Institute for Polymer Mechanics

The electrical conductivity of carbon nanotube–epoxy composites is investigated analytically and experimentally. The theoretical predictions of the effective electrical conductivity of carbon nanotube–epoxy composites were performed by the analytical approach based on a micromechanical model of composites. The parametric analysis carried out revealed an influence of geometrical and electrical parameters of the micromechanical model on the effective electrical conductivity of carbon nanotube–epoxy nanocomposite. The nanocomposites made from the DGEBA-based and RTM6 epoxy resins filled with different weight content of Baytubes C150P and N7000 multi-walled carbon nanotubes were prepared. The experimental values of the electrical conductivity of the nanocomposites were compared with those calculated by means of the analytical model.

The problem of crack pattern formation due to thermal shock loading at the surface of half space is solved numerically using the two-dimensional boundary element method. The results of numerical simulations with 100-200 random simultaneously growing and interacting cracks are used to obtain scaling relations for crack length and spacing. The numerical results predict that such a process of pattern formation with quasistatic crack growth is not stable and at some point the excess energy leads to unstable propagation of one of the longest cracks. This single-crack scenario should be understood in a local sense. There could be other unstable cracks far away that together can form a new pattern. The onset of instability has also been determined from numerical results.

Polyisocyanurate foams have been developed using a polyol system partially derived from rapeseed oil (RO). The effect of nanofillers with iso-dimensional geometry (zinc oxide), nanofibers (carbon nanotubes), and nanoplatelets (organically modified montmorillonite) on stiffness and strength of the foams has been studied. It was demonstrated that the tensile properties of the filled foams are enhanced by roughly the same proportion as the stiffness and strength of monolithic filled polymers.

Designs of grips for flat strips made of fiber-reinforced polymers (FRPs) are put forward. They can be used for tests in tension, prestretching, and long-term loading. In order to prevent the rise of stress concentrations, special profiled grips with a varying surface curvature allowing the transmission of tensile loads to the strip by means of gradually increasing shear stresses (without peaks) have been elaborated. The results of a mathematical analysis of the stress state in the strip, an example of calculation, and experimental data obtained from testing a carbon-fiber-reinforced polymer strip in profiled model grips specially constructed for this purpose are presented.

Amplitude variations of radial waves in an anisotropic thick-walled spherical shell caused by a harmonic source located on its inner surface are considered. The contact interaction between the outer surface of the shell with the surrounding liquid is taken into account. The relative vibration speed of the outer surface is found using the operational method. The analytical solution, expressed as a series in residues of a complex solution, allows for the interaction between forced and natural vibrations found from the corresponding boundary-value problem. The amplitudes and their graphical description represent the basic source for a parametric investigation of the transmission ability of sphere wall for an acoustic disturbance in relation to its thickness and material properties. Vibrations under resonance conditions are also considered.

External tanks of the spacecrafts need not only efficient, but also safe cryogenic insulation materials and the issues of their development are still urgent. At present, polyurethane (PUR) or polyisocyanurate (PIR) foams’ cryogenic insulation is widely applied in the partially reusable launch systems. Factors influencing the cryogenic resistance of external thermal insulation performed of spray-on PUR or PIR foams are characterised based on a wide literature search. They include chemical structure and macromolecules’ architecture of polymeric matrix, physical and mechanical properties of foams, thermal stability and combustibility, cellular structure of foams etc. Experimental data on physical and mechanical properties at room and cryogenic temperatures are presented for IWC developed PUR foams further named as IWC-Cryo. Technological processes of spray-on PUR and PIR foams cryogenic insulation, cryo-pumping and the main defects of external tank insulation are analysed as well as applications of foams’ insulation in space technologies (Space Shuttle, Ariane and Buran).

As a development of the model where only one weak microvolume (WMV) and only a pulsating cyclic loading are considered, in the current version of the model, we take into account the presence of several weak sites where fatigue damage can accumulate and a loading with an arbitrary (but positive) stress ratio. The Poisson process of initiation of WMVs is considered, whose rate depends on the size of a specimen. The cumulative distribution function (cdf) of the fatigue life of every individual WMV is calculated using the Markov model of fatigue. For the case where this function is approximated by a lognormal distribution, a formula for calculating the cdf of fatigue life of the specimen (modeled as a chain of WMVs) is obtained. Only a pulsating cyclic loading was considered in the previous version of the model. Now, using the modified energy method, a loading cycle with an arbitrary stress ratio is “transformed” into an equivalent cycle with some other stress ratio. In such a way, the entire probabilistic fatigue diagram for any stress ratio with a positive cycle stress can be obtained. Numerical examples are presented.

Abstract Polymer/carbon nanotube (CNT) composites are one of the most perspective advanced materials developed in recent years. The properties of CNT‐reinforced polymer composites, however, strongly depend on structural aspects of the nanostructured filler and on its dispersion quality in a polymer matrix. Consequently, this research was devoted to the investigation of multiwalled‐CNT‐modified poly(vinyl acetate) (PVAc) composites with respect to the mechanical property dependence on some structural characteristics of CNTs. PVAc/CNT nanocomposites were obtained with a solution casting technique. The amount of CNTs was changed from 0.01 up to 2 wt %. The stress–strain characteristics of PVAc/CNT nanocomposites clearly revealed remarkable reinforcing effects of the CNT additions already at 0.01 wt %. At this CNT concentration, the elastic modulus (E) and tensile yield stress increased by 12.5 and 60%, respectively. Special attention was paid to the change of E with respect to some structural characteristics of CNTs. A corresponding mathematical model for the prediction of the elastic properties of CNT polymer nanocomposites is proposed, showing that elastic constants of the nanocomposites largely depend on the agglomeration of CNTs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011