Plastics,Rubber and Composites: Macromolecular Engineering

Adhesive bonding of aeronautical components made of carbon–fibre reinforced plastics is a popular alternative to mechanical fastening. The continuing research is focused on the optimisation of the surface treatments so as to improve the mechanical properties. In this work, the effect of two atmospheric pressure plasma (APP) treatments before bonding on the fracture toughness behaviour of adhesively bonded joints was experimentally investigated. The laminates were in contact with different ancillary materials during the manufacturing process, thus leading to eight different treatment alternatives. For the investigation, a quasi-isotropic layup was subjected to modes I and II fracture toughness test. To support the understanding of the mechanical behaviour observed, non-destructive testing evaluation as well as failure mode analysis at macroscopic level was carried out. As a result, APP showed promising performances regarding surface preparation, revealing an appreciable dependence of the fracture toughness behaviour on the selected alternatives.

With the growing concern about the risk of needle puncture injuries for many professional groups, a study has been undertaken to investigate the interaction between medical (hypodermic) needles and materials used for protective gloves. This paper looks at the impact of glove use conditions on the resistance of their constitutive materials to needle puncture. Mechanical deformations which may result from hand and finger flexion, for example, were shown to induce a large reduction in the puncture force in the case of elastomers. On the other hand, no significant effect of a support material simulating the hand inside the glove was observed on needle puncture resistance. Finally, a reduction in the needle puncture force was recorded with sheets of neoprene rubber after application of a lubricant. These results demonstrate the large contribution of cutting and friction in the needle puncture process.

Sandwich panels are widely used for energy absorbing applications in cases of low and high velocity impacts. The core itself is capable of absorbing energy by progressive collapse, while the skins are necessary for uniformly distributing the local vertical load over the impacted area as well as for the introduction of overall panel bending resistance. In the present work, the failure response of sandwich panels with open lattice cellular cores subjected to low velocity impact is investigated. Experimental tests are performed using a mass drop testing machine. Additionally, a three-dimensional finite element model of the sandwich panels–impactor system is developed using commercial Finite Element (FE) codes. The core homogenisation is introduced in order to improve the efficiency of the FE analysis by reducing the computational time. Numerical results correlate well with experimental data, enabling detailed understanding of the parameters affecting the initiation and propagation of impact damage.

Condensation polyurethanes with different hard segment (HS) content were prepared by condensation reaction of urea, phenol sulphonic acid and formaldehyde and tested for their mechanical, physical and thermal properties. Obtained polyurethane (PUR) films were first heated at 50°C for 120 min and then treated at 135°C for 15 min or 160°C for 10 min. The tensile strength of samples thermally treated at 50°C then at 135°C was 120% higher than for samples treated only at 50°C. The obtained polyurethanes exhibited segmented structures with phase separation between HSs and soft segments (SSs). Films containing 19 and 21%HSs heated at 50°C then 135°C exhibited acceptable mechanical properties and water resistance. The lower and higher end use temperatures of PUR films were affected mainly by the polymer composition. Moreover, the polyurethane samples containing 19 and 21%HSs have shown the highest decomposition temperature (i.e. >165°C), compared to 80°C for polymers with 32%HSs.

Multiwalled carbon nanotube (MWNT) reinforced epoxy resin composites were fabricated and characterised. Several process variables were investigated using design of experiments. The MWNTs (0·5 wt-%) were dispersed in Epon 862 epoxy resin under various sonication conditions. Young's modulus, energy to failure, glass transition temperature T_g and storage modulus E′ were assessed. The first three were selected in a design of experiment optimisation study. The results indicated that as the sonication intensity and the duration of sonication were increased, the material response of the MWNT/epoxy composite, specifically Young's modulus, energy and T_g, was enhanced. The fracture surfaces of the composites were examined using scanning electron microscopy. Improved dispersion was observed in samples fabricated with increased sonication intensities. The Mori–Tanaka model was used to predict the mechanical properties of the MWNT/epoxy composites and was found to be in reasonable agreement with experimental data. Nonetheless, the experimental results yielded slightly inferior properties to those from the model prediction.

Layered organic/inorganic nanocomposites have been widely investigated in recent years. In this work, for the first time, the authors prepared laminated hydroxyapatite (HAp)/poly(methyl metacrylate) (PMMA) nanocomposites via one-step intercalative bulk polymerization. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results revealed that different morphologies of PMMA/HAp nanocomposites were obtained by varying HAp contents. Differential scanning calorimetry (DSC) and tensile strength analysis indicated that both thermal stability and tensile strength were enhanced with incorporation of laminated HAp. The results reported here can be expanded to other HAp polymer systems, thus paving a new way of designing and fabricating biomimetic nanocomposites for biomedical applications.