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The influence of strain amplitude, temperature and frequency on complex shear moduli of polymer materials under kinematic harmonic loading

Hashemi M., Zhuk Y.

Mechanics and Mechanical Engineering

2017

Vol. 21, nr 1

157--170

Modeling of the cyclic deformation of viscoelastic materials as the key aspects of analysis of the structural behavior is performed. The approach that uses the complex-value amplitude relations is preferred rather than direct numerical integration of the complete set of constitutive equation for the material. Time dependent transient inelastic response of polymer materials to monoharmonic kinematic loading is simulated by the Goldberg constitutive model. To predict the steady-state response in terms of amplitudes, the relations between the amplitudes of main field variables are established with making use of complex moduli concept. It is performed by making use of equivalent linearization technique. It is shown that this technique leads to overestimation of stress amplitude. To avoid this, the modified equivalent linearization technique is applied. Characterization of the complex moduli dependence on frequency and temperature as well as amplitude of strain intensity is performed. Results demonstrate a weak dependence of loss moduli on the frequency of the loading within the wide interval of it, while variation of storage moduli with increasing temperature is more pronounced.

Determination of volatile organochalcogens using liquid phase microextraction and gas chromatography with fluorine-induced chemiluminescence detection

Hashemi M., Montes R. A., Chasteen T. G.

Environmental Biotechnology

2012

Vol. 8, No. 2

55--62

In this study, a simple and rapid liquid phase microextraction technique coupled with gas chromatography and fluorineinduced chemiluminescence detection has been developed for determination of volatile organochalcogens (dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide and dimethyl diselenide and dimethyl telluride). The effects of extraction parameters such as extracting solvent and its volume, stirring time extraction time and salt effect were optimized. Also, analytical figures of merit such as response linearity, repeatability and reproducibility, and limits of detection have been evaluated. The proposed method was found to be a simple and rapid analytical procedure for determination of volatile organochalcogens in real aqueous samples with detection limits of 5-620ng·l-1. The relative recoveries of these analytes for spiked bacterial cultures, tap water and lake water ranged from 95 to 105% with the relative standard deviations of 0.3-11.0%.