Abstract
The ability to absorb a large amount of energy during an impact event without generating critical damages represents a key feature of new generation composite systems. Indeed, the intrinsic layered nature of composite materials allows the embodiment of specific hybrid plies within the stacking sequence that can be exploited to increase impact resistance and damping of the entire structure without dramatic weight increase. This work is based on the development of an impact-resistant hybrid composite obtained by including a thin layer of Non-Newtonian silica based fluid in a carbon fibres reinforced polymer (CFRP) laminate. This hybrid phase is able to respond to an external solicitation by activating an order-disorder transition that thickens the fluid increasing its viscosity, hence dissipating the energy impact without any critical failure. Several Shear Thickening Fluids (STFs) were manufactured by changing the dimensions of the particles that constitute the disperse phase and their concentrations into the continuous phase. The dynamic viscosity of the different STFs was evaluated via rheometric tests, observing both shear thinning and shear thickening effects depending on the concentration of silica particles. The solutions were then embedded as an active layer within the stacking sequence to manufacture the hybrid CFRP laminates with different embedded STFs. Free vibration tests were carried out in order to assess the damping properties of the different laminates, while low velocity impact tests were used to evaluate their impact properties. Results indicate that the presence of the non-Newtonian fluid is able to absorb up to 45 % of the energy during an impact event for impacts at 2.5 m/s depending on the different concentrations and particles dimensions. These results were confirmed via C-Scan analyses to assess the extent of the internal delamination.
Highlights
One of the most important aspects that concerns all the structural materials and, more in particular composite structures, is constituted by the behavioural uncertainties associated with impacts with foreign objects
By following this approach, it is possible to enhance the impact properties of a traditional laminate by manufacturing a Shear Thickening Fluid (STF) that can subsequently be included within the laminate sequence as an active layer for impact damage suppression
In order to fully understand how the material would behave when subjected to an impact, experiments were conducted to evaluate the energy absorption of the STF/carbon fibres reinforced polymer (CFRP) composite and a comparison was made with a traditional laminate, obtained with the same prepreg and the same lay-up sequence
Summary
One of the most important aspects that concerns all the structural materials and, more in particular composite structures, is constituted by the behavioural uncertainties associated with impacts with foreign objects. In the work carried out by Fisher et al, an STF was sandwiched between polyvinyl chloride beams, showing good results in damping the vibrations of the entire structure [6], while Soutrenon et al realised a structural damper by embedding the STF within an open-cell foam encapsulated in silicone [7] Another multifunctional system patented by Picken [8] is based on the preparation of an STF using a supramolecular polymer (polymers made of monomers held together by noncovalent interactions [9]) that is used to impregnate the fibres and produce a composite material. The technique does not imply any modifications of the thermoset resin used for the composite manufacturing, the procedure can be carried out using commercial thermoset/carbon fibres prepregs
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