Dielectric properties of a novel high absorbing onion-like-carbon based polymer composite

A novel lightweight onion-like carbon (OLC) based Poly(methyl metacrylate) (PMMA) composite with high electromagnetic (EM) absorption capability determined earlier in microwave range is studied in low frequencies from 20 Hz to 1 MHz by dielectric spectroscopy. The investigation of dielectric properties of PMMA films with incorporated OLC in small concentration (0.5–2 wt.%) have been carried out by varying the temperature between 240 and 520 K. The temperature behavior of the complex permittivity at a given frequency is found to be strongly dependent on the OLC concentration. The experimental data are in quantitative agreement with the results of modified effective medium calculations of OLC-based polymer film's permittivity. Both the experimental observations and theoretical simulation demonstrate that small additions of onion-like carbon particles to a polymer matrix can noticeably modify the composite response to low-frequency EM radiation as well as improve its thermal stability (increased glass transition and melting temperatures, correspondingly).     

On the scale effect in the thin layer delamination problem

Influence of layer thickness on the stress distribution in the vicinity of a crack tip is examined, taking into account the fact that the conventional stress intensity factor concept becomes invalid if the thickness of the layer is not much more than the size of the fracture process zone. An eigen-problem is considered which is characterized by two asymptotes. The first is a near one; it is formed in a small vicinity of the crack tip in the layer thickness scale. The second asymptote is a far one in the same scale. The regions of validity of these asymptotes are determined and shown to depend upon layer thickness, material parameters and crack tip speed. The complete stress distribution in front of the crack is obtained, as well. Some conclusions are made concerning the stress distribution and energy release rate for the general problem. Mode III crack propagation is considered in detail.Parts of this work were carried out in The Eda and Jaime David Dreszer Fracture Mechanics Laboratory.