The development of autonomous healing material has an enormous scientific and technological interest. In this context, this research work deals with the investigation of autonomous healing behavior of epoxidized natural rubber (ENR) and its blends with ethylene methacrylic acid ionomers. The autonomous healing behavior of ENR and its blends containing two different ionomers [poly(ethylene-co-methacrylic acid sodium salt) (EMNa) and poly(ethylene-co-methacrylic acid zinc salt) (EMZn)] has been studied by ballistic puncture tests. Interestingly, EMNa/ENR blends exhibit complete healing just after the ballistic test but EMZn/ENR blends do not show full self-repairing. The healing efficiency has been evaluated by optical microscopy and a depressurized air-flow test. The healing mechanism has been investigated by characterizing thermal and mechanical properties of the blends. The chemical structure studied by FTIR and thermal analysis show that the ion content of ionomers and functionality of ENR has a significant influence on the self-healing behavior.
Biocomposite materials are nowadays often considered as a valid substitution of fiberglass reinforced (FGR) polymers in many relevant applications, especially thanks to the lower costs and environmental impact of the natural fibers. Conversely, they remain mainly confined to nonstructural applications. In consideration of the similar specific properties of glass and hemp fibers, the aim of this work is to compare a biocomposite component, for structural application, with a FGR-epoxy one. The comparison is focused on the issues related to the intrinsic differences of constituents mechanical characteristics as well as on their different response in the manufacturing processes. Beams with the function of wing spars, for small aeronautic structure, have been chosen as representatives. After a preliminary analysis of the materials, four spars were manufactured and were subjected to static mechanical tests up to failure, then the microstructures of failure areas were analyzed by scanning electron microscopy. The most relevant differences resulted related to the resin retention, higher in the case of the hemp fibers, to the failure modes and to the fiber-resin interactions, on which the fibers microstructures have an important role. POLYM. COMPOS., 00:000-000,
Carbon foam showed good ballistic performances for relatively small fragment impacts: low density samples (0.56 g/cm 3 and 0.24 g/cm 3 ) were able to stop and in some cases hold a 5 mm diameter stainless steel sphere shot at a speed up to 240 m/s by a compressed air gun.The results were used to calibrate and benchmark an Ls-Dyna model which had to be based only on a few and easy-to-measure material parameters. Therefore, performing only static compressive loading characterization tests, a suitable cellular Ls-Dyna material model was chosen. To justify the promising energy dissipation results, which cannot only be due to the static performances, a strain rate dependency was supposed. Based on ceramic materials which have inhomogeneities of the same size of the foam pores, a strain rate law typical of these was applied.Similar relations were applied to both the foams, and a calibrating coefficient was made on a single impact velocity test. The same model was then used to reproduce the impact at different impact velocities and very good agreement between experimental results and simulation was achieved.
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