The elastic constants of particulate composites are evaluated employing a theoretical cube-within-cube formation. Two new models of four and five components, respectively, formed by geometrical combination of three-component models existing in the literature, are used as Representative Volume Elements. Using the governing stress and strain equations of the proposed models, two new equations providing the static elastic and shear moduli of particulate composites are formulated. In order to obtain the dynamic elastic and shear moduli, the correspondence principle was applied successively to components connected in series and/or in parallel. The results estimated by the proposed models were compared with values evaluated from existing formulae in the literature, as well as with values obtained by tensile, dynamic, and ultrasonic experiments in epoxy/iron particulate composites. They were found to be close to values obtained by static and dynamic measurements and enough lower compared with values obtained from ultrasonic experiments. The latter is attributed to the high frequency of ultrasonics. Since measurements from ultrasonic's and from dynamic experiments depend on the frequency, the modulus of elasticity estimated by ultrasonic's is compared with that (storage modulus) estimated by dynamic experiments.

No abstract

No abstract

ABSTRACT:The first objective of the present experimental work is to evaluate the storage and loss moduli of plasticized epoxy polymers over a temperature and frequency range, and to correlate with the ability of the ultrasounds for the characterization of such polymers. The materials used were a series of cold-setting epoxy polymers, plasticized with different amounts of plasticizer. After the investigation of dynamic properties through vibration tests, the velocities of longitudinal and transverse elastic waves, and the acoustic attenuation coefficient a were evaluated and, then, using these quantities, the "dynamic" moduli EЈ, GЈ, and Ј were evaluated. Thereafter, it can be stated that the plasticizer content and measuring frequency range strongly influence the elastic moduli of the material in the sense that the plasticizer tends to reduce, whereas the measuring frequency to increase these. The second objective of this work is to asses and discuss the associated plasticizer-induced microstructural damaging effects by combined methods of ultrasounds, tensile modulus, as well as moisture absorption testing and then to correlate this assessment with the storage moduli behavior. It was shown that, despite the nonneglecting scatter in the experimental data, certain irresistible general trends might be assessed. In this context, it was found that the damage "response" is markedly sensitive to the respective applied "detection" technique and, therefore, the damage evolution data obtained by these different techniques are comparable only under certain circumstances. By comparison between the applied techniques, it seems reasonable to assume that the "moisture" technique due to its inherent microscopic mass transport processes, in the form of H 2 O molecules diffusion and therefore its ability to "detect" microstructural detects on a much lower scale, should give a better approach to the internal damage phenomena.

This paper examines the variation in properties of a specific type of 28-year-old concrete, the characteristics of which were known at 7, 28, 36 and 90 days. Beyond the destructive tests (compression, splitting tension and bending), the concrete was studied with non-destructive ultrasound testing. Moreover, the relationship between the compressive strength of this concrete and the ultrasonic longitudinal wave velocity, as well as the dynamic modulus of elasticity were determined. The objective was to control changes in the quality of concrete over a long period of time and to contribute to the development of a non-destructive method for the determination of concrete strength in structures. The presented approach, that seems promising for such development, uses the velocity of ultrasonic waves in concrete.