The effect of cross-linking on the dynamics of amorphous poly(vinyl cinnamate) (PVCN) below and above the glass transition temperature (T g ) was studied by means of mechanical spectroscopy. The polymer is cross-linked by irradiating it with ultraviolet light, and it is controlled by the irradiation time, where the kinetics is observed by means of Fourier transform infrared spectroscopy. The evolving links between molecules hinder molecular mobility and thus influence the mechanical loss in the material, leading to (i) a shift of T g to higher temperatures, (ii) a substantial decrease of the strength of the corresponding R-relaxation, (iii) an increase of Young's modulus, and (iv) an increased damping of PVCN below the glass transition.
Protonated titanate nanotubes (TiNT-H) were surface-modified with (3-aminopropyl)trimethoxy silane (APTMS) by novel method suitable for syntheses of large amounts of materials with low costs. Usage of prepared nanotubes for polymer reinforcement was studied. Since the thermal stability of nanofiller was important to preserve their functional properties, stability was studied by in situ high temperature measurements. The most thermally stable nanotubes, silanized for 20 min, were used for preparation of epoxy-based nanocomposites. The nanofiller formed smaller (few hundreds of nm) and larger (few μm) aggregates in polymer matrix, and the amount of aggregates increased with increasing nanofiller content. APTMS modified titanate nanotubes bonded well with the epoxy matrix since amine groups on the TiNTs surface can react with epoxy group to form covalent bonds between the matrix and the nanofiller. Very small addition (0.19 -1.52 wt%) of nanotubes significantly increased the glass transition temperature and the modulus in rubbery state of the epoxy based polymer. Smaller nanofiller content lead to larger increase in these parameters and therefore better dynamic mechanical properties due to the smaller amount of large aggregates. APTMS-modified titanate nanotubes were proven as promising nanofiller in epoxy based nanocomposites.
In this work, a constitutive model of an intrinsically self-healing composite matrix material is presented. The developed model comprises a micro-damage initiation and evolution model, and a healing evolution model, which are combined with the von Mises linear isotropic hardening plasticity. It is implemented into the Abaqus/Standard user material subroutine UMAT and validated using experimental results of static tensile and two-cycle tensile tests performed on partially neutralised poly(ethylene-co-methacrylic acid) (EMAA) ionomer copolymer, Surlyn® 8940. In the development of the model, Continuum Damage Healing Mechanics (CDHM) concepts of nominal and healing configurations are used. In addition, these concepts are used along with the strain equivalence hypothesis to streamline the numerical implementation. The strain equivalence hypothesis relates strain and stress tensors in the nominal and the healing configuration. Finally, successful validation has shown that the developed model is able to accurately predict behaviour of Surlyn® 8940 coupons during tensile tests and it can precisely predict the accumulation of plastic strain.
The capability of poly(ethylene-co-methacrylic acid) (E/MAA) to self-heal is well known, however, its mechanical properties are weak. In this study, composites with single and double layers of unidirectional (UD) carbon fibers were prepared by compression molding. Even a low mass fraction of fibers substantially improved the polymer. The flexural and tensile properties were tested at 0°, 45° and 90° fibers direction and compared to those of the matrix. The mechanical properties in the 0° direction proved superior. Flexural properties depended on the reinforcement distance from the stress neutral plane. The tensile modulus in the 0° direction was 13 times greater despite only a 2.5% mass fraction of fibers. However, both tensile modulus and strength were observed to degrade in the 90° direction. Dynamic mechanical analysis showed the dependence of both structure and properties on the thermal history of E/MAA. Tensile tests after ballistic impact showed that the modulus of the self-healed E/MAA was not affected, yet the strength, yield point, and particularly the elongation at break were reduced. A composite with higher fiber content could be prepared by mixing milled E/MAA particles in fibers prior to compression.
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