Visco-elastic behavior

Dynamic mechanical experiments, where the material is periodically strained, are common methods to characterize the visco-elastic behavior of elastomers by measuring the storage modulus G and loss modulus G". G is a measure for the maximal, reversibly stored energy for a periodical deformation and G" is proportional to the dissipated energy for the oscillation cycle. It is obvious to investigate, whether the l.c. state of the l.c. elastomers influences the dynamic mechanical properties and whether different modes of linking the mesogenic moieties to the backbone can be detected. 

We will discuss some preliminary results, which have been performed recently l01). In Fig. 39a the results for polymer No. 2d of Table 10 are shown, which were obtained by torsional vibration experiments. At low temperatures the step in the G (T) curve and the maximum in the G"(T) curve indicate a p-relaxation process at about 120-130 K. Accordingly the glass transition is detected at about 260 K. At 277 K the nematic elastomer becomes isotropic. This phase transformation can be seen only by a very small step in G and G" in the tail of glass transition region, which is shown in more detail in Fig. 39 b. From these measurements we can conclude, that the visco-elastic properties are largely dominated by the properties of the polymer backbone the change of the mesogenic side chains from isotropic to liquid crystalline acts only as a small disturbance and in principle the visco-elastic behavior of the elastomer... 

Duquesne, S., Le Bras, M., and Delobel, R. 2002.Visco-elastic behavior of intumescent materials. Thirteenth Annual BCC Conference on Fire Retardant, Stamford, CT, June. 

A similar approach has also been developed by Susteric [108], who compares the behavior during low-amplitude deformation of rubbers, loaded with aggregated carbon black, with the visco-elastic behavior of macromolecules undergoing high-frequency deformation. The specific features of the breaking of carbon black aggregates defined by the deformation amplitude of loaded rubbers are described by the above author by a mathematical model developed for the description of the dynamic, visco-elastic behavior of polymer molecules. This approach revealed... 

Workability of ordinary plain cement mortar is generally estimated with the flow test by Japanese Industrial Standard (JIS). But this test method can not estimate sufficiently the workability of PLCM with visco-elastic behavior. 

The mechanical troweling apparatus for preparation of adhesion specimen of plastering material to concrete substrate can estimate satisfactorily the workability of PLCM with visco-elastic behavior. Workability of existing PLCM is not always sufficient to apply. It is necessary to improve the characteristics of PLCM. 

Plastics processing is made easy with the use of additives. Additives help to solve the processing problems. The problems occur from the inherent visco-elastic behavior of individual plastic types. 

Hamburger, W.J. (1948) Mechanics of elastic performance of textile materials II. The application of sonic techniques to the investigation of the effect of visco-elastic behavior upon stress-strain relationships in certain high polymers. Text. Res. J., 18, 705. 

Papanicolaou, G. C., Kosmidou, T. V, Vatalis, A. S., Delides, C. G. (2006), Water absorption mechanism and some anomalous effects on the mechanical and visco-elastic behavior of an epoxy system, J. Appl. Polym. Sci., 99,1328-39. 

The dimensionless blend time, NO, is a constant for a helical ribbon operating in the laminar regime (see, e.g., Hoogendoom and den Hartog, 1967 Johnson, 1967 Rieger et al., 1986). This means that the blend time is independent of Reynolds number and the fluid viscosity, so that even if the fluid is shear-thinning the blend time will not be affected by the rheological behavior. This is not true for visco-elastic behavior. 

Wang. D. et al Study of the Mechanism of Polymer Solution With Visco-Elastic Behavior Increasing Microscopic Oil Displacement Efficiency and the Forming of Steady Oil Thread Flow Channels, paper SPE 68723 presented at the 2001 SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, 17-19 April. 

The results of meehanieal analysis of two viseo-elastic foams analyzed in this paper show clearly differentiation in stress strain behavior, ereep and eompression srt, and recoverabihty. It was known that mechanical property of foam depends on material chemieal structure, phase morphology, strut dimension, eell structure, and cell orientation and imiformity. The question is why these two visco-elastic foams have different eonqjressive stress strain behavior and compression set. For foam 1 we observed an elastomeric behavior under the compressive stress up to 60% of strain. The foam shows visco-elastic behavior when it was loaded and unloaded at different strain levels. However, for foam sample 2 under the compressive loading we observed elastic deformation, plateau due to possible localized buckling, and densification. 

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