1,721,106 research outputs found
Evaluation of stress equilibrium in dynamic tests on agglomerated cork
No full textIn 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
Ductile viscose fibres and stiff basalt fibres for composite applications. An overview and the potential of hybridisation
No full textIn the present study, the hybridisation of ductile viscose (Danufil) and stiff basalt fibres was investigated. The aim was to combine the positive properties of both fibre types in an epoxy matrix. Composites (round rods) were produced with a fibre volume fraction of 40% with a pultrusion technique from Danufil, basalt and a mixture of Danufil and basalt fibres. The hybrid composites were produced on the one hand with a unidirectional (UD) Danufil core and a UD basalt outer layer and vice versa. On the other hand, a UD core layer of Danufil is covered with a twisted basalt outer layer and vice versa. The results have shown that the most successful hybridisation was realised with the UD composite having a Danufil core and a UD basalt outer layer. An impact strength on the level of the basalt fibre-reinforced composite could be achieved whereby the lightweight construction potential could be improved. The spontaneous failure of the basalt fibre-reinforced composite under bending load could be considerably delayed by the addition of Danufil, whereby the strength, stiffness and temperature resistance were significantly improved by the presence of basalt. For the application of round rods, e.g. in poles for mobile architecture, the load-bearing capacity and the safety aspects could be significantly improved by hybridisation
The compressive behavior and crashworthiness of cork. A review
Full text linkCork, a natural material from renewable resources, is currently attracting increasing interest in different industrial fields because of its cellular structure and the presence of the flexible suberin as its main chemical component. In an agglomerated form, it proved to be a compelling product not only as a thermal and acoustic insulator, but also as core material in sandwich structures and as a liner or padding in energy absorbing equipment. From this perspective, the assessment of its compressive response is fundamental to ensure the right out-of-plane stiffness required to a core material and the proper crashworthiness in the safety devices. Considering the complex nature of cork and the resulting peculiar compressive response, the present review article provides an overview of this paramount property, assessing the main parameters (anisotropy, temperature, strain rate, etc.) and the peculiar features (near-zero Poisson’s ratio and unique dimensional recovery) that characterize it in its natural state. Furthermore, considering its massive exploitation in the agglomerated form, the design parameters that allow its compressive behavior to be tailored and the operating parameters that can affect its crashworthiness were assessed, reporting some potential industrial applications
A systematic literature review on less common natural fibres and their biocomposites
No full textInterest in utilization of renewable resources is increasing because of public's environmental awareness and economic considerations. Lignocellulosic fibres have already attracted growing attention as reinforcement of polymeric matrices instead of synthetic ones (mainly glass) from the academic and industrial fields. In addition to kenaf, hemp, sisal, flax and jute, which are the subject of extensive investigations for composite applications since the 1970s, in the last years several researchers suggested the use of less common natural fibres, due to their low cost and availability. This paper reviews the extraction methods, chemical, morphological, thermal and mechanical properties of these less exploited natural fibres reported in literature, discussing their advantages and challenges through comparison against various traditional plant fibres. The introduction of these less common natural fibres in thermoplastic and thermosetting matrices is critically discussed and compared with several standard biocomposites. These renewable and less investigated plant fibres can also be regarded as a source of nanocellulose aimed to enhance the green character of the final composites, thus pushing the industry to move towards such environmentally friendly materials
Development of thermoplastic starch (TPS) including leather waste fragments
Full text linkA thermoplastic starch (TPS) material is developed, based on corn starch plasticized with glycerol and citric acid in a 9:3:1 ratio and further bonded with isinglass and mono-and diglycerides of fatty acids (E471). In TPS, leather fragments, in the amount of 7.5 15 or 22.5 g/100 g of dry matter, were also introduced. The mixture was heated at a maximum temperature of 80 °C, then cast in an open mold to obtain films with thickness in the range 300 ± 50 microns. The leather fragments used were based on collagen obtained from production waste from shoemaking and tanned with tannins obtained from smoketree (Rhus cotinus), therefore free from chromium. Thermogravimetric (TGA) tests suggested that material degradation started at a temperature around 285 °C, revealing that the presence of leather fragments did not influence the occurrence of this process in TPS. Tensile tests indicated an increase in tensile properties (strength and Young's modulus) with increasing leather content, albeit coupled, especially at 22.5 wt%, with a more pronounced brittle behavior. Leather waste provided a sound interface with the bulk of the composite, as observed under scanning electron microscopy. The production process indicated a very limited degradation of the material after exposure to UV radiation for eight days, as demonstrated by the slight attenuation of amide I (collagen) and polysaccharide FTIR peaks. Reheating at 80 °C resulted in a weight loss not exceeding 3%
3D Printing of Low-Filled Basalt PA12 and PP Filaments for Automotive Components
Full text linkFused Deposition Modeling (FDM) enables many advantages compared to traditional manufacturing techniques, but the lower mechanical performance due to the higher porosity still hinders its industrial spread in key sectors like the automotive industry. PP and PA12 filaments filled with low amounts of basalt fibers were produced in the present work to improve the poor mechanical properties inherited from the additive manufacturing technique. For both matrices, the introduction of 5 wt.% of basalt fibers allows us to achieve stiffness values comparable to injection molding ones without modifying the final weight of the manufactured components. The increased filament density compared with the neat polymers, upon the introduction of basalt fibers, is counterbalanced by the intrinsic porosity of the manufacturing technique. In particular, the final components are characterized by a 0.88 g/cm3 density for PP and 1.01 g/cm3 for PA12 basalt-filled composites, which are comparable to the 0.91 g/cm3 and 1.01 g/cm3, respectively, of the related neat matrix used in injection molding. Some efforts are still needed to fill the gap of 15–28% for PP and of 26.5% for PA12 in tensile strength compared to injection-molded counterparts, but the improvement of the fiber/matrix interface by fiber surface modification or coupling agent employment could be a feasible solution
Effect of fiber surface treatments on thermo-mechanical behavior of poly(lactic acid)/phormium tenax composites
No full textIn the present study, Phormium Tenax fiber reinforced PLA composites were processed by injection molding and twin screw compounding with a fiber content ranging from 10 to 30 wt%. Three surface treatment methods have been used to improve the Phormium Tenax fiber-matrix interfacial bonding that are as follows: (1) aqueous alkaline solution, (2) silane coupling agent, and (3) a combination of alkaline and silane treatment. The mechanical, thermal and morphological properties of the resulting composites were investigated. The results have shown that the moduli of surface treated fiber reinforced composites are lower than the ones obtained for untreated composites (as a consequence of the decrease in fiber modulus caused by the chemical treatments) and no significant increase in strength was observed for any of the composites compared to neat PLA. SEM micrographs of composite fractured surfaces confirmed an improvement in the interfacial strength, which was insufficient nonetheless to significantly enhance the mechanical behavior of the resulting composites. Results from thermogravimetric analysis and differential scanning calorimetry suggest that surface treatment of Phormium affects the ability of PLA to cold crystallize, and the thermal stability of the composites at the different fiber contents was reduced with introduction of alkali and silane treated Phormium fibers
Influence of reprocessing cycles on the morphological, thermal and mechanical properties of flax/basalt hybrid polypropylene composites
No full textVegetable fibers hybridization with basalt ones is a suitable way to exploit the environmental advantages of vegetable fibers while preserving composites mechanical properties. Nevertheless, there are no studies available on the mechanical recycling of short fiber hybrid reinforced polymer composites. In light of this, the present work addressed the mechanical recycling of flax/basalt hybrid polypropylene composites up to seven reproc-essing cycles, evaluating the effect on microstructure, thermal and mechanical behavior and providing a direct comparison with flax composites. The results proved that the interaction of flax and basalt fibers promotes a faster degradation of flax fibers length inducing a significant decrease in hybrid mechanical properties already at the second reprocessing cycle. Despite this, hybrids are able to ensure a higher flexural stiffness and flexural strength by 5.2% and 7.7%, respectively, and an impact strength by 29.8%, 24.0% and 16.6% higher than flax at-50 degrees C, room temperature and + 50 degrees C after the second reprocessing cycle, respectively. Considering the easier processability of hybrid composites thanks to a higher Melt Volume Flow Rate (MVR), they can be conveniently repurposed and mechanically recycled to produce components traditionally manufactured with flax fibers
Effect of temperature and MWCNTs on low velocity impact response of CFRP laminates
No full textThis experimental work addresses the effect of temperature and MWCNTs on the response of carbon fibre reinforced epoxy matrix (CFRP) laminates under low impact velocity. The test temperature ranged from +80 °C down to -40 °C while two sample configurations were examined, namely cross-ply and quasi-isotropic. Results showed the influence of temperature and of stacking sequence on the impact response of CFRP. The presence of carbon nanotubes, despite a larger delaminated area, provided the quasi-isotropic structure with an increased damage tolerance, ascribed to the enhancement of mode II interlaminar fracture toughness
Application of DIC to Static and Dynamic Testing of Agglomerated Cork Material
No full textIn this work, experimental compression tests have been performed on parallelepiped specimens cut from an agglomerated cork slab. The tests have been performed both using a quasi-static testing machine and a polymeric Split Hopkinson Bar, in order to assess the sensitivity of the material to the strain rate. A standard and a high-speed digital camera have been used to collect frames of the samples during the tests. 2D DIC analyses have been conducted on the pictures of lateral faces of the specimens in order to evaluate the actual strain distributions, which showed a significant heterogeneity within each sample. Moreover, the DIC analyses on the dynamic tests have been used for evaluating the local accelerations and to compute the inertia stresses. The latter may affect the global response that can be measured by following the standard Hopkinson bar procedures, and are responsible for the fluctuations in the force histories observed in the tests at highest strain rates
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