extent of the delamination in non-destructive way.
Basalt/epoxy composites with different thicknesses have been realised and characterised by mechanical tests to investigate both fibre-dominated (tensile and flexural behaviour) and matrix-dominated properties (interlaminar shear strength). Specimens were impacted at penetration and at increasing energy values, to explore the damage onset and propagation. The results showed that the damage was concentrated under the impactor–material contact point and that the composite with intermediate thickness had the best balance between the different kinds of impact damages: delamination and indentation. Further, a good agreement was found between the overall data obtained by the two non-destructive techniques, confirming the capability of both techniques to examine the composite impact damage.
Full text
Available for:
NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
The wide biodiversity and economic importance of digeneans have motivated a great deal of research in the last decade, focussing on their phylogenetic positions. Molecular research was instrumental ...for our understanding of phylogeny in the Digenea, but spermatological studies have also provided many results, which are potentially useful for phylogeny; however, the complete spermatological data set has never been reviewed in a whole phylogenetic perspective. Spermatological data are now available for more than 100 species, belonging to 15 superfamilies and 46 families. In this paper, we try to summarize the current knowledge about sperm structure in the digeneans and propose a classification of digenean spermatozoa into five basic models. The main ultrastructural characters used are (1) the type of axoneme, (2) the lateral expansion, (3) the association 'external ornamentation of the plasma membrane + cortical microtubules', (4) the field of cortical microtubules and its number, (5) the location of the external ornamentation, (6) the location of the maximum number of cortical microtubules and (7) the number of mitochondria. We also outline the most interesting features for phylogenetic inference and their possible value in the context of digenean systematics, phylogeny and evolution. Associations between sperm models and superfamilies were found as follows: Type 1 in the Schistosomatoidea; Type 2 in the Hemiuroidea; Type 3 in the Opecoeloidea, Lepocreadioidea, Haploporoidea and Opisthorchioidea; Type 4 in the Gorgoderoidea, Microphalloidea, Plagiorchioidea and Gymnophalloidea; Type 5 in the Echinostomatoidea, Microscaphidioidea, Paramphistomoidea, Pronocephaloidea and Brachylaimoidea.
Laser bending is an innovative technology that uses a laser beam to bend metal sheets and/or components. It offers advantages such as lack of equipment, high flexibility, adaptability to different ...materials (including metal foams), and possibility of automation. Actually, the angle can be measured only after the laser-bending process. The acoustic emission (AE) technique offers a great potential for the “on-time” evaluation of the bending angle: this technique is based on the detection of high-frequency acoustic signals emitted during the phenomena evolution deriving from the deformation and/or fracture of a component/structure. This paper presents an initial approach to understand the relationship between bending angle and the characteristics of the AE signals generated during the laser-material interaction. In this work, a diode laser is used to bend an AISI 304 stainless steel sheet: the laser parameters used and the bending angle obtained were correlated with each other. A useful dependence between laser bending and AE parameters was found.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Despite global efforts to improve surgical care access, many low- and middle-income countries, especially in neurosurgery, face significant shortages. The Gambia exemplifies this, with only 1 fully ...qualified neurosurgeon serving its population of 2.5 million people. This scarcity results in higher morbidity and mortality.
We aim to document the history and current state of neurosurgery in the Gambia to raise awareness and promote neurosurgery development.
The study reviews the Gambia's health care system, infrastructure, neurosurgical history, workforce, disease burden, and progress, with information derived from reference sources as well as author experience and interviews with key partners in Gambian health care.
Neurosurgery in the Gambia began in the 1970s, facing constraints due to competing health care demands. Significant progress occurred much later in the early 2010s, marked by the initiation of Banjul Neuro Missions and the establishment of a dedicated neurosurgery unit. We report significant progress with neurosurgical interventions in the past few years showcasing the unit's dedication to advancing neurosurgical care in the Gambia. However, challenges persist, including a lack of trained neurosurgeons, equipment shortages such as ventilators and diagnostic imaging. Financial barriers for patients, particularly related to the costs of computer tomography scans, pose significant hurdles, impacting the timely diagnosis and intervention for neurological conditions.
Neurosurgery in the Gambia is progressing, but challenges like equipment scarcity hinder further progress. We emphasize the need for addressing cost barriers, improving infrastructure, and fostering research. Engaging the government and international collaborations are vital for sustained development in Gambian neurosurgery.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
